Does grandparental care select for a longer lifespan in non-human mammals?

Abstract

Several non-human mammalian species provide grandparental care but remain fertile until death, unlike our species. This might call into question the ‘grandmother hypothesis’ that the ability to provide grandparental care, associated with an increase in the cost of breeding with age, promote the early cessation of reproduction. Here, we analyse individual longevity records from non-human mammals to determine whether the few species with grandparental care also stand out among mammals in terms of age-specific survival patterns. Indeed, females of species with grandparental care lived on average 43% longer than males (range: 24–61%), compared with 12% in other polygynous species (95% quantile: −8 to 30%), because of low baseline mortality rates and delayed onset of actuarial senescence. We discuss this finding with respect to the ‘stopping early’ vs. ‘living longer’ debate. We review the role of the environmental context and of the decrease in offspring performance with maternal age (Lansing effect). We formalize the idea of a continuum of parental–grandparental allocation instead of a discrete switch to grandparental care only. Lastly, we suggest that the evolution of menopause has been driven by different forces in different species.

Kinship dynamics: patterns and consequences of changes in local relatedness

“…If individuals can provide benefits to kin in late life it may select for longevity [45,[53][54][55]. In support of this prediction, recent work comparing the longevity of females across non-human mammals found that females in species with grandparental care lived longer [56]. Thus, we hypothesize that in species where relatedness increases with individual age selection will favour longevity if there are opportunities for late life helping.…”

Variation in actuarial senescence does not reflect life span variation across mammals

“…To circumvent that issue, we only analyzed the data from extinct cohorts, which are cohorts for which all individuals have been documented as dead or are past the maximum age ever reported for the species. From an initial set of 144 species [38,55], we selected those for which at least 25 females were documented to have reached the age of 1 year, at least five had reached the predicted age at which 90% of an average cohort would be dead (denoted ; Fig 1; explained below), and the model-selection procedure (explained below) yielded evidence of actuarial senescence. The final dataset featured 96 species (S5 Data).…”

A reformulated contextual model of psychotherapy for treating anxiety and depression

“…When drones (male honey bees) lose their reproductive function in the autumn they are expelled from the hive and die. Paleolithic grandparents, despite their weaker physique, provided selective advantage as information providers and educators carers of grandchildren ( Aimé, André, & Raymond, 2017 ; Thouzeau & Raymond, 2017 ), a grandparenting function that differs from those of animals where there are reproductive grandparents ( Péron et al, 2019 ). The evolutionary history of humans shows that, although relationships are important, survival depended on much more, for example, exploration and discovery, planning, nurturing, hunting and aggression, technological skills, education, remembering, problem solving etc., which are summarised to some extent by the primary motives of self-determination theory, connection, autonomy and competence ( Deci & Ryan, 2012 ).…”