The Epigenetics of Sexuality – Wrong on So Many Levels

Another day, another truly execrable epigenetic report. Epigenetics is the study of chemical modifications to our genetic material which influence how genes are expressed. It provides the mechanistic link between our genes and our environment, and is a beautiful area of biology. It is involved in phenomena as diverse as the flowering times of certain plants and the gender of crocodiles, and from novel treatments for cancer to the coat color of calico cats. In the last few years scientists have developed new techniques to analyze the patterns of epigenetic modifications on the genome, and there is a tsunami of papers emerging. And unfortunately some of them are very bad indeed.

The latest awful study hasn’t even been published yet, instead it was presented at the annual meeting of the American Society of Human Genetics. Researchers from the University of California Los Angeles took saliva samples from pairs of identical twins, some of whom were gay and some straight. They analyzed the epigenetic modifications and announced they had found five that together would predict the sexuality of the donor accurately 67 percent of the time. The authors also speculated that this may give us insights into the cause of homosexuality.

Does 67 percent of the time sound good to you? Try thinking of it another way. Would you bet anything beyond a dollar on something that will be wrong a third of the time? In yes/no situations, you could flip a coin and be right 50 percent of the time on average. Sixty-seven percent doesn’t sound so impressive now, does it?

And that’s not the only problem. The number of twin pairs was far too low to generate any genuinely meaningful statistical data. Saliva samples contain a mixture of cell types that may have different epigenetic modifications, and why would —> Read More