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As in rodents, early androgens appear to masculinize spatial ability in humans (Puts, 2007).
In one study, second-trimester testosterone levels correctly predicted spatial abilities when girls were 7 years old (Grimshaw, 1995). And another study showed that girls with male twins had better spatial ability, presumably because she was exposed to her male twin’s androgens during development (Cole-Harding, 1988).
Further evidence for the hormonal role of sex-differences in humans comes from analysis of sex-atypical hormone conditions. Patients with Turner syndrome are phenotypically female, but lack part of their X chromosome. These girls have undifferentiated gonads which lead to extremely low androgen and estrogen levels. Patients with TS express impaired visual-spatial and perceptual abilities, attention, working memory with normal verbal function. Pubertal androgen and estrogen replacement hasn’t been shown to successfully restore these deficits, so it is believed that early androgens are necessary to later organizational effects (Ross, 2006).
Patients with congenital adrenal hyperplasia (CAH) over-produce androgens from the adrenal glands. Studies have found that girls with CAH tend to exhibit masculinized spatial abilities (Hines, 2003).
In the study of sex differences in learning ability, functional, phylogenetic, developmental, and proximate explanations have made complementary contributions to our understanding of a behavioral sex difference. But, it wasn’t until 1986 that the first paper that attempted to explain why sex differences in the hippocampus have evolved (Puts, 2007). The idea of non reproductive sex-differences causes problems with Darwin’s theory of natural selection, because males and females of the same species should theoretically be sharing the same environments, eating the same foods, being preyed upon by the same predators and risking the same diseases. Where skewed sex-ratios or different maximum reproductive potential between the sexes can explain the emergence of sexually-selected, within-species, traits such as bright plumage or antlers to attract a mate, spatial learning differences aren’t as easily explained.
An evolutionary model of spatial learning sex-differences must include two assumptions. First spatial ability is fundamentally a navigational adaptation; animals will be able to navigate better if they can acquire and manipulate data on the location or risks and rewards in an environment. Sex-differences will only occur in species in which males and females exploit the environment differently, for example if only one sex leaves to forage, hunt, or reproduce while the other remains in a smaller home range. The second assumption is that an increase in spatial learning ability comes with some cost to its recipient. Energy is required to travel further and the risk of predation is greater. Without costs, there would be no reason that both sexes wouldn’t acquire the same trait (Gaulin, 1992b).
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