Gayness has a genetic basis and plays a role in natural selection.
Evidence for ‘gay genes’
The debate as to whether gayness is a choice, or whether it’s an inherited characteristic has been resolved by a number of reports that provide evidence of zooming-in on ‘gay genes’ located on the X-chromosome, chromosome 8 and other potential gene candidates. However, replicating these results requires very large sample sizes, and are not always conclusive, which highlights how difficult linking behavioural characteristics with genetics can be.
Linking a trait as complex as sexual orientation to genes is no small task. The peiotropic (many) behavioural effects suggest that many genes are involved, and that the pioneering study reporting men are three times more likely to be gay if they have a gay brother probably represents a number of different genes acting in conjunction with one another.
Dr Dean Hamer and Drs Michael Bailey, Alan Sanders and Gary Beecham have been primarily involved in providing convincing evidence for the location of these genes, but a number of subsequent studies have contributed more detail to the picture. Researchers have warned of the controversial undertones to their work and strongly argue against the development of a genetic test for gayness.
Is everyone who inherits a ‘gay gene’ born wih this sexual orientation?
Therefore, the discovery that the gene(s) located at a position on the X-chromosome termed Xq28 relates to sexual orientation has suggested a genetic basis for homosexuality. This does not mean that all men who inherit the gene will automatically be gay: genetics tend to be far more nuanced than this; and the environment and conditions in which a person grows is likely to have a large effect on the expression of a characteristic as multifaceted as this.
This phenomenon is termed “epigenetics” and relates to changes to gene expression not related to the DNA code that will determine whether a specific gene is expressed (For a non-biochemical summarisation, click here.) For example, hair greys over time because the colour genes are turned off by a number of proteins that shut down the DNA sequence so it cannot be read and turned into protein any longer. This usually occurs by methylation – the addition of methyl (CH3) groups to the DNA molecule.
Why are ‘gay genes’ common?
This brings us back to the gay gene: if it is so rare, and assuming that homosexual men tend to have fewer children that heterosexual, why has the gene not been lost over time? Surely the gene will hit a dead-end in the generation tree at some point?
Not so. It has been suggested that there is an advantage to possessing a gay gene, and this presents itself in the few women that inherit it from a parent: These women tend to have approximately 1,3 more children on average, which in evolutionary terms is a huge win.
More people = more genetic variation = better success as a species.
In effect, then, the gay gene underpins a fairly dramatic evolutionary strategy.