Testing evolutionary theories of menopause (original) (raw)
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American Journal of Physical Anthropology, 2008
The ''mother'' hypothesis is one of the main adaptive explanations of human menopause. It postulates that reproductive cessation constitutes a strategy that has been selected for during human evolution because mothers at older ages might maximize their fitness by investing resources in the survival and reproduction of their living children rather than by continuing to reproduce. This study provides a test of this hypothesis. Fertility functions that maximize fitness are built into a model incorporating the fact that the survival of females during the rearing period is a major determinant of their children's survival. Results are given according to different scenarios of increase with mothers' age of maternal mortality risk and risk of stillbirth and birth defects (on the assumption that these females do not experience
The evolution of premature reproductive senescence and menopause in human females
Human Nature, 1991
Reproductive senescence in human females takes place long before other body functions senesce. This fact presents an evolutionary dilemma since continued reproduction should generally be favored by natural selection. Two commonly proposed hypotheses to account for human menopause are (a) a recent increase in the human lifespan and (b) a switch to investment in close kin rather than direct reproduction. No support is found for the proposition that human lifespans have only recently increased ed. Data from Ache hunter-gatherers are used to test the kin selection hypothesis. Ache data do not support the proposition that females can gain greater fitness benefits in old age by helping kin rather than continuing to reproduce. Nevertheless, one crucial parameter in the model, when adjusted to the highest value within the measured 95% cbnfidence interval, would lead to the evolution of reproductive senescence at about 53 years of age. Further investigation is necessary to determine whether the kin selection hypothesis of menopause can account for its current maintenance in most populations.
An evolutionary perspective on the origin and ontogeny of menopause.
The “grandmother hypothesis” proposes that menopause evolved because ancestral middle-aged women gained greater reproductive success from investing in extant genetic relatives than from continuing to reproduce [Williams GC. Pleiotropy, natural selection, and the evolution of senescence. Evolution 1957;11:398–411]. Because middle-aged women faced greater risks of maternal death during pregnancy and their offspring’s infancy than did younger women, offspring of middle-aged women may not have received the needed level of prolonged maternal investment to survive to reproductive age. I put forward the “absent father hypothesis” proposing that reduced paternal investment linked with increasing maternal age was an additional impetus for the evolution of menopause. Reduced paternal investment was linked with increasing maternal age because men died at a younger age than their mates and because some men were increasingly likely to defect from their mateships as their mates aged. The absent father hypothesis is not an alternative to the grandmother hypothesis but rather a complement. It outlines an additional cost—reduced paternal investment—associated with continued reproduction by ancestral middle-aged women that could have been an additional impetus for the evolution of menopause. After reviewing additional explanations for the origin of menopause (“patriarch hypothesis,” “lifespan-artifact” hypotheses), I close by proposing a novel hypothesis for the ontogeny of menopause. According to the “adaptive onset hypothesis,” the developmental timing of menopause is a conditional reproductive strategy in which a woman’s age at onset is influenced by the likelihood that any children she could produce would survive to reproductive age. Twelve variables predicted to be associated with age at onset and evidence that bears upon the predictions is discussed.
Menopause Female Reproductive Senescence from the Viewpoint of Evolutionary Anthropology
A Multidisciplinary Look at Menopause, 2017
Female reproductive senescence is characterized by the so-called menopausal transition taking place between the ages of 40 and 60 years. The major event of menopausal transition is menopause itself, which is biomedically defined as the cessation of menstrual function and the irreversible termination of female reproductive capability. Recent human females experience a postreproductive period from about 30 years. Such a long postreproductive period is absolutely uncommon among animals. Consequently, human menopause is still an evolutionary puzzle and several theories to explain the evolutionary basis of menopause have been presented. Menopausal transition, however, is also seen as a period of increased somatic and psychic symptoms which make this phase of life quite uncomfortable for affected women. In the present study, menopause and climacteric complaints are discussed from the viewpoint of evolutionary anthropology.
Grandmothering, menopause, and the evolution of human life histories
Proceedings of the National Academy of Sciences of the United States of America, 1998
Long postmenopausal lifespans distinguish humans from all other primates. This pattern may have evolved with mother-child food sharing, a practice that allowed aging females to enhance their daughters' fertility, thereby increasing selection against senescence. Combined with Charnov's dimensionless assembly rules for mammalian life histories, this hypothesis also accounts for our late maturity, small size at weaning, and high fertility. It has implications for past human habitat choice and social organization and for ideas about the importance of extended learning and paternal provisioning in human evolution.
