dbd%benden@LANL.GOV (Dan Davison) (11/20/88)
In a recent Science, there is an article titled "Huge impact is favored for K-T boundry killer", which concerns the mechanism of the dying off of dinosaurs 65 million years ago. The article is a summary of a recent meeting. Near the end, some interesting claims are made. [Science, 11 November 1988, p.865-867] Stephen J. Gould noted that mass extinctions caused by external forces (comets, meteors, *massive* volcanism) means that Darwin's and neo-Darwinists' view of "biological competition for niches that are altered from time to time by moderate physical changes on the Earth's surface, does not have the opportunity to dominate evolution".[p 867] This also carries the implication that molecular evolution is not as important as periodic mass extinction. In this view the molecular clock is slowly ticking over but is ineffective in influencing long-term evolution. I wish to briefly contest this implication. First, it is not at all clear to me that the slow changes of base and amino acid sequence are relevant for *organismal* evolution. Instead, my view is that the important events in organismal evolution are the result of mutations in regulatory apparati. The neotany (sp?) of humans relative to great apes is often cited; similarly the homeotic loci of Drosophila (mutations that, for instance, change an antenna on the head into a fully formed leg) are additional examples. Bob Moyzis of LANL recently pointed out another possible example: the convergent evolution of marsupial wolves and cats with mammalian wolves and cats. It may be that there are is a limited repertoire of morphological changes inducible by simple regulatory mutations. A view such as this preserves the position of mutation in evolution, while accepting the possibility that catastrophic events may over-ride the system. In my view it also frees us from the view of *either* gradual change *or* evolution by the gradual accumulation of mutations. The actual event is neither or both, depending on which end (morphology or gene sequence) you care to look from. [Joe and Henry, I'm aware that I'm on a thin line here, but I believe it's a useful view]. dan davison