[Taxacom] teleology example

[Michael Heads]

In the modern synthesis, mutation per se isn't important - the key thing is
the gene pool which is always already full of anything that might be
useful. But many geneticists are questioning this (see Michael Lynch's book
on the evolution of genomic architecture for example). This would mean
that mutation itself could be of direct significance for fixation in
populations and evolutionary direction.

Rob, you suggest the blog text could be rephrased: "It is hard to see how
these hair like processes would become and remain typical of a variety of
snail species if they were not subject to positive selection". This still
overlooks the idea that they may not be due to any
purpose/end/advantage but to a prior trend in genome evolution. It's not
just the hairs - you also have to explain the bizarre paddles on Kokopapa,
'flanges', 'ornamentation', 'grid lattices' etc. etc. on other snails. The
whole lot could be explained with just a few trends to reduction, fusion
etc., rather than through each individual morphology and any 'advantages'
it might have *after* it has evolved.

Michael Heads
On Thu, Mar 7, 2013 at 5:02 PM, Rob Smissen <SmissenR at landcareresearch.co.nz
> wrote:

> "...biased gene-conversion etc" (as suggested by Michael Heads) as well as
> many more or less random mutational mechanisms might explain how a novel
> character arises in an individual organism or pedigree, but seems a pretty
> poor explanation for the fixation of morphological characters in
> populations and species.
>
> Perhaps the article should have been written more along the lines of  "It
> is hard to see how these hair like processes would become and remain
> typical of a variety of snail species if they were not subject to positive
> selection".
>
> They might of course be a by-product of some other characteristic which is
> advantageous, but, all other things being equal, being covered with hairs
> seems likely to come with some disadvantages (he writes while scratching)
> so selection would favour any snails that managed to decouple the hairs
> from the hypothetical selected character.
>
> Am I missing or exemplifying John's point?
>
> Cheers
> Rob
>
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