View source for Evolution of human intelligence

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{{Use dmy dates|date=June 2022}}
The '''evolution of human intelligence''' is closely tied to the evolution of the [[human brain]] and to the [[origin of language]]. The [[timeline of human evolution]] spans approximately seven million years,<ref>{{cite book | vauthors = Klug WS, Cummings MR, Spencer CA, Palladino MA |title=Concepts of Genetics |date=2012 |edition=Tenth |publisher=Pearson |isbn=978-0-321-75435-6 |page=719 |quote=Assuming that chimpanzees and humans last shared a common ancestor about 8-6 million years ago, the tree shows that Neanderthals and humans last shared a common ancestor about 706,000 years ago and that the isolating split between Neanderthals and human populations occurred about 370,000 years ago.}}</ref> from the separation of the genus ''[[Pan (genus)|Pan]]'' until the emergence of [[behavioral modernity]] by 50,000 years ago. The first three million years of this timeline concern ''[[Sahelanthropus tchadensis|Sahelanthropus]]'', the following two million concern ''[[Australopithecus]]'' and the final two million span the history of the genus ''[[Homo]]'' in the [[Paleolithic]] era.

Many traits of human intelligence, such as [[empathy]], [[theory of mind]], [[mourning]], [[ritual]], and the use of [[symbol]]s and [[tool]]s, are somewhat apparent in other [[great ape]]s, although they are in much less sophisticated forms than what is found in humans like the [[great ape language]].

==History==

===Hominidae===
{{Human timeline}}
{{Further|Primate empathy|Great ape language|Lucy Temerlin}}
The [[great ape]]s (Hominidae) show some [[cognition|cognitive]] and [[empathy|empathic]] abilities. [[Common chimpanzee|Chimpanzee]]s can make [[tool]]s and use them to acquire foods and for [[social display]]s; they have mildly complex [[hunting]] strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of [[deception]]; they can learn to use [[symbol]]s and understand aspects of human [[language]] including some relational [[syntax]], concepts of [[number]] and numerical sequence.<ref>{{cite web | url = http://www.indiana.edu/~origins/teach/A105/lectures/A105L12.html | title = Chimpanzee intelligence | publisher = [[Indiana University]] | access-date = 24 March 2008 | date = 2000-02-23 | archive-date = 17 September 2016 | archive-url = https://web.archive.org/web/20160917161331/http://www.indiana.edu/~origins/teach/A105/lectures/A105L12.html | url-status = dead }}</ref> One common characteristic that is present in species of "high degree intelligence" (i.e. dolphins, great apes, and humans - ''Homo sapiens'') is a brain of enlarged size. Additionally, these species have a more developed neocortex, a folding of the cerebral cortex, and [[Spindle neuron|von Economo neurons]]. Said neurons are linked to social intelligence and the ability to gauge what another is thinking or feeling and are also present in bottlenose dolphins.<ref>{{cite journal| vauthors = Bearzi M, Stanford CB |date=2007|title=Dolphins and African apes: comparisons of sympatric socio-ecology |journal=Contributions to Zoology|volume=76|issue=4|pages=235–254|doi=10.1163/18759866-07604003 |url=https://escholarship.org/content/qt5gv9w4jw/qt5gv9w4jw.pdf?t=krnonn|doi-access=free}}</ref>

===Homininae===
[[File:chimpanzee mom and baby.jpg|thumb|left|upright|Chimpanzee mother and baby]]Around [[Miocene|10 million years ago]], the Earth's climate entered a cooler and drier phase, which led eventually to the [[Quaternary glaciation]] beginning some 2.6 million years ago. One consequence of this was that the north African [[subtropical or tropical moist lowland forest|tropical forest]] began to retreat, being replaced first by open [[grasslands]] and eventually by [[desert]] (the modern [[Sahara]]). As their environment changed from continuous forest to patches of forest separated by expanses of grassland, some primates adapted to a partly or fully ground-dwelling life where they were exposed to [[predator]]s, such as the [[big cats]], from whom they had previously been safe.

These environmental pressures caused selection to favor [[Savanna theory|bipedalism]] - walking on hind legs. This gave the Homininae's eyes greater elevation, the ability to see approaching danger further off, and a more efficient means of locomotion.{{Citation needed|date=June 2009|reason=This is only one explanation}} It also freed their arms from the task of walking and made the hands available for tasks such as gathering food. At some point the bipedal [[primate]]s developed [[handedness]], giving them the ability to pick up sticks, [[bone]]s and stones and use them as [[weapon]]s, or as [[tool]]s for tasks such as killing smaller animals, cracking [[Nut (fruit)|nut]]s, or cutting up [[carrion|carcasses]]. In other words, these primates developed the use of primitive [[technology]]. Bipedal tool-using primates from the subtribe [[Hominina]] date back to as far as about 5 to 7 million years ago, such as one of the earliest species, ''[[Sahelanthropus tchadensis]]''.

From about 5 million years ago, the hominin brain began to develop rapidly in both size and differentiation of function.
There has been a gradual increase in brain volume as humans progressed along the timeline of evolution (see [[Homininae]]), starting from about 600&nbsp;cm<sup>3</sup> in ''[[Homo habilis]]'' up to 1500&nbsp;cm<sup>3</sup> in ''[[Homo neanderthalensis]]''. Thus, in general there's a positive correlation between brain volume and intelligence.<ref>{{Cite journal |last1=Pietschnig |first1=Jakob |last2=Penke |first2=Lars |last3=Wicherts |first3=Jelte M. |last4=Zeiler |first4=Michael |last5=Voracek |first5=Martin |date=October 2015 |title=Meta-analysis of associations between human brain volume and intelligence differences: How strong are they and what do they mean? |url=http://dx.doi.org/10.1016/j.neubiorev.2015.09.017 |journal=Neuroscience & Biobehavioral Reviews |volume=57 |pages=411–432 |doi=10.1016/j.neubiorev.2015.09.017 |pmid=26449760 |s2cid=23180321 |issn=0149-7634|url-access=subscription }}</ref> However, modern ''[[Homo sapiens]]'' have a brain volume slightly smaller (1250&nbsp;cm<sup>3</sup>) than neanderthals, and the Flores hominids (''[[Homo floresiensis]]''), nicknamed hobbits, had a cranial capacity of about 380&nbsp;cm<sup>3</sup> (considered small for a chimpanzee) about a third of that of ''[[Homo erectus]]''. It is proposed that they evolved from ''H. erectus'' as a case of insular dwarfism. With their three-times-smaller brain, the Flores hominids apparently used fire and made tools as sophisticated as those of their ancestor ''H. erectus''.

===''Homo''===
{{Further|Homo{{!}}''Homo''}}
Roughly 2.4 million years ago ''[[Homo habilis]]'' had appeared in [[East Africa]]: the first known [[Homo|human]] species, and the first known to make [[stone tool]]s, yet the disputed findings of signs of tool use from even earlier ages and from the same vicinity as multiple ''[[Australopithecus]]'' fossils may put to question how much more intelligent than its predecessors ''H. habilis'' was.

The use of tools conferred a crucial evolutionary advantage, and required a larger and more sophisticated brain to co-ordinate the fine hand movements required for this task.<ref>{{cite journal| vauthors = Ko KH |title=Origins of human intelligence: The chain of tool-making and brain evolution|journal=Anthropological Notebooks|date=2016|volume=22|issue=1|pages=5–22|url=http://www.drustvo-antropologov.si/AN/PDF/2016_1/Anthropological_Notebooks_XXII_1_Ko.pdf}}</ref><ref name=":9">{{Cite journal |last1=Nowzari |first1=Hessam |last2=Jorgensen |first2=Michael |date=June 2022 |title=Human Dento-Facial Evolution: Cranial Capacity, Facial Expression, Language, Oral Complications and Diseases |journal=Oral |language=en |volume=2 |issue=2 |pages=163–172 |doi=10.3390/oral2020016 |issn=2673-6373|doi-access=free }}</ref> Our knowledge of the complexity of behaviour of ''Homo habilis'' is not limited to stone culture; they also had habitual therapeutic use of toothpicks.<ref>Puech P.-F., Puech S., Cianfarani F., Albertini H. (1989). [[iarchive:ToothWearAndDexterityInHomoErectus|"Tooth wear and dexterity in ''Homo erectus''"]], pp. 247–251 in ''Hominidae. Proceedings of the 2nd International Congress of Human Paleontology'', Jaca Book (Milan: Italy)</ref>

A larger brain requires a larger [[human skull|skull]], and thus is accompanied by other morphological and biological evolutionary changes. One such change required for the [[female]] to have a wider [[birth canal]] for the newborn's larger skull to pass through. The solution to this was to give birth at an early stage of fetal development, before the skull grew too large to pass through the birth canal. Other accompanying adaptations were the smaller maxillary and mandibular bones, smaller and weaker facial muscles, and shortening and flattening of the face resulting in modern-human's complex cognitive and linguistic capabilities as well as the ability to create facial expressions and smile.<ref name=":9"/> Consequentially, dental issues in modern humans arise from these morphological changes that are exacerbated by a shift from nomadic to sedentary lifestyles.<ref name=":9" />

Humans' increasingly sedentary lifestyle to protect their more vulnerable offspring led them to grow even more dependent on tool-making to compete with other animals and other humans, and rely less on body size and strength.<ref name=":9"/>

About 200,000 years ago [[Europe]] and the [[Middle East]] were colonized by [[Neanderthal|Neanderthals]], [[Neanderthal extinction|extinct]] by 39,000 years ago following the appearance of modern humans in the region from 40,000 to 45,000 years ago.

'''History of humans'''

In the Late Pliocene, hominins were set apart from modern great apes and other closely related organisms by the anatomical evolutionary changes resulting in bipedalism, or the ability to walk upright.<ref>{{Cite book |last1=Conroy |first1=Glenn C. |url=https://wwnorton.com/books/9780393912890/about-the-book/product-details |title=Reconstructing Human Origins: A Modern Synthesis |last2=Pontzer |publisher=W.W. Norton |others=Herman Pontzer |year=2012 |isbn=978-0-393-91289-0 |edition=3rd |location=New York |oclc=760290570}}</ref><ref name=":12">{{Cite journal |last=Stuart-Fox |first=Martin |date=2022-04-18 |title=Major Transitions in Human Evolutionary History |url=https://doi.org/10.1080/02604027.2021.2018646 |journal=World Futures |volume=79 |pages=29–68 |doi=10.1080/02604027.2021.2018646 |s2cid=248251299 |issn=0260-4027|url-access=subscription }}</ref> Characteristics such as a supraorbital torus, or prominent eyebrow ridge, and flat face also makes ''Homo erectus'' distinguishable. Their brain size substantially sets them apart from closely related species, such as ''H. habilis'', as seen by an increase in average cranial capacity of 1000 cc. Compared to earlier species, ''H. erectus'' developed keels and small crests in the skull showing morphological changes of the skull to support increased brain capacity. It is believed that ''Homo erectus'' were, anatomically, modern humans as they are very similar in size, weight, bone structure, and nutritional habits. Over time, however, human intelligence developed in phases that is interrelated with brain physiology, cranial anatomy and morphology, and rapidly changing climate and environments.<ref name=":12" />
[[File:Acheulean_handaxe.png|thumb|Drawing of Acheulean handaxe from Spain from front, back, side, and top profile]]

==== Tool-use ====
The study of the evolution of cognition relies on the archaeological record made up of assemblages of material culture, particularly from the [[Paleolithic|Paleolithic Period]], to make inferences about our ancestors' cognition. Paleo-anthropologists from the past half-century have had the tendency of reducing [[stone tool]] artifacts to physical products of the metaphysical activity taking place in the brains of hominins. Recently, a new approach called 4E cognition (see Models for other approaches) has been developed by cognitive archaeologists [[Lambros Malafouris]], [[Thomas G. Wynn]], and [[Karenleigh A. Overmann]], to move past the "internal" and "external" dichotomy by treating stone tools as objects with agency in both providing insight to hominin cognition and having a role in the development of early hominin cognition.<ref name=":22">{{Cite journal |last1=Wynn |first1=Thomas |last2=Overmann |first2=Karenleigh A |last3=Malafouris |first3=Lambros |date=2021 |title=4E cognition in the Lower Palaeolithic |journal=Adaptive Behavior |language=en |volume=29 |issue=2 |pages=99–106 |doi=10.1177/1059712320967184 |s2cid=228957681 |issn=1059-7123|doi-access=free }}</ref> The 4E cognition approach describes cognition as embodied, embedded, enactive, and extended, to understand the interconnected nature between the mind, body, and environment.<ref name=":22"/>

There are four major categories of tools created and used throughout human evolution that are associated with the corresponding [[evolution of the brain]] and intelligence. Stone tools such as flakes and cores used by ''[[Homo habilis]]'' for cracking bones to extract marrow, known as the [[Oldowan]] culture, make up the oldest major category of tools from about 2.5 and 1.6 million years ago. The development of stone tool technology suggests that our ancestors had the ability to hit cores with precision, taking into account the force and angle of the strike, and the cognitive planning and capacity to envision a desired outcome.<ref name=":32">{{Cite book |last1=Shook |first1=Beth |title=Explorations |last2=Nelson |first2=Katie |last3=Aguilera |first3=Kelsie |last4=Braff |first4=Lara |publisher=Pressbooks |year=2019 |isbn=978-1-931303-62-0 |location=}}</ref>
[[File:Lower_Palaeolithic.jpg|alt=Stone tool artifacts include flakes, cores, and hammers used by hominins during the Paleolithic Period|thumb|Stone tools from the [[Paleolithic|Paleolithic Period]], also known as the Stone Age, are indicative of cognitive advancements throughout human evolutionary history.]]
[[Acheulean]] culture, associated with ''Homo erectus'', is composed of bifacial, or double-sided, hand-axes, that "requires more planning and skill on the part of the toolmaker; he or she would need to be aware of principles of symmetry".<ref name=":32" /> In addition, some sites show evidence that selection of raw materials involved travel, advanced planning, cooperation, and thus communication with other hominins.<ref name=":32" />

The third major category of tool industry marked by its innovation in tool-making technique and use is the [[Mousterian]] culture. Compared to previous tool cultures, in which tools were regularly discarded after use, Mousterian tools, associated with [[Neanderthal]]s, were specialized, built to last, and "formed a true toolkit".<ref name=":32" /> The making of these tools, called the [[Levallois technique]], involves a multi-step process which yields several tools. In combination with other data, the formation of this tool culture for hunting large mammals in groups evidences the development of speech for communication and complex planning capabilities.<ref name=":32" />

While previous tool cultures did not show great variation, the tools of early modern ''Homo sapiens'' are robust in the amount of artifacts and diversity in utility. There are several styles associated with this category of the [[Upper Paleolithic]], such as blades, boomerangs, [[atlatl]]s (spear throwers), and archery made from varying materials of stone, bone, teeth, and shell. Beyond use, some tools have been shown to have served as signifiers of status and group membership. The role of tools for social uses signal cognitive advancements such as complex language and abstract relations to things.<ref name=":32" />

