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Angier's article, while written for a non-scientifically oriented audience, gave a very accurate synopsis of Dr. Hamer's work. Initially, Hamer et.al (1993), in an attempt to determine a genetic basis for homosexuality, studied the families of 114 homosexual men. The study consisted of creating lineage charts for each family, and studying the occurrence of homosexuality. Hamer and his colleagues found increased instances of homosexuality in uncles and cousins on the mother's side. They did not, however, find the same results in paternal uncles and cousins. This important piece of research led Hamer et.al. to study the X chromosome to determine if there was a specific genetic similarity between homosexual brothers. Hamer chose the sibling pair setup for a multitude of reasons. In the research article, Hamer et.al. state, "This sib-pair experimental design has several theoretical and practical benefits (i) it is nonparametric and independent of gene penetrance and frequency; (ii) it is capable of detecting a single linked locus even if additional genes or environmental conditions are required to express the trait; (iii) it is more powerful to study siblings than more distant relatives for traits displaying limited familiality; (iv) "false negatives" are not studied; (v) "false positives" are expected to be rare; (vi) the sib-pair method is more stable to errors in genotyping and to mistakes or alterations in phenotype than are large pedigree methods; and (vii) it was more practical to obtain the cooperation of nuclear sib-pair families than of multigenerational families," (Hamer, et.al, 1993). Using a technique known as linkage analysis, Hamer and his colleagues found that 33 of the 40 sibling pairs studied shared the same markers in the Xq28 region of the X chromosome. .
In the Angier article and the Hamer article, both warn that these findings are not to be taken as an indicator that homosexuality is purely genetic.
