Wednesday, July 26, 2017

What Science Has to Say about Gender Identity

Today President Trump announced that transgender individuals would not be allowed to serve in the U.S. Military.  This follows a previous Trump reversal of guidelines put in place by President Obama regarding how public schools should handle their transgender students’ use of bathrooms. In discussions of these issues, a distinction is often made between “biological sex” and a psychological state of “gender identity” with the latter weighted as less important, less biological, or less real. Political commentator Ben Shapiro, for example, illustrates the attitude in his response to a transgender rights advocate questioning him at a recent lecture: “I’m not going to modify basic biology because it threatens your subjective sense of what you are.”  [Emphasis added.]  This sort of statement presupposes that Mr. Shapiro understands the basic biology, which I'm sure he doesn't given that biologists are still working it out.  

What we do know from basic biology is that the classic model of sexual differentiation is probably wrong.  

There is a classic understanding of the biology of sex: X and Y gene expression leads to the determination of female or male gonads (ovaries, testes), which in turn secrete hormones that lead to a wide range of sexual differentiation in females and males from external genitalia to body size and shape to behavior.  Recent research, however, has demonstrated a more complex biology in which non-gonadal sex differences, including in the brain and the behaviors it controls, result from gene expression directly in these non-gonadal tissues.  Much of the evidence for this new view has come from a range of animal studies demonstrating that manipulation of hormone levels does not fully account for non-gonadal sexual differentiation, even when it comes to behavior. To provide one example, castrated male zebra finches develop normal male song patterns and hormone-modified genetically female finches, who develop testes as a result of the hormone manipulation, nonetheless retained their normal female song pattern.

If it is the case, as the existing science indicates, that biology operates along parallel pathways to determine and differentiate male and female phenotypes, then it is biological feasible that genetic variation could lead to individuals with mixed sex differentiation, that is, with the gonads of one sex and a brain that leans the other way.  One theory is that transgender individuals are the phenotypic realization of this biological state of affairs. 

To put it into lay terms that policy makers and political commentators can understand, what this may mean is that your subjective sense of what you are IS due to basic biology even if it disagrees with your gonads.  And if this is true, the individual who Shapiro chastised might have responded, "I'm not going to modify basic biology because it threatens your subjective sense of what I am."

To be clear, science does not yet have a definitive answer regarding the biology of gender identity. The underlying biology is complex and particularly difficult to study in humans.  But at the same time, it is quite clear that if lawmakers, lawyers, and presidents are to engage in a debate that turns on biology, then state-of-the-art biological science must be part of the discussion. 



William Matchin said...

Do you have any references for the theory that transgender people result from conflicting genetic and gonadal factors? That would be very useful!

Piero said...

This is absolute nonsense. No other animal species has "transgender" individuals. They do have homosexual or bisexual ones, but certainly not transgender individuals who, though having a penis, refrain from attempting to copulate with females because they "feel" they are female (and mutatis mutandis for the fenale case).

Greg Hickok said...

Have a look at Eric Vilain's work. Here's a link to an article about him and his work in Nature:

Greg Hickok said...

Not even sure how you'd measure transgenderism in animals and therefore how you know something similar doesn't exist. The finch example I mentioned seems to contradict your assertion. Moreover, even if it were unique to humans doesn't mean it isn't biological. We are animals after all and there are things that are unique to humans with a biological basis, e.g., language.

Russ Hedger said...

Small point, but gonads secrete (not excrete) hormones.

squirrelywrath2 said...

re Piero: No other animals exhibit schizophrenia or dyslexia either, however both certainly exist.

Greg Hickok said...

Thanks for catching that, Russ. I've updated the post.

Jeebus 420 said...

Non-gonadal genetic factors are still be tied to genes on the sex chromosomes as per the cited sources, so not sure how this relates to transgender brains. And I think intersex conditions like androgen insensitivity kind of rule out the idea that non-hormonal factors are more important in determining gender identity.

PolitelyCorrect said...

Doesn't this article do little more than attempt to refine the 'basic-biology'-defined term, "gender," into something self-determined by the the individual?

If so, Mr Shapiro is right in so far that he's been expected to redefine something objectively determinable into something entirely subjective.

Furthermore, if we are to allow the established definition to be so-redefined, then we risk it remaining entirely subjective (and fluid (no pun)) for the foreseeable future -- we'd be expected to have a vastly improved understanding of neurology itself, in order to determine gender... This begs the question of why we'd bother trying to determine it - at all - beyond the 'basic biological' sense we already have.

Finally, I fail to see how the finch example does anything more than reinforce the position that gender is biologically determined.

Antonia Hamilton said...

This account assumes there is a 'male brain' and a 'female brain' that are distinct and somehow feel different. I thought we'd moved beyond that?

