Ths paper was presented at a colloquium entled "Tempo and Mode in Evolution" organized by Walter M. Fitch and Francisco J. Ayala, held January 27-29, 1994, by the National Academy of Sciences, in Irvine, CA.
The role of extinction in evolution
DAVID M. RAUP
Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637
The extinction of species is not normally consideed an important element of neodarwinian theory, in contrast to the opposite phenomenon, specation. This is surprising in view of the special importance Darwin attced to extinction, and because the number of species extinctions in the history of life is almost the same as the number of originations; present-day biodiversity is the result of a trivial surplus of tions, cumulated over millions of years. For an evolutionary biologist to ignore extinction is probably as foolhardy as for a demographer to ignore mortality. The past decade has seen a resurgence of interest in extinction, yet research on the topic Is stifl at a reconnaissance level, and our present undernding of its role in evolution is weak. Despite uncertainties, extinction probably contains three important elements. (a) For geographically wide d species, extinction is likely only if the killing stress is one so rare as to be beyond the experience of the species, and thus outside the reach of natural selection. (is) The largest mass extinctions produce major ruc gof the biosphere wherein some successful groups are elmited, allowing previously minor groups to expand and diversify. (iih) Except for a few cases, there is little evidence that extinction is selective in the positive sense argued by Darwin. It has generally been possible to predict, before the fact, which species will be victims of an extinction event.
Source: Proc. Nati. Acad. Sci. USA, Vol. 91, pp. 6758-6763, July 1994