Nature or Nurture

“We do not even in the least know the final cause of sexuality. The whole subject is hidden in darkness”. So wrote my relative Charles Darwin. Over a century later and we’re no closer to knowing. One of the hardest questions to answer when someone begins to realise their sexuality is different to others is “Why am I like this?” As recently as last year the “Nature or Nurture” debate was still receiving attention in scientific circles.

For this very brief historical overview I’ll try to go through various studies and theories from recent decades in chronological order. All have been summarised as briefly as possible without going into scientific detail because they’d take up too much room. Think of this as a summary of research rather than a scientific analysis of the evidence.

1957    Karen Hooper carries out a psychological test on gay and straight men. She says that homosexuality does not effect the IQ or development of gay men. Because of this the American Psychological Association removes homosexuality from its list of mental disorders.

1980    Michel Foucault speculates that the modern concept of a gay man did not really exist before the word “homosexuality” was invented in the 1800s. He states that the word created the concept.

1987    A study finds that 14% of a sample group of gay men are left handed compared to 9% of a sample group of straight men. A later study finds similar results between lesbians and straight women.

1991    Research on twins found that there were 52% of identical twins, 22% of non-identical twins, and 5% of adopted brothers, who were both gay. It also found that more gay men usually have gay brothers than lesbians sisters, and lesbians have more lesbian sisters than gay brothers.

1991    Simon Le Vay studies the brains of gay and straight men and woman. He finds that the hypothalamus (the organ largely responsible for emotions and sexual drive) in gay men and straight women have a smaller cluster of specific cells (called INAH-3) than straight men. However, all the brains of gay men were of AIDS victims and may not have accurately represented the whole community.

1993    Dean Hamer looked at 114 families of gay men. He found that same-sex orientation was higher on the maternal side of the families. Hamer looked at part of the X chromosome called Xq28 which we all inherit from our mother. This is a gender marker. From Hamer’s research came the popular notion of a “gay gene”. His research has since been questioned.

1995    A colleague of Hamer’s continues research on the Xq28 gender marker and finds that is was present in families of gay men but not that of lesbians.

1997    A study of siblings shows that the more older brothers you have you are 33% more likely to be gay.

1999    More research on the Xq28 marker indicates that gay brothers are no more likely to have this marker that a set of straight brothers.

2005    A further study looks at Xq28 in the light of the recently catalogued human genome. It finds other markers on DNA which gay men inherit from their mother, but also finds that similar markers are inherited from their father.

2006    Research is made on X-inactivation. Women have 2 X chromosomes (men have one X and one Y – male – chromosome). One X is inactivated when female gender is determined in the embryo. Some parts on the inactive X can still be active – this is skewed X-inactivation (its what causes tortoiseshell cats to have different coloured patches – the light patches are caused by skewed X-inactivation). The research shows that women with high skewed X-inactivation are more likely to have homosexual sons.

2012    The Quarterly Review of Biology publishes a paper which claims homosexuality may be caused by epi-marks, genetic switches on DNA that helps the embryo to develop but “die” when their job is done (like the “male switch” on the Y chromosome in men). When sex-specific epi-marks survive and pass from parent to child they may influence the emergence of same-sex attraction.

2013    Neil Whitehead claims that all the studies on twins, where one is gay and the other not, proves homosexuality is not inherited or genetic. However, Whitehead is a Christian-based writer with a known anti-Nature-not-Nurture and transphobic bias.