Greg Hickok said...

PolitelyCorrect, the main point of the article is that the biology of gender is more than sex organs, that genes act also directly on the brain (rather than just through hormones secreted by the gonads) that presumably shape aspects of behavior. Exactly how this works is not known. But it does suggest that whether one identifies as male or female (1) is biologically, i.e., genetically, driven and (2) not necessarily the same as the sex of the individual as determined by sex organs. This is a different view that Mr. Shapiro's, who seems to assume that the biology of sex is all about the gonads and any psychological deviation from one's "gonadal sex" is cultural or self-determined by the individual, as you put it.

You are correct that we don't understand the neurology of gender identity, but it is quite clear now that gender is more complicated that the simple model Shapiro assumes. This fact needs to be part of the political discussion.

The finch example shows that gonadal sex and the hormones they secrete are dissociable from sex-specific behaviors, suggesting a non-identical underlying biology.

Greg Hickok said...

Antonia, I think we *have* moved beyond that with respect to many things but to deny sex differences in the brain is to deny the facts. The most obvious example is mating preference. The vast majority of females prefer to mate with males and vise versa. That is a massive psychological difference that presumably has a basis in the brain and the genes that shape it (there are compelling reasons why evolution should favor such a difference). And now there is new emerging evidence for sex differences in the brain and behavior coming out of the connectome and other large scale projects. I've listed a few below. This doesn't mean better or worse, imply a strict dichotomy, or justify differential treatment is the social arena. Rather, it shows that sex differences exist in the population distribution of various brain traits and my article raises the possibility that gender identity is one of them.

Ingalhalikar, M., Smith, A., Parker, D., Satterthwaite, T. D., Elliott, M. A., Ruparel, K., . . . Verma, R. (2014). Sex differences in the structural connectome of the human brain. Proc Natl Acad Sci U S A, 111(2), 823-828.

Tunc, B., Solmaz, B., Parker, D., Satterthwaite, T. D., Elliott, M. A., Calkins, M. E., . . . Verma, R. (2016). Establishing a link between sex-related differences in the structural connectome and behaviour. Philos Trans R Soc Lond B Biol Sci, 371(1688), 20150111. doi: 10.1098/rstb.2015.0111

Paus, T., Wong, A. P., Syme, C., & Pausova, Z. (2017). Sex differences in the adolescent brain and body: Findings from the saguenay youth study. J Neurosci Res, 95(1-2), 362-370.

PolitelyCorrect said...

Hello Greg,

Thank you for the reply. Respectfully, I'd say that this implies little more than greater/additional biological forces in play; including those which impact the development of the brain.

Without wanting to dwell too much upon Ben Shapiro, I don't think his statement has been at all negated -- this line of thinking you present here suggests he could've simply inserted 'even' before "basic biology."

The evidence of more complex biological considerations simply doesn't override the basic ones; surely at least not until they're better understood.


Greg Hickok said...

Hi PC,
You seem to draw a distinction in biology between genetic effects on sex organs and genetic effects on brain and behavior. Why? Why would a biological effect on one organ (gonads) be more "basic" than a biological effect on another (brain)?

PolitelyCorrect said...

Hey Greg,

Yeah, I can see how I could be clearer.

The basic/complex distinction here pertains to genetic outcomes, rather than processes; indeed it's you yourself who points out the complexity of the brain (neurologically/psychologically), compared to reproductive organs.

My main point here is that neither are self-determined -- both are biological. As another commenter points to: this seems to reinforce the idea that there is a male & female brain; to which you've agreed; at least to the extent that there are undeniable sex differences.

So where would this leave us in terms of the issue itself?.. That Male vs Female identification is not just a 'basic' case of reproductive organs, but could also be determined by more complex issues involving genetic outcomes on something as complex as the brain?...

..Not to mention how much of a challenge it would be to draw any socially-beneficial distinction of these effects (even after they're better understood), between what is a genetic/biological effect vs a social/psychological one.

...Could people conceivably identify as 'neurologically Male,' but 'gonadally' female (I realise you're not actually arguing this - but to illustrate my point re potentially infinite convolution of terms).

Not to say that this nor any other state-of-the art scientific pursuit isn't worthy, but I it think fair to say that -- right now -- that in any practical sense, our 'basic' biology is our best determination of gender.

Finally, in the linked video, Ben Shapiro seems to primarily argue that gender isn't something "malleable." Everything heretofore, from yourself included, seems to support that - at least for now - and until our understanding of the less 'basic' biological factors is better.

Greg Hickok said...

Hi PC,

So it sounds like you are stipulating that sex organ development is "basic" whereas brain develop is not "basic" even if both are under genetic control. I don't understand why you would assume that?

