Re: Evolution, "adaptation", and what's currently adaptive

Stephen Barnard (steve@megafauna.com)
Thu, 05 Sep 1996 19:31:19 -0800

Len Piotrowski wrote:
>
> In article <322E3C24.2A18@megafauna.com> Stephen Barnard <steve@megafauna.com> writes:
>
> >[snip]
>
> >You must be joking.
>
> You're right! I am joking.

I don't think your were joking. I think your were just ignorant of the facts.

>
> >Either that or you don't know what you're talking about.
>
> That's possibly true as well!

That's more like it.

>
> >Many
> >kinds of molluscs have eyes. Some, such as scallops, have lots of eyes. Snails are
> >molluscs.
>
> Not all eyes are the same. Perhaps some gastropods haven't any eyes. I bow
> to a mollusk expert!

I'm not an expert. Just a reasonably well-read layman who doesn't make ex-cathedra
pronouncements on a topic of which I'm ignorant. Ask your beloved S. Gould about
snail's eyes. He's the expert.

>
> > What do you think are on the ends of those stalks? Eyes.
>
> Couldn't say this is true, but I presume what is at the ends of those stalks
> is sensitive to light, at least as measured by my own experience, OKay?
>

They are eyes. Take my word for it, or ask Gould.

> > Octopuses, which
> >are closely related to molluscs, have superb eyes. (I'm pretty sure that Firl knows all
> >this.)
>
> "Octopuses" related to mollusks? I wouldn't know about that, or the nature of
> Firl's expertise. Sometimes I wonder though.

Look it up.

>
> >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.
>
> I think I disagreed with the functionalist argument as method, not with any
> facts of adaptive importance.

You stated unequivocally that molluscs don't have eyes. That is a question of fact.

>
> >The path from no eyes to eyes is quite plausible.
>
> ... but just so!
>
> > First a patch of light-sensitive
> >cells develop.
>
> ... first step on the slippery slope, the need for a patch ...

Not the "need" for a patch. Rather, the fact that having a patch puts one at an
advantage compared to those that don't have a patch.

>
> >Then this patch forms a cavity,
>
> ... followed by the need for a cavity ...
>

See above.

> >which is better able to resolve the
> >direction of the light source.
>
> ... culminated by the need to resolve the light source.

See above.

>
> >Then the cavity closes over on itself and a crude
> >pinhole lens forms,
>
> Another need to fold the cavity ...

See above.

>
> >which allows for the resolution of shapes.
>
> ... and the need for resolution of shapes.

See above.

>
> > (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.
>
> I don't doubt the historicity of your museum of " incremental improvements." I
> doubt the efficacy of the functional method used to account for each of their
> appearances and the purpose of the final system.

So just what is it that you don't doubt? It's easy to doubt. I can easily doubt that
your posts are coming from an actual human being, as opposed to an automatic mailer set
up to flood the net with crypto-creationist mumbo jumbo.

>
> >How do you suppose all these phyla got eyes?
>
> I don't know how exactly these myriad series of historically related
> increments came about. Do you?
>

I explained my hypothesis. What's yours?

> >Did genetic drift miraculously produce
> >them independently.
>
> I don't know. Do you believe that one proto-eye was ancestral to all eyes?

No. They have evolved independently. That is perhaps the most compelling evidence that
eyes are an important adaptive characteristic

>
> >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.
>
> I don't know of a plausible explanation for "eyeness." Your "incremental
> steps" form a nice story, but hardly substitutes for understanding. Maybe the
> snail's eye did arise just the way you claim. I don't doubt the "forces of
> evolution" playing such a role. I question the methodological structure of
> functionalism as a plausible explanation for each and every manifestation of
> the steps of "eyeness."
>

You seem to be coming around to an adaptationist point of view. Congratulations.

Cheers,
Steve Barnard