Rates of Evolution and the Notion of "Living Fossils"

Abstract

In one sense, any science is only as sound as the knowledge of its state variables. For paleontology, several of those variables are tied up in the topic of rates of evolution. So uncertain is the mean duration of species that when problems in paleontology are subjected to computer simulation, the values that are used extend over four orders of magnitude (103 to 107 yr; Raup 1981). It should come as no surprise that conclusions over this 104 range support vastly different world views about the extent of determinism versus stochasticity in major evolutionary events. On the one hand, this lack of precision means that virtually any answer is possible. On the other hand, it means that the traditional paleontologic assertion in favor of specific deterministic stories must be tempered by a high degree of uncertainty. The chief body of material to be considered, which was not known to those who formulated the currently prevailing paleontological views on rates of evolution [especially Simpson (1944, 1949, 1953, and largely reaffirmed even in 1983)] lies in information provided on the molecular biology of genomic change. The genome is simply a convenient term for the genetic constitution of an individual or species. Genomic compatibility lies at the basis of reproductive compatibility, and thus genomic change introduces the notion of geonomically regulated reproductive incompat­ ibility. I consider in this article two interrelated aspects of speciation theory. The first is an attempt to integrate the main results from molecular biology that