Received: by alpheratz.cpm.aca.mmu.ac.uk id CAA06757 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-bounces@mmu.ac.uk); Mon, 27 Aug 2001 02:48:17 +0100 From: <joedees@bellsouth.net> To: memetics@mmu.ac.uk Date: Sun, 26 Aug 2001 20:52:28 -0500 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT Subject: Re: Dawkins & Convergent Evolution- the final word (?) Message-ID: <3B89618C.27175.337018@localhost> In-reply-to: <002901c12e67$eab00d40$6f24f4d8@teddace> X-mailer: Pegasus Mail for Win32 (v3.12c) Sender: fmb-bounces@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
On 26 Aug 2001, at 12:47, Dace wrote:
> From: "Vincent Campbell"
> > > Hi everyone,
> > >
> > > Before the Joe/Ted dispute gets too personal (too late...) I
> > > though I'd check out Ted's use of Dawkins to show that convergent
> > > evolution can't
> be
> > > explained by genes alone, offering a hole for MR to fill. I
> > > should say
> I
> > > don't believe Ted ever claimed Dawkins believes in MR. But, this
> > > is the way Ted quoted Dawkins from 'The Blind Watchmaker':
> > >
> > > <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.">
> > >
> > > This mis-represents what Dawkins was saying significantly. The
> > > passage
> is
> > > from a chapter in the book where Dawkins is going through various
> aspecys
> > > of natural selection- such as its gradual nature (he does the
> > > classic 5% of the eye argument), and immediately prior to the
> > > couple of paragraphs Ted quotes, he's talking about "Dollo's Law"
> > > which says that evolution
> is
> > > irreversible- that is it is highly statistically improbable that
> > > exactly the same evolutionary trajectory could be followed twice
> > > in either direction (p. 94). He concludes the paragraph with the
> > > sentence 'It [Dollo's Law] follows simply from the elementary laws
> > > of probability'.
> > >
> > > He goes on:-
> > >
> > > 'For just the same reason, it is vanishingly improbable that
> > > exactly the same evolutionary pathway should ever be travelled
> > > twice. And it would seem improbable, for the same statistical
> > > reasons, that two lines of evolution should converge on exactly
> > > the same endpoint from different starting points.
> > >
> > > It is all the more striking a testimony to the power of natural
> selection,
> > > therefore, that numerous examples can be found in real nature, in
> > > which independent lines of evolution appear to have converged,
> > > from very different starting points, on what looks very like the
> > > same endpoint. When we look in detail we find- it would be very
> > > worrying if we didn't- that the convergence is not total. The
> > > different lines of evolution betray their independent origins in
> > > numerous points of detail. For instance, octopus eyes are very
> > > like ours, but the wires leading from their photocells don't point
> > > forwards towards the light, as ours do. Octopus eyes are, in this
> > > respect, more 'sensibly' designed. They have arrived at a similar
> > > endpoint, from a very different starting point.
> And
> > > the fact is betrayed in details like this.
> > >
> > > Such superficially convergent resemblances are oftene extremely
> striking,
> > > and I shall devote the rest of this chapter to some of them. They
> provide
> > > impressive demonstrations of the power of natural selection to put
> > > together good designs. Yet the fact that the superficially
> > > similar designs also differ, testifies to their independent
> > > evolutionary origins and histories. The basic rationale is that,
> > > if a design is good enough
> to
> > > evolve once, the same design principle is good enough to evolve
> > > twice, from different starting points, in different parts of the
> > > animal
> kingdom.
> > > This is nowhere better illustrated than in the case we used for
> > > our
> basic
> > > illustration of good desing itself- echolocation.'
> > >
> > > [nb: original emphasis]
> > >
> > > He goes on to talk about echolocation in two unrelated species of
> > > bird, whales and dolphins; about electrolocation used by a couple
> > > of unrelated species of weak electric fish- the remarkably
> > > similarity between is
> spoilt
> > > by the rather obvious difference that the African variety has a
> > > fin alll the way along it's back, the South American variety, all
> > > along its
> belly;
> > > about periodical cicadas who all have either 13 or 17 year long
> > > juvenile stages (he says no-one knows exactly why, although the
> > > fact that 13 and
> 17
> > > are prime numbers may allow the cicadas to exploit gaps in the
> > > reproductive cycle of would be predators); he gets broader in
> > > comparing
> at
> > > length the development of the Old World, South America and
> > > Australia, comparing different 'trades' (e.g. anteating) that
> > > produced similar animals independently in these regions; he
> > > finishes with talking about similarities and differences between
> > > ants and termites, and then driver ants and army ants.
> > >
> > > Dawkins seems to me to be very clear on the matter, and there's
> > > nothing
> to
> > > suggest here that there's some mystery over convergence that needs
> > > a theory like MR to explain it.
>
> Dawkins does concede that evolutionary convergence is "vanishingly
> improbable" in the neo-Darwinian model. He's simply willing to accept
> this improbability. Sheldrake is not. As I stated before, there are
> numerous examples of convergence with no explanation according to
> natural selection, such as traits that come in handy in relation to a
> predator that's never existed in other locations where it crops up.
>
In fact, such convergence is not in the least improbable, as it is
caused by the selection, by similar environmental pressures in
different locales, of similar configurational and behavioral traits. In
a related way, superfluous traits can be explained by the shared
evolutionary geographic history of predator and prey. A predator
might be extinct in a range it formerly hunted, or a prey might have
spread to a new range; in either case, their evolutionary coevolution
would have selected for such responses.
>
>
> Ted
>
>
>
> ===============================================================
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===============================================================
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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