Re: [asa] Question on speciation

Thanks, Keith. I was not doubting that speciation occurs -- I've looked at some
of the literature on it. But I knew there had to be more to it than the simple
model I had in mind.
--- Keith Miller <kbmill@ksu.edu> wrote:

> Bill asked:
>
> > A biological species is a population that is reproductively isolated
> > from other species -- while interbreeding may be possible, such unions
> > don't produce fertile offspring.
> >
> > I have heard it said that speciation usually takes place in small,
> > isolated populations.
> >
> > Here's my question: Suppose one individual carries a mutation that
> > makes him/her reproductively isolated from the members of his (former)
> > species. Then in order for this new species to propagate, a member of
> > the opposite sex in the same population must carry the same mutation.
> > And of course the two must mate. Whatever the probability of the
> > mutation in question is, say p, the probability of two individuals
> > carrying the same mutation is p^2, where I have used ^ to signify
> > exponentiation. Isn't this an incredibly small probability?
>
> Reproductive isolation does not develop (except very rarely) through
> some single mutation. Rather a particular population of individuals
> becomes reproductively isolated from the rest of that species. In that
> isolated condition it continues to evolve - to accumulate mutations -
> independently of the parent population. After some period of time,
> that isolated population may become sufficiently divergent that it does
> not interbreed with the rest of the species when that population comes
> back into contact again.
>
> There are a number of ways in which a population may become isolated.
> The easiest to understand is that of geographic separation such as
> often exists on island populations. Populations can also become
> separated due to partitioning of resources or environments -- for
> example insects being isolated on particular hosts or food sources.
>
> The types of evolutionary changes that can result in reproductive
> isolation once the population are reunited are also highly varied.
> Some examples include: mating behavior changes, changes in features
> associated with sexual recognition and selection, changes in breeding
> times, changes in resource specialization, genetic barriers to
> interfertility, anatomical barriers to interfertility, etc.
>
> There is also the possibility of producing reproductive isolation
> through a single mutation on a single individual. However, this will
> only work in a an organism that can reproduce asexually or clonally.
> This is actually quite common in plants. I can also occur in animals,
> and even some vertebrates.
>
> I should also state that speciation is a reality having been observed
> in many examples of plants and animals in the wild.
>
> Keith
>
>

William E. (Bill) Hamilton, Ph.D.
248.652.4148 (home) 248.821.8156 (mobile)
"...If God is for us, who is against us?" Rom 8:31
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Received on Fri Feb 1 14:13:13 2008