Cope's rule

Last updated
Cope's rule states that lineages increase in size over evolutionary time.
Juramaia NT.jpg
Juramaia was one of the earliest mammals, a basal eutherian from the Late Jurassic, no more than 10 cm long.
Elephant white background.png
The African bush elephant, a modern mammal, may reach a height of almost 4 metres.

Cope's rule, named after American paleontologist Edward Drinker Cope, [1] [2] postulates that population lineages tend to increase in body size over evolutionary time. [3] It was never actually stated by Cope, although he favoured the occurrence of linear evolutionary trends. [4] It is sometimes also known as the Cope–Depéret rule, [5] because Charles Depéret explicitly advocated the idea. [6] Theodor Eimer had also done so earlier. [4] The term "Cope's rule" was apparently coined by Bernhard Rensch, [1] based on the fact that Depéret had "lionized Cope" in his book. [4] [lower-alpha 1] While the rule has been demonstrated in many instances, it does not hold true at all taxonomic levels, or in all clades. Larger body size is associated with increased 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.

Contents

Function

Effects of growth

Directional selection appears to act on organisms' size, whereas it exhibits a far smaller effect on other morphological traits, [10] though it is possible that this perception may be a result of sample bias. [3] This selectional pressure can be explained by a number of advantages, both in terms of mating success and survival rate. [10]

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. [3] They may also potentially benefit from better thermal efficiency, increased intelligence, and a longer lifespan. [3]

Offsetting these advantages, larger organisms require more food and water, and shift from 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. [3]

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. [3] 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. [3] 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 kg almost always prey on organisms larger, not smaller, than themselves. [11] If such a niche is already occupied, competitive pressure may oppose the directional selection. [3] The three Canidae clades (Hesperocyoninae, Borophaginae, and Caninae) all show a trend towards larger size, although the first two are now extinct. [12]

Validity

Cope recognised that clades of Cenozoic mammals appeared to originate as small individuals, and that body mass increased through a clade's history. [13] Discussing the case of canid evolution in North America, Blaire Van Valkenburgh of UCLA and coworkers state:

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. [11]

In some cases, the increase in body size may represent a passive, rather than an active, trend. [14] 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 stricto , but is considered by many workers to be an example of "Cope's rule sensu lato ". [15] 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. [13]

However, many palaeobiologists are skeptical of the validity of Cope's rule, which may merely represent a statistical artefact. [3] [16] 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. [17] 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. [15] 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. [18] Giant dinosaurs appear to have evolved dozens of times, in response to local environmental conditions. [19] [20]

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. [21] Collectively, dinosaurs exhibit an increase in body length over their evolution. [22] 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, [23] although a subsequent reanalysis of the same data suggested otherwise. [24]

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. [25]

Notes

  1. ↑ In his paper, Rensch reproduced an erroneous citation of a work of Cope's [7] [8] [9] (that he apparently had not read) from the English translation of Depéret's book. [4]

Related Research Articles

<span class="mw-page-title-main">Clade</span> Group of a common ancestor and all descendants

In biological phylogenetics, a clade, also known as a monophyletic group or natural group, is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. In the taxonomical literature, sometimes the Latin form cladus is used rather than the English form. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields.

<span class="mw-page-title-main">Evolution</span> Change in the heritable characteristics of biological populations

Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation.

<span class="mw-page-title-main">Vertebrate</span> Subphylum of chordates with backbones

Vertebrates are deuterostomal animals with bony or cartilaginous axial endoskeleton — known as the vertebral column, spine or backbone — around and along the spinal cord, including all fish, amphibians, reptiles, birds and mammals. The vertebrates consist of all the taxa within the subphylum Vertebrata and represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described.

<span class="mw-page-title-main">Megafauna</span> Large animals

In zoology, megafauna are large animals. The precise definition of the term varies widely, though a common threshold used in paleontology is approximately 45 kilograms (99 lb), with other thresholds as low as 10 kilograms (22 lb) or as high as 1,000 kilograms (2,200 lb). Large body size is generally associated with other traits, such as having a slow rate of reproduction, and in large herbivores, reduced or negligible adult mortality from being killed by predators.

The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins.

