4. Bailey and Pillard’s Data: The concordance among the monozygotic twins was higher than that of the dizygotic twins, which was higher than the adoptive brothers. This could show a strong hereditary influence on sexual orientation is rooted in genetics. However, there is a significant difference in the concordance of dizygotic twins and the concordance of non-twins brothers. As non-twin brothers and dizygotic twin brothers have roughly the same amount of genetic material in common, if sexual orientation was solely genetic, one would expect to find much more similar figures. Also, if the trait was genetic only, the concordance rate for monozygotic twins should have been one hundred percent. From this, one can conclude that other factors also played a role.
5. LINKAGE BETWEEN GENETIC MARKERS ON THE X CHROMOSOME AND MALE HOMOSEXUALITY Dean Hamerattempted to demonstrate a linkage between genetic markers on the X chromosome and male homosexuality. In Hamer’s study, he discovered forty pairs of homosexual brothers that had a higher concordance for certain DNA sequences on Xq28, a segment of the X chromosome, than expected.Because these sets of homosexual brothers were chosen for study based on an absence of homosexual relatives in their paternal lines, Hamer was more able to infer that the inheritance came from the brothers’ mothers. Hamer was clear in stating that he did not discover a “gay gene” in the Xq28 region, but a correlation.
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7. LINKAGE BETWEEN GENETIC MARKERS ON THE X CHROMOSOME AND MALE HOMOSEXUALITY In 1999, George Rice carried out a study in an attempt to duplicate Hamer’s Xq28 findings. Rice’s data did not support Hamer’s.
8. RESPONSE TO HUMAN PHEROMONES BY HOMOSEXUALS Studies have been conducted to observe human response to pheromones. Based on findings, it has been suggested that homosexual men respond to pheromones in a similar manner as do heterosexual women. When a similar study was conducted, this time including homosexual women, the results were that homosexual women were less responsiive to male odors. Their response to female odors were similar to that of heterosexual males. This research suggests that sexual orientation may have a biological basis, with pheromones playing a role.
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