Week 8 Reading C - Proc R Soc B(2007 274 26792684...

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Spatial adaptations for plant foraging: women excel and calories count Joshua New 1, * , Max M. Krasnow 2 , Danielle Truxaw 2 and Steven J. C. Gaulin 3 1 Department of Psychology, Yale University, 2 Hillhouse Avenue, New Haven, CT 06520-8205, USA 2 Department of Psychology, and 3 Department of Anthropology, University of California, Santa Barbara, CA 93106-9660, USA We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources. In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate that a simple but ecologically important shift in content can reverse this sex difference. This effect is predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for gathering-specific spatial mechanisms, some of which are sexually differentiated. The hypothesis that gathering-specific spatial adaptations exist in the human mind is further supported by our finding that spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density). This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efficient foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain specific and designed by natural selection to mesh with important regularities of the ancestral world. Keywords: foraging adaptations; sex differences; optimal foraging theory; spatial cognition; navigation 1. INTRODUCTION Spatialcognitioninhumansisnotaunitaryfaculty( Halpern 2000 );rather,itseemstoreflecttheoperationofanumberof functionally distinct (and neurally dissociable) cognitive specializations,eachdesignedforsolvingadifferentadaptive problem. The selection pressures shaping some of these specializations would have been similar for ancestral men and women, producing sexually monomorphic compu- tationaldesign.Incertain cases, however, ancestral men and women would have faced distinct spatial demands; in these cases, we should find that the resultant cognitive mechanisms are sexually dimorphic. Such sex differences are well documented in the existing literature on human spatial abilities. Spatial tasks exhibit some of the largest and most reliable sex differences in cognitive performance. On many spatial tasks, male advantage is typical ( Linn & Petersen 1985 ; Voyer et al . 1995 ) and these findings have often been used to conclude that men have superior spatial ability ( Linn & Petersen 1985 ). Using an evolution-minded approach, however, Silverman & Eals (1992) predicted and documented a specific female advantage. Their foraging adaptation theory argues that hunting mobile prey and gathering immobile resources have different computational requirements; to the extent that the universal sexual division of foraging labour among described hunter–gatherers ( Murdock 1967 ) characterized our ancestral past, sexually dimorphic fora-
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