===''Homo sapiens''===

[[File:Lion man photo.jpg|thumb|upright|"[[Lion-man|The Lion-man]]", found in the [[Hohlenstein-Stadel| Hohlenstein-Stadel cave]] of Germany's [[Swabian Alb]] and dated to 40,000 years ago, is associated with the [[Aurignacian culture]] and is the oldest known [[anthropomorphic]] animal figurine in the world.]]
<timeline>
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 bar:&nbsp; at:-2000000 color:period3 shift:(-20,7) text:[[Homo|Genus]]~[[Homo]]

 bar:&nbsp; color:period3
 from:-200000 till:-1800000
 at:-1800000 shift:(0,8) text:[[Homo erectus|H. erectus]]
 at:-1800000 text:[[Homo ergaster|H. ergaster]]
 at:-1800000 shift:(0,-24) text:[[Homo georgicus|H. georgicus]]

 bar:&nbsp; color:period3
 from:-1400000 till:end 
 at:-1400000 shift:(0,-16) text:[[Homo habilis|H. habilis]]

 bar:&nbsp; color:period3
 from:2013 till:-200000 
 at:-200000 text:[[Homo sapiens|H. sapiens]]

 bar:&nbsp; color:period3
 from:-1200000 shift:(0,4) till:-800000 text:[[Homo antecessor|H. antecessor]]

 bar:&nbsp; color:period3
 from:-29000 till:-230000
 at:-230000 shift:(0,-10) text:[[Homo neanderthalensis|H. neanderthalensis]]
 
 bar:&nbsp; color:period3 
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 at:-600000 shift:(0,5) width:5 text:[[Homo heidelbergensis|H. heidelbergensis]]

 bar:Events color:nil mark:(line,black)
 at:-77000 shift:(0,5) text:[[Toba catastrophe theory|Toba]]
 at:-640000 shift:(0,5) text:[[Yellowstone Caldera|3rd Y. Caldera]]
 at:-1300000 shift:(0,5) text:[[Yellowstone Caldera|2nd Y. Caldera]]

 bar:Events color:nil mark:(line,white)
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 from:-781000 till:-13000 text:[[Quaternary extinction event|Q.]]~[[Quaternary extinction event|extinction]]
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::<small>'''Dates approximate, consult articles for details'''</small>
::<small>(''From 2,000,000 BC to 2013 AD in (partial) [[exponential notation]]'')</small>
::<small>''See also'': [[Java Man]] (−1.75e+06), [[Yuanmou Man]] (−1.75e+06: -0.73e+06),</small>
::<small>[[Lantian Man]] (−1.7e+06), [[Nanjing Man]] (- 0.6e+06), [[Tautavel Man]] (- 0.5e+06),</small>
::<small>[[Peking Man]] (- 0.4e+06), [[Solo Man]] (- 0.4e+06), and [[Peștera cu Oase]] (- 0.378e+05)</small>

====''Homo sapiens'' intelligence====
{{Further|Intelligence|Archaic humans|Behavioral modernity|Early human migration}}

The eldest findings of ''[[Homo sapiens]]'' in [[Jebel Irhoud]], Morocco date back {{circa|300,000}} years<ref>{{cite journal | vauthors = Richter D, Grün R, Joannes-Boyau R, Steele TE, Amani F, Rué M, Fernandes P, Raynal JP, Geraads D, Ben-Ncer A, Hublin JJ, McPherron SP | display-authors = 6 | title = The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age | journal = Nature | volume = 546 | issue = 7657 | pages = 293–296 | date = June 2017 | pmid = 28593967 | doi = 10.1038/nature22335 | s2cid = 205255853 | bibcode = 2017Natur.546..293R }}
"Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of ''H. sapiens''. A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible.";
{{cite journal | vauthors = Smith TM, Tafforeau P, Reid DJ, Grün R, Eggins S, Boutakiout M, Hublin JJ | title = Earliest evidence of modern human life history in North African early ''Homo sapiens'' | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 15 | pages = 6128–6133 | date = April 2007 | pmid = 17372199 | pmc = 1828706 | doi = 10.1073/pnas.0700747104 | doi-access = free | bibcode = 2007PNAS..104.6128S }}</ref><ref>{{cite journal | vauthors = Richter D, Grün R, Joannes-Boyau R, Steele TE, Amani F, Rué M, Fernandes P, Raynal JP, Geraads D, Ben-Ncer A, Hublin JJ, McPherron SP | display-authors = 6 | title = The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age | journal = Nature | volume = 546 | issue = 7657 | pages = 293–296 | date = June 2017 | pmid = 28593967 | doi = 10.1038/nature22335 | s2cid = 205255853 | bibcode = 2017Natur.546..293R }}
{{cite journal | vauthors = Smith TM, Tafforeau P, Reid DJ, Grün R, Eggins S, Boutakiout M, Hublin JJ | title = Earliest evidence of modern human life history in North African early ''Homo sapiens'' | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 15 | pages = 6128–6133 | date = April 2007 | pmid = 17372199 | pmc = 1828706 | doi = 10.1073/pnas.0700747104 | doi-access = free | bibcode = 2007PNAS..104.6128S }}
{{cite journal| vauthors = Callaway E |title=Oldest ''Homo sapiens'' fossil claim rewrites our species' history|url=http://www.nature.com/news/oldest-homo-sapiens-fossil-claim-rewrites-our-species-history-1.22114|date=7 June 2017|journal=[[Nature (journal)|Nature]]|doi=10.1038/nature.2017.22114|access-date=5 July 2017|url-access=subscription|doi-access=free}}</ref>
Fossils of ''Homo sapiens'' were found in [[East Africa]] which are c. 200,000 years old. It is unclear to what extent these early modern humans had developed [[origin of language|language]], [[origin of music|music]], [[evolutionary origin of religions|religion]], etc. The [[cognitive tradeoff hypothesis]] proposes that there was an evolutionary tradeoff between short-term working memory and complex language skills over the course of human evolution.<ref name=":13">Matsuzawa, T. (2009). [https://www.sciencedirect.com/science/article/abs/pii/S0959438809000269 Symbolic representation of number in chimpanzees]. Current Opinion in Neurobiology, 19(1), pp. 92–98.</ref>

According to proponents of the [[Toba catastrophe theory]], the climate in non-tropical regions of the earth experienced a sudden freezing about 70,000 years ago, because of a huge explosion of the Toba volcano that filled the atmosphere with volcanic ash for several years. This reduced the human population to less than 10,000 breeding pairs in equatorial Africa, from which all modern humans are descended. Being unprepared for the sudden change in climate, the survivors were those intelligent enough to invent new tools and ways of keeping warm and finding new sources of food (for example, adapting to ocean fishing based on prior fishing skills used in lakes and streams that became frozen).{{citation needed|date=February 2015}}

Around 80,000–100,000 years ago, three main lines of ''Homo sapiens'' diverged, bearers of mitochondrial [[Haplogroup L1 (mtDNA)|haplogroup L1]] (mtDNA) / [[Haplogroup A (Y-DNA)|A]] (Y-DNA) colonizing [[Southern Africa]] (the ancestors of the [[Khoisan]]/[[Capoid]] peoples), bearers of [[Haplogroup L2 (mtDNA)|haplogroup L2]] (mtDNA) / [[Haplogroup B (Y-DNA)|B]] (Y-DNA) settling [[Central Africa|Central]] and [[West Africa]] (the ancestors of [[Niger–Congo]] and [[Nilo-Saharan]] speaking peoples), while the bearers of [[Haplogroup L3 (mtDNA)|haplogroup L3]] remained in East Africa.{{citation needed|date=February 2015}}

The "Great Leap Forward" leading to full [[behavioral modernity]] sets in only after this separation. Rapidly increasing sophistication in tool-making and behaviour is apparent from about 80,000 years ago, and the [[recent African origin|migration out of Africa]] follows towards the very end of the [[Middle Paleolithic]], some 60,000 years ago. Fully modern behaviour, including [[figurative art]], [[music]], self-ornamentation, [[trade]], [[burial rite]]s etc. is evident by 30,000 years ago. The oldest unequivocal examples of [[prehistoric art]] date to this period, the [[Aurignacian]] and the [[Gravettian]] periods of [[prehistoric Europe]], such as the [[Venus figurines]] and [[cave painting]] ([[Chauvet Cave]]) and the earliest [[prehistoric music|musical instruments]] (the bone pipe of [[Geissenklösterle]], [[Germany]], dated to about 36,000 years ago).<ref>{{cite book|chapter-url=http://www.mus.cam.ac.uk/~ic108/lithoacoustics/BAR2002/BARpreprint.pdf | vauthors = Cross I, Zubrow E, Cowan F |year=2002 |chapter=Musical behaviours and the archaeological record: a preliminary study |editor=J. Mathieu |title=Experimental Archaeology |publisher=British Archaeological Reports International Series |volume=1035 |pages=25–34 |archive-url=https://web.archive.org/web/20120610150342/http://www.mus.cam.ac.uk/~ic108/lithoacoustics/BAR2002/BARpreprint.pdf |archive-date=2012-06-10 }}</ref>

[[File:Blausen 0102 Brain Motor&Sensory.png|thumb|284x284px|Motor and sensory areas of the cerebral cortex; dashed areas shown are commonly left hemisphere dominant.]]

The human brain has evolved gradually over the passage of time; a series of incremental changes occurring as a result of external stimuli and conditions. It is crucial to keep in mind that evolution operates within a limited framework at a given point in time. In other words, the adaptations that a species can develop are not infinite and are defined by what has already taken place in the evolutionary timeline of a species. Given the immense anatomical and structural complexity of the brain, its evolution (and the congruent evolution of human intelligence), can only be reorganized in a finite number of ways. The majority of said changes occur either in terms of size or in terms of developmental timeframes.<ref>{{cite journal | vauthors = Iriki A, Sakura O | title = The neuroscience of primate intellectual evolution: natural selection and passive and intentional niche construction | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 363 | issue = 1500 | pages = 2229–2241 | date = June 2008 | pmid = 18426757 | pmc = 2394573 | doi = 10.1098/rstb.2008.2274 }}</ref> 

The [[cerebral cortex]] is divided into four lobes (frontal, parietal, occipital, and temporal) each with specific functions. The cerebral cortex is significantly larger in humans than in any other animal and is responsible for higher thought processes such as reasoning, abstract thinking, and decision making.<ref>{{cite book|title=Brain Facts: A Primer on The Brain and Nervous System|publisher=Society for Neuroscience|year=2018|location=Washington, D.C.|pages=51}}</ref> Another characteristic that makes humans special and sets them apart from any other species is our ability to produce and understand complex, syntactic language. The cerebral cortex, particularly in the temporal, parietal, and frontal lobes, are populated with neural circuits dedicated to language. There are two main areas of the brain commonly associated with language, namely: [[Wernicke's area]] and [[Broca's area]]. The former is responsible for the understanding of speech and the latter for the production of speech. Homologous regions have been found in other species (i.e. Area 44 and 45 have been studied in chimpanzees) but they are not as strongly related to or involved in linguistic activities as in humans.<ref>{{cite journal | vauthors = Schenker NM, Hopkins WD, Spocter MA, Garrison AR, Stimpson CD, Erwin JM, Hof PR, Sherwood CC | display-authors = 6 | title = Broca's area homologue in chimpanzees (Pan troglodytes): probabilistic mapping, asymmetry, and comparison to humans | journal = Cerebral Cortex | volume = 20 | issue = 3 | pages = 730–742 | date = March 2010 | pmid = 19620620 | pmc = 2820707 | doi = 10.1093/cercor/bhp138 }}</ref>

==Models==

===Massive modularity of mind===
{{multiple image
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| image1            = Wason selection task cards.svg
| caption1          = Each card has a number on one side, and a patch of color on the other. Which card or cards must be turned over to test the idea that if a card shows an even number on one face, then its opposite face is blue?
| image2            = Wason selection task cards - drinking variant.svg
| caption2          = Each card has an age on one side, and a drink on the other. Which card or cards must be turned over to test the idea that if someone is drinking alcohol then they must be over 18?
}}

In 2004, psychologist [[Satoshi Kanazawa]] argued that ''[[g factor (psychometrics)|g]]'' was a [[Domain specificity|domain-specific]], [[Species-typical behavior|species-typical]], [[Information processing (psychology)|information processing]] [[psychological adaptation]],<ref>{{cite journal | vauthors = Kanazawa S | title = General intelligence as a domain-specific adaptation | journal = Psychological Review | volume = 111 | issue = 2 | pages = 512–523 | date = April 2004 | pmid = 15065920 | doi = 10.1037/0033-295X.111.2.512 | publisher = [[American Psychological Association]] }}</ref> and in 2010, Kanazawa argued that ''g'' correlated only with performance on evolutionarily unfamiliar rather than evolutionarily familiar problems, proposing what he termed the "Savanna-IQ interaction hypothesis".<ref name="Kanazawa 2010a">{{Cite journal | vauthors = Kanazawa S |date=2010-02-16 |title=Why Liberals and Atheists Are More Intelligent |journal=Social Psychology Quarterly |volume=73 |issue=1 |pages=33–57 |doi=10.1177/0190272510361602 |issn=0190-2725|citeseerx=10.1.1.395.4490 |s2cid=2642312 }}</ref><ref name="Kanazawa 2010b">{{cite journal | vauthors = Kanazawa S | title = Evolutionary psychology and intelligence research | journal = The American Psychologist | volume = 65 | issue = 4 | pages = 279–289 | date = May–June 2010 | pmid = 20455621 | doi = 10.1037/a0019378 }}</ref> In 2006, ''[[Psychological Review]]'' published a comment reviewing Kanazawa's 2004 article by psychologists [[Denny Borsboom]] and [[Conor Dolan]] that argued that Kanazawa's conception of ''g'' was empirically unsupported and purely hypothetical and that an evolutionary account of ''g'' must address it as a source of [[Differential psychology|individual differences]].<ref>{{cite journal | vauthors = Borsboom D, Dolan CV | title = Why g is not an adaptation: a comment on Kanazawa (2004) | journal = Psychological Review | volume = 113 | issue = 2 | pages = 433–437 | date = April 2006 | pmid = 16637768 | doi = 10.1037/0033-295X.113.2.433 }}</ref> In response to Kanazawa's 2010 article, psychologists [[Scott Barry Kaufman]], [[Colin G. DeYoung]], Deirdre Reis, and Jeremy R. Gray gave 112 subjects a 70-item computerized version of the [[Wason selection task]] (a [[logic puzzle]]) in a [[social relation]]s context as proposed by [[Leda Cosmides]] and [[John Tooby]] in ''[[The Adapted Mind]]'',<ref name="Cosmides & Tooby 1992 pp. 163–184">{{cite book| vauthors = Cosmides L, Tooby J | veditors = Barkow JH, Cosmides L, Tooby J |editor-link1=Jerome H. Barkow|title=The Adapted Mind: Evolutionary Psychology and the Generation of Culture|title-link=The Adapted Mind|chapter=3. Cognitive Adaptations for Social Exchange|place=New York|publisher=[[Oxford University Press]]|orig-date=1992|year=1995|pages=163–184|isbn=978-0195101072}}</ref> and found instead that "performance on non-arbitrary, evolutionarily familiar problems is more strongly related to general intelligence than performance on arbitrary, evolutionarily novel problems".<ref name="Kaufman et al. 2010">{{cite journal | vauthors = Kaufman SB, DeYoung CG, Reis DL, Gray JR |date=May–June 2010|title=General intelligence predicts reasoning ability even for evolutionarily familiar content|journal=[[Intelligence (journal)|Intelligence]]|volume=39|issue=5|pages=311–322|doi=10.1016/j.intell.2011.05.002|url=https://scottbarrykaufman.com/wp-content/uploads/2011/08/Kaufman-DeYoung-Reis-Gray-2011.pdf|access-date=16 February 2018}}</ref><ref name="Kaufman 2011">{{cite journal| vauthors = Kaufman SB |date=2 July 2011|title=Is General Intelligence Compatible with Evolutionary Psychology?|journal=[[Psychology Today]]|publisher=Sussex Publishers|url=https://www.psychologytoday.com/blog/beautiful-minds/201107/is-general-intelligence-compatible-evolutionary-psychology|access-date=16 February 2018}}</ref>

