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 fairly constant rate.
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.
Figure: the crucial difference between punctuated equilibrium and phyletic gradualism concerns the rate at, and between, splitting events. (a) Punctuated equilibrium. (b) Phyletic gradualism. (c) Under a strict interpretation of punctuated equilibrium, sudden change without splitting contradicts the theory.