Abstract The fact that human females exhibit a post-reproductive life-span (menopause) and males do not is considered in evolutionary perspective. Two possible non-adaptive (incidental) explanations are discussed and rejected on available evidence. This sex difference is then considered as a possible adaptive response to differential parental investment tendencies of the two sexes. This hypothesis is evaluated in the context of sexual selection theory and the pattern of other observed sex differences in Homo sapiens . Finally, an attempt is made to explain the emergence of contemporary human investment patterns in terms of the changing patterns of parental certainty brought about by the Neolithic revolution. Cross-cultural data on investment patterns by subsistence type are used to test this hypothesis.