Peter S Kim, 2012
http://home.utah.edu/~u0552264/Kim%20et%20al%202012.pdf
Abstract
Postmenopausal longevity may have evolved in our
lineage when ancestral grandmothers subsidized their daughters’ fertility by provisioning grandchildren,
but the verbal hypothesis has lacked mathematical support until now. Here,
we present a formal simulation in which life spans similar to those of modern
chimpanzees lengthen into the modern human range as a consequence of
grandmother effects. Greater long-evity raises the chance of living through
the fertile years but is opposed by costs that differ for the sexes. Our
grandmother assumptions are restrictive. Only females who are no longer fertile
themselves are eligible, and female fertility extends to age 45 years.
Initially, there are very few eligible grandmothers and effects are small.
Grandmothers can support only one dependent at a time and do not care
selectively for their daughters’ offspring. They must take the oldest juveniles
still relying on mothers; and infants under the age of 2 years are never
eligible for subsidy. Our model includes no assumptions about brains, learning
or pair bonds. Grandmother effects alone are sufficient to propel the
doubling of life spans in less than sixty thousand years.
[Under modern circumstances women live quite a few years longer than men. Maybe the "selection for longevity" did really primarily act on women.]
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