When PZ Meyers does these explainations, it makes me want to stand up and applaud.
Here's some very cool news: scientists have directly observed the evolution of a complex, polygenic, polyphenic trait by genetic assimilation and accommodation in the laboratory. This is important, because it is simultaneously yet another demonstration of the fact of evolution, and an exploration of mechanisms of evolution—showing that evolution is more sophisticated than changes in the coding sequences of individual genes spreading through a population, but is also a consequence of the accumulation of masked variation, synergistic interactions between different alleles and the environment, and perhaps most importantly, changes in gene regulation.
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I'll try to give a simple introduction to those peculiar words, and explain why the evolution of a polyphenic pigment pattern in a caterpillar is a fascinating and significant result.
(... skipping all the good stuff ...)
What this tells us about evolution is that there can be a reservoir of 'invisible' variation in populations, which is typically buffered by developmental mechanisms. The buffering allows the variants to accumulate without compromising the viability of carriers. Enabling mutations or changes in the environment, however, can rapidly shift the effect of these variants out of the range that can be buffered, exposing new phenotypic effects that can then be subject to selection. This can be fast, fast, fast, since we aren't waiting for a single new mutation (or worse, for polygenic traits, many mutations) to expand into a population, but are exploiting a large pool of diversity that is already present, mixing extant alleles by recombination to produce new phenotypes.
http://scienceblogs.com/pharyngula/2006/02/evolution_of_a_polyphenism.php#more