[[Peter Cathcart Wason]] originally demonstrated that not even 10% of subjects found the correct solution and his finding was replicated.<ref>{{cite book | vauthors = Wason PC |year=1977 |chapter=Self-contradictions |editor-link=Philip Johnson-Laird | veditors = Johnson-Laird PN, Wason PC |title=Thinking: Readings in cognitive science |location=Cambridge |publisher=Cambridge University Press |isbn=978-0521217569 |url-access=registration |url=https://archive.org/details/thinking00ives }}</ref><ref name="EvansNewstead1993">{{cite book| vauthors = St Evans JB, Newstead SE, Byrne RM |title=Human Reasoning: The Psychology of Deduction|url=https://books.google.com/books?id=iFMhZ4dl1KcC|year=1993|publisher=Psychology Press|isbn=978-0-86377-313-6}}</ref> Psychologists [[Patricia Cheng]], [[Keith Holyoak]], [[Richard E. Nisbett]], and Lindsay M. Oliver demonstrated experimentally that subjects who have completed semester-long college courses in [[propositional calculus]] do not perform better on the Wason selection task than subjects who do not complete such college courses.<ref>{{cite journal | vauthors = Cheng PW, Holyoak KJ, Nisbett RE, Oliver LM | title = Pragmatic versus syntactic approaches to training deductive reasoning | journal = Cognitive Psychology | volume = 18 | issue = 3 | pages = 293–328 | date = July 1986 | pmid = 3742999 | doi = 10.1016/0010-0285(86)90002-2 | publisher = [[Elsevier]] | hdl-access = free | s2cid = 10376933 | hdl = 2027.42/26121 }}</ref> Tooby and Cosmides originally proposed a social relations context for the Wason selection task as part of a larger computational theory of social exchange after they began reviewing the previous experiments about the task beginning in 1983.<ref name="Cosmides & Tooby 1992 pp. 163–184" /> Despite other experimenters finding that some contexts elicited more correct subject responses than others, no theoretical explanation for differentiating between them was identified until Tooby and Cosmides proposed that disparities in subjects performance on contextualized versus non-contextualized variations of the task was an [[Artifact (error)|artifact]] of the task measuring a [[Cognitive specialization|specialized]] [[Cheating (biology)|cheater-detection]] [[Cognitive module|module]].<ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |title=The Handbook of Evolutionary Psychology|chapter=20. Neurocognitive Adaptations Designed for Social Exchange|pages=584–600|year=2005|edition=1st|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-0471264033}}</ref><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |year=2016|orig-date=2005|title=The Handbook of Evolutionary Psychology, Volume 2: Integrations|edition=2nd|chapter=25. Adaptations for Reasoning About Social Exchange|pages=625–640|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-1118755808}}</ref> Tooby and Cosmides later noted that whether there are evolved cognitive mechanisms for the content-blind [[Rule of inference|rules of logical inference]] is disputed,<ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |title=The Handbook of Evolutionary Psychology|chapter=20. Neurocognitive Adaptations Designed for Social Exchange|pages=600–603|year=2005|edition=1st|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-0471264033}}</ref><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |year=2016|orig-date=2005|title=The Handbook of Evolutionary Psychology, Volume 2: Integrations|edition=2nd|chapter=25. Adaptations for Reasoning About Social Exchange|pages=640–643|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-1118755808}}</ref> and consistently noted that a body of research about the Wason selection task had concluded that cognitive adaptations for social exchange were not a [[Spandrel (biology)|by-product]] of general-purpose reasoning mechanisms, [[domain-general learning]] mechanisms, or ''g''.<ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Barkow JH, Cosmides L, Tooby J |editor-link1=Jerome H. Barkow|title=The Adapted Mind: Evolutionary Psychology and the Generation of Culture|title-link=The Adapted Mind|chapter=3. Cognitive Adaptations for Social Exchange|place=New York|publisher=[[Oxford University Press]]|orig-date=1992|year=1995|pages=184-206|isbn=978-0195101072}}</ref><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |title=The Handbook of Evolutionary Psychology|chapter=20. Neurocognitive Adaptations Designed for Social Exchange|pages=603–623|year=2005|edition=1st|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-0471264033}}</ref><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Buss DM |year=2016|orig-date=2005|title=The Handbook of Evolutionary Psychology, Volume 2: Integrations|edition=2nd|chapter=25. Adaptations for Reasoning About Social Exchange|pages=643–663|place=[[Hoboken, New Jersey|Hoboken, NJ]]|publisher=[[Wiley (publisher)|Wiley]]|isbn=978-1118755808}}</ref>

Relatedly, economist [[Thomas Sowell]] has noted that numerous studies finding [[Race and intelligence|disparities between the mean test scores of ethnic groups]] on [[Intelligence quotient|intelligence tests]] have found that ethnic groups with lower mean test scores have tended to perform worst on [[Spatial visualization ability|spatial]], non-verbal, or [[Abstraction|abstract reasoning]] test items.<ref>{{cite book| vauthors = Sowell T |year=1994|title=Race and Culture: A World View|publisher=[[Basic Books]]|place=New York|pages=162–165|isbn=978-0465067978}}</ref><ref>{{cite book| vauthors = Sowell T |year=2013|title=Intellectuals and Race|publisher=[[Basic Books]]|place=New York|pages=67–69|isbn=978-0465058723}}</ref> Writing after the completion of the [[Human Genome Project]] in 2003, psychologist [[Earl B. Hunt]] noted in 2011 that no genes related to [[Race and intelligence#Genetics of race and intelligence|differences in cognitive skills across various racial and ethnic groups]] had ever been discovered.<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|page=447}}</ref> In 2012, ''[[American Psychologist]]'' published a review by Nisbett, psychologists [[Joshua Aronson]], [[Clancy Blair]], [[Diane F. Halpern]], and [[Eric Turkheimer]], economist [[William Dickens]], and philosopher [[James Flynn (academic)|James R. Flynn]] of findings since the publication of the [[Intelligence: Knowns and Unknowns|1995 American Psychological Association report on intelligence]] that concluded that almost no [[Single-nucleotide polymorphism|single-nucleotide]] [[Gene polymorphism|genetic polymorphisms]] that have [[Missing heritability problem|been discovered are consistently associated]] with [[Heritability of IQ|variation in IQ]] in the normal range, and that [[Race and intelligence#Adoption studies|adoption research on race and intelligence]] showed that differences could be entirely accounted for by environmental factors.<ref>{{cite journal|vauthors=Nisbett RE, Aronson J, Dickens W, Flynn JR, Blair C, Halpern DF, Turkheimer E|title=Intelligence: New Findings and Theoretical Developments|journal=[[American Psychologist]]|year=2012 |publisher=[[American Psychological Association]]|volume=67|issue=3|pages=130–159|pmid=22233090|doi=10.1037/a0026699}}</ref><ref>{{cite journal|vauthors=Nisbett RE, Aronson J, Blair C, Dickens W, Flynn JR, Halpern DF, Turkheimer E|year=2012|title=Group differences in IQ are best understood as environmental in origin|journal=American Psychologist|publisher=American Psychological Association|volume=67|pages=503–504|doi=10.1037/a0029772|issn=0003-066X|pmid=22963427|number=6}}</ref> In 2021, subsequent research using [[polygenic score]]s for educational attainment and cognitive performance in African and European samples from the [[1000 Genomes Project]] found no evidence of [[Divergent evolution|divergent selection]] by race and a [[Statistical significance|statistically insignificant]] contribution to racial differences in IQ.<ref>{{cite journal|vauthors=Bird KA|year=2021|title=No support for the hereditarian hypothesis of the Black–White achievement gap using polygenic scores and tests for divergent selection|journal=[[American Journal of Biological Anthropology|American Journal of Physical Anthropology]]|publisher=Wiley|volume=175|issue=2|pages=465–476|doi=10.1002/ajpa.24216}}</ref><ref>{{Cite journal|vauthors=Bird KA, Jackson JP, Winston AS|year=2024|title=Confronting Scientific Racism in Psychology: Lessons from Evolutionary Biology and Genetics|url=https://psycnet.apa.org/doiLanding?doi=10.1037%2Famp0001228|journal=American Psychologist|publisher=American Psychological Association|volume=79|issue=4|pages=497–508|doi=10.1037/amp0001228|pmid=39037836}}</ref>

Flynn had argued earlier that the [[Flynn effect]] presented multiple paradoxes for ''g'' as a psychological trait with a heritable basis because the increases in the statistical average scores among later [[Generation|birth year cohorts]] born in the 20th century were occurring without sufficient increases in vocabulary size, general knowledge, and ability to solve arithmetical problems, and that the increases were so large that they would imply that the statistically average members of the birth year cohorts in the late 19th century and early 20th century (the [[Lost Generation]] and the [[Greatest Generation]]) would have been [[Intellectual disability|intellectually disabled]] (as well as more distant human ancestors).<ref>{{cite book|vauthors=Flynn JR|year=2009|orig-year=2007|title=What Is Intelligence? Beyond the Flynn Effect|title-link=What Is Intelligence?|place=New York|publisher=[[Cambridge University Press]]|pages=1–10|edition=Expanded paperback|isbn=978-0521741477}}</ref> Hunt noted that the latter paradox would imply that half of the soldiers who served in the [[Military history of the United States during World War II|U.S. military during World War II]] would not pass the [[Armed Services Vocational Aptitude Battery]] in 2008.<ref name="Hunt pp. 261–270">{{cite book|vauthors=Hunt EB|title=Human Intelligence|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=261–270}}</ref> Flynn proposed that these paradoxes could be answered by the increasing use of abstraction, logic, and scientific reasoning to address problems,<ref>{{cite book|vauthors=Flynn JR|year=2009|orig-year=2007|title=What Is Intelligence? Beyond the Flynn Effect|title-link=What Is Intelligence?|place=New York|publisher=[[Cambridge University Press]]|pages=10–47|edition=Expanded paperback|isbn=978-0521741477}}</ref> while Nisbett argued that the Flynn effect was largely attributable to increases in formal education among human populations during the 20th century.<ref>{{cite book|vauthors=Nisbett RE|year=2010|orig-year=2009|title=Intelligence and How to Get It: Why Schools and Cultures Count|title-link=Intelligence and How to Get It|place=New York|publisher=W. W. Norton & Company|pages=39–56|edition=Paperback|isbn=978-0393337693}}</ref>

In 2010, psychologist [[David Marks (psychologist)|David Marks]] found through 8 statistical analyses that average population IQ scores across race, time, and nationality correlated with [[Literacy|literacy rates]] between a range of 0.79 and 0.99, which led to the conclusion that both the Flynn effect and racial differences in mean scores on intelligence tests were statistical artifacts of uncontrolled variation in literacy rates due to test performance requiring literacy.<ref>{{Cite journal | vauthors =Marks DF |year=2010 |title=IQ Variations across Time, Race, and Nationality: An Artifact of Differences in Literacy Skills |url=https://journals.sagepub.com/doi/10.2466/pr0.106.3.643-664 |journal=[[Psychological Reports]] |language=en |volume=106 |issue=3 |pages=643–664 |doi=10.2466/pr0.106.3.643-664 |pmid=20712152 |issn=0033-2941 |publisher=[[Sage Publishing]]|url-access=subscription }}</ref><ref>{{cite web|vauthors=Kaufman SB|title=The Flynn Effect and IQ Disparities Among Races, Ethnicities, and Nations: Are There Common Links?|url=https://www.psychologytoday.com/blog/beautiful-minds/201008/the-flynn-effect-and-iq-disparities-among-races-ethnicities-and-nations|website=Psychology Today|publisher=Sussex Publishers, LLC|access-date=20 March 2025|date=August 23, 2010}}</ref> However, in reference to theoretical issues with [[Constructivism (philosophy of education)|constructivism]] in [[mathematics education]] and the failure of [[whole language]] in literacy education, psychologist [[David C. Geary]] and cognitive scientist [[Steven Pinker]] have noted that literacy, [[numeracy]], and formal [[Mathematics|mathematical]] and [[logical reasoning]] are not psychological adaptations but biologically secondary cognitive skills (i.e. [[acquired characteristic]]s) that require extensive practice after formal, explicit, and direct instruction in contrast with [[natural language]] and [[number sense]], since [[language acquisition]] and numerosity develop [[Automatic and controlled processes|automatically]] and [[Adaptive unconscious|unconsciously]] due to specialized [[Neurobiological origins of language|neurobiological systems for language]] and [[numerical cognition]] which the biologically secondary cognitive skills lack.{{refn|name=Geary/Pinker|<ref>{{cite book|vauthors=Geary DC|year=1994|title=Children's Mathematical Development: Research and Practical Applications|place=Washington, DC|publisher=American Psychological Association|pages=1–130; 261–266|isbn=978-1557982582}}</ref><ref>{{cite book|vauthors=Pinker S|year=1997|title=How the Mind Works|title-link=How the Mind Works|publisher=[[W. W. Norton & Company]]|place=New York|pages=333–342|isbn=978-0393318487}}</ref><ref>{{cite book| vauthors = Bjorklund DF, Blasi CH |author-link1=David F. Bjorklund | veditors = Buss DM |title=The Handbook of Evolutionary Psychology |chapter=29. Evolutionary Developmental Psychology |pages=842–844 |year=2005 |edition=1st |place=[[Hoboken, New Jersey|Hoboken, NJ]] |publisher=[[Wiley (publisher)|Wiley]] |isbn=978-0-471-26403-3}}</ref><ref>{{cite book|vauthors=Pinker S|year=2007|orig-year=1994|title=The Language Instinct: How the Mind Creates Language|title-link=The Language Instinct|publisher=[[Harper Perennial]]|place=New York|pages=20–34; 140–147; 186; 265–388; PS14|edition=3rd|isbn=978-0061336461}}</ref>}}

