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Genetics and Male Sexual Orientation, Science, 285, Aug. 6, 1999, pp 803a.Dean Hamer; George Rice, Neil Risch, & Gene Ebers."Sexual orientation is a complex trait that is probably shaped by many different factors, including multiple genes, biological, environmental, and sociocultural influences. In a 1993 report, my group (1) provided initial evidence that a locus at the q28 region of the X chromosome was involved in male sexual orientation in some, but not all, individuals." These words begin Dean Hamer's 1999 defense of the X chromosome theory of homosexuality. For those who are dogmatic about the heritable nature of homosexuality, please note that Hamer is clear that sexual orientation in his view derives from a combination of factors in interaction. Also, he does not claim that all homosexual orientation derives from the X chromosome. This is actually a fascinating exchange between Dean Hamer and Canadian researchers George Rice, Neil Risch and George Ebers. Hamer argues that the research of Rice, et al actually replicates his findings. The arguments are complex but essentially Hamer is arguing that the subjects used by Rice et al were possibly not fully homosexual due to errors in labeling and sampling. He claims his methods were superior. He then presents a meta analysis that combines his data with that of Rice et al. For further evidence of the genetic nature of sexual orientation, he quotes the work of Bailey and Pillard. Writing in 1999, he could not have known that the concordance rates of identical twins in Bailey and Pillard's studies were probably inflated by ascertainment bias. Bailey himself says so in his study that found 20% (male) and 24% (female) concordance for homosexuality. Rice et al vigorously defend their methods and results: "Considering only the two studies performed by independent investigators, ours and the unpublished data of Sanders et al., we obtain Xq28 allele sharing of 60/106 = 56.6%, which is not statistically greater than the null hypothesis value of 50% sharing (p > 0.05). In fact, the two independent replication studies combined deviate significantly from the results from Hamer's group (chi-square = 6.53, p < .02). Thus, the conclusion remains that the original studies of Hamer and colleagues are not replicated." They defended their participant selection procedures and note, "we still contend that an X-linked gay gene could not exist in the population with any sizeable frequency, due to the strong selection against it." Basically, there are many reasons that a gay gene would not proliferate. As noted above, these researchers state that Hamer's study is not replicated. |
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