A Theory for the Origin of Human Menopause

Abstract

A complete and compelling evolutionary explanation for the origin of human menopause is wanting. Menopause onset is defined clinically as the final menses, confirmed after 1 year without menstruation. The theory proposed herein explains at multiple levels – ultimately genetic but involving (1) behavioral, (2) life history, and (3) social changes – the origin and evolution of menopause in women. Individuals in Lower Paleolithic human populations were characterized by short lifespans with diminished late-age survival and fertility, similar to contemporary chimpanzees, and thence were subject to three changes. (1) A mating behavior change was established in which only young women reproduced, thereby rendering as effectively neutral female-specific late-onset fertility-diminishing mutations, which accumulated subsequently. (2) A lifespan increase was manifested adaptively, revealing the reproductive senescence phenotype encoded in late-onset fertility-diminishing mutation genotypes, which, heretofore, had been unexpressed in the shorter lifespan. (3) A social interaction change emerged exaptively, when older non-reproductive women exclusively started assisting in rearing grandchildren rather than giving birth to and caring for their own children, ultimately leading to menstrual cycle cessation. The changes associate in a one-to-one manner with existing, non-mutually exclusive hypotheses for the origin of human menopause. Evidence for each hypothesis and its associated change having occurred are reviewed, and the hypotheses are combined in a synthetic theory for the origin of human menopause. The new theory simultaneously addresses the main theoretical problem with each hypothesis and yields predictions for future testing.

The evolutionary ecology of age at natural menopause: implications for public health

“…Female reproductive skew, and the front loading of reproductive events, is invoked as a mechanism that could be the cause of the evolution of menopause as it would decrease selection on extended reproductive lifespan (Peccei, 2001). However, given that the preference for younger females is found in humans (Chan et al, 2020;Takahashi, Singh, & Stone, 2017) but not particularly in chimpanzees (Takahashi et al, 2017), the human male mate preference is likely a derived trait and thus the outcome, rather than the cause, of early reproductive cessation in women.…”

Menopause Female Reproductive Senescence from the Viewpoint of Evolutionary Anthropology

“…A gradual decline in fertility is observable between the ages 35 and 40 years, after this period the decline accelerates. This reduced fertility from about 35 years onward is mainly due to defects in oocytes [31]. Oocyte or follicular depletion accelerates as menopause got closer.…”

“…In the female embryo, primordial germ cells originating from the yolk sac develop into oogonia, immature sex cells. Germ cell numbers peak at approximately 3 × 10 5 -7 × 10 6 by the ifth month of fetal development [31]. Oogonia develop to oocytes.…”

“…According to the mate-choice hypothesis, male mating preference for younger females may lead to the accumulation of mutations deleterious to female fertility and thus lead to the evolution of an extended postreproductive period in human females [68]. Takahashi et al [31] tried to explain the origin and evolution of menopause by combining a genetic basis, behavioral factors such as mating behavior, a life history perspective, and social changes in human evolution.…”

“…Since 1970s, several evolutionary scenarios of human menopause were proposed to explain the phenomenon of female reproductive senescence and in particular menopause; however, there is still no consensus about which of these hypotheses should be preferred [31,45,47,48]. In general, two diferent types of evolutionary explanations of menopause can be distinguished: nonadaptive or by-product hypotheses and adaptive hypotheses [23].…”