A critique of the grandmother hypotheses: old and new.

The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis-the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females.

Genetic correlation between the ages of menarche and menopause.

Using mostly prospective menstrual data from mothers and daughters in the Tremin Trust Menstrual Reproductive History Program, this study produces the first estimates of the genetic correlation between the ages of menarche and menopause. I carried out two separate analyses. Standard regression analysis of 21 mother/daughter dyads with natural menopause yielded a nonsignificant negative mean genetic correlation of r A =-0.

A hypothesis for the origin and evolution of menopause.

Menopause is widely believed by biological anthropologists and life history theorists to have arisen early in human evolution. In this paper, I suggest that female reproductive senescence was the result of the escalating energetic cost of gestation, lactation and childcare that accompanied the continuing encephalization of early hominid offspring and the ensuing increase in infant altriciality, or helplessness, and the concomitant prolongation of juvenile dependence. Natural selection favored females who became prematurely infertile, as the escalating cost of raising each offspring led to maternal depletion and made it more profitable in terms of lifetime reproductive success to continue investing in existing offspring rather than attempting late pregnancies.