Re: Species diversity through time

dkomo wrote:

John Harshman wrote:

r norman wrote:



On Tue, 13 Nov 2007 12:03:55 -0800, John Harshman
<jharshman.diespamdie@xxxxxxxxxxx> wrote:




dkomo wrote:




John Harshman wrote:

<snip top>

dkomo wrote:






John Harshman wrote:




I wouldn't go examining the metaphor all that closely. He merely means
that life is not some grand progression toward some predetermined goal.
If the world is chaotic (in the mathematical sense), then all you need
would be an infinitesimal change in initial conditions, or a little bit
of randomness here and there, to make the end result vary wildly. Where
are you going with this? Do you think that the history of life is indeed
a series of inevitable events?

Gould is wrong. There are basins of attraction in the state space of
life. Replay the tape of life and the end result will be close to what
it was before, as long as you don't vary the major historical
contingencies. A little bit of randomness here and there won't perturb
evolution's trajectory all that much.


Can you present any evidence for this interesting claim? And could you
clarify what you mean by "close"? Would we necessarily have humans, or
mammals, or chordates? Or is it just that, given animals, we would
almost certainly have many species with eyes and legs?


I have just as much evidence for my claim as Gould has for his, and I'm
just as likely to be right.

Or so you assert. Since you claim that Gould has no evidence, I will
take this as an admission that you have none yourself.




I've merely restated the idea of convergent
evolution in a more modern way. For instance, Simon Conway Morris
thinks that if you replay the tape of life convergent evolution will
lead to the evolution of pretty much the same set of plants and animals
as before.

Define "pretty much the same". Or let Conway Morris do it if you prefer.
What exactly does this mean? I have offered some notions, and you may
pick one if you like, or present your own.




Eyes and legs are attractors. Hairy homeotherms producing
live young are attractors. Large brains with thinking minds are attractors.

Let's eliminate mumbo jumbo whenever possible. When you talk about
"attractors" you are talking about things that are commonly evolved as
responses to selection, yes? I don't see any other mechanism. I agree
that eyes seem to be like that in animals. But legs, or anything you
would want to call legs, seem to have evolved only twice, with a few
borderline cases. Hairy homeotherms only once. Large brains only once.
So what makes you think they're "attractors"? If they are, why haven't
they attracted more groups? I'll tell you what an attractor looks like:
a tree. The tree form has evolved independently some hundreds of times
in diverse groups of plants. Clearly, trees are going to happen if we
rewind the tape, assuming we first get land plants at all. But if you
think anything that's happened once during life's history is inevitable,
I don't think you can appeal to anything other than faith as a
justification.




You do think Morris has the same chance of being right as Gould does,
don't you?

No, I don't. (By the way, his last name is "Conway Morris" -- a
hyphenated name without the hyphen).




"Evolution shows an eerie predictability, leading to the direct
contradiction of the currently accepted wisdom that insists on evolution
being governed by the contingencies of circumstance."

http://en.wikipedia.org/wiki/Simon_Conway_Morris

Yes, and this is nonsense. For every example of convergence, usually in
ways you would find uninteresting, there are many examples of failure of
convergence.

Now we can't do the Gould experiment directly -- "rewinding the tape of
life". The closest we come is various natural experiments comparing
evolution on isolated islands and continents. There are of course
caveats -- starting conditions are never quite the same, including input
species. But if all is so stereotyped as you seem to claim, shouldn't we
see the same groups evolving multiple times? Take Australia vs. most of
the rest of the world. Sure, we see marsupial "wolves". But instead of
bovids we get kangaroos. The similarities are interesting, though mostly
simple and obvious, there being not all that many ways to be a mammalian
carnivore. But the differences are profound. Or take Madagascar. In
Africa we have woodpeckers, in Madagascar we have aye-ayes. Convergent
on some level, sure, but again profound differences.

I would also like to point out that starting point is important. Many
forms have evolved multiple times within some group, but never or seldom
outside it. Is eusociality inevitable? Perhaps it is in hymenopterans,
where it's happened dozens of times. But how many times has it happened
outside of hymenopterans? Just a few. So the argument that eusociality
is inevitable would seem to transform largely into some argument that
hymenopterans are inevitable, or whatever it is (perhaps haplodiploidy?)
that makes them evolve that character so much. Hence, contingency.


"Attractors" are mathematics devices to describe the space in which
solutions to differential equations reside. In evolutionary terms I
guess it would just mean an 'upland' region on the fitness landscape,
a region toward which evolution must necessarily be drawn. Yes, it is
really just an appropriated buzz-word in this context but a reasonable
one in my opinion.


I think it mystifies a fitness peak to call it an "attractor". And I
still wonder if dkomo is talking about selective landscapes at all.
Remember, he doesn't think much of selection.



I have temporarily suspended judgement on this issue.

Have you? I seems that you have merely claimed to have suspended
judgment. But what you say below seems to be an argument, founded in
your own certainty, that selection is not important.

There is one
biophysicist, Brian Goodman, who believes that important structural
features of organisms are in fact attractors (his term) in morphological
space, and are independent of selection. For some reason, this proposal
really makes straight biologists livid.

Along with some colleagues, he created a detailed simulation model of a
simple organism which looks eerily similar to the real one. They used
*only* the laws of physics to do it -- absolutely no simulation of
variation or selection was involved.

I would be interested to know what you are talking about here.

Now, if there is only one such example extant, I think I'd be a fool to
believe that *every* important structural feature of living things is a
result of adaptation, wouldn't you say?

I think you would be a fool to believe that a simulation of unknown
nature would have to have anything much to do with the evolution of
actual organisms. But of course it's quite reasonale to suspect that not
every important structural feature is a result of adaptation.

In fact, I didn't believe this
even before I ran across Goodman's ideas. Gould was another one who
didn't believe it, as doesn't Larry Moran here on t.o.

And to a certain extent, I am too. But then we get into an argument
about what being "the result of adaptation" means. There are clearly
some physical constraints on variation, and there are developmental
constraints too, some of them also matters of simple physical rules,
others being matters of the difficulty of getting to one place from
another. But whatever the source of variation, it's clear that selection
preserves what is adaptive and rejects what is not.

And, going in another direction, many features of organisms are clearly
neutral, and for others there are a great number of arbitrary
arrangements that would do as well.

All of this might fall under the description of not being "a result of
adaptation". But I suspect you mean something else, some sort of
orthogenesis that creates and maintains major structures without regard
to selection, even in the face of selection. That, I doubt.

It is rare in fact to see *direct* evidence that a particular feature of
some plant or animal is an adaptation. Most of the time it is simply
argued that such a feature must logically be an adaptation, because,
isn't it obvious?

You need to delve more deeply into the literature. There are many tests
of the selective value of various characters, in lab and nature. Just
about every issue of Evolution has at least one such test.

Just so! I made a post here once presenting evidence
that the long neck of the giraffe wasn't the obvious adaptive feature
everyone just assumes it is. Just so, indeed.

That's nice. So what's your alternative claim? Long necks are just the
inevitable consequence of physical laws acting on giraffes? I've heard
the sexual selection idea, if that's where your old post was going; but
of course that's still selection.

.

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