An examination of sex differences in spatial abilities reveals comparative superiority of males and females on mental rotation and location memory tasks, respectively. The existing cross-cultural data focus primarily on male-biased spatial tests and suggests that the sex difference in mental rotation ability is near universal. While cultural pressures can enhance or diminish performance, its magnitude is preserved. Proximate causes, including the organizational and activational effects of hormones, may move these performance distributions closer or further apart. Evolutionary-based theories have focussed mainly on sexual selection versus division of labour as the critical factors in the selection of male-female spatial specializations. A unified model of human spatial judgment is proposed considering fundamental differences between three-dimensional judgments of spatial rotation and two-dimensional judgments associated with spatial location memory. Mental rotation ability is favored when a stationary viewer tracks where a moving target is headed, while location memory is engaged when a mobile viewer inventories what is present in a space. While these mental abilities may be considered complementary, cultural pressures for a male-female division of labor will favor depth judgments by males and location memory judgments by females.