Let back up and think about first principles. Suppose you want to build a species that reproduces sexually. You design female and male types with appropriate reproductive organs. How do you make sure they mate? If they don't, they will quickly go extinct. You need to build in an instinct to mate, attraction, drive, etc. You might also want to build in different criteria for mating attraction depending on whether your species is tournament or pair-bonding and fine tune the males vs females for parental investment factors. So where do you build that in? In the organ that controls behavior, of course.

The point is, you can't point to the gonads and say "that's the basics of sex & gender." It takes a brain configured in the right way to make sure the organs get used to successful reproduction.

If you have to have genetic programs for the sex organs and the brain, then it becomes possible that the two can mismatch leading to individuals that are neurologically male but gonadally female, as you say.

Shapiro is right, I think: gender isn't malleable. But he's wrong in assuming that it is determined only by the gonads and that it is unmalleably male or female; "mixed" individuals are quite possible given the basic biology.

PolitelyCorrect said...


My words were "genetic outcomes, rather than processes." Even assuming any and all formative bioprocesses equal, a formed brain is more complex than are reproductive organs; as you've already outlined (and indeed very well made the point yourself); least not by highlighting that our understanding of one is much more advanced than the other.

One could argue that this is the very definition of basic/complex - at least the basic one...

Re species building: the point apparently well made and understood by all is that the human brain is more complex than those we see in the rest of the kingdom. I'm sure this needs no emphasis. The psychological effects of the complexities of our societies also can't be overlooked, when attempting to draw equivalencies.

This really speaks to the core of the argument.. A trans person may argue that their gender is beyond all science - including the basic/understood along with the complex/state-of-the-art - and that it is purely and ultimately subjective/self-determined, as a sentient human being, and as the only one who lives inside their own head and feels their own feelings.

Indeed they may very well be right... Considering even potential scientific advances well-beyond our current stage, who's to say that someone shouldn't be able to self-identify as: reproductively-male, neurologically-female, yet emotionally and sexuality either or fluid.

Personally I wouldn't, either now or even with a much advanced understanding of the neurology of the issue. If they're happy then I'm happy.

However, for now and the foreseeable future, we do live in a society wherein we do have to draw practical distinctions - beyond small group social/ interpersonal ones.

As such, and only when necessary, and with the utmost respect and courtesy (Shapiro could probably do better here), we have little choice to rely upon the science we can consider most pragmatically reliable -- even if there exists the possibility that it will one day be negated, undermined or even completely superseded...

I think it pretty fair to refer to use the term "basic biology" in reference to this current level of understanding.


Greg Hickok said...

I think a better solution is to remove the adjective and just talk about biology. Here the scientific facts indicate that sex is not determined just by the gonads as many, including Shapiro, seems to assume, but by additional biological (genetic) effects that operate in parallel to gonadal influences. Calling these additional biological influences "complex" does not remove them from biology or diminish their relevance.

Here is an interesting review article for you to look at, which provides details of the arguments. The title is telling in the context of this discussion: "The end of gonad-centric sex determination in mammals"

Here is a link to an open-access version of the article in full:

PolitelyCorrect said...

And so, by this logic, Shapiro would've been correct by simply leaving out the word "basic." This has kinda been my point, all along..

I.e. 'I’m not going to modify biology because it threatens your subjective sense of what you are.'

As for your assertion: "Calling these additional biological influences "complex" does not remove them from biology or diminish their relevance" -- I made no such insinuation; the opposite, if anything.

Your own words (asterisks added): "The underlying biology is ***complex*** and particularly difficult to study in humans. But at the same time, it is quite clear that if lawmakers, lawyers, and presidents are to engage in a debate that turns on biology, then ***state-of-the-art*** biological science must be part of the discussion.

As for adjectives... this issue, perhaps more than other currently contentious one, is all about adjectives/pronouns/semantics. Although I'd agree with anyone who thought too much importance is being placed upon them.

Thank you for the article. Ben himself may also find it reinforcing...


Greg Hickok said...

No, deleting "basic" doesn't make Shapiro's statement correct. It seems we are talking past each other at this point. Thanks for your comments!

PolitelyCorrect said...

Perhaps I'll finish by rephrasing "correct" to 'not incorrect.'

Thank you very much, too :)

Apolon KAF. said...

They do. Due to hormonal adnormallities some animals behave as the "opposite" sex. Beyond that, ypur argument is invalid. Just because something happens only to some spiecies and not others(although is not like this, as i said) it doesnt make it less real. There are studies which show that trabs people have the same brain activity on the gender areas in the brain, as the gender they identify with. So its real and not a choise or a modernistic point of view for gender.