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Epigenetics model for homosexuality, but don't get too excited ...

by Bruno Van de Casteele

January 13, 2013

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Donate Sometimes science too has its "fashion trends". One of them, in my opinion, is epigenetics, according to Wikipedia the study of heritable changes without any changes to the DNA itself. These changes are then visible through gene expression or the lack thereof.

It's a very interesting and rather new field of study within evolutionary biology that in no way negates the aspect of evolution, but actually supplemented. There are some fascinating results, notable the study of the Dutch Famine of 1944 ("Hunger Winter") where people who were fetuses during that time showed an increased risk of schizophrenia later on. Another study from that tragic event showed that children from those in utero during that time have a slightly lower birth weight than expected. This provides a fascinating view on how genes could get expressed differently even across generations. It also shows that there is hardly such a thing as "gene for X", but that the actual scientific reality is much more complex.

But sometimes I worry it gets a bit overused. In this article, three researches (US and Sweden) propose a model where homosexuality could be explained by the effect mothers have on their sons (and fathers on their daughters). Not in a psychoanalytical sense, but because of differences in sensitivity to proteins during their own sexual differentiation in the womb. These so-called epi-marks (term by the researches, I couldn't immediately find more about it) would then increase female differentiation (as passed on by the mother) in a male son and vice-versa.

First of all, let me state that this is a model, and not a study with test subjects or with chemical experimentation in a lab. The article seems one big speculation after another, based on several hypothesis and inference from a low number of data points. This article in the The Scientist sums up several valid remarks. However, when reading the abstract, it's easy to forget it's a model, a proposition for further study. No actual data has been gathered, no tests have been done.

As such this is not an issue. This happens more, and the only reason it got picked up by media, is that it's a "sexy" topic. The model might increase our understanding of homosexuality, as indeed there seems no "gene" to be found for it. I even learned that twins are only 20% of the time both homosexual. I thought it was way higher than that, based on anecdotal evidence.

But I would caution against the model. As I said, there is a lot of speculation within it, and maybe it's not that good as a basis for further study. The article in the New Scientist even quotes other researches who looked at the model, doubting that it is even testable. The researches do point to some possible tests, but to me, there seems too much wrong with it. For instance, I find that it mixes sexual development (primary sex organs) of the parent with sexual orientation of the child (without apparent influence on those organs). I feel that a couple of assumptions need to be checked first before actually testing the model itself. For instance, the term epi-marks (temporary switches) needs further study as I couldn't really find more information about its validity.

In conclusion, there is no issue on principle with publishing a model, even though media have picked it up way too enthusiastically (it makes for great headlines). This is indeed how science works: an idea gets proposed, gets criticized and if it holds up, gets tested. What I don't like is that these researchers have gone a bit too fast in my opinion, and should have based their model in more sound research first before attempting to formulate it. It's nice to try to attach one's ideas to a popular subject that is still evolving rapidly itself, but I'd wish they would have been more prudent. They should have known (or maybe they did know) that such a topic would get more press reporting.

by Bruno Van de Casteele

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