Pinker has also noted that [[writing]] is not a [[cultural universal]] since [[History of writing#Emergence|writing systems were independently invented only a few times in human history]] and most societies documented by [[Ethnography|ethnographers]] lacked writing systems,<ref>{{cite book|vauthors=Pinker S|year=2007|orig-year=1994|title=The Language Instinct: How the Mind Creates Language|title-link=The Language Instinct|publisher=[[Harper Perennial]]|place=New York|pages=186–187|edition=3rd|isbn=978-0061336461}}</ref> while literacy rates in European countries did not begin to exceed 50 percent until the 17th century since the [[Movable type|movable-type]] [[printing press]] was not invented until the 15th century.<ref>{{cite book|vauthors=Pinker S|year=2011|title=The Better Angels of Our Nature: Why Violence Has Declined|title-link=The Better Angels of Our Nature|place=New York|publisher=Penguin Books|pages=172–174|isbn=978-0143122012}}</ref> Similarly to the lack of improvement in performance on the Wason selection task by college students that take courses in propositional calculus, Pinker referenced the response by professional mathematicians and statisticians to the solution to the [[Monty Hall problem]] published in ''[[Parade (magazine)|Parade]]'' in 1990 in noting the dominance of automatic processes over controlled processes for formal logical reasoning following the [[Dual process theory|dual process model]] proposed by psychologists [[Daniel Kahneman]] and [[Amos Tversky]].<ref>{{cite book|vauthors=Pinker S|year=2021|title=Rationality: What It Is, Why It Seems Scarce, Why It Matters|title-link=Rationality (book)|place=New York|publisher=Penguin Books|pages=8–22|isbn=978-0525562016}}</ref><ref>{{cite book|vauthors=Kahneman, D|year=2013|orig-year=2011|title=Thinking, Fast and Slow|title-link=Thinking, Fast and Slow|place=New York|publisher=Farrar, Straus and Giroux|pages=19–105|isbn=978-0374533557}}</ref> While Pinker has suggested that the evolution of human intelligence could be explained by intelligence itself being the product of [[metaphor]] (stemming from the ability to create [[Sign (semiotics)|arbitrary]] [[morpheme]]s) and [[Generative grammar|combinatorial grammar]] (allowing [[Recursion|nesting]] of [[verb phrase]]s in [[syntax]]) that together enable the [[Digital infinity|infinite composition of sentences]],<ref>{{cite book|vauthors=Pinker S|year=2007|title=The Stuff of Thought: Language As a Window Into Human Nature|title-link=The Stuff of Thought|place=New York|publisher=Basic Books|pages=241–245; 435–439|isbn=978-0465072699}}</ref><ref>{{cite book|vauthors=Pinker S|year=2007|orig-year=1994|title=The Language Instinct: How the Mind Creates Language|title-link=The Language Instinct|publisher=[[Harper Perennial]]|place=New York|edition=3rd|isbn=978-0061336461}}</ref><ref>{{cite book|vauthors=Pinker S|year=1999|title=Words and Rules: The Ingredients of Language|title-link=Words and Rules|place=New York|publisher=Basic Books|isbn=978-0465072699}}</ref> Pinker has also argued that the Flynn effect is likely caused by increased amounts of formal education in addition to other factors.<ref>{{cite book|vauthors=Pinker S|year=2011|title=The Better Angels of Our Nature: Why Violence Has Declined|title-link=The Better Angels of Our Nature|place=New York|publisher=Penguin Books|pages=650–656|isbn=978-0143122012}}</ref>

Noting that Kaufman and psychologist [[Robert Sternberg]] identified a lack of consensus about how to define human intelligence,<ref>{{cite book|vauthors=Sternberg RJ, Kaufman SB|veditors=Sternberg RJ, Kaufman SB|year=2011|title=The Cambridge Handbook of Intelligence|chapter=Preface|place=New York|publisher=Cambridge University Press|edition=1st|page=xv|isbn=978-0521518062}}</ref> psychologists [[Jay Joseph]] and [[Ken Richardson (psychologist)|Ken Richardson]] have argued that the [[construct validity]] of intelligence tests is questionable due to definitions of intelligence being based on the intuitions of psychologists, that tests measure formal education more than [[Psychological nativism|innate]] intelligence because test items are included because of how such items reflect academic performance, and that the Flynn effect provides evidence against heritability causing even within-group differences in general intelligence due to the [[confounding]] effect of [[Twin study#Classical twin method|shared birth dates and nationalities between pairs of identical twins reared apart]] from different generations in test performance.<ref>{{cite book|vauthors=Joseph J, Richardson K|veditors=Lerner RM, Greenberg, G|editor-link1=Richard M. Lerner|year=2025|title=The Heredity Hoax: Challenging Flawed Genetic Theories of Human Development|chapter=23. The Bell Curve at 30: A Closer Look at the Within- and Between-Group IQ Genetic Evidence|place=New York|publisher=Routledge|pages=433–476|isbn=978-1032699578|doi=10.4324/9781032702988}}</ref> While Hunt defended the methodology of twin and [[Adoption study|adoption research]] in [[Behavioural genetics|behavioral genetics]],<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|chapter=8. The Genetic Basis of Intelligence|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=203–256}}</ref> Hunt also noted that the only [[candidate gene]]s behavioral geneticists had proposed being related to ''g'' were associated with below average IQ scores and that none had been identified that were associated with above average IQ scores.<ref name="Hunt pp. 261–270" />

Although Hunt expressed some reservations about the construct validity of ''g'' (referencing the research of psychologist [[Louis Leon Thurstone]]) and acknowledged the impact of literacy on IQ test performance,<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=19–20; 97–99}}</ref> Hunt defended the [[fluid and crystallized intelligence]] models of ''g'' in [[psychometrics]],<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|chapter=4. Psychometric Theories|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=79–110}}</ref> and argued that alternatives to psychometric models (such as the [[theory of multiple intelligences]] and the [[triarchic theory of intelligence]]) lacked empirical support.<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|chapter=5. Taking Intelligence Beyond Psychometrics|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=111–139}}</ref> Hunt also argued that research on the [[evolution of the brain]] showed evidence for ''g'' as a general problem-solving mechanism.<ref>{{cite book|vauthors=Hunt EB|title=Human Intelligence|publisher=[[Cambridge University Press]]|place=New York|year=2011|isbn=978-0521707817|pages=21–22; 183–190; 203–208}}</ref> Conversely, Pinker has argued that research in [[cognitive neuroscience]] has shown that the brain is more characterized by [[Functional specialization (brain)|functional specialization]].<ref>{{cite book|vauthors=Pinker S|year=1997|title=How the Mind Works|title-link=How the Mind Works|publisher=[[W. W. Norton & Company]]|place=New York|pages=25–26|isbn=978-0393318487}}</ref><ref>{{cite book|vauthors=Pinker S|year=2016|orig-year=2002|title=The Blank Slate: The Modern Denial of Human Nature|title-link=The Blank Slate|place=New York|publisher=Penguin Books|pages=41–45|isbn=978-0142003343}}</ref> While Geary has attempted to integrate ''g'' with [[evolutionary psychology]],<ref>{{cite book|vauthors=Geary DC|year=2005|title=The Origin of Mind: Evolution of Brain, Cognition, and General Intelligence|chapter=8. Evolution of General Intelligence|place=Washington, DC|publisher=American Psychological Association|pages=253–305|isbn=978-1591471813}}</ref> Tooby, Cosmides, and Pinker have all argued that the [[Mind|human mind]] is better understood as a [[Modularity of mind|system of dedicated intelligences]] and [[Domain-specific learning|domain-specific learning]] systems that are adaptively specialized rather than characterized by a general intelligence factor and a domain-general learning system that enables the passive [[cultural learning]] and [[socialization]] of a [[Tabula rasa|blank slate]].{{refn|name=Tooby/Cosmides/Pinker|<ref name="Kaufman 2011" /><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Barkow JH, Cosmides L, Tooby J |editor-link1=Jerome H. Barkow|title=The Adapted Mind: Evolutionary Psychology and the Generation of Culture|title-link=The Adapted Mind|chapter=1. The Psychological Foundations of Culture|place=New York|publisher=[[Oxford University Press]]|orig-date=1992|year=1995|pages=49–123|isbn=978-0195101072}}</ref><ref>{{cite book|vauthors=Pinker S|year=1997|title=How the Mind Works|title-link=How the Mind Works|publisher=[[W. W. Norton & Company]]|place=New York|pages=21–31; 60–93; 179–198|isbn=978-0393318487}}</ref><ref>{{cite book|vauthors=Pinker S|year=2016|orig-year=2002|title=The Blank Slate: The Modern Denial of Human Nature|title-link=The Blank Slate|place=New York|publisher=Penguin Books|pages=1–102|isbn=978-0142003343}}</ref><ref name="Cosmides Barrett & Tooby 2010">{{cite journal|vauthors=Cosmides L, Barrett HC, Tooby J|year=2010|title=Adaptive specializations, social exchange, and the evolution of human intelligence|journal=[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]]|publisher=[[National Academy of Sciences]]|volume=107|issue=2|pages=9007–9014|doi=10.1073/pnas.0914623107|pmid=20445099|pmc=3024027|bibcode=2010PNAS..107.9007C}}</ref>}}

Although Tooby and Cosmides suggested that the human mind does have a domain-general, content-independent, and general-purpose improvisational intelligence that resembles general intelligence, and which possibly evolved to generate solutions in novel situations where the dedicated intelligences did not produce an optimal response,<ref>{{cite book|vauthors=Cosmides L, Tooby J|year=2001|title=The Evolution of Intelligence|chapter=8. Unraveling the Enigma of Human Intelligence: Evolutionary Psychology and the Multimodular Mind|veditors=Sternberg RJ, Kaufman JC|place=Mahwah, NJ|publisher=Lawrence Erlbaum Associates|pages=145–198|isbn=978-0585380858}}</ref><ref name="Kaufman 2011" /><ref name="Kaufman et al. 2010" /> in light of the [[frame problem]] in [[artificial intelligence]] and because all [[adaptation]]s require [[selection pressure]] from recurrent problems, Tooby and Cosmides argue that a complete blank slate mind entirely shaped by general intelligence following the [[standard social science model]] is not computationally capable of performing the cognitive tasks or solving the adaptive problems that the human mind evolved to perform and solve, such as [[visual perception]], language acquisition, recognizing [[emotional expression]]s, [[mate choice]], cultural learning, and cheater-detection in social exchange.<ref>{{cite journal|vauthors=Tooby J, Cosmides L|year=1989|title=Evolutionary Psychology and the Generation of Culture, Part I: Theoretical Considerations|journal=Ethology and Sociobiology|volume=10|issue=1–3|pages=29–49|publisher=Elsevier|doi=10.1016/0162-3095(89)90012-5|doi-access=free}}</ref><ref>{{cite book| vauthors = Cosmides L, Tooby J | veditors = Barkow JH, Cosmides L, Tooby J |editor-link1=Jerome H. Barkow|title=The Adapted Mind: Evolutionary Psychology and the Generation of Culture|title-link=The Adapted Mind|chapter=1. The Psychological Foundations of Culture|place=New York|publisher=[[Oxford University Press]]|orig-date=1992|year=1995|pages=19–49|isbn=978-0195101072}}</ref><ref name="Cosmides Barrett & Tooby 2010" />

===Social brain hypothesis===
{{further|Dunbar's number}}

The social brain hypothesis was proposed by British anthropologist [[Robin Dunbar]], who argues that human intelligence did not evolve primarily as a means to solve ecological problems, but rather as a means of surviving and reproducing in large and complex social groups.<ref name="The Social Brain Hypothesis"/><ref>{{cite journal | vauthors = Dávid-Barrett T, Dunbar RI | title = Processing power limits social group size: computational evidence for the cognitive costs of sociality | journal = Proceedings. Biological Sciences | volume = 280 | issue = 1765 | pages = 20131151 | date = August 2013 | pmid = 23804623 | pmc = 3712454 | doi = 10.1098/rspb.2013.1151 }}</ref> Some of the behaviors associated with living in large groups include reciprocal altruism, deception, and coalition formation. These group dynamics relate to [[Theory of Mind]] or the ability to understand the thoughts and emotions of others, though Dunbar himself admits in the same book that it is not the flocking itself that causes intelligence to evolve (as shown by [[ruminant]]s).<ref name="The Social Brain Hypothesis">{{cite journal| vauthors = Dunbar RI |url=http://archives.evergreen.edu/webpages/curricular/2006-2007/languageofpolitics/files/languageofpolitics/Evol_Anthrop_6.pdf |doi=10.1002/(SICI)1520-6505(1998)6:5<178::AID-EVAN5>3.0.CO;2-8|title=The social brain hypothesis|year=1998|journal=Evolutionary Anthropology: Issues, News, and Reviews|volume=6|issue=5|pages=178–90|s2cid=9555943 }}</ref>

Dunbar argues that when the size of a social group increases, the number of different relationships in the group may increase by orders of magnitude. Chimpanzees live in groups of about 50 individuals whereas humans typically have a social circle of about 150 people, which is also the typical size of social communities in small societies and personal social networks;<ref name = "Dunbar_2014">{{cite journal | doi = 10.1177/0963721413517118| title = The Social Brain: Psychological Underpinnings and Implications for the Structure of Organizations| journal = Current Directions in Psychological Science| volume = 23| issue = 2| pages = 109–114| year = 2014| vauthors = Dunbar RI | s2cid = 146463887}}</ref> this number is now referred to as [[Dunbar's number]]. In addition, there is evidence to suggest that the success of groups is dependent on their size at foundation, with groupings of around 150 being particularly successful, potentially reflecting the fact that communities of this size strike a balance between the minimum size of effective functionality and the maximum size for creating a sense of commitment to the community.<ref name = "Dunbar_2014" /> According to the social brain hypothesis, when hominids started living in large groups, selection favored greater intelligence. As evidence, Dunbar cites a relationship between neocortex size and group size of various mammals.<ref name="The Social Brain Hypothesis"/>

====Criticism====
[[Phylogeny|Phylogenetic]] studies of brain sizes in primates show that while diet predicts primate brain size, sociality does not predict brain size when corrections are made for cases in which diet affects both brain size and sociality. The exceptions to the predictions of the social intelligence hypothesis, which that hypothesis has no predictive model for, are successfully predicted by diets that are either nutritious but scarce or abundant but poor in nutrients.<ref name=":0"/> Researchers have found that [[frugivore]]s tend to exhibit larger brain size than [[folivore]]s.<ref name=":0">{{cite journal | vauthors = DeCasien AR, Williams SA, Higham JP | title = Primate brain size is predicted by diet but not sociality | journal = Nature Ecology & Evolution | volume = 1 | issue = 5 | pages = 112 | date = March 2017 | pmid = 28812699 | doi = 10.1038/s41559-017-0112 | bibcode = 2017NatEE...1..112D | s2cid = 205564046 }}</ref> One potential explanation for this finding is that frugivory requires "extractive foraging", or the process of locating and preparing hard-shelled foods, such as nuts, insects, and fruit.<ref name=":2">{{cite journal| vauthors = King BJ |date=August 1986|title=Extractive foraging and the evolution of primate intelligence |journal=Human Evolution |volume=1 |issue=4 |pages=361–372 |doi=10.1007/BF02436709 |s2cid=83885668}}</ref> Extractive foraging requires higher cognitive processing, which could help explain larger brain size.<ref name=":2" /> However, other researchers argue that extractive foraging was not a catalyst in the evolution of primate brain size, demonstrating that some non primates exhibit advanced foraging techniques.<ref name=":2" /> Other explanations for the positive correlation between brain size and frugivory highlight how the high-energy, frugivore diet facilitates fetal brain growth and requires spatial mapping to locate the embedded foods.<ref name=":0"/>

