saltationism >versus< gradualism?

[mirrormundo]

Is S.J. Gould's punctuated equilibrium really at odds with adaptationism / gradualism? Environmental changes (climate, geology) can lead to ecological changes like (mass) extinction, and or adaptive advantages for mutations that had been not advantageous before. These ecological changes in population-numbers and new succesful mutations influence / disturb the balaces in the eco-system, giving other mutations in other species a chance, leading to a snowball effect. In other words: if a mutation becomes an adaptive succes (for whatever reason), this can give rise to a chain reaction throughout the eco-system, resulting in a changing environment giving opportunities for yet other mutations, or am I wrong? So in that case we have regular darwinism behaving like saltationism. So evolution doesn't always have the same pace, as is acknowledged by most / all adaptationists / gradualists. What then is the dispute between Gould/Lewontin etc. and Dawkins etc? Or am I missing the point by failing to understand saltationism?

[chadn737]

Punctuated equilibrium (lets not forget the contributions of Eldridge) has been widely misunderstood, both in science and out. Punctuated equilibrium is very different than saltationism. The former is essentially a form of gradualism and is Darwinian, but proceeding in discrete bursts from time to time followed by periods of statism. Saltationism, on the other hand, is the idea that essentially speciation occurs in a single step...it is equivalent in many ways to Goldschmidt's "Hopeful Monsters". While Saltationism is likely wrong in the majority of cases of speciation, there are a few exceptions where it seems to have been verified. Consider the case of allopolyploidy in plants, where two different species will hybridize, forming a new species in a single generation. While this is quite a bit more common in plants than most people think, it seems very unlikely in animals.

 

Punctuated equilibrium itself is not at odds with gradualism, but is rather a certain interpretation of gradualism. Dawkins did make a distinction however in one of his later books. He pointed out that though punctuated equilibrium is a type of gradualism, it is a very specific type. Its not merely the fact that rates of evolution are variable. You can imagine a gradualist view where life is constantly evolving, even as the rate at which they evolve varies continuously along a scale. Punctuated equilibrium, however, asserts that there are extended periods of no apparent evolution, a sort of stationary phases that exists in between periods of evolution.