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eng no icha of M inal r e 2D: al te direc dapt as to 1998). During gestation, the brain undergoes rapid develop- reliable approximations of the prenatal influence of testos-Evolution and Human Behavior 3ment and exposure to testosterone permanently organizes the structure of the brain in a way that influences, for example, aggression, spatial abilities, interests, gender identity, and sexual orientation (Berenbaum & Beltz, 2011). Prenatal exposure to testosterone also appears to contribute to the well-established sex difference in the ratio of the second digit to the fourth digit: the 2D:4D ratio (Manning, Scutt, Wilson, terone. Likewise, Hönekopp, Bartholdt, Beier, and Liebert (2007) found that 2D:4D ratios are not associated with adult hormone levels. Other findings lend credence to the claim that the 2D:4D ratio reflects intrauterine exposure to testosterone (and, perhaps also, increased sensitivity to testosterone via intrauterine regulation of testosterone receptors). In rats, elevated prenatal exposure to testosterone appears to yield lower 2D:4D ratios (Talarovicová, Krsková, & Blazeková,scores for either sex. These results suggest that prenatal testosterone exposure in this sample is significantly related to hand grip strength in men, but not in women (and to local muscular endurance in neither sex), and, therefore, that strength, rather than local muscular endurance, potentially drives the relationship between 2D:4D ratios and physical prowess