Human lifespan: what determines the intrinsic length of human lives?

Abstract

Humans have an intrinsic lifespan of approximately 120 years. Classic evolutionary theories of ageing explain the limit as a response to inevitable cellular damage. The theories share the notion that natural selection acts less strongly to purge deleterious genes that are expressed after reproduction. Reproduction schedules are influenced by a species' ecology and so it is ecological factors which explain interspecies variation in lifespan. Human ecology has favoured the selection of an unusually large brain that both confers advantages that promote longevity and requires longevity to make it a worthwhile investment. The relatively long human lifespan therefore co-evolved with the large human brain.