From: John Wilkins (j.wilkins1@uq.edu.au)
Date: Fri 28 Oct 2005 - 11:34:56 GMT
Most speciation is thought to occur through geographical isolation
and subsequent evolution, mostly by drift, founder effect sampling of
the original gene pool and selection for local adaptation. But the
selection here is not speciating selection most of the time.
Speciation is a by-product of evolution of the isolate population
that results in reproductive isolation when back in sympatry.
The type of speciation in which selection plays a role *in causing
speciation* is sympatric speciation. In this case variants within a
local population adapt to divergent fitness peaks, and so results in
divergent selection, leading to lowered fitness of hybrids. But most
of the time this is caused more by sexual selection than ecological
adaptation. And it requires quite rare circumstances.
Darwin thought that most speciation was caused by divergent selection
but it seems not, at least in sexual organisms, to be a major factor.
Selection causes adaptation, but adaptation doesn't drive most
speciation events.
On 28/10/2005, at 7:28 PM, Chris Taylor wrote:
>> But of course most speciation now is in fact thought to occur
>> through random variation and random fixation rather than by
>> selection as Darwin thought. There's good reason to think that
>> some speciation is due to selection, but not much. I worry that
>> we think only that Darwinian evolution is about selection
>> (natural or sexual), when in fact another really deep aspect of
>> his view is common descent, and this is not tied now to selection.
>>
>
> ???
>
> Selection has _no role_ in the generation of species the majority
> of the time? Are you just purely talking about permanent absolute
> allopatry / completely discrete allochrony or whatever equivalent
> you care to pick?
>
> Elephants and fleas will never successfully mate (having diverged
> somewhat); but where this matters (i.e. in recent speciation
> events, where those species ranges [or whatever] overlap) selection
> is key in ensuring that hybrids are (1) demonstrably crap and that
> (2) parents who find a way to avoid sinking their genes into such
> crappy hybrids propagate more of those genes forwards to subsequent
> generations..?
>
> Random variation and fixation is _not good_ at producing adaptation
> without selection. Have I misunderstood you?
>
> Cheers, Chris.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~
> chris.taylor@ebi.ac.uk
> http://psidev.sf.net/
> ~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
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-- John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project University of Queensland - Blog: evolvethought.blogspot.com "Darwin's theory has no more to do with philosophy than any other hypothesis in natural science." Tractatus 4.1122 =============================================================== This was distributed via the memetics list associated with the Journal of Memetics - Evolutionary Models of Information Transmission For information about the journal and the list (e.g. unsubscribing) see: http://www.cpm.mmu.ac.uk/jom-emit
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