[[Meerkat]]s have far more social relationships than their small brain capacity would suggest. Another hypothesis is that it is actually intelligence that causes social relationships to become more complex, because intelligent individuals are more difficult to learn to know.<ref>Kluger, Jeffrey (16 August 2010). [https://web.archive.org/web/20110826141517/http://www.time.com/time/magazine/article/0,9171,2008867,00.html "Inside The Minds of Animals"]. ''[[Time (magazine)|Time]]''.</ref>

There are also studies that show that Dunbar's number is not the upper limit of the number of social relationships in humans either.<ref>{{cite journal| vauthors = McCarty C, Killworth PD, Bernard HR, Johnsen E, Shelley G |title=Comparing Two Methods for Estimating Network Size|journal=Human Organization|volume=60|pages=28–39|year=2000|url=http://www.bebr.ufl.edu/files/Comparing%20Two%20Methods%20for%20Estimating%20Network%20Size_0.pdf|doi=10.17730/humo.60.1.efx5t9gjtgmga73y|url-status=dead|archive-url=https://web.archive.org/web/20120206174952/http://www.bebr.ufl.edu/files/Comparing%20Two%20Methods%20for%20Estimating%20Network%20Size_0.pdf|archive-date=2012-02-06}}</ref><ref>{{cite journal|author1=Bernard, H. Russell|author2=Shelley, Gene Ann|author3=Killworth, Peter|year=1987|title=How Much of a Network does the GSS and RSW Dredge Up?|url=http://nersp.nerdc.ufl.edu/~ufruss/documents/network%20dredging.pdf|journal=Social Networks|volume=9|pages=49–63|doi=10.1016/0378-8733(87)90017-7|access-date=22 July 2013|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304225438/http://nersp.nerdc.ufl.edu/~ufruss/documents/network%20dredging.pdf|url-status=dead}}</ref>

The hypothesis that it is brain capacity that sets the upper limit for the number of social relationships is also contradicted by computer simulations that show simple unintelligent reactions to be sufficient to emulate "ape politics"<ref>How the body shapes the way we think: A new view of intelligence, Rolf Pfeifer, Josh Bongard</ref> and by the fact that some social insects such as the paper wasp do have hierarchies in which each individual has its place (as opposed to herding without social structure) and maintains their hierarchies in groups of approximately 80 individuals with their brains smaller than that of any mammal.<ref>Micromonsters, David Attenborough 2013</ref>

Insects provide an opportunity to explore this since they exhibit an unparalleled diversity of social forms to permanent colonies containing many individuals working together as a collective organism and have evolved an impressive range of cognitive skills despite their small nervous systems.<ref>{{cite journal | vauthors = Chittka L, Niven J | title = Are bigger brains better? | journal = Current Biology | volume = 19 | issue = 21 | pages = R995–R1008 | date = November 2009 | pmid = 19922859 | doi = 10.1016/j.cub.2009.08.023 | s2cid = 7247082 | doi-access = free | bibcode = 2009CBio...19.R995C }}</ref><ref>{{cite book | vauthors = Hölldobler B, Wilson E |title=The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies |date=17 November 2008 |publisher=W. W. Norton & Company |isbn=9780393067040}}</ref><ref>{{cite book | vauthors = Costa J |title=The Other Insect Societies |date=30 September 2006 |publisher=Harvard University Press |isbn=9780674021631}}</ref> Social insects are shaped by ecology, including their social environment. Studies aimed to correlating brain volume to complexity have failed to identify clear correlations between sociality and cognition because of cases like social insects. In humans, societies are usually held together by the ability of individuals to recognize features indicating group membership. Social insects, likewise, often recognize members of their colony allowing them to defend against competitors. Ants do this by comparing odors which require fine discrimination of multicomponent variable cues.<ref>{{cite journal | vauthors = Guerrieri FJ, Nehring V, Jørgensen CG, Nielsen J, Galizia CG, d'Ettorre P | title = Ants recognize foes and not friends | journal = Proceedings. Biological Sciences | volume = 276 | issue = 1666 | pages = 2461–2468 | date = July 2009 | pmid = 19364750 | pmc = 2690455 | doi = 10.1098/rspb.2008.1860 }}</ref> Studies suggest this recognition is achieved through simple cognitive operations that do not involve long-term memory but through sensory adaptation or habituation.<ref>{{cite journal | vauthors = Bos N, d'Ettorre P | title = Recognition of social identity in ants | journal = Frontiers in Psychology | volume = 3 | pages = 83 | date = 2012 | pmid = 22461777 | pmc = 3309994 | doi = 10.3389/fpsyg.2012.00083 | doi-access = free }}</ref> In honeybees, their symbolic 'dance' is a form of communication that they use to convey information with the rest of their colony. In an even more impressive social use of their dance language, bees indicate suitable nest locations to a swarm in search of a new home. The swarm builds a consensus from multiple 'opinions' expressed by scouts with different information, to finally agree on a single destination to which the swarm relocates.<ref>{{cite book | vauthors = Seeley TD |title=Honeybee democracy |date=2010 |publisher=Princeton University Press |location=Princeton, N.J. |isbn=9780691147215}}</ref>

=== Cultural intelligence hypothesis ===

==== Overview ====
Similar to, but distinct from the social brain hypothesis, is the cultural intelligence or cultural brain hypothesis, which dictates that human brain size, cognitive ability, and intelligence have increased over generations due to cultural information from a mechanism known as social learning.<ref>{{cite journal | vauthors = van Schaik CP, Isler K, Burkart JM | title = Explaining brain size variation: from social to cultural brain | language = English | journal = Trends in Cognitive Sciences | volume = 16 | issue = 5 | pages = 277–284 | date = May 2012 | pmid = 22513173 | doi = 10.1016/j.tics.2012.04.004 | s2cid = 3387019 | url = https://www.zora.uzh.ch/id/eprint/65158/1/Explaining_brain_size_CvS_etal_2012.pdf }}</ref> The hypothesis also predicts a positive correlation between species with a higher dependency and more frequent opportunities for social learning and overall cognitive ability.<ref name=":1">{{cite journal | vauthors = Muthukrishna M, Doebeli M, Chudek M, Henrich J | title = The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history | journal = PLOS Computational Biology | volume = 14 | issue = 11 | pages = e1006504 | date = November 2018 | pmid = 30408028 | pmc = 6224031 | doi = 10.1371/journal.pcbi.1006504 | bibcode = 2018PLSCB..14E6504M | veditors = Tarnita CE | doi-access = free }}</ref> This is because social learning allows species to develop cultural skills and strategies for survival; in this way it can be said that heavily cultural species should in theory be more intelligent.<ref>{{cite journal | vauthors = van Schaik CP, Burkart JM | title = Social learning and evolution: the cultural intelligence hypothesis | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 366 | issue = 1567 | pages = 1008–1016 | date = April 2011 | pmid = 21357223 | pmc = 3049085 | doi = 10.1098/rstb.2010.0304 }}</ref>

Humans have been widely acknowledged as the most intelligent species on the planet, with big brains with ample cognitive abilities and processing power which outcompete all other species.<ref>{{Cite book | vauthors = Henrich JP |url=http://worldcat.org/oclc/1096377221|title=The Secret of Our Success: How Culture is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter|year=2016 |publisher=Princeton University Press |isbn=978-0-691-16685-8|oclc=1096377221}}</ref> In fact, humans have shown an enormous increase in brain size and intelligence over millions of years of evolution.<ref>{{cite journal | vauthors = Roth G, Dicke U | title = Evolution of the brain and intelligence | language = English | journal = Trends in Cognitive Sciences | volume = 9 | issue = 5 | pages = 250–257 | date = May 2005 | pmid = 15866152 | doi = 10.1016/j.tics.2005.03.005 | s2cid = 14758763 }}</ref> This is because humans have been referred to as an 'evolved cultural species'; one that has an unrivalled reliance on culturally transmitted knowledge due to the social environment around us.<ref>{{Cite book| vauthors = Buss DM |title=Handbook of evolutionary psychology, volume 2|publisher=John Wiley & Sons, Inc|year=2015|isbn=9781118755853|pages=749–769|language=English}}</ref> This is down to social transmission of information which spreads significantly faster in human populations relative to changes in genetics.<ref>{{Cite journal| vauthors = Laland KN |date=1992-03-01|title=A theoretical investigation of the role of social transmission in evolution|url=https://dx.doi.org/10.1016/0162-3095%2892%2990020-5|journal=Ethology and Sociobiology|language=en|volume=13|issue=2|pages=87–113|doi=10.1016/0162-3095(92)90020-5|issn=0162-3095|url-access=subscription}}</ref> Put simply, humans are the most cultural species there is, and are therefore the most intelligent species there is. The key point when concerning evolution of intelligence is that this cultural information has been consistently transmitted across generations to build vast amounts of cultural skills and knowledge throughout the human race.<ref>{{Cite journal| vauthors = Henrich J |date=2011|title=A cultural species: How culture drove human evolution|url=http://dx.doi.org/10.1037/e519392012-002|access-date=2022-02-11|website=PsycEXTRA Dataset|doi=10.1037/e519392012-002 |url-access=subscription}}</ref> Dunbar's social brain hypothesis on the other hand dictates that our brains evolved primarily due to complex social interactions in groups,<ref>{{Cite journal| vauthors = Dunbar RI |date=1998|title=The social brain hypothesis|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291520-6505%281998%296%3A5%3C178%3A%3AAID-EVAN5%3E3.0.CO%3B2-8|journal=Evolutionary Anthropology: Issues, News, and Reviews|language=en|volume=6|issue=5|pages=178–190|doi=10.1002/(SICI)1520-6505(1998)6:5<178::AID-EVAN5>3.0.CO;2-8|s2cid=9555943 |issn=1520-6505|url-access=subscription}}</ref> so in this way the two hypotheses are distinct from each other in that the cultural intelligence hypothesis focuses more on an in increase in intelligence from socially transmitted information. A shift in focus from 'social' interactions to learning strategies can be seen through this.<ref name=":1" /> The hypothesis can also be seen to contradict the idea of human 'general intelligence' by emphasising the process of cultural skills and information being learned from others.<ref name=":8">{{cite journal | vauthors = Herrmann E, Call J, Hernàndez-Lloreda MV, Hare B, Tomasello M | title = Humans have evolved specialized skills of social cognition: the cultural intelligence hypothesis | journal = Science | volume = 317 | issue = 5843 | pages = 1360–1366 | date = September 2007 | pmid = 17823346 | doi = 10.1126/science.1146282 | bibcode = 2007Sci...317.1360H | s2cid = 686663 }}</ref>

In 2018, [[Michael Muthukrishna|Muthukrishna]] and researchers constructed a model based on the cultural intelligence hypothesis which revealed relationships between brain size, group size, social learning and mating structures.<ref name=":1" /> The model had three underlying assumptions:

# Brain size, complexity and organisation were grouped into one variable
# A larger brain results in larger capacity for adaptive knowledge 
# More adaptive knowledge increases fitness of organisms

Using evolutionary simulation, the researchers were able to confirm the existence of hypothesised relationships. Results concerning the cultural intelligence hypothesis model showed that larger brains can store more information and adaptive knowledge, thus supporting larger groups. This abundance of adaptive knowledge can then be used for frequent social learning opportunities.

==== Further empirical evidence ====
As previously mentioned, social learning is the foundation of the cultural intelligence hypothesis and can be described simplistically as learning from others. It involves behaviours such as imitation, observational learning, influences from family and friends and explicit teaching from others.<ref>{{cite journal | vauthors = Gariépy JF, Watson KK, Du E, Xie DL, Erb J, Amasino D, Platt ML | title = Social learning in humans and other animals | journal = Frontiers in Neuroscience | volume = 8 | pages = 58 | date = 31 March 2014 | pmid = 24765063 | pmc = 3982061 | doi = 10.3389/fnins.2014.00058 | doi-access = free }}</ref> What sets humans apart from other species is that, due to our emphasis on culturally acquired information, humans have evolved to already possess significant social learning abilities from infancy. Neurological studies on nine month old infants were conducted by researchers in 2012 to demonstrate this phenomenon.<ref>{{cite journal | vauthors = Paulus M, Hunnius S, Bekkering H | title = Neurocognitive mechanisms underlying social learning in infancy: infants' neural processing of the effects of others' actions | journal = Social Cognitive and Affective Neuroscience | volume = 8 | issue = 7 | pages = 774–779 | date = October 2013 | pmid = 22689219 | pmc = 3791065 | doi = 10.1093/scan/nss065 }}</ref> The study involved infants observing a caregiver making a sound with a rattle over a period of one week. The brains of the infants were monitored throughout the study. Researchers found that the infants were able to activate neural pathways associated with making a sound with the rattle without actually doing the action themselves, showing human social learning in action- infants were able to understand the effects of a particular action simply by observing the performance of the action by someone else. Not only does this study demonstrate the neural mechanisms of social learning, but it also demonstrates our inherent ability to acquire cultural skills from those around us from the very start of our lives- it therefore shows strong support for the cultural intelligent hypothesis.

Various studies have been conducted to show the cultural intelligence hypothesis in action on a wider scale. One particular study in 2016 investigated two orangutan species, including the more social Sumatran species and the less sociable Bornean species. The aim was to test the notion that species with a higher frequency of opportunities for social learning should evolve to be more intelligent.<ref>{{cite journal | vauthors = Forss SI, Willems E, Call J, van Schaik CP | title = Cognitive differences between orang-utan species: a test of the cultural intelligence hypothesis | journal = Scientific Reports | volume = 6 | issue = 1 | pages = 30516 | date = July 2016 | pmid = 27466052 | pmc = 4964338 | doi = 10.1038/srep30516 | bibcode = 2016NatSR...630516F }}</ref> Results showed that the Sumatrans consistently performed better in cognitive tests compared to the less sociable Borneans. The Sumatrans also showed greater inhibition and more cautious behaviour within their habitat. This was one of the first studies to show evidence for the cultural intelligence hypothesis in a non human species- frequency of learning opportunities had gradually produced differences in cognitive abilities between the two species.

==== Transformative cultural intelligence hypothesis ====
A study in 2018 proposed an altered variant of the original version of the hypothesis called the 'transformative cultural intelligence hypothesis'.<ref>{{Cite journal| vauthors = Moll H |date=2018-03-01|title=The Transformative Cultural Intelligence Hypothesis: Evidence from Young Children's Problem-Solving |journal=Review of Philosophy and Psychology|language=en|volume=9|issue=1|pages=161–175|doi=10.1007/s13164-017-0342-7 |s2cid=39117653 |issn=1878-5166}}</ref> The research involved investigating four year old's problem solving skills in different social contexts. The children were asked to extract a floating object from a tube using water. Nearly all were unsuccessful without cues, however most children succeeded after being shown a pedagogical solution suggesting video. When the same video was shown in a non pedagogical manner however, the children's success in the task did not improve. Crucially, this meant that the children's physical cognition and problem solving ability was therefore affected by how the task was socially presented to them. Researchers thus formulated the transformative cultural intelligence hypothesis, which stresses that our physical cognition is developed and affected by the social environment around us. This challenges the traditional cultural intelligence hypothesis which states that it is human's social cognition and not physical cognition which is superior to our nearest primate relatives;<ref name=":8" /> showing unique physical cognition in humans affected by external social factors. This phenomenon has not been seen in other species.

