Thursday, July 05, 2007

Final thoughts on adaptation   posted by p-ter @ 7/05/2007 06:44:00 PM

Larry Moran has responded again on adaptation, disapprovingly quoting Dawkins, who writes:
Natural selection is all-powerful with respect to those visible changes that affect survival and reproduction. Natural selection is the only explanation we know for the functional beauty and apparently "designed" complexity of living things. But if there are any changes that have no visible effect-changes that pass right under natural selection's radar-they can accumulate in the gene pool with impunity and may supply just what we need for an evolutionary clock.
Besides the possibly questionable use of the term "all-powerful", that sounds about right. The extraordinary power of the neutral theory to explain certain parts of molecular evolution cannot be denied (nor should anyone want to--it's quite elegant!). Yet the power of natural selection on the phenotypic level is becoming clear from molecular evidence, even if it wasn't already clear from simple observation (John Hawks provides a couple pictures to "frame" the debate, so to speak).

It's worth pointing out that evolution is stochastic-- most beneficial mutations are lost from the population immediately, and if we were to restart the evolutionary process multiple times, there would certainly be major differences in what shows up. But that's a very different process than genetic drift, which I think is perhaps the source of Larry's confusion.

In any case, Larry also has an interesting post up on mutation rates, in which he concludes:
With a population of 6 billion individuals on the planet, there will be 120 x 6 x 109 = 7.2 x 10^11 new mutations in the population every generation. This means that every single nucleotide in our genome will be mutated in the human population every 20 years or so.
Now that's something to think about.

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