What is Cope's Rule?

Cope's rule is one of several "biological rules" -- biological trends found in patterns across data about many plants and animals. Cope's rule states that population lineages tend to increase in size over evolutionary time. There are numerous examples throughout evolutionary history -- mammals increasing in size after the demise of the dinosaurs; reptiles increasing in size after the demise of the therapsids; amphibians increasing in size after making it onto the land; all animals increasing in size after the Cambrian Explosion 540 million years ago... and so on. Greater size gives evolutionary advantages to both individuals and species for a number of reasons, the most superficial being that a larger beast is harder to kill and can kill or defend oneself more easily. In fact, larger size may be so evolutionarily beneficial that the only brakes on Cope's rule are that clades composed of larger individuals are more likely to go extinct in times of trouble (mostly because they have ...  more

Cope’s rule, the gradual trend towards an increase in body size over time, has long been a source of controversy in evolutionary ecology. Edward Drinker Cope was a palaeontologist who described the first important faunas from North America (Alroy, 1998). While working with these specimens he discovered that there was an increase in the average size of mammals during the Cenozoic time period (Alroy, 1998). He came to the conclusion that this pattern must have been the result of a tendency for new groups to evolve at small sizes and a continuous push towards a larger body size (Alroy, 1998). Since the time of Cope, studies have been performed for many taxa with differing results. The debate focuses mainly on whether this macroevolutionary process actually exists and if it does, what are the microevolutionary processes that drive it.  more

> Something which is very much misunderstood by many people on the net... :-) Cope (Edward Drinker Cope, that is, famous 19th Century vertebrate paleontologist AND ichthyologist AND herpetologist AND general marine biologist [as many of us within Vert Paleo sometimes forget]) actually proposed several different "rules" which he saw governing the evolution of life. Unlike his contemporary and rival, O.C. Marsh, Cope was not a Darwinist: he did not consider natural selection necessary nor sufficient to explain evolution. Like others of his time (and his student, H.F. Osborn), Cope believed in some inborn forces which drove evolution in predetermined directions. The most famous formulation Cope offered, which is often called "Cope's Rule", is "In animal taxa [note: NOT just tetrapod, or even vertebrate; but animals], there is a long-term phylogenetic trend toward increased body size". To Cope, this was due to some inborn drive. As others have shown (for a classic: Steve Stanley, 1973, ...  more