Issues in evolutionary medicine

Abstract

This paper illustrates the utility of applying evolutionary thought to medical issues with three examples: selection arenas, aging, and tradeoffs. First, the human female reproductive tract functions as a selection arena at two levels: in the ovaries, where atresia reduces the number of oocytes by more than 99.99% before any are ovulated, and in the uterus, where early embryos homozygous for immune genes are spontaneously aborted. These selective filters early in life have implications both for eugenics and for the anti-abortion movement. Second, the evolutionary theory of aging predicts that intrinsic mortality should reflect extrinsic mortality: if life for adults is risky, then it does not pay to invest in maintenance at the expense of reproduction. This idea is well confirmed, at least in populations where density effects are not important. While only organisms that reproduce asymmetrically should age, even bacteria reproduce asymmetrically, and they do age, suggesting that all organisms reproduce asymmetrically and therefore age. Third, tradeoffs are central to theories of phenotypic design, but the mechanisms that cause them remain obscure. A method is suggested to get at the mechanisms of tradeoffs by examining conflicts among functions over gene expression. It could be applied in humans to the tradeoff between reproductive performance and disease resistance.