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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
> > explained by genes alone, offering a hole for MR to fill. I should say
> > 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
> > 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
> > from a chapter in the book where Dawkins is going through various
> > 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
> > 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
> > 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.
> > the fact is betrayed in details like this.
> > Such superficially convergent resemblances are oftene extremely
> > and I shall devote the rest of this chapter to some of them. They
> > 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
> > evolve once, the same design principle is good enough to evolve twice,
> > from different starting points, in different parts of the animal
> > This is nowhere better illustrated than in the case we used for our
> > 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
> > 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
> > 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
> > are prime numbers may allow the cicadas to exploit gaps in the
> > reproductive cycle of would be predators); he gets broader in comparing
> > 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
> > 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.
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