===Reduction in aggression===
Another theory that tries to explain the growth of human intelligence is the reduced aggression theory (aka [[self-domestication]] theory). According to this strand of thought, what led to the evolution of advanced intelligence in ''Homo sapiens'' was a drastic reduction of the aggressive drive. This change separated us from other species of monkeys and primates, where this aggressivity is still in plain sight, and eventually lead to the development of quintessential human traits such as empathy, social cognition, and culture.<ref name="Eccles, John C. 1989">Eccles, John C. (1989). Evolution of the Brain: Creation of the Self. Foreword by Carl Popper. London: Routledge {{ISBN| 9780415032247}}.</ref><ref name="Waal, Frans B. M. 1989">de Waal, Frans B. M. (1989). Peacemaking among primates. Cambridge, MA: Harvard University Press.{{ISBN| 9780674659216 }}.</ref> This theory has received strong support from studies of animal domestication where selective breeding for tameness has, in only a few generations, led to the emergence of impressive "humanlike" abilities. Tamed foxes, for example, exhibit advanced forms of social communication (following pointing gestures), pedomorphic physical features (childlike faces, floppy ears) and even rudimentary forms of [[theory of mind]] (eye contact seeking, gaze following).<ref name="Belyaev">Belyaev, D. K. 1984. "Foxes" pp. 211-214. In Mason I. L. ed., ''Evolution of Domesticated Animals''. Prentice Hall Press.{{ISBN| 0582460468 }}.</ref><ref name="Trut, L. N., Plyusnina, I., & Oskina, I. N. 2004 pp. 644-655">{{cite journal |doi= 10.1023/B:RUGE.0000033312.92773.c1 | title= An experiment on fox domestication and debattable issues of evolution of the dog |year=2004 | vauthors = Trut LN, Plyusnina I, Oskina IN |journal= Russian Journal of Genetics |volume=40 |issue=6 |pages=644–655 | s2cid= 19741949 }}</ref> Evidence also comes from the field of [[ethology]] (which is the study of animal behavior, focused on observing species in their natural habitat rather than in controlled laboratory settings) where it has been found that animals with a gentle and relaxed manner of interacting with each other – for example stumptailed macaques, orangutans and bonobos – have more advanced socio-cognitive abilities than those found among the more aggressive chimpanzees and baboons.<ref>{{cite web|url=http://www.indiana.edu/~p1013447/dictionary/ethology.htm|title=ETHOLOGY|website=www.indiana.edu|access-date=2019-04-10}}</ref> It is hypothesized that these abilities derive from a selection against aggression.<ref name="Waal, Frans B. M. 1989"/><ref name="Brothers, L., Ring, B., & Kling, A. 1990 pp. 199-213">{{cite journal | vauthors = Brothers L, Ring B, Kling A | title = Response of neurons in the macaque amygdala to complex social stimuli | journal = Behavioural Brain Research | volume = 41 | issue = 3 | pages = 199–213 | date = December 1990 | pmid = 2288672 | doi = 10.1016/0166-4328(90)90108-Q | s2cid = 4023773 }}</ref><ref name="Brothers, L., & Ring, B. 1993 pp. 53-61">{{cite journal | vauthors = Brothers L, Ring B | title = Mesial temporal neurons in the macaque monkey with responses selective for aspects of social stimuli | journal = Behavioural Brain Research | volume = 57 | issue = 1 | pages = 53–61 | date = October 1993 | pmid = 8292255 | doi = 10.1016/0166-4328(93)90061-T | s2cid = 4014644 }}</ref><ref name="Hare, B., Wobber, V., & Wrangham, R. 2012 pp. 573-585">{{cite journal |doi= 10.1016/j.anbehav.2011.12.007 | title= The self-domestication hypothesis: evolution of bonobo psychology is due to selection against aggression |year=2012 | vauthors = Hare B, Wobber V, Wrangham R |journal= Animal Behaviour |volume=83 |issue=3 |pages=573–585 | s2cid= 3415520 }}</ref>

On a mechanistic level, these changes are believed to be the result of a systemic downregulation of the sympathetic nervous system (the fight-or-flight reflex). Hence, tamed foxes show a reduced adrenal gland size and have an up to fivefold reduction in both basal and stress-induced blood cortisol levels.<ref name="Osadschuk">Osadschuk, L. V. 1997. "Effects of domestication on the adrenal cortisol production of silver foxes during embryonic development ". In In L. N. Trut and L. V. Osadschuk eds., ''Evolutionary-Genetic and Genetic-Physiological Aspects of Fur Animal Domestication''. Oslo: Scientifur.{{ISSN|0105-2403}}.</ref><ref name="Trut, L. N., Oskina, I. N. & Kharlamova, A. 2009 pp. 349-360">{{cite journal | vauthors = Trut L, Oskina I, Kharlamova A | title = Animal evolution during domestication: the domesticated fox as a model | journal = BioEssays | volume = 31 | issue = 3 | pages = 349–360 | date = March 2009 | pmid = 19260016 | pmc = 2763232 | doi = 10.1002/bies.200800070 }}</ref> Similarly, domesticated rats and guinea pigs have both reduced adrenal gland size and reduced blood corticosterone levels.<ref name="Künzl, C., & Sachser, N. 1999 pp. 28-37">{{cite journal | vauthors = Künzl C, Sachser N | title = The behavioral endocrinology of domestication: A comparison between the domestic guinea pig (Cavia aperea f. porcellus) and its wild ancestor, the cavy (Cavia aperea) | journal = Hormones and Behavior | volume = 35 | issue = 1 | pages = 28–37 | date = February 1999 | pmid = 10049600 | doi = 10.1006/hbeh.1998.1493 | s2cid = 33327158 }}</ref><ref>{{cite journal | vauthors = Albert FW, Shchepina O, Winter C, Römpler H, Teupser D, Palme R, Ceglarek U, Kratzsch J, Sohr R, Trut LN, Thiery J, Morgenstern R, Plyusnina IZ, Schöneberg T, Pääbo S | display-authors = 6 | title = Phenotypic differences in behavior, physiology and neurochemistry between rats selected for tameness and for defensive aggression towards humans | journal = Hormones and Behavior | volume = 53 | issue = 3 | pages = 413–421 | date = March 2008 | pmid = 18177873 | doi = 10.1016/j.yhbeh.2007.11.010 | s2cid = 4609177 }}</ref> It seems as though the [[neoteny]] of domesticated animals significantly prolongs the immaturity of their hypothalamic-pituitary-adrenal system (which is otherwise only immature for a short period when they are pups/kittens) and this opens up a larger "socialization window" during which they can learn to interact with their caretakers in a more relaxed way.

This downregulation of sympathetic nervous system reactivity is also believed to be accompanied by a compensatory increase in a number of opposing organs and systems. Although these are not as well specified, various candidates for such "organs" have been proposed: the parasympathetic system as a whole, the septal area over the amygdala,<ref name="Eccles, John C. 1989"/> the oxytocin system,<ref name=Carter>{{cite journal | vauthors = Carter CS | title = Oxytocin pathways and the evolution of human behavior | journal = Annual Review of Psychology | volume = 65 | pages = 17–39 | year = 2014 | pmid = 24050183 | doi = 10.1146/annurev-psych-010213-115110 }}</ref> the endogenous opioids<ref name="Nelson, E., & Panksepp, J. 1998 pp. 437-452">{{cite journal | vauthors = Nelson EE, Panksepp J | title = Brain substrates of infant-mother attachment: contributions of opioids, oxytocin, and norepinephrine | journal = Neuroscience and Biobehavioral Reviews | volume = 22 | issue = 3 | pages = 437–452 | date = May 1998 | pmid = 9579331 | doi = 10.1016/S0149-7634(97)00052-3 | s2cid = 14345053 }}</ref> and various forms of quiescent immobilization which antagonize the fight-or-flight reflex.<ref name=Porges>{{cite journal | vauthors = Porges SW | title = Social engagement and attachment: a phylogenetic perspective | journal = Annals of the New York Academy of Sciences | volume = 1008 | issue = 1 | pages = 31–47 | date = December 2003 | pmid = 14998870 | doi = 10.1196/annals.1301.004 | s2cid = 1377353 | bibcode = 2003NYASA1008...31P }}</ref><ref>{{cite journal |doi=10.1007/s40806-017-0112-x |title=Theory of Mind: Towards an Evolutionary Theory |year=2018 | vauthors = Tsoukalas I |journal= Evolutionary Psychological Science |volume=4 | issue = 1|pages=38–66|doi-access=free }}[https://drive.google.com/file/d/1CCwSs2TrvPwwSU8rDyUkvtLYAuYfylMD/view?usp=sharing Pdf.]</ref>

===Sexual selection===
{{Main|Sexual selection in humans|Human mating strategies}}

This model, which invokes [[sexual selection]], is proposed by [[Geoffrey Miller (psychologist)|Geoffrey Miller]] who argues that human intelligence is unnecessarily sophisticated for the needs of [[hunter-gatherers]] to survive. He argues that the manifestations of intelligence such as [[language]], [[music]] and [[art]] did not evolve because of their utilitarian value to the survival of ancient hominids. Rather, intelligence may have been a [[fitness (biology)|fitness]] indicator. Hominids would have been [[mate choice|chosen]] for greater intelligence as an indicator of healthy genes and a [[Fisherian runaway]] [[positive feedback]] loop of sexual selection would have led to the evolution of human intelligence in a relatively short period.<ref name="Miller">{{cite book| vauthors = Miller G | author-link=Geoffrey Miller (evolutionary psychologist)|title=The Mating Mind|isbn=978-0-8058-5749-8|title-link=The Mating Mind|year=2008| publisher=Taylor & Francis}}</ref> Philosopher [[Denis Dutton]] also argued that the [[Evolutionary aesthetics|human capacity for aesthetics]] evolved by sexual selection.<ref>{{cite book| vauthors = Dutton D |author-link=Denis Dutton|title=The Art Instinct: Beauty, Pleasure, and Human Evolution|year=2009|pages=135–163|place=New York|publisher=[[Bloomsbury Publishing|Bloomsbury Press]]|isbn=978-1596914018}}</ref>

