View source for Cope's rule

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 |header=Cope's rule states that lineages increase in size over evolutionary time.
 |image1=Juramaia NT.jpg
 |caption1=''[[Juramaia]]'' was one of the earliest [[mammal]]s, a [[Basal (phylogenetics)|basal]] [[eutheria]]n from the [[Late Jurassic]], no more than 10 cm long.
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 |caption2=The [[African bush elephant]], a modern mammal, may reach a height of almost 4 metres.
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'''Cope's rule''', named after American paleontologist [[Edward Drinker Cope]],<ref name="Rensch_1948">{{cite journal | last=Rensch | first=B. | authorlink=Bernhard Rensch | title=Histological Changes Correlated with Evolutionary Changes of Body Size | journal=[[Evolution (journal)|Evolution]] | volume=2 | issue=3 | pages=218–230 | date=September 1948 | jstor=2405381 | doi=10.2307/2405381| pmid=18884663 }}</ref><ref name="Stanley_1973">{{cite journal | last=Stanley | first=S. M. | authorlink=Steven M. Stanley | title=An Explanation for Cope's Rule | journal=[[Evolution (journal)|Evolution]] | volume=27 | issue=1 | pages=1–26 | date=March 1973 | jstor=2407115 | doi=10.2307/2407115| pmid=28563664 }}</ref> postulates that population [[Lineage (evolution)|lineages]] tend to increase in body size over evolutionary time.<ref name=Hone2005>{{cite journal |author1=Hone DW |author2=Benton MJ |title=The evolution of large size: how does Cope's Rule work? |journal=Trends in Ecology and Evolution |volume=20 |issue=1 |pages=4–6 |year=2005 |pmid=16701331 |doi=10.1016/j.tree.2004.10.012|url=http://doc.rero.ch/record/14848/files/PAL_E1985.pdf }}</ref> It was never actually stated by Cope, although he favoured the occurrence of [[orthogenesis|linear evolutionary trends]].<ref name="Polly1998">{{cite journal |last1=Polly |first1=P. D. |author2=Alroy, J. |title=Cope's Rule |journal=Science |volume=282|issue=5386|date= 1998-10-02 |pages= 50–51 |doi= 10.1126/science.282.5386.47f |pmid=9786796 |bibcode=1998Sci...282...47P |s2cid=41642689 }}</ref> It is sometimes also known as the '''Cope–Depéret rule''',<ref name="MonroeBokma2010">{{cite journal|last1=Monroe|first1=M. J.|last2=Bokma|first2= F.|title=Little evidence for Cope's rule from Bayesian phylogenetic analysis of extant mammals |journal=Journal of Evolutionary Biology |volume= 23 |issue=9 |date=2010 |pages= 2017–2021 |doi= 10.1111/j.1420-9101.2010.02051.x|pmid=20629852|s2cid=20184065}}</ref> because [[Charles Depéret]] explicitly advocated the idea.<ref name="Depéret1907">{{cite book |author=Charles Jean Julien Depéret |title=Les transformations du monde animal|url=https://archive.org/details/lestransformati00depgoog |language=French  |year=1907 |publisher=E. Flammarion}}</ref> [[Theodor Eimer]] had also done so earlier.<ref name="Polly1998"/> The term "Cope's rule" was apparently coined by [[Bernhard Rensch]],<ref name="Rensch_1948"/> based on the fact that Depéret had "lionized Cope" in his book.<ref name="Polly1998"/>{{efn| In his paper, Rensch reproduced an erroneous citation of a work of Cope's<ref name="Cope1885a">{{cite journal | last=Cope | first=E. D. | authorlink=Edward Drinker Cope | title=On the Evolution of the Vertebrata, Progressive and Retrogressive | journal=American Naturalist | volume=19 | issue=2 | pages=140–148| date=February 1885 | jstor=2450032 | doi=10.1086/273881| doi-access=free | bibcode=1885ANat...19..140C }}</ref><ref name="Cope1885b">{{cite journal| title=On the Evolution of the Vertebrata, Progressive and Retrogressive (Continued) | journal=American Naturalist | volume=19 | issue=3 | pages=234–247 | date=March 1885 | jstor=2450075 | doi=10.1086/273900| last1=Cope | first1=E. D. | bibcode=1885ANat...19..234C | s2cid=84538510 }}</ref><ref name="Cope1885c">{{cite journal| title=On the Evolution of the Vertebrata, Progressive and Retrogressive (Continued) | journal=American Naturalist | volume=19 | issue=4 | pages=341–353 | date=April 1885 | jstor=2450836 | doi=10.1086/273923| last1=Cope | first1=E. D. | doi-access=free | bibcode=1885ANat...19..341C }}</ref> (that he apparently had not read) from the English translation of Depéret's book.<ref name="Polly1998"/>}} While the rule has been demonstrated in many instances, it does not hold true at all [[Taxonomy (biology)|taxonomic]] levels, or in all [[clade]]s. Larger body size is associated with increased [[Fitness (biology)|fitness]] for a number of reasons, although there are also some disadvantages both on an individual and on a clade level: clades comprising larger individuals are more prone to [[extinction]], which may act to limit the maximum size of [[organisms]].

