Speciation and changing environment

Abstract

The current genetical theories regarding the effects of environmental changes in shaping new species are first reviewed briefly; Matthew's concept based upon paleontological and zoogeographic data is then compared and found in accord with the genetical set. This theory proposes that changing climates, whether of an annual or long-term nature, induce speciation. Accordingly the north temperate continental land-masses are viewed as the main arenas of vertebrate evolution, especially temperate Eurasia. A more recent concept from biogeographic sources, that of Darlington, proves discordant to all the foregoing but agrees more closely with observed facts of recent distribution and the geologic record. Its major premises are that speciation proceeds most rapidly under tropical conditions and in regions of vast extent; hence, the Old World tropics are pointed to as the principal theater of speciation. These two zoogeographic concepts are then harmonized by showing that, during the period in which most of the evolution of the vertebrate taxa occurred, the tropical belts were much more extensive than at present and included what are now north temperate regions. The genetic theories are shown to be especially valuable in elucidating the changes involved in the life cycle of a species rather than the effects of major climatic changes. © 1970 by the American Society of Zoologists.