Money et al. (1957) identified "imprinting" and "conditioning" as the two major learning mechanisms which shaped a girl's primary femininity. Money also noted that strikingly feminine behavior (that is, caricatured female behaviors) appeared even before the girl's first birthday, with a critical period for female gender behaviors reached about the age of 18 months.

Over the last decade, empirical and observational research in child development has shown that a girl develops her femininity not through a series of defensive adaptations to her recognized inferiority to males (occurring during the phallic period) but through a series of positive and, at times, conflictual exchanges with her parents and caretakers during the preoedipal period.

From the very outset, Freud's theories of femininity were attacked by feminist analysts. Indeed, his paper on "Some psychical consequences of the anatomical distinction between the sexes" (1925) seemed to be a direct reply to some of Karen Horney's (1924) criticisms of his theories.

Because of Freud's patriarchal value system (see Breger, 1981), or what Schafer (1976) has called his "patriarchal complacency," he seemed to ignore "his tremendous discoveries concerning. prephallic factors" in the psychology of women, and centered his theory of female sexuality and femininity on the phallic phase and oedipus complex, leading to the idea that penis envy was the bedrock of a woman's femininity.

While Freud hinted at the possibility that the preoedipal period might have an important influence in shaping femininity and female sexuality, he seemed to ignore his own insights and failed to follow through on his ideas.

For almost half a century Freud's theories of female sexuality and femininity have dominated clinical thinking (1925, 1931, 1933). While his pioneering studies (which provided rich clinical material and new speculations concerning femininity and female sexuality) have undergone transformations and revisions, they are still viewed as the point of departure for any serious investigations of female sexuality.

This section reviewes some of the major research developments which have attempted to uncover the possible biological origins of female transsexualism. The research is quite varied and has focused on diverse bio logical hypotheses, including the roles of genes, chromosomes, enzymes, neurotransmitters, neurohormones, prenatal hormones, and H Y antigen in the etiology of female transsexualism.

In March 1981 Science devoted an entire issue to the question of "sexual dimorphism," with two of the articles discussing the role of H Y antigen in human sexuality. Gordon and Ruddle (1981) outlined the difficulties faced in H Y antigen research and suggested that the situation was not as clear cut as it first appeared.

In the light of all the confusion regarding transsexualism and its possible biological underpinnings, it was only natural that researchers should have focused their attention on the possible relationship between H Y antigen and transsexualism. Indeed, Eicher et al. (ibid.) investigated the presence of the histocompatibility of H Y antigen in seven male to female, and seven female to male transsexuals.

The most recent, and promising research area has focused on a newly discovered H Y antigen factor. This factor, discovered by Eichwald and Silmser (1955), was "proposed to be the testis determining substance" by Silvers and Wachtel (1977).