The origin and evolution of menopause: The altriciality-lifespan hypothesis

Abstract

Reproductive senescence, a life-history trait virtually unique to human females, is thought to be the result of a fitness trade-off between increased maternal investment in existing progeny and continued reproduction. With the altriciality-life span hypothesis I propose (1) that menopause arose because continuing encephalization caused hominid infants to be born in an increasing state of secondary altriciality, requiring a mother to invest more prolonged and more intensive care in her own offspring; (2) that, originally, hominid females underwent menopause at an earlier age; and (3) that reproductive senescence was instrumental in increasing maximum potential lifespan and average life expectancies, which set up a feedback that resulted in its own upward secular trend. A model generated by the altriciality-life span hypothesis supports the propositions that premature reproductive cessation can offer fitness benefits before age 50 years if it results in increases in maternal care leading to substantial improvement in offspring survival and fertility.