The right size for a mammal

Abstract

Intr.: Elephants live slow lives, voles fast lives - vole populations may pass through 50 generations while an elephant grows up. Many facets of mammalian life history combine in this slow-fast continuum: species with long generation times produce small litters oflarge offspring who wean late, mature late and live longer after maturity! Why do these components of life history co-vary as they do? In a paper in American Naturalist, Kozlowski and Weiner propose an elegant and comprehensive model oflife-history evolution for animals, such as mammals, that stop growing when they reach reproductive maturity. Their model accords with the comparative patterns and may, as a bonus, resolve another knotty problem - the skewed frequency distribution of body sizes among species, whereby far more species are small than large.