Heat-Induced Sterility and Its Possible Bearing on Evolution

Abstract

The advantages accruing to an animal having a higher than normal temperature, in combination with the existence of a limiting heat sensitivity characterizing the male spermatogenic mechanism, has inevitably led to a conflict between interests which may have been resolved by changes in habits, habitat selections, or the development of general body cooling, or specific testicular cooling devices. Failure to solve the conflicting requirements may have led to either actual or virtual extinction. It appears probable that in many instances, there has been some compromise between opposing interests and that only minor heat strains have been incurred. If the effects of heat on Drosophila may be taken as an indication of historic thermal response of spermatogenesis characterizing all organisms, at some or all stages of development, we may logically expect that this thermal civil conflict expedited the process of evolution by accelerating the mutational rate. The extinction of the archosaurians, also extinction of the primitive mammals and many other terrestrial animals, as well as many other phenomena apparently fit this concept of heat as a factor in the process of evolution.