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Life history costs and benefits of encephalization: a comparative test using data from long-term studies of primates in the wild


Barrickman, N L; Bastian, M L; Isler, K; van Schaik, C P (2008). Life history costs and benefits of encephalization: a comparative test using data from long-term studies of primates in the wild. Journal of Human Evolution, 54(5):568-590.

Abstract

The correlation between brain size and life history has been investigated in many previous studies, and several viable explanations have been proposed. However, the results of these studies are often at odds, causing uncertainties about whether these two character complexes underwent correlated evolution. These disparities could arise from the mixture of wild and captive values in the datasets, potentially obscuring real relationships and from differences in the methods of controlling for phylogenetic non- independence of species values. This paper seeks to resolve these difficulties by (1) proposing an overarching hypothesis that encompasses many of the previously proposed hypotheses; (2) testing the predictions of this hypothesis using rigorously compiled data and utilizing multiple methods of analysis. Our hypothesis is that the adaptive benefit of increased encephalization is an increase in reproductive lifespan or efficiency, which must be sufficient to outweigh the costs due to growing and maturing the larger brain. These costs and benefits are directly reflected in the length of life history stages. We tested this hypothesis on a wide range of primate species. Our results demonstrate that encephalization is significantly correlated with prolongation of all stages of developmental life history except the lactational period, and is significantly correlated with an extension of the reproductive lifespan. These results support the contention that the link between brain size and life history is caused by a balance between the costs of growing a brain and the survival benefits the brain provides, and specifically the slowing of life history during human evolution is caused by increased encephalization.

The correlation between brain size and life history has been investigated in many previous studies, and several viable explanations have been proposed. However, the results of these studies are often at odds, causing uncertainties about whether these two character complexes underwent correlated evolution. These disparities could arise from the mixture of wild and captive values in the datasets, potentially obscuring real relationships and from differences in the methods of controlling for phylogenetic non- independence of species values. This paper seeks to resolve these difficulties by (1) proposing an overarching hypothesis that encompasses many of the previously proposed hypotheses; (2) testing the predictions of this hypothesis using rigorously compiled data and utilizing multiple methods of analysis. Our hypothesis is that the adaptive benefit of increased encephalization is an increase in reproductive lifespan or efficiency, which must be sufficient to outweigh the costs due to growing and maturing the larger brain. These costs and benefits are directly reflected in the length of life history stages. We tested this hypothesis on a wide range of primate species. Our results demonstrate that encephalization is significantly correlated with prolongation of all stages of developmental life history except the lactational period, and is significantly correlated with an extension of the reproductive lifespan. These results support the contention that the link between brain size and life history is caused by a balance between the costs of growing a brain and the survival benefits the brain provides, and specifically the slowing of life history during human evolution is caused by increased encephalization.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Anthropology
Dewey Decimal Classification:300 Social sciences, sociology & anthropology
Language:English
Date:May 2008
Deposited On:22 Aug 2008 14:15
Last Modified:05 Apr 2016 12:26
Publisher:Elsevier
ISSN:0047-2484
Publisher DOI:10.1016/j.jhevol.2007.08.012
Permanent URL: http://doi.org/10.5167/uzh-3313

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