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

Len Piotrowski (
Wed, 11 Sep 1996 19:28:35 GMT

In article <512lgo$> (Bryant) writes:


>In article <51206t$>,
>Gerold Firl <> wrote:

>>2. Linkage between the eye and vision centers in the brain: if the
>>presence of an eye necessitates the devotion of some portion of the
>>brain to vision, then those neurons could be better used elsewhere.
>>Maybe the eye has to go before those brain cells can be freed-up for
>>other tasks.
>>3. Injury, disease, parasite infection: eyes are more vulnurable than
>>other tissues to external insult;

>Nice, informed speculation, Gerold. Vertebrate brain tissue is
>tremendously expensive stuff, metabolically. Evolutionary
>biologists have tended to attribute eye loss across
>taxa evolving in caves to simple mutation accumulation. Like drift and
>constraint stories, this explanation is difficult to test, however.

That's a tremendously entertaining story but lets take a closer look at what's
going on behind all this back slapping. Firl says: cave organisms may lose
there eyes because of a need for the brain tissue to do - what? We are now
faced with the hoary possibility of "brain tissue craving." The moral of
this trope is: don't stay too long in one spot or you risk losing your senses
because something recycled the brain tissue.

>Is enough known about some of the simpler creatures' neurobiology to see
>if vision centers in their brains are similarly degraded as the eyes? If
>the eyes, but not related brain tissues, are degraded in these creatures,
>it would argue for something other than your second hypothesis.

Curious this. Firl speculates that eyes go, brain tissue stays. Bryant
speculates that if eyes go but brain tissue stays, than something other than
Firl's speculation must be going on.

> The
>third seems testable against the parasitology literature.

Firl claims that eyes are more vulnerable to assault in caves, therefore, cave
organisms lose their eyes. This, says Bryant, is a testable hypothesis in the
parasitology literature. Lets see: would a higher degree of eye assaults in
eyeful cave organisms versus eyeless cave organisms be sufficient proof of
this need to unevolve the eye trait? Or would a higher incident of eye
assaults in eyeful and eyeless cave dweller compared to eyeful and eyeless
non-cave dwellers be convincing? Even if the data display a bimodal
distribution, can there be an overall high incidence of assaults in cave
environments untestable by the parasitology literature? At what point can we
identify these kinds of stories as just so without fear of being labelled
ourselves as anti-science?



"If you can't remember what mnemonic means, you've got a problem."
- perlstyle