<span class="mw-page-title-main">Afrotheria</span> Clade of mammals containing elephants and elephant shrews

Afrotheria is a superorder of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews, otter shrews, tenrecs, aardvarks, hyraxes, elephants, sea cows, and several extinct clades. Most groups of afrotheres share little or no superficial resemblance, and their similarities have only become known in recent times because of genetics and molecular studies. Many afrothere groups are found mostly or exclusively in Africa, reflecting the fact that Africa was an island continent from the Cretaceous until the early Miocene around 20 million years ago, when Afro-Arabia collided with Eurasia.

<span class="mw-page-title-main">Eumetazoa</span> Basal animal clade as a sister group of the Porifera

Eumetazoa, also known as diploblasts, Epitheliozoa or Histozoa, are a proposed basal animal clade as a sister group of Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. The competing hypothesis is the Myriazoa clade.

<span class="mw-page-title-main">Bergmann's rule</span> Biological rule stating that larger size organisms are found in colder environments

Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer regions. The rule derives from the relationship between size in linear dimensions meaning that both height and volume will increase in colder environments. Bergmann's rule only describes the overall size of the animals, but does not include body proportions like Allen's rule does.

<i>Dimetrodon</i> Genus of carnivorous synapsids from the Permian

Dimetrodon is an extinct genus of non-mammalian synapsid belonging to the family Sphenacodontidae that lived during the Cisuralian age of the Early Permian period, around 295–272 million years ago. With most species measuring 1.7–4.6 m (5.6–15.1 ft) long and weighing 28–250 kg (62–551 lb), the most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It was an obligate quadruped and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the Southwestern United States, the majority of these coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, its fossils have also been found in Germany and over a dozen species have been named since the genus was first erected in 1878.

<span class="mw-page-title-main">Tetanurae</span> Clade containing most theropod dinosaurs

Tetanurae is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans. Tetanurans are defined as all theropods more closely related to modern birds than to Ceratosaurus and contain the majority of predatory dinosaur diversity. Tetanurae likely diverged from its sister group, Ceratosauria, during the late Triassic. Tetanurae first appeared in the fossil record by the Early Jurassic about 190 mya and by the Middle Jurassic had become globally distributed.

<span class="mw-page-title-main">Allometry</span> Study of the relationship of body size to shape, anatomy, physiology, and behavior

Allometry is the study of the relationship of body size to shape, anatomy, physiology and behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in On Growth and Form and by Julian Huxley in 1932.

<span class="mw-page-title-main">Pareiasauria</span> Extinct clade of reptiles

Pareiasaurs are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct in the Permian–Triassic extinction event.

<span class="mw-page-title-main">Phenotypic plasticity</span> Trait change of an organism in response to environmental variation

Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompasses all types of environmentally induced changes that may or may not be permanent throughout an individual's lifespan.

Phylogenetic comparative methods (PCMs) use information on the historical relationships of lineages (phylogenies) to test evolutionary hypotheses. The comparative method has a long history in evolutionary biology; indeed, Charles Darwin used differences and similarities between species as a major source of evidence in The Origin of Species. However, the fact that closely related lineages share many traits and trait combinations as a result of the process of descent with modification means that lineages are not independent. This realization inspired the development of explicitly phylogenetic comparative methods. Initially, these methods were primarily developed to control for phylogenetic history when testing for adaptation; however, in recent years the use of the term has broadened to include any use of phylogenies in statistical tests. Although most studies that employ PCMs focus on extant organisms, many methods can also be applied to extinct taxa and can incorporate information from the fossil record.

In phylogenetics, basal is the direction of the base of a rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to the root. Note that extant taxa that lie on branches connecting directly to the root are not more closely related to the root than any other extant taxa.

The evolution of biological complexity is one important outcome of the process of evolution. Evolution has produced some remarkably complex organisms – although the actual level of complexity is very hard to define or measure accurately in biology, with properties such as gene content, the number of cell types or morphology all proposed as possible metrics.

<span class="mw-page-title-main">Evolution of the brain</span> Overview of the evolution of the brain

There is much to be discovered about the evolution of the brain and the principles that govern it. While much has been discovered, not everything currently known is well understood. The evolution of the brain has appeared to exhibit diverging adaptations within taxonomic classes such as Mammalia and more vastly diverse adaptations across other taxonomic classes. Brain to body size scales allometrically. This means as body size changes, so do other physiological, anatomical, and biochemical constructs connecting the brain to the body. Small bodied mammals have relatively large brains compared to their bodies whereas large mammals have smaller brain to body ratios. If brain weight is plotted against body weight for primates, the regression line of the sample points can indicate the brain power of a primate species. Lemurs for example fall below this line which means that for a primate of equivalent size, a larger brain would be expected. Humans lie well above the line indicating that humans are more encephalized than lemurs. In fact, humans are more encephalized compared to all other primates. This means that human brains have exhibited a larger evolutionary increase in complexity relative to size. Some of these evolutionary changes have been found to be linked to multiple genetic factors, such as proteins and other organelles.

