Firstly, for those for whom this topic may be particularly sensitive. I do not maintain that "gender" is entirely genetic, biologic, morphologic, neurological, psychological, or social in nature. Nor do I suppose that gender is binary or even discrete in nature. Nor do I expect that gender is a spectrum which is to say a two dimensional continuum. Rather, I'm inclined to think that one's "gender identity" is composed of a wide variety of highly variable and interconnected elements that create a many-dimensional "gender space" through which individuals may potentially move.

For those of you who aren't interested in the issues important to those who feel ill-served by dominant definitions of gender, feel free to pass over that little disclaimer without thought (though some would reasonably hope you don't).

At any rate. My questions are these:

There are variety of obvious physiological characteristics that have been used to distinguish males from females. Functional morphology of genitalia, skeletal differences and hormonal differences to name a few. Is there any research yet on possible differences in the structure or behavior of the neural networks of males and females? If so, and if there are differences, are they significant enough that gender might be reliably identified by observing the characteristics of an individuals neural structure/behavior? If so, is it possible that some individuals who identify as transgendered might atypically possess the neurological make-up of the "wrong" gender?

Some transgendered people report surprise at finding they don't have a penis upon inspection, for example. Is it possible that their neural body map is actually creating a phantom penis? Might an experiment akin to V.S. Ramachandran's experiments with phantom limbs be able to impact their perception?

sexual dimorphism in the brain has been well established, particularly in some areas of the hypothalamus. It seems to be initiated by the testosterone surge during development that occurs in males.

Might it be possible for an aptly timed testosterone surge to affect the structure of the hypothalamus in individuals with no y chromosome, thus rendering a male-like hypothalamus to an individual that is otherwise female?

yes. In fact, I think this has been done experimentally in rodents. I'll have to check pubmed to confirm this though

BenGreen, I will paste an entry that I made in the 'homosexuality' talk in the 'Cognitive Science & Psychology' folder.

This is relevant, I think, to your second question.

''The thing is... there's plenty of biological evidence for homosexuality. The problem is that it's correlational. The sexual dimorphic nucleus is smaller in homosexual males, differences in the hypothalamus, SCN, and some other structures I can't think of off the top of my head.

Also, they have replicated these brain abnormalities in male and female animal models (primarily rats). Given extra testosterone they act have masculine characteristics and try to mate with other male rats. Give estrogen the same in reverse with females. There's also prenatal evidence. Prenatal stress can alter sexual development (again, done in rats). The mothers were confined in tight Plexiglas tubes for ~2 hrs. each day with bright lights. Very stressful for rat mothers. Anyways, the female pups were fine, but the male rats arched their back as female rats normally do for mating. The reasoning: stress releases endorphins which antagonize the effects of testosterone on the hypothalamus. Stress also causes elvated levels of corticosterone which decreases testosterone release. So the male pups are affected both anatomically in the brain and behaviorally.

Also, how do you explain the androgen insensitivity debate? Born XY but appear as a woman. What would you say about their sexual prefrence? Homosexual because genetically XY or homosexual because they appear and act like women and are attracted to other women? What about intersexuals?''