dmark@cs.Buffalo.EDU (David Mark) (08/06/89)
In article <4514@uhccux.uhcc.hawaii.edu> lee@uhccux.uhcc.hawaii.edu (Greg Lee) writes: >From article <19229@vax5.CIT.CORNELL.EDU>, by b27y@vax5.CIT.CORNELL.EDU: >" What about "reverse" evolution? ... >" ... More specifically: A type of >" pike, whose teeth where evovling so that they stick outwards, which made >" cating and eating prey MORE difficult? This doesn't seem possible under the >" orignal Darwinian discriptions. ... > >In _The Meaning of Evolution_, Simpson proposes an explanation of how >such things can happen. He gives an example of a type of elk whose >antlers came to be burdonsomely large, and claims this happened because >of a genetic link between antler size and overall body size. Increased >body size was sufficiently advantageous to overcome the disadvantage of >the outsized antlers. The essence of Darwinian evolution combines the following: (a) populations generally exhibit natural variation; (b) resources are limited yet reproduction almost always is (potentially) geometric. Combine these (because of (b), not all individuals can survive), and we get "more fit" individuals having a greater probability or surviving and reproducing than do "less fit" individuals. It is probabilistic, so a "less fit" individual might by chance survive while a "more fit" one might not. But generally, advantageous characters are retain, whereas negative and (usually) neutral characters are lost from the gene pool. Of course, not all characters are independent. Greg Lee was alluding, probably, to allometric effects in the relation of antler size to body size. But perhaps antler size *was* directly selected for, through sexual selection for mating, even though it was disadvantageous for living between breeding. In evolution, the winners are the ones that leave the most descend- ants. And that could mean trading off reproductive success against personal survival. There are all sorts of cases where evloution reduces individual survival chance in males, in order to promote reproductive success if they should survive. Just think of all the brightly colored male birds in sexually-dimorphic species. Also, some characteristics of a species can be barely adequate, if competition for resources is not linked to that character. The fish teeth could be a release of selective pressure for maximally-efficient mouths in a situation where food resources were abundant and perhaps breeding space or territory was limited. Antlers are of some use for defence against predators, but seem primarily to be there to battle other males and/or to impress females into selecting them. In most deer, only the males have them. Inefficiencies of "hacked-together" anatomical features do not mean that Darwin was wrong. Stephen J. Gould's essay "The Panda's Thumb" uses the imperfection and inefficiency of that anatomical feature as a fact favoring organic evolution over creationsim (at least, that is what I remember from the essay). Organic evolution tends to favor the characteristics of those individuals that are good enough and lucky enough to leave a maximum number of descendants. David Mark dmark@cs.buffalo.edu