No Sex or Age Difference in Dead-Reckoning Ability among Tsimane Forager-Horticulturalists

Benjamin C. Trumble, Steven J. C. Gaulin, Matt D. Dunbar, Hillard Kaplan, Michael Gurven

Sex differences in reproductive strategy and the sexual division of labor resulted in selection for and maintenance of sexual dimorphism across a wide range of characteristics, including body size, hormonal physiology, behavior, and perhaps spatial abilities. In laboratory tasks among undergraduates there is a general male advantage for navigational and mental-rotation tasks, whereas studies find female advantage for remembering item locations in complex arrays and the locations of plant foods. Adaptive explanations of sex differences in these spatial abilities have focused on patterns of differential mate search and routine participation in distinct subsistence behaviors. The few studies to date of spatial ability in nonindustrial populations practicing subsistence lifestyles, or across a wider age range, find inconsistent results. Here we examine sex- and age-based variation in one kind of spatial ability related to navigation, dead-reckoning, among Tsimane forager horticulturalists living in lowland Bolivia. Seventy-three participants (38 male) aged 6-82 years pointed a handheld global positioning system (GPS) unit toward the two nearest communities and the more distant market town. We find no evidence of sex differences in dead reckoning (p = 0.47), nor do we find any evidence of age-related decline in dead-reckoning accuracy (p = 0.28). Participants were significantly more accurate at pointing toward the market town than toward the two nearest villages despite its being significantly farther away than the two nearest communities. Although Tsimane do show sexual dimorphism in foraging tasks, Tsimane women have extensive daily and lifetime travel, and the local environment lacks directional cues that typically enhance male navigation. This study raises the possibility that greater similarity in mobility patterns because of overlapping subsistence strategies and activities may result in convergence of some male and female navigation abilities.