<span class="mw-page-title-main">Biological rules</span> Generalized principle to describe patterns observed in living organisms

A biological rule or biological law is a generalized law, principle, or rule of thumb formulated to describe patterns observed in living organisms. Biological rules and laws are often developed as succinct, broadly applicable ways to explain complex phenomena or salient observations about the ecology and biogeographical distributions of plant and animal species around the world, though they have been proposed for or extended to all types of organisms. Many of these regularities of ecology and biogeography are named after the biologists who first described them.

The Lilliput effect is an observed decrease in animal body size in genera that have survived a major extinction. There are several hypotheses as to why these patterns appear in the fossil record, some of which are

<span class="mw-page-title-main">Laboratory experiments of speciation</span> Biological experiments

Laboratory experiments of speciation have been conducted for all four modes of speciation: allopatric, peripatric, parapatric, and sympatric; and various other processes involving speciation: hybridization, reinforcement, founder effects, among others. Most of the experiments have been done on flies, in particular Drosophila fruit flies. However, more recent studies have tested yeasts, fungi, and even viruses.

References

  1. 1 2 Rensch, B. (September 1948). "Histological Changes Correlated with Evolutionary Changes of Body Size". Evolution . 2 (3): 218–230. doi:10.2307/2405381. JSTOR   2405381. PMID   18884663.
  2. ↑ Stanley, S. M. (March 1973). "An Explanation for Cope's Rule". Evolution . 27 (1): 1–26. doi:10.2307/2407115. JSTOR   2407115. PMID   28563664.
  3. 1 2 3 4 5 6 7 8 9 Hone DW; Benton MJ (2005). "The evolution of large size: how does Cope's Rule work?" (PDF). Trends in Ecology and Evolution. 20 (1): 4–6. doi:10.1016/j.tree.2004.10.012. PMID   16701331.
  4. 1 2 3 4 Polly, P. D.; Alroy, J. (1998-10-02). "Cope's Rule". Science. 282 (5386): 50–51. Bibcode:1998Sci...282...47P. doi:10.1126/science.282.5386.47f. PMID   9786796. S2CID   41642689.
  5. ↑ Monroe, M. J.; Bokma, F. (2010). "Little evidence for Cope's rule from Bayesian phylogenetic analysis of extant mammals". Journal of Evolutionary Biology. 23 (9): 2017–2021. doi:10.1111/j.1420-9101.2010.02051.x. PMID   20629852. S2CID   20184065.
  6. ↑ Charles Jean Julien Depéret (1907). Les transformations du monde animal (in French). E. Flammarion.
  7. ↑ Cope, E. D. (February 1885). "On the Evolution of the Vertebrata, Progressive and Retrogressive". American Naturalist. 19 (2): 140–148. doi: 10.1086/273881 . JSTOR   2450032.
  8. ↑ Cope, E. D. (March 1885). "On the Evolution of the Vertebrata, Progressive and Retrogressive (Continued)". American Naturalist. 19 (3): 234–247. doi:10.1086/273900. JSTOR   2450075. S2CID   84538510.
  9. ↑ Cope, E. D. (April 1885). "On the Evolution of the Vertebrata, Progressive and Retrogressive (Continued)". American Naturalist. 19 (4): 341–353. doi: 10.1086/273923 . JSTOR   2450836.
  10. 1 2 Kingsolver, J. G.; Pfennig, D. W. (July 2004). "Individual-level selection as a cause of Cope's rule of phyletic size increase". Evolution. 58 (7): 1608–1612. doi:10.1554/04-003. PMID   15341162. S2CID   198159428.