Evolutionary biologist [[George Christopher Williams|George C. Williams]] and [[Evolutionary psychiatry|evolutionary psychiatrist]] [[Randolph M. Nesse]] cite evolutionary psychologists [[John Tooby]] and [[Leda Cosmides]] as referring to the [[emotion]]s as "Darwinian [[Computational theory of mind|algorithms of the mind]]",<ref>{{cite book| vauthors = Nesse R, Williams GC |author-link1=Randolph M. Nesse|author-link2=George Christopher Williams|title=Why We Get Sick: The New Science of Darwinian Medicine|year=1994|pages=209–212|publisher=[[Vintage Books]]|place=New York|isbn=978-0679746744}}</ref> while social psychologist [[David Buss]] has argued that the [[Sex differences in psychology|sex-specialized differences]] in the emotion of [[Sexual jealousy|jealousy]] are adaptive [[Strategy (game theory)|strategies]] for detecting [[infidelity]] by a [[Human mating strategies|mating partner]] and anthropologists [[Donald Brown (anthropologist)|Donald E. Brown]] and [[Ward Goodenough]] have argued that [[marriage]] is a [[cultural universal]] that evolved to regulate sexual access to [[Age and female fertility|fertile women]] within a particular culture in response to [[male intrasexual competition]] and [[Dominance hierarchy|dominance]].{{refn|name=Buss/Brown/Pinker|<ref>{{cite book| vauthors = Buss DM |author-link=David Buss|title=The Evolution of Desire: Strategies of Human Mating|title-link=The Evolution of Desire|year=2016|orig-date=1994|publisher=[[Basic Books]]|place=New York|edition=3rd|isbn=978-0465097760|pages=189–221}}</ref><ref>{{cite book| vauthors = Buss DM |author-link=David Buss|title=The Dangerous Passion: Why Jealousy Is as Necessary as Love and Sex|year=2011|orig-date=2000|place=New York|publisher=[[Free Press (publisher)|Free Press]]|edition=2nd|isbn=978-1451673135}}</ref><ref>{{cite book|vauthors=Brown DE|author-link=Donald Brown (anthropologist)|year=1991|title=Human Universals|place=[[Philadelphia]], [[Pennsylvania|PA]]|publisher=[[Temple University Press]]|page=80|isbn=978-0877228417}}</ref><ref>{{cite book|vauthors=Pinker S|author-link=Steven Pinker|year=2016|orig-year=2002|title=The Blank Slate: The Modern Denial of Human Nature|title-link=The Blank Slate|place=New York|publisher=[[Penguin Books]]|page=457|edition=2nd|isbn=978-0142003343}}</ref>}} Citing [[Cross-cultural psychology|cross-cultural research]] conducted by Buss,<ref>{{cite journal| vauthors = Buss DM |author-link=David Buss|title=Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures|year=1989|journal=[[Behavioral and Brain Sciences]]|volume=12|issue=1|pages=1–49|publisher=[[Cambridge University Press]]|doi=10.1017/S0140525X00023992|doi-access=free}}</ref><ref name="Buss 1992">{{cite book| vauthors = Buss DM | veditors = Barkow JH, Cosmides L, Tooby J |title=The Adapted Mind: Evolutionary Psychology and the Generation of Culture|title-link=The Adapted Mind|chapter=5. Mate Preference Mechanisms: Consequences for Partner Choice and Intrasexual Competition|place=New York|publisher=[[Oxford University Press]]|orig-date=1992|year=1995|pages=253–256|isbn=978-0195101072}}</ref> Miller has argued that if humans [[Mating preferences|prefer]] altruistic mating partners that would select by [[mate choice]] for [[Altruism (biology)|altruism]] directly.<ref>{{cite book| vauthors = Miller GF |author-link=Geoffrey Miller (psychologist)|title=The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature|place=New York|publisher=[[Doubleday (publisher)|Doubleday]]|year=2000|edition=1st|pages=292–340|isbn=978-0385495165|url-access=registration|url=https://archive.org/details/matingmind00geof}}</ref> Additionally, Nesse and theoretical biologist [[Mary Jane West-Eberhard]] view sexual selection as a subcategory of [[social selection]],{{refn|name=West-Eberhard/Lyon/Montgomerie/Nesse|<ref name="West-Eberhard 1975">{{cite journal| vauthors = West-Eberhard MJ |title=The Evolution of Social Behavior by Kin Selection|journal=[[The Quarterly Review of Biology]]|publisher=[[University of Chicago Press]]|year=1975|volume=50|issue=1|pages=1–33|doi=10.1086/408298|jstor=2821184|s2cid=14459515}}</ref><ref name="West-Eberhard 1979">{{cite journal| vauthors = West-Eberhard MJ |title=Sexual Selection, Social Competition, and Evolution|journal=[[Proceedings of the American Philosophical Society]]|publisher=[[American Philosophical Society]]|year=1979|volume=123|issue=4|pages=222–34|jstor=986582}}</ref><ref name="West-Eberhard 1983">{{Cite journal| vauthors = West-Eberhard MJ |year=1983|title=Sexual Selection, Social Competition, and Speciation|journal=[[Quarterly Review of Biology]]|publisher=[[University of Chicago Press]]|volume=58|issue=2|pages=155–183|doi=10.1086/413215|jstor=2828804|s2cid=54711556|url=https://www.journals.uchicago.edu/doi/abs/10.1086/413215|url-access=subscription}}</ref><ref>{{cite journal | vauthors = Lyon BE, Montgomerie R | title = Sexual selection is a form of social selection | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 367 | issue = 1600 | pages = 2266–2273 | date = August 2012 | pmid = 22777015 | pmc = 3391428 | doi = 10.1098/rstb.2012.0012 | access-date =  | publisher = [[Royal Society]] | place = [[London]], [[United Kingdom|UK]] }}</ref><ref name="West-Eberhard 2014">{{cite journal | vauthors = West-Eberhard MJ | title = Darwin's forgotten idea: the social essence of sexual selection | journal = Neuroscience and Biobehavioral Reviews | volume = 46 Pt 4 | issue = 4 | pages = 501–508 | date = October 2014 | pmid = 25003806 | doi = 10.1016/j.neubiorev.2014.06.015 | publisher = [[Elsevier]] | s2cid = 1604935 }}</ref><ref name="Nesse 2019 pp. 172–76">{{cite book| vauthors = Nesse R |author-link=Randolph M. Nesse|title=Good Reasons for Bad Feelings: Insights from the Frontier of Evolutionary Psychiatry|publisher=[[Dutton (imprint)|Dutton]]|year=2019|pages=172–176|isbn=978-1101985663}}</ref>}} with Nesse and anthropologist [[Christopher Boehm]] arguing further that altruism in humans held [[Fitness (biology)|fitness advantages]] that enabled evolutionarily extraordinary [[Cooperation|cooperativeness]] and the human capability of creating [[culture]], as well as [[capital punishment]] by [[Band society|band societies]] against [[Bullying|bullies]], [[Theft|thieves]], [[Free-rider problem|free-riders]], and [[Psychopathy|psychopaths]].{{refn|name=Nesse/Boehm|<ref>{{cite journal | vauthors = Boehm C | title = The natural selection of altruistic traits | journal = Human Nature | volume = 10 | issue = 3 | pages = 205–252 | date = September 1999 | pmid = 26196335 | doi = 10.1007/s12110-999-1003-z | publisher = [[Springer Science+Business Media]] | s2cid = 207392341 | author-link = Christopher Boehm }}</ref><ref>{{cite book| vauthors = Boehm C |year=2001|orig-date=1999|title=Hierarchy in the Forest: The Evolution of Egalitarian Behavior|place=[[Cambridge, Massachusetts|Cambridge, MA]]|publisher=[[Harvard University Press]]|edition=Revised|isbn=978-0674006911}}</ref><ref name="Nesse 2007">{{cite journal| vauthors = Nesse RM |author-link=Randolph M. Nesse|title=Runaway social selection for displays of partner value and altruism|journal=[[Biological Theory (journal)|Biological Theory]]|year=2007|volume=2|issue=2|publisher=[[Springer Science+Business Media]]|pages=143–55|doi=10.1162/biot.2007.2.2.143|s2cid=195097363}}</ref><ref name="Nesse 2009">{{cite book| vauthors = Nesse RM |author-link=Randolph M. Nesse|chapter=10. Social Selection and the Origins of Culture| veditors = Schaller M, Heine SJ, Norenzayan A, Yamagishi T, Kameda T |editor-link1=Mark Schaller |editor-link2=Steven Heine (psychologist)|title=Evolution, Culture, and the Human Mind|place=Philadelphia|publisher=[[Taylor & Francis]]|year=2009|pages=137–50|isbn=978-0805859119}}</ref><ref>{{cite book| author = Boehm, C |year=2012|title=Moral Origins: Social Selection and the Evolution of Virtue, Altruism, and Shame|place=New York|publisher=[[Basic Books]]|isbn=978-0465020485}}</ref><ref>{{cite journal| vauthors = Boehm C |year=2014|title=The moral consequences of social selection|journal=[[Behaviour (journal)|Behaviour]]|publisher=[[Brill Publishers]]|volume=151|issue=2–3|pages=167–183|doi=10.1163/1568539X-00003143|url=https://brill.com/view/journals/beh/151/2-3/article-p167_4.xml|access-date=7 July 2021|url-access=subscription}}</ref>}}

In many species, only males have impressive [[secondary sexual characteristics]] such as ornaments and show-off behavior, but sexual selection is also thought to be able to act on females as well in at least partially [[Monogamy in animals|monogamous species]].<ref>{{cite journal|author1=Jones, Ian L. |author2=Hunter, Fiona M. |title=Mutual sexual selection in a monogamous seabird|journal=Nature |volume=362|pages=238–239 |year=1993| doi=10.1038/362238a0|issue=6417|bibcode=1993Natur.362..238J|s2cid=4254675 }}</ref> With complete monogamy, there is [[assortative mating]] for sexually selected traits. This means that less attractive individuals will find other less attractive individuals to mate with. If attractive traits are good fitness indicators, this means that sexual selection increases the [[genetic load]] of the offspring of unattractive individuals. Without sexual selection, an unattractive individual might find a superior mate with few deleterious mutations, and have healthy children that are likely to survive. With sexual selection, an unattractive individual is more likely to have access only to an inferior mate who is likely to pass on many deleterious mutations to their joint offspring, who are then less likely to survive.<ref name="Miller" />

Sexual selection is often thought to be a likely explanation for other female-specific human traits, for example breasts and buttocks far larger in proportion to total body size than those found in related species of ape.<ref name="Miller" /> It is often assumed that if breasts and buttocks of such large size were necessary for functions such as suckling infants, they would be found in other species. That human female breasts (typical mammalian breast tissue is small)<ref>[https://books.google.com/books?id=ngtMd5YoWi4C&q=great+ape+breast+tissue&pg=PA51 "Heredity and Society". Author Ian Porter. 1972. Page 51.]</ref> are found [[sexually attractive]] by many men is in agreement with sexual selection acting on human females secondary sexual characteristics.

Sexual selection for intelligence and judging ability can act on indicators of success, such as highly visible displays of wealth. Growing human brains require more nutrition than brains of related species of ape. It is possible that for females to successfully judge male intelligence, they must be intelligent themselves. This could explain why despite the absence of clear differences in intelligence between males and females on average, there are clear differences between male and female propensities to display their intelligence in ostentatious forms.<ref name="Miller" />

====Critique====
The sexual selection by the disability principle/fitness display model of the evolution of human intelligence is criticized by certain researchers for issues of timing of the costs relative to reproductive age. While sexually selected ornaments such as peacock feathers and moose antlers develop either during or after puberty, timing their costs to a sexually mature age, human brains expend large amounts of nutrients building [[myelin]] and other brain mechanisms for efficient communication between the neurons early in life. These costs early in life build facilitators that reduce the cost of neuron firing later in life, and as a result the peaks of the brain's costs and the peak of the brain's performance are timed on opposite sides of puberty with the costs peaking at a sexually immature age while performance peaks at a sexually mature age. Critical researchers argue the above shows that the cost of intelligence is a signal which reduces the chance of surviving to reproductive age, and does not signal fitness of sexually mature individuals. Since the disability principle is about selection from disabilities in sexually immature individuals, which increases the offspring's chance of survival to reproductive age, disabilities would be selected against and not for by the above mechanism. These critics argue that human intelligence evolved by natural selection citing that unlike sexual selection, natural selection have produced many traits that cost the most nutrients before puberty including immune systems and accumulation and modification for increased toxicity of poisons in the body as a protective measure against predators.<ref>The Evolution of Intelligence; Robert J. Sternberg, James C. Kaufman, 2013</ref><ref>The First Idea: How Symbols, Language, and Intelligence Evolved from Our Primate Ancestors to Modern Humans; Stanley I. Greenspan, Stuart Shanker, 2009</ref>

===Intelligence as a disease-resistance sign===

The number of people with severe [[cognition|cognitive]] impairment caused by childhood viral infections like [[meningitis]], [[protist]]s like ''[[Toxoplasma]]'' and ''[[Plasmodium]]'', and animal parasites like [[Parasitic worm|intestinal worm]]s and [[schistosomes]] is estimated to be in the hundreds of millions.<ref name="olness">{{cite journal | vauthors = Olness K | title = Effects on brain development leading to cognitive impairment: a worldwide epidemic | journal = Journal of Developmental and Behavioral Pediatrics | volume = 24 | issue = 2 | pages = 120–130 | date = April 2003 | pmid = 12692458 | doi = 10.1097/00004703-200304000-00009 | s2cid = 31999992 }}</ref> Even more people with moderate mental damages, such as an inability to complete difficult tasks, that are not classified as 'diseases' by medical standards, may still be considered as inferior mates by potential sexual partners.

Thus, widespread, [[virulence|virulent]], and archaic infections are greatly involved in natural selection for cognitive abilities. People infected with parasites may have brain damage and obvious maladaptive behavior in addition to visible signs of disease. Smarter people can more skillfully learn to distinguish safe non-polluted water and food from unsafe kinds and learn to distinguish mosquito infested areas from safe areas. Additionally, they can more skillfully find and develop safe food sources and living environments. Given this situation, preference for smarter child-bearing/rearing partners increases the chance that their descendants will inherit the best resistance [[allele]]s, not only for [[immune system]] resistance to disease, but also smarter brains for learning skills in avoiding disease and selecting nutritious food. When people search for mates based on their success, wealth, reputation, disease-free body appearance, or psychological traits such as benevolence or confidence; the effect is to select for superior intelligence that results in superior disease resistance.{{citation needed|date=November 2019}}

===Ecological dominance-social competition model===

Another model describing the evolution of human intelligence is ecological dominance-social competition (EDSC),<ref name=flinn>{{cite journal|url=http://web.missouri.edu/~gearyd/Flinnetal2005.pdf|title=Ecological dominance, social competition, and coalitionary arms races: Why humans evolved extraordinary intelligence|journal=Evolution and Human Behavior|author=Flinn, M. V.|author2=Geary, D. C.|author3=Ward, C. V.|year=2005|doi=10.1016/j.evolhumbehav.2004.08.005|volume=26|issue=1|pages=10–46|bibcode=2005EHumB..26...10F |access-date=25 November 2007|archive-date=4 June 2007|archive-url=https://web.archive.org/web/20070604224126/http://web.missouri.edu/~gearyd/Flinnetal2005.pdf|url-status=dead}}</ref> explained by Mark V. Flinn, David C. Geary and Carol V. Ward based mainly on work by [[Richard D. Alexander]]. According to the model, human intelligence was able to evolve to significant levels because of the combination of increasing domination over [[habitat]] and increasing importance of social interactions. As a result, the primary selective pressure for increasing human intelligence shifted from learning to master the [[nature|natural world]] to competition for dominance among members or groups of its own species.

As advancement, survival and reproduction within an increasing complex social structure favored ever more advanced social skills, [[communication]] of concepts through increasingly complex language patterns ensued. Since competition had shifted bit by bit from controlling "nature" to influencing other humans, it became of relevance to outmaneuver other members of the group seeking [[leadership]] or [[acceptance]], by means of more advanced social skills. A more social and communicative person would be more easily selected.

===Intelligence dependent on brain size===

Human intelligence is developed to an extreme level that is not necessarily adaptive in an evolutionary sense. Firstly, larger-headed babies are more difficult to give [[birth]] to and large brains are costly in terms of [[nutrient]] and [[oxygen]] requirements.<ref name="isler">{{cite journal | vauthors = Isler K, van Schaik CP | title = Metabolic costs of brain size evolution | journal = Biology Letters | volume = 2 | issue = 4 | pages = 557–560 | date = December 2006 | pmid = 17148287 | pmc = 1834002 | doi = 10.1098/rsbl.2006.0538 }}</ref> Thus the direct adaptive benefit of human intelligence is questionable at least in modern societies, while it is difficult to study in prehistoric societies. Since 2005, scientists have been evaluating genomic data on gene variants thought to influence head size, and have found no evidence that those genes are under strong selective pressure in current human populations.<ref>{{cite book | vauthors = Ossorio PN |title=Race and the Genetic Revolution: Science, Myth, and Culture | veditors = Krimsky S, Sloan K |chapter=Chapter 9: Myth and Mystification: The Science of Race and IQ |chapter-url=https://books.google.com/books?id=OVg4AAAAQBAJ |access-date=31 August 2013 |date=2011 |publisher=Columbia University Press |isbn=978-0-231-52769-9|page=189 |quote=Since 2005, other researchers have evaluated the same data on MCHPI and ASPM, plus some additional data, and concluded that there is no evidence that these genes have been under natural selection in modern humans. These reanalyses undercut the idea that the particular variants found at high frequency among people of European descent somehow made Europeans better adapted for modern civilization. Additional studies have discovered that the MCHPI and ASPM variants reported in the 2005 papers do not correlate with larger (or smaller) than average head size. The genes were originally described as having to do with head size because some variants of these genes can cause microcephaly (extremely small heads that lack major portions of the brain). However, those microcephaly-causing variants were not included in the studies published in 2005. Finally, several research groups have tried and failed to show any correlation between the variants described in the 2005 papers and IQ reading abilities, or verbal abilities. (citing "Comment on 'Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in ''Homo sapiens''{{'}} and 'Microcephalin, a Gene Regulating Brain Size Continues to Evolve Adaptively in Humans", ''Science'' 313 (2006): 172 (a); F.Yu, S.R.Hill, S.F. Schaffner, et al., "Comment on 'Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in ''Homo sapiens''{{'"}}, ''Science'' 316 (2007): 370 (b). ) }}</ref> The trait of head size has become generally fixed in modern human beings.<ref>{{cite book | vauthors = Klug WS, Cummings MR, Spencer CA, Palladino MA |title=Concepts of Genetics |date=2012 |edition=Tenth |publisher=Pearson |isbn=978-0-321-75435-6 |page=669 |quote=h<sup>2</sup> values vary, but heritability tends to be low for quantitative traits that are essential to an organism's survival. Remember, this does not indicate the absence of a genetic contribution to the observed phenotypes for such traits. Instead, the low h<sup>2</sup> values show that natural selection has already largely optimized the genetic component of these traits during evolution.}}</ref>

While decreased brain size has strong correlation with lower intelligence in humans, some modern humans have brain sizes as small as with ''Homo erectus'' but normal intelligence (based on IQ tests) for modern humans. Increased brain size in humans may allow for greater capacity for specialized expertise.<ref>{{cite journal | vauthors = Skoyles JR | title = Human evolution expanded brains to increase expertise capacity, not IQ. | journal = Psycoloquy | date = 1999 | volume = 10 | issue = 2 | url =http://www.human-existence.com/publications/Skoyles%20Human%20evolution%20expanded%20brains%20expertise%20not%20IQ.pdf }}</ref>

