[Flankk]

Darwin believed that each successive generation of a species had increasing mutations leading to a gradual divergence. Another school of thought believes that a species remains at equilibrium until some environmental stressor activates a rapid divergence. If this "punctuated equilibrium" is true, climate change will give rise to many new species, as would all mass extinctions.

[seandhuine]

What Darwin knew about biology is incommensurate with a modern understanding of the word "mutation". A generation later than him, biologists still believed cells were formless blobs of jelly, so to speak. Punctuated equilibrium is even less defensible given our present understanding of the molecular basis of genetics.

[Flankk]

Mutation means the same thing now as it did back then. What has changed is that we now understand how it works. The concept of punctuated equilibrium was introduced in 1972. It is the leading theory based on present understanding. I'm not sure what you mean by "less defensible."

[seandhuine]

That a hypothesis that has no feasible molecular basis can be called "leading" is a mark of the bankruptcy of Darwinian evolutionary theory.

[whatshisface]

Punctuated equilibrium still involves gradual Darwinian change, but over very short periods of time compared to the long periods where the species is adapted as well as it can be (without major, unlikely changes) to its present environment.

[seandhuine]

I'm hoping that gradually over a very short period of time folks will realize the contradiction in terms that is called "punctuated equilibrium". It has no feasible molecular basis. Without such, it might as well be fairy dust for its explanatory power. But gradual fairy dust, that operates over very short periods of time.

The pertinent question remains: at the molecular level, how?

[whatshisface]

Large interbreeding populations are "locked in" and recessive traits are rare. Small isolated populations can make recessive traits permanent. This is well-known to everbody who has stopped to consider what conditions produce major genetic changes in human morphology (inbreeding). Large gene pools protect against morphological changes in humans and animals alike.

Species are sent back and forth between those two extremes by changes in the environment brought on by our planet's constantly changing climate, topography and ecosystems. Sometimes, when the isolation ends, the combination of made-permanent recessive traits turns out to be harmful and the isolated population is replaced by the larger one (if the larger one survived), and other times it is helpful and they spread out into the larger environment. It isn't a contradiction any more than first and second gear on your bike are - you can't have them both at once, but they are switched between by systems external to the bike itself (the rider).

The idea is that every species is descendant from a highly inbred population of another species. Curiously, this happens in the Bible (Noah's ark).

The molecular basis is the same as that of Darwinian evolution (transcription errors plus whole-organism natural selection), combined with the usual laws of population genetics.