  11. 1 2 Van Valkenburgh, B.; Wang, X; Damuth, J (2004). "Cope's Rule, Hypercarnivory, and Extinction in North American Canids". Science. 306 (5693): 101–4. Bibcode:2004Sci...306..101V. doi:10.1126/science.1102417. PMID   15459388. S2CID   12017658.
  12. ↑ Finarelli, John A. (2008). "Testing hypotheses of the evolution of encephalization in the Canidae (Carnivora, Mammalia)". Paleobiology. 34 (1): 35–45. Bibcode:2008Pbio...34...35F. doi:10.1666/07030.1. S2CID   86060945.
  13. 1 2 Alroy, J. (1998). "Cope's Rule and the Dynamics of Body Mass Evolution in North American Fossil Mammals" (PDF). Science. 280 (5364): 731–734. Bibcode:1998Sci...280..731A. doi:10.1126/science.280.5364.731. PMID   9563948.
  14. ↑ Carrano, M.T. (2006). Body-Size Evolution in the Dinosauria. University of Chicago Press. ISBN   978-0-226-09478-6.{{cite book}}: |journal= ignored (help)
  15. 1 2 Jablonski, D. (1997). "Body-size evolution in Cretaceous molluscs and the status of Cope's rule". Nature. 385 (6613): 250–252. Bibcode:1997Natur.385..250J. doi:10.1038/385250a0. S2CID   4322252.
  16. ↑ Gould, Stephen Jay (1997). "Cope's rule as psychological artefact". Nature. 385 (6613): 199–200. Bibcode:1997Natur.385..199G. doi: 10.1038/385199a0 . S2CID   205026571.
  17. ↑ Sereno, P. C.; A. L. Beck; D. B. Dutheil; B. Gado; H. C. E. Larsson; G. H. Lyon; J. D. Marcot; O. W. M. Rauhut; R. W. Sadlier; C. A. Sidor; D. J. Varricchio; G. P. Wilson; J. A. Wilson (1999). "Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs" (PDF). Science. 286 (5443): 1342–1347. doi:10.1126/science.286.5443.1342. PMID   10558986.
  18. ↑ Laurin, M (2004). "The evolution of body size, Cope's rule and the origin of amniotes". Systematic Biology. 53 (4): 594–622. doi: 10.1080/10635150490445706 . PMID   15371249.
  19. ↑ D'Emic, Michael Daniel (8 May 2023). "The evolution of maximum terrestrial body mass in sauropod dinosaurs". Current Biology. 33 (9): 349–350. Bibcode:2023CBio...33R.349D. doi: 10.1016/j.cub.2023.02.067 . PMID   37160089.
  20. ↑ "The Largest Animals To Ever Walk on Earth – New Research Reveals How Super-Giant Sauropods Achieved Their Record-Breaking Sizes". SciTechDaily. 8 July 2023. Retrieved 10 July 2023.
  21. ↑ Novack-Gottshall, Philip M. (2008). "Ecosystem-wide body-size trends in Cambrian–Devonian marine invertebrate lineages" (PDF). Paleobiology. 34 (2): 210–228. doi:10.1666/0094-8373(2008)034[0210:EBTICM]2.0.CO;2. ISSN   0094-8373. S2CID   21388114. Archived from the original (PDF) on 2 May 2021. Retrieved 12 August 2020.
  22. ↑ Hone, D. W. E.; Keesey, T. M.; Pisani, D.; Purvis, A. (2005). "Macroevolutionary trends in the Dinosauria: Cope's rule". Journal of Evolutionary Biology. 18 (3): 587–595. doi: 10.1111/j.1420-9101.2004.00870.x . PMID   15842488. S2CID   14122343.
  23. ↑ Hone, W.; Dyke, J.; Haden, M.; Benton, J. (Mar 2008). "Body size evolution in Mesozoic birds". Journal of Evolutionary Biology. 21 (2): 618–624. doi: 10.1111/j.1420-9101.2007.01483.x . ISSN   1010-061X. PMID   18194232. S2CID   8065382.
  24. ↑ Butler, R. J.; Goswami, A. (2008). "Body size evolution in Mesozoic birds: little evidence for Cope's rule". Journal of Evolutionary Biology. 21 (6): 1673–1682. doi: 10.1111/j.1420-9101.2008.01594.x . PMID   18691237. S2CID   21162784.
  25. ↑ Heim, N. A.; Knope, M. L.; Schaal, E. K.; Wang, S. C.; Payne, J. L. (2015-02-20). "Cope's rule in the evolution of marine animals" (PDF). Science. 347 (6224): 867–870. Bibcode:2015Sci...347..867H. doi: 10.1126/science.1260065 . PMID   25700517. S2CID   14062772.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.