[GedByrne]

Does genetic variation rise in response to selective pressure?

It seems to me that this is a two stage process.

1. Variation is introduced at a fairly constant rate by mutation. 2. Variation is filtered out by natural selection based on how well it fits the environment.

The shocks occur when the environment changes so that the criteria for fit change and new variations survive for the long term.

So when we look at evolution we see a rate of change driven by the rate of mutation.

When we look at the long term we see a rate of change driven by the environment.

[FullMtlAlcoholc]

I agree. When I look at the long term though, the environment and mutation are just different parts of the same whole. Both are necessary for phenotypic changes and speciation. Even that is simplistic. It doesn't take into account the significance of viral transfer of dna and other epigenetic factors, how an environment can cause normally dormant genes to express themselves, sexual selection where attractiveness != most environmentally fit, etc.