Evolutionary Theories of Menopause

• Main Author: Hägg, Fanny
• Format: Bachelor Thesis
• Language: English
• Published: Linköpings universitet, Institutionen för fysik, kemi och biologi 2020
• Subjects: Menopause; Post-reproduction; The grandmother hypothesis; The reproductive conflict hypothesis; Inclusive fitness; Kin selection; Odontoceti; Orcinus orca; Evolutionary Biology; Evolutionsbiologi; Orca; toothed whales
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-167618

Menopause, the cessation of female reproduction well before death, is a puzzling phenomenon, because evolutionary theory suggests there should be no selection for survival when reproduction has ended. Nevertheless, menopause does exist in a limited number of species, and besides humans it has predominately evolved among toothed whales (Odontoceti). The aim of this thesis is to review both adaptive and non-adaptive theories. Of the latter, the most prominent proposes that menopause is a product of a physiological trade-offs between reproductive benefits early in life and negative late-life reproduction. Among the adaptive theories the grandmother hypothesis is the most acknowledged. This theory is based on inclusive fitness benefits gained from increasing the reproductive success of kin at an advanced age, when prospects of successfully raising additional offspring is reduced. Alternatively, the mother hypothesis suggests that increased investment in already produced offspring at late life explains menopause. There are support for both the care of mothers and grandmothers, but whether this is enough to compensate for repressed reproduction is debated. The reproductive conflict hypothesis provides a complementary explanation, and suggests that inter-generational conflict between either in-laws or kin selects the older female to shift investment into the younger female’s offspring due to asymmetries in how older and younger females are related to one another’s offspring. The evolution of menopause is a complex issue, containing many factors, kinship dynamics among the most important. Theories apply unequally to various species and populations, meaning an integrated approach is necessary for decrypting the evolution of menopause.