Received: by alpheratz.cpm.aca.mmu.ac.uk id PAA13270 (8.6.9/5.3[ref firstname.lastname@example.org] for cpm.aca.mmu.ac.uk from email@example.com); Wed, 29 Aug 2001 15:28:56 +0100 Message-ID: <3B8CFBAC.AE958210@bioinf.man.ac.uk> Date: Wed, 29 Aug 2001 15:26:52 +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: Dawkins etc References: <3B8C7133.15509.CB3665@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
> > Of course there are differences. Why shouldn't there be? They're
> > different species in different locations. But they're also profoundly
> > similar.
No, I bet you couldn't find a single protein with the same sequence, let
alone a gene; all the similar traits will ontologically be from
different developmental pathways. Similarity at the macro level, which
is all you are considering, is a small percentage of what makes an
Btw, what about my clincher (final extinction of species through drift)?
> Precisely due to the similarity of the selectional environmental
> pressures and opportunities with which they are presented.
> > This is perhaps a better example of parallel evolution (a
> > term now in wide currency), since the starting points for these
> > ant-eaters, moles, flying squirrels, cats, wolves, mice, jerboas,
> > etc., were the same tree shrews that diverged 110 million years ago
> > into marsupials and placentals.
> A correct way to phrase this would be divergence followed by
> convergence, both environmentally selectionally shaped.
> > Parallel evolution is quite common
> > and crops up in human origins. Witness the incredibly similar
> > development of Eurasian Homo sapiens (Neanderthal) and the African
> > model.
That is drivel. They only just *DI*verged so of course they're similar.
> Except for superficial changes, such as pigmentation and hair
> texture, not much has changed, or had much time to, evolutionarily
> speaking. Here we are most definitely talking (geologically recent)
> common ancestor.
> > I do understand the point you're making about Dawkins. He applies the
> > phrase "vanishingly improbable" not to convergence as it actually
> > occurs but to some sort of imaginary, ideal convergence. In other
> > words, he's saying nothing, which is why the passage is so confusing.
> > In fact, convergence as it actually occurs is vanishingly improbable
> > even when natural selection is involved. And there are many examples
> > in which natural selection plays no conceivable role.
I had no problem with Dawkin's prose - made clear sense to me. Picking
millions of nucleotides to be the same is 'vanishingly improbable';
making something that looks the same, out of different stuff, isn't.
> Actually, natural, selection is that which renders it reasonable, and
> ther are NO examples in which naturale selection can be conceived
> to play no role, since it is as universally ubiquitous a process as is
> random mutation.
> > > <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.>
> > > >
> > > Well, I'd like some examples here, since most that we know of
> > > species moving from one environment to another is usually chaos as
> > > native species are unable to deal with the intruders (again,
> > > Australasia with
> > it's
> > > cane toad and rabbit plagues etc. etc.).
> > F. W. Went studied convergence among shrubs in New Zealand. He found
> > about 50 species of shrubs that had independently developed the same
> > pattern of "interlaced, tortuous branches and reduced leaves." This
> > would presumably have protected them from herbivores. But there are
> > no herbivores native to New Zealand. Moreover, this pattern "occurs
> > in so many shrubs from different habitats, it does not seem to be an
> > adaptation to the environment." He provides several other examples of
> > convergence which he contends cannot be explained by natural
> > selection. He argues that the chromosomes associated with these
> > traits must have somehow hopped across species. (Went, "Parallel
> > Evolution," Taxon 20:197-226, 1971.)
> Perhaps his rejected explanation was not the right one, yet a right
> one existed, such as minimizing evaporation water loss.
NZ has a crap flora and fauna (crap in the sense of always gets a
kicking from alien species); do we know that these weren't recent
immigrants (from somewhere with big herbivores) that have diverged
recently into several species? Did he even look for other reasons? (like
> > This unlikely explanation can't account for convergence across widely
> > separated areas. Bernhard Rensch studied butterflies with similar
> > color patterns on their wings. Some of these could be explained by
> > mimicry of butterflies avoided by predators. But often these similar
> > patterns appear on butterflies in completely different places in which
> > such mimicry would be useless. (Rensch, Evolution Above the Species
> > Level, Methuen, 1959.)
> The wind does tend to carry butterflies all over, away from where
> such coloration evolved and was useful. Give 'em a couple of
> million years of the coloration being of no use, and more useful
> coloration will more likely emerge.
Also there are the Goodwin-related arguments, and the question of
whether there was more mimicry than crypsis, and whether they were *all*
mimicking something else (bird, other butterfly with big range, all
sorts of shit). Lesson one in biology is you have to have a lot of
different cases before you even start looking for rules because you can
*always* find a species somewhere that does something freaky.
> > In the February 1999 issue of Scientific American, Stiassny and Meyer
> > discuss the inexplicable similarity of color patterns on the scales of
> > cichlids in separate African lakes.
> I'd bet that these lakes are close to each other and that they either
> were once connected or that humans or animals have transported
> the cichlids, or their eggs, between lakes.
Just downloaded the article (yay site licence)...
I've put a scan of the relevant page at
and Vincent's right - the authors posit convergence (due to ecological
selection pressures) and there seems no reason to doubt this (after all
the habitats are equivalent, the raw 'stuff' is similar, and frankly
they aren't that alike anyway - there's a few passerine birds that are
almost indistinguishable [more so than these cichlids] but are
completely different species).
I just don't understand how one could go shopping for new explanations
anyway when there don't appear to be any problems with existing
theories. Just because they don't explain everything straight away
doesn't mean that they can't (remember they're just tools in our hands,
which implies some skill in their use). To get MR's foot in the door
with me, you'd have to prove that there is something that current
thinking clearly doesn't have a hope of explaining.
Chris Taylor (email@example.com)
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