What’s this? Science blogging on Pharyngula? I never thought I’d see the day when PZ Myers blogged about science!
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I’m kidding, but it is true that most of his posts aren’t strictly about science, and when they are they’re usually not educational on any meaningful level. This is probably due to the sheer volume of posts he churns out – he can’t write educational pieces about science for every post – however, when he does get around to clarifying a scientific issue, usually biological in nature, he always writes fantastically, which this most recent example about the evolutionary process demonstrates.
In summary, PZ explains why the basic concept of evolutionary change, “random mutation plus natural selection”, is fundamentally correct but doesn’t always apply in the way you would first think. Evolution proceeds by altering systems and networks of genes, all of which contribute to the Darwinian fitness of organisms within populations. Change is fluid and functional alteration is layered, relying on the shuffling of allele combinations as well as the addition of new alleles and genes through mutation.
Here’s a taste:
Stop thinking of mutations as unitary events that either get swiftly culled, because they’re deleterious, or get swiftly hauled into prominence by the uplifting crane of natural selection. Mutations are usually negligible changes that get tossed into the stewpot of the gene pool, where they simmer mostly unnoticed and invisible to selection. Look at human faces, for instance: they’re all different, and unless you’re looking at the extremes of beauty or ugliness, the variations simply don’t make much difference. Yet all those different faces really are the result of subtly different combinations of mutant forms of genes.
“Combinations” is the magic word. A single mutation rarely has a significant effect on a feature, but the combination of multiple mutations may have a detectable or even novel effect that can be seen by natural selection. And that’s what’s going on all the time: the population is a huge reservoir of genetic variation, and what we do when we reproduce is sort and mix and generate new combinations that are then tested in the environment.
PZ’s post is actually a distillation of a recent scientific paper about systems biology (Bard J (2010) A systems biology view of evolutionary genetics. Bioessays 32: 559-563.), which I recommend you check out if you’re interested in the subject at a more technical level.
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