I’ve recently been conversing with a Christian on townhall.com about homosexuality. He is making many dubious claims about homosexuals and condoms that have led me to develop this post and probably more to follow. The primary basis for his claims is that homosexuality is a purely psychodynamic process and has no physiological basis. This contradicts all reputable scientific, medicine and psychological organizations that I am aware of so I did a quick review of the literature.
Homosexuality has been demonstrated to have an underlying physiological influence by many different examples of research that have evolved from twin-sibling studies to more recent brain and physical trait studies.
The earliest study that I’ve found supporting a physiological influence on homosexuality was a twin study from 1952 [Twin and Subship Study of Overt Male Homosexuality. Am J Hum Genet]. The author stated:
“It is also quite evident that the presently available genetic evidence, especially the observation of practically complete concordance as to overt homosexuality in monozygotic male twin pairs, throws considerable doubt upon the validity of purely psychodynamic theories of predominantly or exclusively homosexual behavior patterns in adulthood.”
There have been many twin studies since and they have all pointed to a physiological basis to homosexuality. Here is the short list:
A family history study of male sexual orientation using three independent samples. Behav Genet. 1999;29:79–86.
Evidence for maternally inherited factors favoring male homosexuality and promoting female fecundity. Proc Roy Soc London B. 2004;271:2217–2221.
Familial aspects of male homosexuality. Arch Sex Behav. 2000;29:155–163.
Family size in white gay and heterosexual men. Arch Sex Behav. 2005;34:117–122.
Sperm competition and the persistence of genes for male homosexuality. Biosystems. 1993;31:223–233.
Homosexuality, birth order, and evolution: Toward an equilibrium reproductive economics of homosexuality. Arch Sex Behav. 2000;29:1–34.
A genome-wide scan of male sexual orientation. Hum Genet. 2005;116:272–278.
Molecular investigations into complex behavior: lessons from sexual orientation studies. Hum Biol. 1998;70:367–386.
Is homosexuality familial? A review, some data, and a suggestion. Arch Sex Behav. 1981;10:465–475.
A family study of sexual orientation. Arch Sex Behav. 1982;11:511–520.
Human sexual orientation has a heritable component. Hum Biol. 1998;70:347–365.
Biological versus nonbiological older brothers and men’s sexual orientation
Proc Natl Acad Sci U S A. 2006 July 11; 103(28): 10771–10774.
Sexual orientation and the size of the anterior commissure in the human brain.
Proc Natl Acad Sci U S A. 1992 August 1; 89(15): 7199–7202.
Twin and sibship study of overt male homosexuality
Am J Hum Genet. 1952 June; 4(2): 136–146.
It should be noted that these studies are often cited as evidence for a genetic influence to homosexuality but they are also compatible with a hormonal influence, maternal immunity or any combination, thereof. It should also be noted that very few aspects of human nature are dependent upon a single variable but is the culmination of interactions between physical and environmental factors.