Re: A question of timing
- From: "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx>
- Date: Sun, 28 Aug 2005 18:17:16 -0400 (EDT)
"Michael Nuwer" <StopSpam@xxxxxxxxx> wrote in message news:derght$1ti6$1@xxxxxxxxxxxxxxxxxxxxxx
> whitesickle@xxxxxxx wrote:
>
> > Darwinian evolution in "general" is an extremely long and gradual and
> > incremental process which doesn't occur in a generation's lifetime or
> > innumerable generations. The changes are imperceptible. It's only
> > really been through molecular genetics we've recently been able to draw
> > some rough but good speculations and conclusions.
>
> Hi Michael,
>
> In your view is a long and gradual process a necessary property of
> Darwinian evolution? Or is it just that Darwinian evolution happens to
> be a long and gradual process in the biological world?
>
> What I'm wishing to understand is whether the principles of Darwinian
> evolution (variation, inheritance, and selection) can be applied to
> human culture and institutions. Gould once argued that biological
> evolution is a bad analogue for cultural change. One of his three reason
> is that "cultural evolution can be faster by orders of magnitude than
> biological change at it maximal Darwinian rate--and questions of timing
> are of the essence in evolutionary arguments." But he doesn't elaborate
> on this point.
>
> So I am wondering what it is about Darwinian evolution that _requires_ a
> long and gradual process.
Interesting question. I will attempt two different answers, each of
which interprets your question slightly differently.
First, neo-Darwinian evolution (based on genes) is inherently slower
than cultural evolution (based on memes). Genes can only be passed to
offspring and there is a limit to the number of offspring one organism
can have. It takes time for a gene to spread in a population - a
time proportional to the logarithm of the population size. The time
is also proportional to the selection coefficient - the number which
measures just how advantageous this innovation is. So neo-Darwinian
evolution takes place on a minimal time scale of hundreds or thousands
of organism generations.
However, this is still pretty fast - potentially much faster than is
suggested by the fossil record, though slower than cultural evolution.
So, apparently, evolution moves slower than it theoretically could, based
solely on population genetics arguments. Why so slow? Well, it could
be that most evolutionary change is the result of mutations with very
small selection coefficients. Or it could be that the mechanism of
mutation simply takes a long time to generate new advantageous variations
upon which selection can work.
And this brings me to my second answer. Darwin vociferously insisted that
evolution under natural selection must be gradual. That is, in modern
terms, he held that the selection coefficients must be small. He was
well aware that artificial selection can result in rapid change. But
he insisted that such rapid change would rarely happen out there in
the real world. Gould does a good job of noting and explaining this
commitment of Darwin to "gradualism". Why did Darwin insist on gradualism?
Apparently because he was worried that if change were rapid, it would
be far more difficult to identify NS as the sole and sufficient cause
of the change. In fact, he was right, at least psychologically. People
who believe in sporadic sudden change (such as Goldschmidt or Gould
himself) frequently present their theories as challenges not just to
Darwin's gradualism, but rather as a challenge to natural selection itself.
.
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