Fetal hormones, the Brain, and human sex differences: A heuristic, integrative review of the recent literature

The data presented clearly compel the conclusion that a fetal hormonal effect is influential in the subsequent development of sex differences, but in most cases its effect must be seen as limited in scope and of a diffuse quality rather than directly related to specific behaviors.

Abstract

Many investigators of sex differences have suggested that underlying physiological-biological factors probably account, at least in part, for some of the sexually dimorphic behaviors identified in humans. Although few have conjectured as to the specific nature of the mechanism mediating these differential tendencies, the evidence reported here from animal behavior experiments, brain studies, and human clinical syndromes strongly suggests that it is the presence or absence of androgen during the period critical for the organization and differentiation of the human brain that is the operative agent. Further, it is necessary to qualify the hypothesis by placing it in proper perspective in terms of the many influential postnatal factors. Psychosexual differentiation must be understood as an end result or complex of various component factors and not as a single or global entity (Money and Ehrhardt, 1968). The data presented clearly compel the conclusion that a fetal hormonal effect is influential in the subsequent development of sex differences, but in most cases its effect must be seen as limited in scope and of a diffuse quality rather than directly related to specific behaviors. In view of the evidence from the animal experiments that the nature of the mammalian genetic constitution is a "plastic, pluripotential matrix, highly susceptible to shaping and selection by environmental influences such as hormones" (Goy, 1970) and considering the dependence of the human species on experience and learning processes for the expression of complex patterns of behavior, the influence of the prenatal hormones is best understood as setting a bias on the neural substratrum, which in turn predisposes the individual to the acquisition and expression of sexually dimorphic patterns of response and behavior (Goy, 1970; Hamburg and Lunde, 1966). It is not possible at this point in research to identify the response patterns and behavior styles which are directly or indirectly the result of prenatal hormonal influences, but it appears evident that at least some of those mentioned in this discussion are related to hormonally mediated brain differences.