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Review
. 2010 Sep;151(9):4116-22.
doi: 10.1210/en.2010-0041. Epub 2010 Jul 14.

Minireview: Organizational hypothesis: instances of the fingerpost

S Marc Breedlove  1
Affiliations
Review

Minireview: Organizational hypothesis: instances of the fingerpost

S Marc Breedlove. Endocrinology. 2010 Sep.

Abstract

There is now compelling evidence that the ratio of the length of the second digit divided by the length of the fourth digit (2D:4D) is affected by prenatal androgens in humans. This ratio is greater in females than males from fetal life through adulthood, correlates with polymorphism in the androgen receptor gene in men, is feminine in XY androgen insensitivity syndrome, and masculinized in congenital adrenal hyperplasia. Using 2D:4D as a correlate, researchers have found evidence that prenatal androgens affect many sexually differentiated human behaviors, including sexual orientation in women (but not in men), attention deficit disorder, autism, eating disorders, aggression, and risk-taking. In each case, lower 2D:4D, indicative of greater prenatal androgen stimulation, is associated with behavior more commonly displayed by males than females. The correlation between 2D:4D and prenatal androgen stimulation is too imperfect to accurately predict the phenotype of a particular individual, even in terms of sex. However, digit ratio is the best available retrospective marker of average differences in prenatal androgen stimulation between groups of people, and/or correlations of prenatal androgen stimulation with particular behaviors and characteristics within a group. Thus digit ratios offer a valid test of the organizational hypothesis that androgens act early in life to masculinize various human behaviors.

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Figures

Figure 1
Figure 1
Instances of the fingerposts. A, Many different experimental findings concerning 2D:4D are consistent with the notion that prenatal androgens affect digit ratios in humans, while several point away from alternative hypotheses, such as a direct role of sex chromosomes, or social influences. B, The correlations of digit ratio with various behaviors, each of which is normally displayed more by one sex than the other, all point in a particular direction—the direction indicating that prenatal androgen stimulation contributes to the masculinization of diverse human behaviors, despite the obvious importance of social factors and learning. The particular behavior-digit ratio relationships displayed are among those that have been replicated at least once (see text).
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