The issue rages as to whether homosexuality is biologically or environmentally based�the age-old question of "nurture" versus "nature"�has reared its knotty head again. As Dr. Thomas S. Schoenfeld of the Frances L. Hiatt School of Psychology at Clark University says:

The ambiguity of psychological and biological determinates in sexual orientation is just as Schoenfeld states. To the untrained eye it seems that a multitude of research has been completed, but on closer observation, one finds that is not the case at all�much, much more research is needed to determine a decisive answer. Disclaimers aside, the research that has been completed leans away from the notion of a biological component. Data from the varying research has had a wide range of research intentions and interpretations, but has been shown time and time again to lack evidence in favor of an overwhelming biological component. In this report we'll examine research and scholarly opinion as to the role biological and psychological factors play in determining sexual orientation.

The first genetic study to gain notice was that of Kallman. In it he reported a 100% concordance rate in thirty-seven monozygotic twin pairs that when one twin was homosexual, so was the other. There was a 12% rate in twenty-six dizygotic pairs. (Kallman, 1952, 283) At the time it rocked the scientific community and seemly proved a genetic component. This study is still quoted frequently to this day. Later damning evidence emerged that Kallman used unreliable sources to find his research pool and Kallman himself later conceded that his very high concordance rate for monozygous twins was a "statistical artifact" (Cooper, 1974, 5). This first major study in favor of genetic favoritism shows how researchers on both sides of the issue have tainted or convoluted research to their own viewpoints. Determining genuinely scientific research in this subject is very difficult. Nevertheless, Kallman's study is still frequently referenced.

Bailey and Pillard have superceded Kallman's extreme concordance rate in popularity. His study was replicated in use of monozygotic twins by Bailey and Pillard and their conclusion that homosexuality has a genetic basis. Their concordance values were as follows: 52% of monozygotic male twins were both homosexual if one twin was, 22% for dizygotic twins, 9.2% for non-twin brothers, and 11% for adoptive brothers (Bailey and Pillard, 1991, 1089). These figures, they felt, presented clear evidence of a genetic determinate for homosexuality. Nearly every website, book, or other source attempting to take a pro-genetic stand reference Bailey and Pillard: their popular influence cannot be emphasized enough. The rub is that Bailey and Pillard personally pointed out the deficiencies of their own studies:

In light of such conclusions made in the study itself, and comments made after the fact like, "genetic factors are insufficient explanation of the development of sexual orientation." (Bailey and Pillard, 1992, 407) One of the banner cases doesn't seem to be as decisive as the popular media and causal internet searches seem to suggest.

To round out the major research studies referenced as evidence for overwhelming biological evidence is the study of brain structure in August 1991 by Simon LeVay. His study focused on a cluster of neurons in the hypothalamus. The cluster was identified as INAH3 (interstitial nuclei of the anterior hypothalamus�group 3) and was discovered to be smaller in a majority of the homosexuals than the heterosexuals. LeVay concluded: "that INAH is dimorphic [different for males and females] with sexual orientation, at least in men, and suggests that sexual orientation has a biological nature." This case is also frequently referenced as source evidence of biological sureties. But, just as Bailey and Pillard's study, a number of questionable and uncertain factors have come to light. He worked only on cadavers and had to rely on medical records to determined the person's sexual orientation. Also, according to his findings, three of the "heterosexual" brains fit LeVay's "homosexual" pattern, and three of the "homosexual" brains should have been heterosexual. He has left science to become a full-time gay activist. While the sexual orientation of the researchers doesn't lend or retract credence from their work, the empirical loopholes and fudging of the scientific method do not provide convincing evidence.

So in lack of an great evidence for a biological determinant, we turn to psychological or social factors. Brancroft present one theory, a series of "push" factor (lead away from heterosexuality) and "pull" factors (lead towards homosexuality). His results are summarized below:

The idea of Brancroft that frustration over the lack, confusion, or anxiety heterosexual experiences leads one to seek sexual fulfillment in homosexual encounters find some supporting evidence in the Kinsley report. The Kinsley report showed that 37% of the white male population of the United States had at least some homosexual experience to the point of orgasm, between adolescence and old age. Approximately 7% among the white male population of the United States had more than incidental homosexual experience or reactions over at least a 3-year period between the ages of 16 and 55, but were still predominately heterosexual. This study seems to lead to the notion that there are more than enough homosexual encounters in the population at large to provide fodder for questioning, concerning, or frustrated youth and allow them to make the switch to a homosexual mindset.

Another interesting piece of a personal-social effect is that of gender nonconformity, as studied by Bell, Weinburg and Hammersmith (1981). Whereas 70% of the heterosexual men had enjoyed sports activities such as baseball and football as children, only 11% of homosexual men had. In contrast, 68% of homosexual men, but only 34% of heterosexual men, had enjoyed such solitary activities as drawing or reading when they were children. As children, 46% of homosexual men and 11% of heterosexual men had enjoyed playing house, hopscotch and jacks. Childhood cross-dressing occurred in 37% of homosexual men, and 10% of heterosexual subjects. As the author of the study states:

So what is the answer to the question of where homosexual orientation comes from? No one is sure. As we've seen, the likelihood of an overwhelming genetic factor has not been found. A complete psychological or social model as to the production of a homosexual individual is so complex and varied that no one has one all inclusive answer. Certainly, a greater understanding of studies done, their viability and interpretations need to be better understand by policy makers and the general population. From the studies seen, it seems that from the empirical evidence we have the likelihood of an overwhelming genetic factor is considerably low. As Voth says:

Someday data may be found in support, but as of now none exists.