February 2, 2012

New genetic study of male and female behavior

American scientists develop an interesting model of how genes and hormones influence sex behavior, a model that might also throw light on transgender conditions.

Regular readers of this blog know my skepticism towards reducing human gender behavior to biology alone.

The interaction between cultural factors, personal experiences, the body itself and the genetic variables is just too complex to be reduced to a simple "one gene determine all gender behavior" kind of theory.

Indeed, we now know that not only is the brain "plastic" in that learning changes it; we also know that genes may be switched on and off because of stress and various environmental influences.

On the other hand, the discussion of the transgender conditions taking place on this blog and in other online forums,  as well as my own personal experience, has led me to believe there is some kind of biological core to at least some of these experiences, including my own crossdreaming.

The social pressure to conform to traditional gender stereotypes is extremely strong, so strong in fact, that these transgender traits should have disappeared if they were anchored in personal experiences only.

I can see a clear parallell in homosexuality. I have many homosexual friends who get seriously angry when someone suggest their experience is based on "mother complexes" or teenage seductions. As one gay friend told me: "If that was the case, ten years of therapy would have cured me!"

Then, of course, there is the large number of heterosexual men with similar childhood experiences.

In other words: homosexuality as well as transsexuality are most likely to have a strong biological basis.

That does not mean, of course, that there are no same-sex relationships or no types of cross-gender behavior that are not anchored in these kinds of hormonal or genetic starting points. Humans behavior is amazingly diverse, and I suspect that both sexual orientation and gender behavior are quite flexible.

Simplistic biological models

There has been a tendency among biologist to fall into the trap of social projections.  That is: They take the social stereotypes of their own culture and projects it onto animal behavior.

Their interpretation of animal behavior is then taken as proof of the social stereotypes being based in biology. Nature trumps nurture, and sexism trumps humanism. (See my series on Joan Roughgarden for examples).

These studies are often based on a simplistic reductionism where all "masculine" behavior is understood as the effect of one single factor (for instance a gene or prenatal hormones).

Ray Blanchard's transgender theory is, for instance, reductionistic in the sense that sex identity, gender specific behavior and sexual orientation are chained together. A transwoman can only be feminine if she (or "he" if we use Blanchard's vocabulary) is attracted to men. If she is attracted to women, she is per definition masculine, ungainly and ugly.

The Nirao Shah study

A new study done by Nirao Shah and his group at the University of California, San Franscisco, is interesting in that it brings a new level of complexity to the sexual behavior arena.

According to them sexual behavior in mice (which are much less complex organisms than human beings) cannot be reduced to one single gene. Instead each gene regulates a few components of a behavior without affecting other aspects of male and female behavior.

The idea is that genes may trigger a wide variety of hormone mixes from life in the womb to old age, and that different "mixes" leads to different combinations of "male" and "female" behavior.

In these experiments the researchers are looking at pretty simple behavioral dimensions. Still, even these dimensions add up to an amazing complexity:

Their website reports:

"Scientists have long suspected that sex hormones ultimately influence gene expression in the brain. About six years ago, Shah and his colleagues set out to find such genes by using DNA microarrays, a routine laboratory assay, to analyze sex differences in gene expression in the hypothalamus, a region of the brain known to be involved with hormone sensing.

"They found 16 genes that were expressed differently between males and females in the hypothalamus and showed that such differences were regulated by sex hormones. But in identifying these 16 genes, Shah and his colleagues also discovered they could tease apart classic, male and female hormone-driven behaviors into individual elements—each governed by its own genes." (...)

Breaker switches

Shah & Co compares the sexual behavior of mice to a  main electrical box with many breaker switches. Male and female behaviors in mice are actually made up of many behaviors, like sex drive or an inclination to fight.

Shah and his colleagues were able to turn off genes with drugs and by other means. They found that they could selectively knock out some male behaviors so that males continued to fight and mark territory normally, but altered their mating routine with females. Likewise they could modulate female mouse behaviors to make them maintain active interest in sex but spend less time caring for their young.

In the case of humans you would have to add cultural and social factors to this mix, which would -- of course --  make the number of variables mindbogglingly large. Still, if you do so, you end up with a model that is very close to the slider model presented by Natalie and myself.

In other words: In humans male and female behavior cannot be reduced to one and only one combination of traits and behaviors, and because of this it is also impossible to develop one "ideal" stereotypical model of how a woman or a man (trans or not) ought to be.

Sexual orientation is, for instance, separate from mating behavior (the copulatory instinct) and -- in the case of humans -- from a sex identity.

(I have no idea of knowing whether a mouse has a sex identity.)

It should be possible, though, to identify a core of genetic and/or hormonal triggers that might lead to the development of a transgender condition.

And as several such triggers exist, the idea that a transwoman is "a woman trapped in a man's body" may make sense. But we would also have to accept that there are people out there with a mix that makes it close to impossible for them to identify with one gender only.

For more on Shah, see my post On hormones, gender, mice and men.

The article, "Modular genetic control of sexually dimorphic behaviors" by Xiaohong Xu, Jennifer K. Coats, Cindy F. Yang, Amy Wang, Osama M. Ahmed, Maricruz Alvarado, Tetsuro Izumi, and Nirao M. Shah appears in the February 3, 2012 issue of the journal Cell.


"Sex hormones such as estrogen and testosterone are essential for sexually dimorphic behaviors in vertebrates. However, the hormone-activated molecular mechanisms that control the development and function of the underlying neural circuits remain poorly defined. 

"We have identified numerous sexually dimorphic gene expression patterns in the adult mouse hypothalamus and amygdala. We find that adult sex hormones regulate these expression patterns in a sex-specific, regionally restricted manner, suggesting that these genes regulate sex typical behaviors. 

"Indeed, we find that mice with targeted disruptions of each of four of these genes (Brs3, Cckar, Irs4, Sytl4) exhibit extremely specific deficits in sex specific behaviors, with single genes controlling the pattern or extent of male sexual behavior, male aggression, maternal behavior, or female sexual behavior. Taken together, our findings demonstrate that various components of sexually dimorphic behaviors are governed by separable genetic programs."

Discuss crossdreamer and transgender issues!