Many supporters of homosexuality cite issues of genetics and heredity to argue for the natural tendency of individuals to be homosexual. While it was once considered a disorder or disease by scientists and psychologists, discussions today focus on its genetic basis rather than labeling it as such. The American Psychological Association (APA) classified homosexuality as a mental disorder until 1973, when it was removed from that classification. Since then, the focus of psychological discussions has shifted toward heredity and genetics.
The first attempt to link homosexuality to genes was initiated by the psychiatrist Franz Josef Kalman.
1. Review of Twins
Franz Josef Kalman presented a study about twins and concluded: “If one twin brother is homosexual, the other will be the same.” This implies a 100% conformity rate in sexual orientation. However, the deception in this research was quickly revealed; philosopher and jurist Eduard Stein criticized Kalman’s study, stating that he “did not provide any reason for the fact that the examined twins are practically genetically identical.”
Following Kalman’s research, other studies attempted to explore the connection between genes and homosexuality but failed to establish any definitive link. For instance, research conducted by Dr. Neil Whitehead in 2011 concluded: “Due to the small fraction of the calculated genes, we have to say that people are not originally born this way (homosexual).”
Lawrence Meyer, a biometric scientist, and Paul McHugh, a psychologist, after a comprehensive review of research on homosexuality published in 2016, expressed their findings as follows: “By summarizing the research on twins, we can say that there is no reliable scientific reason stating that genes determine people’s sexual orientation. The understanding of sexual orientation as being natural for humans and biologically determined—that is, the idea that people are born this way—is unsupported by scientific evidence.”
2. Genetic Science
The first efforts to investigate a genetic basis for homosexuality were undertaken by Dean Hamer, a geneticist, in 1993. He examined 40 homosexual couples and reported a possible link between the 28Xq genetic marker on the X chromosome and homosexuality. However, he did not claim that this genetic marker was the cause of homosexuality; rather, he suggested that there was only a possible connection. Subsequently, Dr. George Raizo and his research group conducted a larger-scale study and indicated: “It is not clear why our results are completely different from those of Dean Hamer’s research. Our research has been more extensive than that of Hamer and his colleagues. We had sufficient power to detect genetic influence at the same level as described in that study; nevertheless, our findings do not support the existence of a gene with a strong influence on sexual orientation, nor do they support the significance of the 28Xq genetic marker.”
The largest attempt to determine genes associated with homosexuality occurred in 2012 when the American Society of Human Genetics conducted a study involving 23,000 participants—note that this is 23,000 people, not just a few hundred. The results were as follows: “A common cause between sexual identity and variations in single nucleotide polymorphisms (SNPs) on the X chromosome in males and females or combined samples has not been found to be of genomic significance.”
In 2015, the same association presented a study from the University of California, which, as reported by the Telegraph, indicated: “Homosexuality can be caused by the life environment after birth.” During a visit in 2010, Dr. Paul McHugh, head of the psychiatry department at Johns Hopkins Hospital and a long-time researcher on homosexuality, was asked for his opinion. He responded:
“As I said before, there is no such thing as a homosexual gene, and there are factors that are more influential than biology. Of course, the best data is related to Framingham’s research.”
“Although many studies have examined genetic, hormonal, developmental, social, and cultural influences on sexual orientation, none of the findings have revealed to scientists that sexual orientation is determined by a specific factor or set of factors.”
Drs. Meyer and McHugh, reviewing Saunders’ latest research on the 28Xq gene, stated: “However, since the said effect is small, the genetic factor will not be a suitable indicator of sexual orientation.” Even if a specific gene were identified, its influence would be weak compared to upbringing and other biological and environmental factors affecting a homosexual person.
Dr. Neil Whitehead, a biologist and statistician, adds: “In the most optimistic case, heredity is considered a minor factor…the effect of genes on individual behavior is very weak because genes make proteins, not choices.”
By 
