Received: by alpheratz.cpm.aca.mmu.ac.uk id TAA13756 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-bounces@mmu.ac.uk); Wed, 29 Aug 2001 19:47:04 +0100 From: Philip Jonkers <P.A.E.Jonkers@phys.rug.nl> X-Authentication-Warning: rugth1.phys.rug.nl: www-data set sender to jonkers@localhost using -f To: memetics@mmu.ac.uk Subject: Re: FW: Dawkins & Convergent Evolution- the final word (?) Message-ID: <999110703.3b8d382f0a7eb@rugth1.phys.rug.nl> Date: Wed, 29 Aug 2001 20:45:03 +0200 (CEST) References: <2D1C159B783DD211808A006008062D3101746043@inchna.stir.ac.uk> In-Reply-To: <2D1C159B783DD211808A006008062D3101746043@inchna.stir.ac.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit User-Agent: IMP/PHP IMAP webmail program 2.2.5 X-Originating-IP: 62.100.11.165 Sender: fmb-bounces@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
I guess all the sensible things on this convergence issue
have already aptly been said by Vincent and Joe, but I can't resist to add
one little comment.
> > <Dawkins discusses this dilemma in The Blind Watchmaker: "It is
> > vanishingly improbable that the same evolutionary pathway should
> > ever be followed twice.
> > And it would seem similarly improbable, for the same statistical
> > reasons, that two lines of evolution should converge on the same
> > endpoint from different starting points. It is all the more
> > striking... that numerous examples can be found in real nature,
> > in which independent lines of eovlution appear to have converged,
> > from very different starting points, on
> > what looks very like the same end-point.
As it stands it is somewhat confusing as the passage casts a little doubt on
natural selection, I have to agree this much with Ted.
He raises confusion in the second part (It is all the ...).
Nonetheless, no unsurmountable problems for the theory of natural selection
arise.
I agree, the probability of two species parellely traversing
(i.e. both going through the same genetic changes) the same path of
evolution is statistically non-existent. But the emergence of two
species that superficially resemble one-another is quite finite.
Compare, for instance, carcharadontosaurus with tyrannosaurus-rex.
The odds of the showing-up of two similar species is very small, nonetheless.
However, given the fact that the earth has known and still knows many
species, the expectation value, i.e. number of species-pairs * prob. of
similarity at any given time, might be quite large. Therefore, from
a brute-force statistical point of view, emergence of two similar species
(albeit from entirely different genera) is not a sheer impossibility
but a fair possibility. Nature has obeyed this statistical rule at
least to fair degree by presenting a sufficient number of cases.
Philip Jonkers.
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