title: The trade-off between number and size of offspring in humans and other primates.
abstract: Life-history theory posits a fundamental trade-off between number and size of offspring that structures the variability in parental investment across and within species. We investigate this 'quantity-quality' trade-off across primates and present evidence that a similar trade-off is also found across natural-fertility human societies. Restating the classic Smith-Fretwell model in terms of allometric scaling of resource supply and offspring investment predicts an inverse scaling relation between birth rate and offspring size and a (-1/4) power scaling between birth rate and body size. We show that these theoretically predicted relationships, in particular the inverse scaling between number and size of offspring, tend to hold across increasingly finer scales of analyses (i.e. from mammals to primates to apes to humans). The advantage of this approach is that the quantity-quality trade-off in humans is placed into a general framework of parental investment that follows directly from first principles of energetic allocation.
authors: Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany. robert_walker@eva.mpg.de
authors: Robert S
authors: RS
authors: Walker
authors: Michael
authors: M
authors: Gurven
authors: Oskar
authors: O
authors: Burger
authors: Marcus J
authors: MJ
authors: Hamilton
mesh_terms: D000818:Animals; D001723:Birth Rate; D049628:Body Size; D005260:Female; D005298:Fertility; D006801:Humans; D008954:Models, Biological; D011323:Primates / Q000502:physiology*; D012098:Reproduction / Q000502:physiology