Phyletic Gradualism

∞ generated and posted on 2016.11.05 ∞

Evolutionary change in organisms, particularly in the course of speciation, that is both slow and steady.

The term phyletic gradualism was created to contrast the ideas of punctuated equilibrium. Whereas the concept of phyletic gradualism is meant to suggest a slow and steady evolutionary pace, especially in terms of morphological change along with speciation, punctuated equilibrium is meant to suggest quite the opposite: great variance in rates of evolution, with substantial periods of stasis interrupted by rapid change.

There is some controversy about whether phyletic gradualism both exists and has been adhered to by many, including by Darwin. The concept does serve a purpose, though, in providing a descriptor for the opposite of punctuated equilibrium. Altogether, however, phyletic gradualism's basic prediction is that gaps in the fossil record are a consequence of a low "resolution" of the fossil record rather than gaps specifically over those periods during which rapid morphological change is occurring.

Another way of saying this is that with phyletic gradualism a lack of sampling can be most anywhere in the fossil record and still yield abrupt changes in morphologies whereas with punctuated equilibrium it is only very specific times and places that a lack of fossils will result in an absence of intermediate forms.