Received: by alpheratz.cpm.aca.mmu.ac.uk id OAA10259 (8.6.9/5.3[ref firstname.lastname@example.org] for cpm.aca.mmu.ac.uk from email@example.com); Thu, 9 Aug 2001 14:16:01 +0100 Message-ID: <3B728C91.B865E1D8@bioinf.man.ac.uk> Date: Thu, 09 Aug 2001 14:13:53 +0100 From: Chris Taylor <Christopher.Taylor@man.ac.uk> Organization: University of Manchester X-Mailer: Mozilla 4.77 [en] (Windows NT 5.0; U) X-Accept-Language: en To: firstname.lastname@example.org Subject: Re: Convergence References: <3B715AAD.9309.69CD01@localhost> Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: email@example.com Precedence: bulk Reply-To: firstname.lastname@example.org
> Random mutation (within the same range of genetic possibilities),
> followed by selection by similar environments for similar niches
> should just about do it. Notice the word 'similar'; they are not the
> same (or they could interbreed).
There's another part to this story; as well as convergent evolution,
there are 'morphogenetic attractors' which species are morphologically
drawn to. This covers all the stuff that convergent evolution can't get.
Brian Goodwin (inter alia) did some good stuff on these morphogenetic
constraints (although I don't agree that his work 'challenges' Darwinism
- just dust cover blag methinks). To summarise - there are some aspects
of the physical world that affect the paths open to evolution; stuff
like how many peaks and troughs of a concentration 'wave' of some
molecule can you get along a body axis or around the circimference of a
structure (Turing-style) - e.g. some animals are spotted, but the tails
are ringed, because you can't set up complex enough concentration
gradients in such a narrow structure. Or the Fibonacci sequence of side
branch (etc.) angles on plants would be another.
Additionally, for the tree with similar leaves, this could
also/alternatively be a side effect of one or more traits of the
organism that *are* truly evolutionarily convergent (answering the same
question with the 'obvious' answer); this is known as pleiotropy (for
the non-biologists here who may not have heard the word, its the
situation where genes affect multiple traits, necessitating trade-offs).
We don't need no hoodoo here. We just have to look hard for a good
explanation, rather than running for the nearest shaman.
Chris Taylor (email@example.com)
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