Reply #178: Gradualism.

[ozone_man]

All gradualism says is that changes take place over a number of generations, but definitely not one. Darwin explains how the fossil record may show sudden appearances of new species because of the relatively sudden adaptations to fit new ecological niches. Punctuated Equilibrium does not conflict in any way with the concept of gradualism, rather it complements it. Even Darwin explains it below, though Gould and others have developed the theory much further.

Punctuated equilibrium (plural punctuated equilibria) is a part of evolutionary theory that states that evolution, particularly speciation, occurs relatively quickly with long periods of little change—equilibria—in between. This theory is one of the proposed explanations of the evolutionary patterns of species as observed in the fossil record, particularly the relatively sudden appearance of new species in a geologically short time period, and the perhaps typical lack of substantial change of species during their existence.

http://en.wikipedia.org/wiki/Punctuated_equilibrium

At first blush, (4) Gradualism seems like it might conflict with Gould & Eldredge's "punctuated equilibrium" theory; but on closer examination, not so.

Here are two relevant quotes from On the Origin of Species:


"... it is probable that the periods, during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition." (from the final 6th edition, 1872)

"Varieties are often at first local...rendering the discovery of intermediate links less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they do spread, if discovered in a geological formation, they will appear as if suddenly created there, and will simply be classed as new species."

Darwin did not claim that evolutionary change is slow and continuous -- only that it does not proceed by "jumps" in a single generation (what Mayr calls "saltational" change). That is, despite the distortions of some anti-evolutionists, Darwin explictly did not think that evolution proceeds by the production of "hopeful monsters" -- Darwin himself never proposed that a fully-dinosaur parent gave birth to fully-bird progeny. Rather, the change took place in a series of intermediate, perhaps nearly insensible, steps in successive generations. Note that change over a thousand generations of any species appears as "sudden" or "abrupt" change in the fossil record, because a thousand generations is such an infinitesimally small fraction of Earth's history.

http://www.talkorigins.org/faqs/darwinism.html