Cope's law

In evolutionary biology, Cope's law states that population lineages tend to increase body size over geological time. It is named for Edward Drinker Cope. Genus Equidae is often used to illustrate the law, with small animals evolving into larger ones; but critics such as Stephen Jay Gould point out a number of shortcomings of this example.

Cope's law is interesting because it appears to make the apparently paradoxical suggestion that possession of large body size favours the individual but renders the clade more susceptible to extinction.

Writing in Science, 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.

(Science, Vol 30 [DOI: 10.1126/science.1102417])

Cope's law has come under sustained criticism, including the observation that counterexamples to Cope's law are common throughout geological time. Critics also point out that the so-called law is worthless without a mechanism; palaeontologist Johnathan R. Wigner has stated that "Cope's Rule is a twisted version of the ... historical-narrative (that is, a just-so story ). It takes a perceived historical trend and tries to explain it".