Grandmothers' longevity negatively affects daughters' fertility

Abstract

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 and the grandmother hypotheses with a historical data set from which we bootstrapped random samples of women from different families who lived from the 1500s to the 1900s in the central valley of Costa Rica. We also compute the heritability of longevity, which allows us to determine if genes involved in longevity are nearly fixed in this population. Here we show that although longevity positively affects a woman's fertility, it negatively affects her daughter's fertility; for this reason, the heritability of longevity is unexpectedly high. Our data provide strong grounds for questioning the universality of the grandmother hypothesis and for supporting the mother hypothesis as a likely explanation for the evolution of human postreproductive longevity.

Caring for parents: an evolutionary rationale

“…It implies a trade-off between rearing existing, still altricial children and giving birth to a new one. The second is the mother hypothesis, which states that a post-fertile grandmother can help her fertile daughter [17]. They found that neither of these ideas alone is sufficient to explain the evolution of menopause under a realistic range of life-history parameters; however, a combined model can explain it [16, 18].…”

Comparing population structure as inferred from genealogical versus genetic information

“…The only way to ensure that isolates are not cryptically structured is through geneaological reconstruction. 6,7 In general, however, reconstructed pedigrees tend to span very few generations, and hence one has to resort to indirect evidence about structuring, typically obtained through analyses of genetic variation. To our knowledge, there has been no empirical comparison of genealogically and genetically inferred relationships in isolated populations.…”

A Theory for the Origin of Human Menopause

“…Analyses conducted on data that were collected to test this hypothesis have yielded equivocal results (Hill and Hurtado, 1991, 1996; Peccei, 1995, 2001; Alvarez, 2000; Lahdenperä et al, 2004; Kuhle, 2007; Madrigal and Meléndez-Obando, 2008; Hawkes et al, 2011; Kachel et al, 2011). Grandmothers in contemporary hunter-gatherer societies (e.g., Aché) typically gain through kin selection only approximately 5% an additional offspring (Hawkes et al, 1998).…”

“…Grandmothers in contemporary hunter-gatherer societies (e.g., Aché) typically gain through kin selection only approximately 5% an additional offspring (Hawkes et al, 1998). Researchers also have tested whether menopause, itself, is adaptive and found that, in premodern European (e.g., Finnish) societies, grandmothers gained 2 additional grandchildren per decade past age 50 years (Lahdenperä et al, 2004); in other premodern (e.g., Costa Rican) societies, in contrast, longer lifespan was associated with fewer grandchildren (Madrigal and Meléndez-Obando, 2008). No research has demonstrated genetic accounting consistent with inclusive fitness gains expected through kin selection to compensate for lost individual fitness.…”