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Being and nothingness.

Being and nothingness

How many animals aren't there, and what don't they look like?

Comparative zoologists, paleontologists and a chemist convened last week to ponder a conundrum set by Einstein: Did God have a choice in creation? Or, to put it in evolutionary terms, does natural selection work on randomly occurring forms, or is the pattern-generating system itself limited?

Monsters "are a very good example of the internal rules of morphology,' says Pere Alberch of Harvard University. Two-headed monsters, for instance, occur (if rarely) in many species; in a random system, three-headed ones should be as likely, says Alberch, but "you never find them.' The relative profusion of the two-headed and the dearth of the three-headed variety reflect not only limits at the level of gene or organism, he says, but also constraints on the types of possible patterns.

To R. D. K. Thomas of Franklin and Marshall College in Lancaster, Pa., evolutionary convergences also indicate the limits of the possible. To investigate structural possibilities and constraints, Thomas and W.-E. Reif of West Germany's Tubingen University defined a "skeleton space' made up of seven structural variables such as internal or external skeleton and rigid or flexible materials. Once they eliminated nonsensical combinations, the number of design combinations was reduced to fewer than 1,000. Of those, Thomas says, more than half are abundantly represented and fewer than one-third are rare. This suggests, Thomas says, that "the number of shapes is not only finite, but has been nearly fully exploited.'
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Title Annotation:constraints on types of possible patterns in evolution
Publication:Science News
Date:Jun 7, 1986
Words:250
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