==== Expanded cortical regions ====
The two major perspectives on primate brain evolution are the [[Concerted evolution|concerted]] and [[Mosaic evolution|mosaic]] approaches.<ref name=":3">{{cite book |title=Evolution of nervous systems| vauthors = Kaas JH |isbn=9780128040966|edition=Second |location=Kidlington, Oxford, United Kingdom|oclc=964620094|date=2016-11-23}}</ref> In the concerted evolution approach, cortical expansions in the brain are considered to be a by-product of a larger brain, rather than adaptive potential.<ref name=":3" /> Studies have supported the concerted evolution model by finding cortical expansions between [[macaque]]s and [[marmoset]]s are comparable to that of humans and macaques.<ref name=":3" /> Researchers attribute this result to the constraints on the evolutionary process of increasing brain size.<ref name=":3" /> In the mosaic approach, cortical expansions are attributed to their adaptive advantage for the species.<ref name=":4">{{cite journal | vauthors = Foley RA | title = Mosaic evolution and the pattern of transitions in the hominin lineage | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 371 | issue = 1698 | pages = 20150244 | date = July 2016 | pmid = 27298474 | pmc = 4920300 | doi = 10.1098/rstb.2015.0244 }}</ref> Researchers have attributed hominin evolution to mosaic evolution.<ref name=":4" />

Simian primate brain evolution studies show that specific cortical regions associated with high-level cognition have demonstrated the greatest expansion over primate brain evolution.<ref name=":3" /> Sensory and motor regions have showcased limited growth.<ref name=":3" /> Three regions associated with complex cognition include the [[frontal lobe]], [[temporal lobe]], and the medial wall of the cortex.<ref name=":3" /> Studies demonstrate that the enlargement in these regions is disproportionately centered in the [[temporoparietal junction]] (TPJ), [[lateral prefrontal cortex]] (LPFC), and [[anterior cingulate cortex]] (ACC).<ref name=":3" /> The TPJ is located in the [[parietal lobe]] and is associated with morality, [[theory of mind]], and [[spatial awareness]].<ref name=":3" /> Additionally, the [[Wernicke's area]] is located in the TPJ.<ref name=":3" /> Studies have suggested that the region assists in language production, as well as language processing.<ref>{{cite journal | vauthors = Binder JR | title = The Wernicke area: Modern evidence and a reinterpretation | journal = Neurology | volume = 85 | issue = 24 | pages = 2170–2175 | date = December 2015 | pmid = 26567270 | pmc = 4691684 | doi = 10.1212/WNL.0000000000002219 }}</ref> The LPFC is commonly associated with planning and working memory functions.<ref name=":3" /> The [[Broca's area]], the second major region associated with language processing, is also located in the LPFC.<ref name=":3" /> The ACC is associated with detecting errors, monitoring conflict, motor control, and emotion.<ref name=":3" /> Specifically, researchers have found that the ACC in humans is disproportionately expanded when compared to the ACC in macaques.<ref name=":3" />

Fossils show that although ''Homo sapiens''' total brain volume approached modern levels as early as 300,000 years ago, parietal lobes and cerebella grew relative to total volume after this point, reaching current levels of variation at some point between the approximate dates of 100,000 and 35,000 years ago.<ref name="Neubauer2018">{{cite journal|last1=Neubauer|first1=Simon|last2=Hublin|first2=Jean-Jacques|last3=Gunz|first3=Philipp|title=The evolution of modern human brain shape.|journal=Science Advances|year=2018 |volume=4 |issue=1 |pages=eaao5961 |doi=10.1126/sciadv.aao5961|pmid=29376123 |pmc=5783678 |doi-access=free|bibcode=2018SciA....4.5961N }}</ref>

Studies on cortical expansions in the brain have been used to examine the evolutionary basis of neurological disorders, such as [[Alzheimer's disease]].<ref name=":3" /> For example, researchers associate the expanded TPJ region with Alzheimer's disease. However, other researchers found no correlation between expanded cortical regions in the human brain and the development of Alzheimer's disease.<ref>{{cite journal | vauthors = Fjell AM, Amlien IK, Sneve MH, Grydeland H, Tamnes CK, Chaplin TA, Rosa MG, Walhovd KB | display-authors = 6 | title = The Roots of Alzheimer's Disease: Are High-Expanding Cortical Areas Preferentially Targeted?† | journal = Cerebral Cortex | volume = 25 | issue = 9 | pages = 2556–2565 | date = September 2015 | pmid = 24658616 | pmc = 6276920 | doi = 10.1093/cercor/bhu055 }}</ref>

===Cellular, genetic, and circuitry changes===
Human brain evolution involves cellular, genetic, and circuitry changes.<ref name=":5">{{cite journal | vauthors = Sherwood CC, Schumacher M | url= https://www.scientificamerican.com/article/what-makes-the-human-brain-special/ |title=What Makes the Human Brain Special| journal = Scientific American | date = September 2018 }}</ref> On a genetic level, humans have a modified [[FOXP2|FOXP2 gene]], which is associated with speech and language development.<ref>{{cite web|url=https://ghr.nlm.nih.gov/gene/FOXP2|title=FOXP2 gene |website=Genetics Home Reference |access-date=2019-04-11}}</ref> The human variant of the gene [[SRGAP2]], [[SRGAP2C]], enables greater dendritic spine density which fosters greater neural connections.<ref>{{cite journal | vauthors = Charrier C, Joshi K, Coutinho-Budd J, Kim JE, Lambert N, de Marchena J, Jin WL, Vanderhaeghen P, Ghosh A, Sassa T, Polleux F | display-authors = 6 | title = Inhibition of SRGAP2 function by its human-specific paralogs induces neoteny during spine maturation | journal = Cell | volume = 149 | issue = 4 | pages = 923–935 | date = May 2012 | pmid = 22559944 | pmc = 3357949 | doi = 10.1016/j.cell.2012.03.034 }}</ref> On a cellular level, studies demonstrate [[Von economo neurons|von Economo neurons]] (VENs) are more prevalent in humans than other primates.<ref name=":6">{{cite journal | vauthors = Allman JM, Tetreault NA, Hakeem AY, Manaye KF, Semendeferi K, Erwin JM, Park S, Goubert V, Hof PR | display-authors = 6 | title = The von Economo neurons in the frontoinsular and anterior cingulate cortex | journal = Annals of the New York Academy of Sciences | volume = 1225 | issue = 1 | pages = 59–71 | date = April 2011 | pmid = 21534993 | pmc = 3140770 | doi = 10.1111/j.1749-6632.2011.06011.x | bibcode = 2011NYASA1225...59A }}</ref> Studies show that VENs are associated with empathy, social awareness and self-control.<ref name=":6" /> Studies show that the striatum plays a role in understanding reward and pair-bond formation.<ref>{{cite journal | vauthors = Báez-Mendoza R, Schultz W | title = The role of the striatum in social behavior | journal = Frontiers in Neuroscience | volume = 7 | pages = 233 | date = December 2013 | pmid = 24339801 | pmc = 3857563 | doi = 10.3389/fnins.2013.00233 | doi-access = free }}</ref> On a circuitry level, humans exhibit a more complex [[mirror neuron system]], greater connection between the two major language processing areas (Wernicke's area and Broca's area), and a vocal control circuit that connects the motor cortex and brain stem.<ref name=":5" /> The mirror neuron system is associated with [[social cognition]], theory of mind, and empathy.<ref name=":7">{{cite journal | vauthors = Rajmohan V, Mohandas E | title = Mirror neuron system | journal = Indian Journal of Psychiatry | volume = 49 | issue = 1 | pages = 66–69 | date = January 2007 | pmid = 20640069 | pmc = 2900004 | doi = 10.4103/0019-5545.31522 | doi-access = free }}</ref> Studies have demonstrated the presence of the mirror neuron system in both macaques in humans; However, the mirror neuron system is only activated in macaques when observing transitive movements.<ref name=":7" />

===Group selection===

[[Group selection]] theory contends that organism characteristics that provide benefits to a group (clan, tribe, or larger population) can evolve despite individual disadvantages such as those cited above. The group benefits of intelligence (including language, the ability to communicate between individuals, the ability to teach others, and other cooperative aspects) have apparent utility in increasing the survival potential of a group.

In addition, the theory of group selection is inherently tied to Darwin's theory of natural selection. Specifically, that "group-related adaptations must be attributed to the natural selection of alternative groups of individuals and that the natural selection of alternative alleles within populations will be opposed to this development".<ref>Williams, George C and Dawkins, R. "Group Selection". ''Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought''. Princeton University Press, Princeton; Oxford, 2019, pp. 92–124.</ref>

Between-group selection can be used to explain the changes and adaptations that arise within a group of individuals. Group-related adaptations and changes are a byproduct of between-group selection as traits or characteristics that prove to be advantageous in relation to another group will become increasingly popular and disseminated within a group. In the end, increasing its overall chance of surviving a competing group.

However, this explanation cannot be applied to humans (and other species, predominantly other mammals) that live in stable, established social groupings. This is because of the social intelligence that functioning within these groups requires from the individual. Humans, while they are not the only ones, possess the cognitive and mental capacity to form systems of personal relationships and ties that extend well beyond those of the nucleus of family. The continuous process of creating, interacting, and adjusting to other individuals is a key component of many species' ecology.

These concepts can be tied to the social brain hypothesis, mentioned above. This hypothesis posits that human cognitive complexity arose as a result of the higher level of social complexity required from living in enlarged groups. These bigger groups entail a greater amount of social relations and interactions thus leading to an expanded quantity of intelligence in humans.<ref name=":0"/> However, this hypothesis has been under academic scrutiny in recent years and has been largely disproven. In fact, the size of a species' brain can be much better predicted by diet instead of measures of sociality as noted by the study conducted by DeCasien et al. They found that ecological factors (such as: folivory/frugivory, environment) explain a primate brain size much better than social factors (such as: group size, mating system).<ref name=":0" />

===Nutritional status===

Early hominins dating back to pre 3.5 Ma in Africa ate primarily plant foods supplemented by insects and scavenged meat.<ref name=":22"/> Their diets are evidenced by their 'robust' dento-facial features of small canines, large molars, and enlarged masticatory muscles that allowed them to chew through tough plant fibers. Intelligence played a role in the acquisition of food, through the use of tool technology such as stone anvils and hammers.<ref name=":22" />

There is no direct evidence of the role of nutrition in the evolution of intelligence dating back to ''Homo erectus'', contrary to dominant narratives in paleontology that link meat-eating to the appearance of modern human features such as a larger brain. However, scientists suggest that nutrition did play an important role, such as the consumption of a diverse diet including plant foods and new technologies for cooking and processing food such as fire.<ref>{{Cite journal |last1=Barr |first1=W. Andrew |last2=Pobiner |first2=Briana |last3=Rowan |first3=John |last4=Du |first4=Andrew |last5=Faith |first5=J. Tyler |date=2022 |title=No sustained increase in zooarchaeological evidence for carnivory after the appearance of ''Homo erectus'' |journal=Proceedings of the National Academy of Sciences |language=en |volume=119 |issue=5 |pages=e2115540119 |doi=10.1073/pnas.2115540119 |doi-access=free |issn=0027-8424 |pmc=8812535 |pmid=35074877|bibcode=2022PNAS..11915540B }}</ref>

Diets deficient in [[iron]], [[zinc]], [[protein]], [[iodine]], [[B vitamins]], [[omega 3 fatty acids]], [[magnesium]] and other nutrients can result in lower intelligence<ref>{{cite journal|title=Vitamin and Mineral Supplements Increase Intelligence| vauthors = Hoffer A |journal= Nutrition Health Review|volume=52| year=1989}}</ref> either in the mother during pregnancy or in the child during development. While these inputs did not have an effect on the evolution of intelligence they do govern its expression. A higher intelligence could be a signal that an individual comes from and lives in a physical and social environment where nutrition levels are high, whereas a lower intelligence could imply a child, its mother, or both, come from a physical and social environment where nutritional levels are low. Previc emphasizes the contribution of nutritional factors to elevations of [[dopaminergic]] activity in the brain, which may have been responsible for the evolution of human intelligence since [[dopamine]] is crucial to working memory, [[cognitive shifting]], abstract, distant concepts, and other hallmarks of advanced intelligence.<ref>{{cite book | vauthors = Previc FH | date = 2009 | title = The dopaminergic mind in human evolution and history | location = Cambridge, England | publisher = Cambridge University Press | isbn = 978-0-521-51699-0 }}</ref>

== See also ==
{{col div|colwidth=40em}}
* [[Behavioral modernity]]
* [[Cetacean intelligence]]
* [[Cephalopod intelligence]]
* [[Denisovan]]
* [[Human evolution]]
* [[Human intelligence]]
* [[Primate cognition]] 
* [[Timeline of human evolution]]
* {{annotated link|Noosphere}}
{{colend}}

== References ==
{{reflist|30em}}

== Further reading ==
{{refbegin}}
* {{cite book | vauthors = Byrne RW | date = 1995 | title = The Thinking Ape: Evolutionary origins of intelligence | publisher = Oxford University Press | location = Oxford, England | isbn = 978-0-19-852188-4 | url-access = registration | url = https://archive.org/details/thinkingapeevolu0000byrn }}
* {{cite book | vauthors = Greenspan SI, Shanker S | date = 2004 | title = The First Idea: How symbols, language, and intelligence evolved from our early primate ancestors to modern humans | publisher = Da Capo Press | location = Cambridge, Mass. | isbn = 978-0-7382-0680-6 | url = https://archive.org/details/firstideahowsymb00gree }}
* {{cite book | vauthors = Skoyles J, Sagan D | author-link1 = John Skoyles (scientist) | author-link2 = Dorion Sagan | date = 2002 | title = Up from Dragons: The evolution of human intelligence | publisher = McGraw-Hill | location = New York | isbn = 978-0-07-137825-3 | title-link = Up from Dragons }}
* {{cite book | vauthors = Tobias PV | year = 1971 | title = The Brain in Hominid Evolution | publisher = Columbia University Press | location = New York | isbn = 978-0-231-03518-7 | url = https://archive.org/details/braininhominidev00tob_f8p }}
* {{cite journal | vauthors = Roth G, Dicke U | title = Evolution of the brain and intelligence | journal = Trends in Cognitive Sciences | volume = 9 | issue = 5 | pages = 250–257 | date = May 2005 | pmid = 15866152 | doi = 10.1016/j.tics.2005.03.005 | s2cid = 14758763 }}
* {{cite book| vauthors = Todorov A, Fiske S, Prentice DA |title=Social Neuroscience: Toward Understanding the Underpinnings of the Social Mind |url= https://books.google.com/books?id=JwgSDAAAQBAJ |date=11 February 2011 |publisher=Oxford University Press, USA |isbn=978-0-19-531687-2 }}
{{refend}}

{{Clear}}
{{Evolutionary psychology}}
{{Human Evolution}}
{{Human intelligence topics}}
{{Evolution}}
{{animal cognition}}

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