==Function==

===Effects of growth===
[[Directional selection]] appears to act on organisms' size, whereas it exhibits a far smaller effect on other morphological traits,<ref name=Kingsolver2008>{{cite journal |last1=Kingsolver| first1=J. G. | last2=Pfennig | first2=D. W.| title=Individual-level selection as a cause of Cope's rule of phyletic size increase | journal=Evolution| volume=58| issue=7| pages=1608–1612| date=July 2004| pmid=15341162| doi=10.1554/04-003| s2cid=198159428 }}</ref> though it is possible that this perception may be a result of sample bias.<ref name=Hone2005/> This selectional pressure can be explained by a number of advantages, both in terms of mating success and survival rate.<ref name=Kingsolver2008/>

For example, larger organisms find it easier to avoid or fight off predators and capture prey, to reproduce, to kill competitors, to survive temporary lean times, and to resist rapid climatic changes.<ref name=Hone2005/> They may also potentially benefit from better [[thermal efficiency]], increased intelligence, and a longer lifespan.<ref name=Hone2005/>

Offsetting these advantages, larger organisms require more food and water, and shift from [[r/K selection|r to K-selection]]. Their longer [[generation time]] means a longer period of reliance on the mother, and on a macroevolutionary scale restricts the clade's ability to evolve rapidly in response to changing environments.<ref name=Hone2005/>

===Capping growth===
Left unfettered, the trend of ever-larger size would produce organisms of gargantuan proportions. Therefore, some factors must limit this process.
At one level, it is possible that the clade's increased vulnerability to extinction, as its members become larger, means that no taxon survives long enough for individuals to reach huge sizes.<ref name=Hone2005/> There are probably also physically imposed limits to the size of some organisms; for instance, insects must be small enough for oxygen to diffuse to all parts of their bodies, flying birds must be light enough to fly, and the length of giraffes' necks may be limited by the blood pressure it is possible for their hearts to generate.<ref name=Hone2005/> Finally, there may be a competitive element, in that changes in size are necessarily accompanied by changes in ecological niche. For example, terrestrial carnivores over 21&nbsp;kg almost always prey on organisms larger, not smaller, than themselves.<ref name="Van Valkenburgh2004">{{cite journal| doi=10.1126/science.1102417| title=Cope's Rule, Hypercarnivory, and Extinction in North American Canids| year=2004| author=Van Valkenburgh, B.| journal=Science| volume=306| pages=101–4| pmid=15459388| last2=Wang| first2=X| last3=Damuth| first3=J| s2cid=12017658| issue=5693| bibcode=2004Sci...306..101V}}</ref> If such a niche is already occupied, competitive pressure may oppose the directional selection.<ref name=Hone2005/> The three [[Canidae]] clades ([[Hesperocyoninae]], [[Borophaginae]], and [[Caninae]]) all show a trend towards larger size, although the first two are now extinct.<ref name=Paleobiol2008>{{cite journal|doi=10.1666/07030.1|title=Testing hypotheses of the evolution of encephalization in the Canidae (Carnivora, Mammalia)|year=2008|author=Finarelli, John A.|journal=Paleobiology|volume=34|issue=1 |pages=35–45|bibcode=2008Pbio...34...35F |s2cid=86060945}}</ref>

==Validity==
Cope recognised that clades of Cenozoic mammals appeared to originate as small individuals, and that body mass increased through a clade's history.<ref name=Alroy1998/> Discussing the case of [[canid]] evolution in [[North America]], [[Blaire Van Valkenburgh]] of [[UCLA]] and coworkers state:
{{quotation| Cope's rule, or the evolutionary trend toward larger body size, is common among mammals. Large size enhances the ability to avoid predators and capture prey, enhances reproductive success, and improves thermal efficiency. Moreover, in large carnivores, interspecific competition for food tends to be relatively intense, and bigger species tend to dominate and kill smaller competitors. Progenitors of hypercarnivorous lineages may have started as relatively small-bodied scavengers of large carcasses, similar to foxes and coyotes, with selection favoring both larger size and enhanced craniodental adaptations for meat eating. Moreover, the evolution of predator size is likely to be influenced by changes in prey size, and a significant trend toward larger size has been documented for large North American mammals, including both herbivores and carnivores, in the Cenozoic.<ref name="Van Valkenburgh2004"/>}}

