From Gary Cziko (940908.1612 GMT]
responding to Bill Powers (940908.0830 MDT)
As usual, you raise some very interesting questions about evolution in your
post which ties in nicely with some recent work in biology (e.g., Cairns et
al.).
But I am now reading a delightful book by Christopher Weiner entitled _The
Beak of the Finch_ which recounts the 20-year-long research of Peter and
Rosemary Grant (or Princeton University) on the evolution of Darwin's
Finches on the Galapagos Islands.
What I find most startling about the Grants' research is that it shows
old-fashioned Darwinian evolution to be remarkedly rapid and extremely
senstive to very small variations. Differences in .5 mm in beak can mean
the difference between survival and death during a year of drought when
only the biggest and toughest seeds are left to eat. The Grants and their
students have shown evolution to work using Darwin's hammer over a single
year! Their work also suggests that much of what the fossil record shows
as long periods of stasis may actually be periods of quite rapid adaptive
evolutionaryfluctuation (responding, for example, to wet and dry periods)
which only looks like stasis over the long run.
What I haven't yet found in the book is any discussion of the variance in
beak among the new progeny hatching out after a period of environmental
stress. The Grants have this data, and I can't imagine that they haven't
looked at it. The trouble is that the selection effect (e.g, for larger
beaks to eat larger seeds during drought) is so strong that I suspect it
would overpower any effect of increased variation.
So while the E. coli effect may indeed be real for some organisms (at least
bacteria), good-old fashioned random variation and selection by Darwin's
hammer seems to account for what's happening on the Galapagos--and on a
much shorter time scale than Darwin himself would have imagined.--Gary