From: CurtAdams@aol.com
Date: Fri Sep 25 1998 - 09:40:22 MDT
hanson@econ.berkeley.edu writes:
>Granting that there is some variation in the rate at which environments
>change, the question is: how much variation is that? If it is just one
>order of magnitude on average, then yes the puntuated equilibrium hypothesis
>is correct in some some sense, but the "small changes dominate" evolution
>view is also correct. It's just that "small" varies by an order of
magnitude,
>sometimes tiny and sometimes very tiny. If environment rate changes vary
>by ten orders of magnitude, on the other hand, then maybe it's a new world.
I should have been more precise by saying that punctuated equilibrium
predominates
in *speciation*. Different but closely related species differ in measurable
traits, but the differences typically arise from only a few genes. Gradual
changes in environment, by Orr's model, wouldn't produce the exponential
trends in gene effects, but then they don't seem to produce new species
either.
Orr's model really wouldn't be useful when the rate of onging environmental
is comparable to the rate at which the gene pool adapts.
>I'd have to go look up those QTL data papers to see how many orders of
>magnitude their data varies over. But I'm not optimistic - Orr brags that
>one of the data sets covers 82 traits, which isn't even enough to see a
>half an order of magnitude.
The variation in effects is a variation in the effect of genes on a given
trait, so hypothetically even a study of one trait could cover an arbitrarily
wide range of magnitude. In practice, the sample sizes go up with the
inverse of the minimum detectable effect, so I doubt *any* study covers
a large range. However, it is known that the most important genes do
roughly follow the exponential model, and the combined effects of the
most important genes explains most of the variation between species. So
even if small-effect genes are affected by environmental variation and
don't follow Orr's model, they're not important for speciation, because
the total effect of all minor genes combined is fairly small.
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