In some cases, the increase in body size may represent a passive, rather than an active, trend.<ref name=Carrano2006>{{cite book | author=Carrano, M.T. | year=2006
 | title=Body-Size Evolution in the Dinosauria | journal=Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and Reptiles: A Volume Honoring James Allen Hopson | url=https://books.google.com/books?id=4uNMCqSRQ9gC&q=carrano&pg=RA4-PA225 | publisher=University of Chicago Press | isbn=978-0-226-09478-6}}</ref> In other words, the maximum size increases, but the minimum size does not; this is usually a result of size varying pseudo-randomly rather than directed evolution. This does not fall into Cope's rule ''[[Sensu|sensu stricto]]'', but is considered by many workers to be an example of "Cope's rule ''[[Sensu|sensu lato]]''".<ref name=Jablonski1997/> In other cases, an increase in size may in fact represent a transition to an optimal body size, and not imply that populations always develop to a larger size.<ref name=Alroy1998>{{cite journal| first1=J. | title=Cope's Rule and the Dynamics of Body Mass Evolution in North American Fossil Mammals | journal=Science | volume=280 | issue=5364 | pages=731–734 | year=1998| pmid=9563948| last1=Alroy|doi=10.1126/science.280.5364.731|bibcode=1998Sci...280..731A | url=http://doc.rero.ch/record/20309/files/PAL_E4068.pdf }}</ref>

However, many [[palaeobiologist]]s are skeptical of the validity of Cope's rule, which may merely represent a statistical artefact.<ref name=Hone2005/><ref name="Gould1996">{{cite journal | first=Stephen Jay |last=Gould | year=1997 | title=Cope's rule as psychological artefact | journal=Nature | volume=385 | pages=199–200 |doi=10.1038/385199a0 | issue=6613|bibcode=1997Natur.385..199G |s2cid=205026571 | doi-access=free }}</ref> Purported examples of Cope's rule often assume that the stratigraphic age of fossils is proportional to their "clade rank", a measure of how derived they are from an ancestral state; this relationship is in fact quite weak.<ref>{{cite journal|last1=Sereno|first1=P. C. | author2=A. L. Beck | author3=D. B. Dutheil | author4=B. Gado | author5=H. C. E. Larsson | author6=G. H. Lyon | author7=J. D. Marcot | author8=O. W. M. Rauhut | author9=R. W. Sadlier | author10=C. A. Sidor | author11=D. J. Varricchio | author12=G. P. Wilson | author13=J. A. Wilson |year=1999 |title=Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs |journal=Science |volume=286 |issue=5443 |pages=1342–1347 |doi=10.1126/science.286.5443.1342 | pmid=10558986|url=http://doc.rero.ch/record/13894/files/PAL_E832.pdf }}</ref> Counterexamples to Cope's rule are common throughout geological time; although size increase does occur more often than not, it is by no means universal. For example, among genera of Cretaceous molluscs, an increase in size is no more common than stasis or a decrease.<ref name=Jablonski1997>{{Cite journal | last1=Jablonski | first1=D. | title=Body-size evolution in Cretaceous molluscs and the status of Cope's rule | journal=Nature | volume=385 | pages=250–252 | year=1997 | doi=10.1038/385250a0 |bibcode=1997Natur.385..250J | issue=6613| s2cid=4322252 }}</ref> In many cases, Cope's rule only operates at certain taxonomic levels (for example, an order may obey Cope's rule, while its constituent families do not), or more generally, it may apply to only some clades of a taxon.<ref>{{cite journal | last1=Laurin | first1=M | year=2004 | title=The evolution of body size, Cope's rule and the origin of amniotes | journal=Systematic Biology | volume=53 | issue=4| pages=594–622 | doi=10.1080/10635150490445706 | pmid=15371249| doi-access=free }}</ref>  Giant dinosaurs appear to have evolved dozens of times, in response to local environmental conditions.<ref>{{cite journal |last1=D'Emic |first1=Michael Daniel |title=The evolution of maximum terrestrial body mass in sauropod dinosaurs |journal=Current Biology |date=8 May 2023 |volume=33 |issue=9 |pages=349–350 |doi=10.1016/j.cub.2023.02.067 |pmid=37160089 |bibcode=2023CBio...33R.349D |language=English|doi-access=free }}</ref><ref>{{cite web |title=The Largest Animals To Ever Walk on Earth – New Research Reveals How Super-Giant Sauropods Achieved Their Record-Breaking Sizes |url=https://scitechdaily.com/the-largest-animals-to-ever-walk-on-earth-new-research-reveals-how-super-giant-sauropods-achieved-their-record-breaking-sizes/ |website=SciTechDaily |access-date=10 July 2023 |language=English |date=8 July 2023}}</ref>