PLOS Computational Biology, 2017
Menopause, the permanent cessation of ovulation, occurs in humans well before the end of the expected lifespan, leading to an extensive post-reproductive period which remains a puzzle for evolutionary biologists. All human populations display this particularity; thus, it is difficult to empirically evaluate the conditions for its emergence. In this study, we used artificial neural networks to model the emergence and evolution of allocation decisions related to reproduction in simulated populations. When allocation decisions were allowed to freely evolve, both menopause and extensive post-reproductive lifespan emerged under some ecological conditions. This result allowed us to test various hypotheses about the required conditions for the emergence of menopause and extensive post-reproductive lifespan. Our findings did not support the Maternal Hypothesis (menopause has evolved to avoid the risk of dying in childbirth, which is higher in older women). In contrast, results supported a shared prediction from the Grandmother Hypothesis and the Embodied Capital Model. Indeed, we found that extensive post-reproductive lifespan allows resource reallocation to increase fertility of the children and survival of the grandchildren. Furthermore, neural capital development and the skill intensiveness of the foraging niche, rather than strength, played a major role in shaping the age profile of somatic and cognitive senescence in our simulated populations. This result supports the Embodied Capital Model rather than the GrandMother Hypothesis. Finally, in simulated populations where menopause had already evolved, we found that reduced post-reproductive lifespan lead to reduced children's fertility and grandchildren's survival. The results are discussed in the context of the evolutionary emergence of menopause and extensive post-reproductive lifespan .
The evolutionary ecology of age at natural menopause: implications for public health
Evolutionary Human Sciences
Evolutionary perspectives on menopause have focused on explaining why early reproductive cessation in females has emerged and why it is rare throughout the animal kingdom, but less attention has been given to exploring patterns of diversity in age at natural menopause. In this paper, we aim to generate new hypotheses for understanding human patterns of diversity in this trait, defined as age at final menstrual period. To do so, we develop a multilevel, interdisciplinary framework, combining proximate, physiological understandings of ovarian ageing with ultimate, evolutionary perspectives on ageing. We begin by reviewing known patterns of diversity in age at natural menopause in humans, and highlight issues in how menopause is currently defined and measured. Second, we consider together ultimate explanations of menopause timing and proximate understandings of ovarian ageing. We find that ovarian ageing is highly constrained by ageing of the folliclethe somatic structure containing the oocytesuggesting that menopause timing might be best understood as a by-product of ageing rather than a facultative adaptation. Third, we investigate whether the determinants of somatic senescence also underpin menopause timing. We show that diversity in age at menopause can be, at least partly, explained by the genetic, ecological and life-history determinants of somatic ageing. The public health implications of rethinking menopause as the by-product rather than the catalyst of biological ageing are discussed.
Reevaluating the grandmother hypothesis
History and philosophy of the life sciences, 2021
Menopause is an evolutionary mystery: how could living longer with no capacity to reproduce possibly be advantageous? Several explanations have been offered for why female humans, unlike our closest primate relatives, have such an extensive post-reproductive lifespan. Proponents of the so-called "grandmother hypothesis" suggest that older women are able to increase their fitness by helping to care for their grandchildren as allomothers. This paper first distinguishes the grandmother hypothesis from several other hypotheses that attempt to explain menopause, and then develops a formal model by which these hypotheses can be compared and tested by empirical researchers. The model is then modified and used to respond to a common objection to the grandmother hypothesis: that human fathers, rather than grandmothers, are better suited to be allomothers due to their physical strength and a high incentive to invest in their own children. However, fathers-unlike maternal grandmother...
Grandmothers' longevity negatively affects daughters' fertility
American Journal of Physical Anthropology, 2008
The evolution of postmenopausal longevity in human females has been the subject of debate. Specifically, there is disagreement about whether the evolution of the trait should be understood as an adaptive or a neutral process, and if the former, what the selective mechanism is. There are two main adaptive proposals to explain the evolution of postreproductive longevity: the grandmother and the mother hypotheses. The grandmother hypothesis proposes that postreproductive longevity evolved because it is selectively advantageous for females to stop reproducing and to help raise their grandchildren. The mother hypothesis states that postmenopausal longevity evolved because it is advantageous for women to cease reproduction and concentrate their resources and energy in raising the children already produced. In this article, we test the mother Grant sponsor: National Institutes of Aging; Grant number: 1-R03-AG022616-01.