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Re: Evolution, "adaptation", and what's currently adaptive
Stephen Barnard (steve@megafauna.com)
Wed, 04 Sep 1996 18:34:12 -0800
Len Piotrowski wrote:
>
> In article <50ieqh$n6l@news.sdd.hp.com> geroldf@sdd.hp.com (Gerold Firl) writes:
>
> >[snip]
>
> >|> In article <504muq$2pqm@argo.unm.edu> mycol1@unm.edu (Bryant) writes:
>
> >|> >Eyes are adaptations because they have design features unlikely to have
> >|> >accumulated by chance.
>
> >|> And too, unlikely to have accumulated as a sequential series of functional
> >|> adaptations with your final goal (to see) as the causal reason!
>
> >Try to do a little research before you make such absolutist
> >pronouncements; you're just flat-out wrong.
>
> Your epistemology boggles the imagination!
>
> >Throughout the biosphere
> >there exists the complete gamut of light-sensing and imaging systems,
>
> What makes this "gamut" complete, aside, I know, from the word of Firlmeister?
>
> >which maps very well to the developmental evolutionary pathway.
>
> Interesting mapping function here: where does this "evolutionary pathway"
> exist?
>
[snip]
>
> >and large numbers of independantly
> >evolved imaging systems ranging from mollusc crude
>
> ... no eyes!
>
[snip]
> >Each incremental step of visual acuity provided
> >adaptive benefits,
>
> Oh, yes, eyes were the result of the "incremental steps" of plants, plankton,
> "mollusc," and mammals, eh? Remarkable!
>
> >which is why vision systems have continued to
> >evolve.
>
> ? Vision systems continue to evolve *because* of the adaptive benefits that
> vision accrues? How come a mollusc can't see then?
>
> >You present "the goal" of being able to see in teleological terms,
>
> ... not I, the functional adaptationist does.
>
> >which is erroneous of course,
>
> Of course!
>
> > but anyone who has thought about the
> >process of evolution can see how natural selection has refined animal
> >vision to produce successively more acute vision.
>
> Except for those poor, crude plants, plankton, and "molluscs," [sigh]!
You must be joking. Either that or you don't know what you're talking about. Many
kinds of molluscs have eyes. Some, such as scallops, have lots of eyes. Snails are
molluscs. What do you think are on the ends of those stalks? Eyes. Octopuses, which
are closely related to molluscs, have superb eyes. (I'm pretty sure that Firl knows all
this.)
The mere fact that so many phyla have independently evolved eyes -- and many different
types of eyes -- very strongly suggests that eyes are an extremely important adaptive
characteristic for mobile animals in a transparent lighted medium.
The path from no eyes to eyes is quite plausible. First a patch of light-sensitive
cells develop. Then this patch forms a cavity, which is better able to resolve the
direction of the light source. Then the cavity closes over on itself and a crude
pinhole lens forms, which allows for the resolution of shapes. (I'm taking about simple
eyes -- not compound eyes like insects have.) Then we're off to the races. We get a
better lens, the iris, the foveated retina, stereo vision, color vision, etc. All of
these are incremental improvements.
How do you suppose all these phyla got eyes? Did genetic drift miraculously produce
them independently. Is there some essential "eyeness" at work in the universe? Did
some Creator decide it was a good idea? Let's hear a plausible explanation that doesn't
involve adaptation.
Steve Barnard
>
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