The Science of Sexuality

Sintija Jurkevica and Jonathan James

The struggle of understanding sexuality begins to muddle even before sexual orientation can be defined. Some sources describe it as a person’s capacity to have erotic experiences and responses. However, in general, sexual orientation or preference, can be defined as “the sex (biological aspects of maleness and femaleness) of those whom one feels romantically and sexually attracted to”, where one’s sexual orientation may be categorised as heterosexual, bisexual, homosexual, queer, pansexual, asexual or among others. However, categorisation of identifiable preferences is more nuanced than it appears; whilst some research may describe orientation as discrete categories, substantial evidence backs up the existence of a sexual continuum or spectrum.

But how does one develop a sexual preference? This riddle is a classic psychological argument of nature versus nurture: do the genes, the environment, or a mixture of them both influence one’s sexual attraction to others? This is obviously an ongoing debate and a matter of significantly more research. A recent September publication, composed by a psychology researcher Michael Bailey and his colleagues in the peer-reviewed journal of Psychological Science in the Public Interest, has been created with the intention of objectively reviewing previous scientific research on sexual orientation to draw impartial conclusions on the topic, without preconceptions of scientific biases and political influences.

Bailey’s review paper concluded that the non-social causes, such as the individual’s genetic make-up, play a larger role than environmental influences in establishment of one’s sexuality. The evidence, supporting such a claim, includes the genetic influences in twin studies and unchanged sexual orientation of infant boys after they are surgically or socially “converted” into girls. Bailey and colleagues also argue against the commonly assumed environmental causes of homosexuality to be weak and distorted in comparison to alternative explanations.

Various genetic hypotheses had been proposed to explain differences in sexuality. In several studies, it was found that a several different genetic markers (i.e. genetic elements) were more likely to be found in gay men in comparison to their straight counterparts. When this news was first published, it caused an outpouring in the media of the discovery of the so called ‘gay gene’, but the media failed to report one significant factor – genetic influences themselves cannot be used to determine predisposition to a trait. In other words, simply having a genetic element doesn’t automatically result in these individual’s sexual orientation. To make matters more complicated, scientists were unable to reproduce these findings in women for same sex attraction, suggesting that sexual orientation is a lot more complex than a few genetic differences.

Other scientists have conducted studies considering the seemingly well establish theory that each additional older brother increases the odds of a male being gay by approximately 33%, with something like 1 in 7 gay males holding their sexual orientation because of having older male siblings. These findings have been controversial, not least because there are several scientific studies that support these proposals, and several that have not found a link.

One attempt to explain this apparent causation is through the maternal immune response. Male fetuses produce H-Y antigens (small proteins) that play a role in sexual development in the womb (i.e. the development of male sex organs). In response to these antigens, the mother will sometimes produce an immune response, which gets stronger with each successive male fetus, resulting in decreased activity of these antigens in later males. One suggestion is that this results in less ‘mascularization’ of the male brain, resulting in the development of same sex attraction. The major flaw with this explanation is simple – the occurrence of the mother’s immune response is significantly lower than the prevalence of homosexuality, suggesting it cannot be the major cause.

The truth of the matter is, despite several attempts to better understand the genetics behind human sexual orientation, scientist know very little about what causes it, or even the true significance of any environmental factors. As Bailey concludes in his paper however, “Sexual orientation is an important human trait, and we should study it without fear, and without political constraint,” Bailey argues. “The more controversial a topic, the more we should invest in acquiring unbiased knowledge and science is the best way to acquire unbiased knowledge.” Therefore, we should look forward to developing a better understanding in the future, in the hope that a better understanding of ourselves, results in a better understanding of each other.