Selection for delayed maturity |
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Authors: | Nicholas Blurton Jones Frank W Marlowe |
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Institution: | (1) University of Leiden, Leiden, The Netherlands;(2) Faculteit der Archeologie, Postbus 9515, 2300 RA Leiden, The Netherlands |
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Abstract: | Humans have a much longer juvenile period (weaning to first reproduction, 14 or more years) than their closest relatives (chimpanzees,
8 years). Three explanations are prominent in the literature. (a) Humans need the extra time to learn their complex subsistence techniques. (b) Among mammals, since length of the juvenile period bears a constant relationship to adult lifespan, the human juvenile period
is just as expected. We therefore only need to explain the elongated adult lifespan, which can be explained by the opportunity
for older individuals to increase their fitness by providing for grandchildren. (c) The recent model by Kaplan and colleagues suggests that longevity and investment in "embodied capital" will coevolve, and
that the need to learn subsistence technology contributed to selection for our extended lifespan.
We report experiments designed to test the first explanation: human subsistence technology takes many years to learn, and
spending more time learning it gives reproductive benefits that outweight lost time. Taking away some of this time should
lead to deficits in efficiency. We paid Hadza foragers to participate in tests of important subsistence skills. We compared
efficiency of males and females at digging tubers. They differ greatly in time spent practicing digging but show no difference
in efficiency. Children who lost "bush experience" by spending years in boarding school performed no worse at digging tubers
or target archery than those who had spent their entire lives in the bush. Climbing baobab trees, an important and dangerous
skill, showed no change with age among those who attempted it. We could show no effects of practice time. |
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