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phyletic

Phyletic gradualism

Phyletic gradualism is a macroevolutionary hypothesis rooted in uniformitarianism. The hypothesis states that species continue to adapt to new challenges over the course of their history, gradually becoming new species. Gradualism holds that every individual is the same species as its parents, and that there is no clear line of demarcation between the old species and the new species. It holds that the species is not a fixed type, and that the population, not the individual, evolves. During this process, evolution occurs at a slow and smooth (but not necessarily constant) rate, even on a geological timescale. (cf. punctuated equilibrium)

Phyletic gradualism has been largely deprecated as the exclusive pattern of evolution by modern evolutionary biologists in favor of the acceptation of occurrence of patterns such as those described on punctuated equilibrium, quantum evolution, and punctuated gradualism.

Authors such as Richard Dawkins argue that such constant-rate gradualism is not present in academic literature, serving only as a straw-man for punctuated equilibrium advocates. He refutes the idea that Charles Darwin himself was a constant-rate gradualist, as suggested by Stephen Jay Gould, for Darwin has explicitly stated that "Many species, once formed, never undergo any further change...; and the periods, during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retain the same form."

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The theory of the punctuated equilibrium goes against the theory of phyletic gradualism.

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