Despite many counter-examples, Cope's rule is supported in many instances. For example, all marine invertebrate phyla except the molluscs show a size increase between the Cambrian and Permian.<ref name="Novack-Gottshall2008">{{cite journal | last=Novack-Gottshall | first=Philip M. | year=2008 | title=Ecosystem-wide body-size trends in Cambrian–Devonian marine invertebrate lineages | url=http://www.ben.edu/faculty/pnovack-gottshall/2008_Novack-Gottshall_Paleobiology.pdf | doi=10.1666/0094-8373(2008)034[0210:EBTICM]2.0.CO;2 | journal=Paleobiology | volume=34 | pages=210–228 | issn=0094-8373 | issue=2 | s2cid=21388114 | access-date=12 August 2020 | archive-date=2 May 2021 | archive-url=https://web.archive.org/web/20210502053634/https://www.ben.edu/faculty/pnovack-gottshall/2008_Novack-Gottshall_Paleobiology.pdf | url-status=dead }}</ref> Collectively, [[dinosaurs]] exhibit an increase in body length over their evolution.<ref name="HoneKeesey2005">{{cite journal |last1=Hone |first1= D. W. E. |last2=Keesey |first2= T. M. |last3=Pisani |first3= D. |last4=Purvis |first4= A. |title=Macroevolutionary trends in the Dinosauria: Cope's rule |journal=Journal of Evolutionary Biology |volume=18 |issue=3 |date=2005 |pages=587–595 |doi=10.1111/j.1420-9101.2004.00870.x |pmid=15842488|s2cid= 14122343 |doi-access=free }}</ref> Cope's rule also appears to hold in clades where a constraint on size is expected. For instance, one may expect the size of birds to be constrained, as larger masses mean more energy must be expended in flight. Birds have been suggested to follow Cope's law,<ref>{{cite journal| last2=Dyke | pages=618–624| issue=2| volume=21| journal=Journal of Evolutionary Biology| date=Mar 2008 | doi=10.1111/j.1420-9101.2007.01483.x| last1=Hone| pmid=18194232| issn=1010-061X | first3=M. | first2=J. | first4=J. | last4=Benton| last3=Haden| title=Body size evolution in Mesozoic birds| first1=W.| s2cid=8065382| doi-access=free}}</ref> although a subsequent reanalysis of the same data suggested otherwise.<ref>{{cite journal | last1=Butler | first1=R. J. | last2=Goswami | first2=A. | year=2008 | title=Body size evolution in Mesozoic birds: little evidence for Cope's rule | journal=Journal of Evolutionary Biology | volume=21 | issue=6| pages=1673–1682 | doi=10.1111/j.1420-9101.2008.01594.x | pmid=18691237| s2cid=21162784 | doi-access=free }}</ref>

An extensive study published in 2015 supports the presence of a trend toward larger body size in marine animals during the [[Phanerozoic]]. However, this trend was present mainly in the [[Paleozoic]] and [[Cenozoic]]; the [[Mesozoic]] was a period of relative stasis. The trend is not attributable simply to neutral drift in body size from small ancestors, and was mainly driven by a greater rate of diversification in classes of larger mean size. A smaller component of the overall trend is due to trends of increasing size within individual families.<ref name="Helm2015">{{cite journal | last1=Heim | first1=N. A. | last2=Knope | first2=M. L. | last3=Schaal | first3=E. K. | last4=Wang | first4=S. C. | last5=Payne | first5=J. L.  | title=Cope's rule in the evolution of marine animals | journal=Science | volume=347 | issue=6224 | pages=867–870 | doi=10.1126/science.1260065 | date=2015-02-20 |bibcode=2015Sci...347..867H | pmid=25700517| s2cid=14062772 | url=http://www.swarthmore.edu/NatSci/swang1/Publications/evolution2019.pdf | doi-access=free }}</ref>

== Notes ==
{{notes}}

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

{{biological rules}}

[[Category:Animal size]]
[[Category:Evolutionary biology]]
[[Category:Biological rules]]