[From Bill Powers (940908.1615 MDT)]
Gary Cziko (940908.1612 GMT) --
?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 evolutionary fluctuation (responding, for
example, to wet and dry periods) which only looks like stasis over the
long run.
This is remarkable indeed. What is most remarkable is the degree of
faith it shows in natural selection. Doesn't it strike you as suspicious
that a change in the right direction could be shown in as short a time
as one generation? How long is a generation in these fiches? Was there
time for random crossovers to be tested against survival criteria, the
consequences to be reflected in the next generation, and for further
crossovers to be selected again, and so on to achieve just the required
adaptation?
What the Grants observed was rapid adaptation. They ascribed this to
natural selection, as all good biologists are supposed to do. But did
they prove that it was only natural selection at work? Did they rule out
spontaneously-generated mutations related to starvation that were
selectively focused on the mechanisms for getting food? Or was such an
explanation dismissed (as LaMarkainism, I suppose) without even being
mentioned?
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.
What I would suggest looking for is a shortening of the interval between
variations when hunger increases, and a lengthening when it decreases.
As you know from the E. coli experiment, this sort of timing has drastic
and immediate effects.
There is also a possibility that selection had nothing to do with it. If
people are raised in an environment where they do not have to work
physically to make a living, they will grow up with weak muscles. But
the first kid who is required to exercise during maturation will grow up
with bigger and bulker muscles -- just enough to do the added work.
Maybe as birds mature, their beaks grow according to use, and if the
seeds are gradually getting harder or bigger, maybe the beaks grow
bigger. If it's accepted that beak size is fixed genetically, such an
effect could easily be overlooked. The experimental test is, of course,
to raise some young birds on bigger seeds and see what their beaks look
like when they grow up.
ยทยทยท
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Best,
Bill P.