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Immune Cells Play Key Role in Determining Male or Female Traits in the Brain (neurosciencenews.com)
69 points by laurex 6 months ago | hide | past | web | favorite | 31 comments

There has always been some speculation that immunology plays a role in sexual traits given the fraternal birth order effect (i.e. a son is more likely to be homosexual the more older brothers he has) [0].

0. https://www.ncbi.nlm.nih.gov/pubmed/28608293

why would the presence of a fraternal birth order effect mean that it's immunological?

The paper explains,

According to this maternal immune hypothesis, cells (or cell fragments) from male fetuses enter the maternal circulation during childbirth or perhaps earlier in pregnancy. These cells include substances that occur only on the surfaces of male cells, primarily male brain cells. The mother’s immune system recognizes these male-specific molecules as foreign and produces antibodies to them. When the mother later becomes pregnant with another male fetus, her antibodies cross the placental barrier and enter the fetal brain. Once in the brain, these antibodies bind to male-specific molecules on the surface of neurons. This prevents these neurons from‘‘wiring-up’’in the male-typical pattern, so that the individual will later be attracted to men rather than women.

It doesn't, but apart from this study the mothers's body is somehow able to remember how many sons she has had and influence the sexuality of her later sons. This memory of past exposure to a foreign object (i.e. a foetus) is the hallmark of immunology.

I assume that it would be the mother’s immune system (sensitized by previous pregnancies) response affecting the fetus while in utero.

Could this play a role in causing Gender dysphoria?

Maybe. Maybe not.

From what I read on the topic, it's much more complicated. People have plenty of typical-female or typical-male parts of brain slushed around, generally people tend to have the most of them that correspond to their gender (IIRC you can guess gender/sex correctly about 80 or 90% of the time by looking at the brain).

It may contribute along with other factors for the cases where the brain does express gender dysphoria.

Gender dysphoria also isn't a clean distinction between "male" and "wanting to be female". The underlying phenomenon is observed to be rooted in sex-specific instincts and feelings inverse to what is normally found in people of the same sex. The interpretation is cultural. Indians believe it means there are two spirits in a single body, Mexicans have the "mux", and even in the west there's been tacit admission by some trans people that they feel different but couldn't tell you they were actually female...the oft-maligned "nonbinary".

So really, I don't personally believe a brain can be cleanly male or cleanly female. Rather, if specific parts are formed differently than usual, then they respond differently to external stimuli. This can result in a wide range of sex-atypical behaviour ranging from mere homosexuality to finding one's genitals revolting. How you interpret that objective phenomenon is really up to the individual.

I think the brains that are cleanly male-trait or female-trait are very very rare, most are a mix but there is usually enough difference to be able to make a very good guess.

Though I also do agree that gender dysphoria can have many different expressions, once you drop gender you get into a whole new world of stuffs where people hate various things about themselves (I've met people with self-described "whole body dysphoria" who are generally okay with their gender and simply hate the physical existence of their body)

To grossly summarize a cocktail factoid - bird cells can individually differentiate, and some birds are truly half and half. Us mammals bombard our cells with hormones, constantly telling them how to differentiate, as though we were some sort of eusocial insect colony.

Yes, other animals have found rather interesting ways to differentiate into genders, IIRC in some cases it's temperature, in others hormones, others do it genetically and I think in a few it's merely "how many females are in my group?", where gender can flip to benefit reproduction.

Does this mean that antihistamines could have an effect on brain development?

Yes, but you'd probably need to take them for long periods at high doses during crucial developmental stages, to provide continuous blockade of the system. Note also receptor specificity and blood brain barrier penetration of over-the-counter anti-histamines may lead to less-than-exciting results.


As someone who is homosexual, I'm... not entirely certain I disagree with that classification. From a purely biological standpoint, if I act on what my body would very much like me to continue doing, I will never reproduce. It's not a lethal condition, but it's an evolutionary dead end, so ... close enough? I haven't studied biology or medicine in great detail though, so I don't know the proper distinctions for something to be considered a disease.

Either way, I don't see the point in trying to be politically correct about what I call myself, or how other scientists try to classify me. My condition is an oddity, a trait is a trait, and classifying those traits is what biological sciences are all about. I think science is awesome, so more of that please. :)

You're not an evolutionary dead end. Evolution takes place at the level of genes, not individuals. If you contribute to the survival and reproductive success of your family, then the genes you have in common with them will live on.

Think of the honey bee. Most of the individuals in the hive will never reproduce but they all contribute to the survival of the genes they share in common.

Humans in a family are not all identical like worker bees but the principle of gene conservation and propagation is the same.

This is an important thing to keep in mind. Survival of a species and a family can be more than just whether or not you reproduce, it can depend on how each individual contributes to a group to ensure overall survival.

And another example of an eusocial species would be the naked mole rat. In the end I think it should be more than fair to say that we are past the point of needing to pass on our genes absolutely, particularly because we're already straining Earth's resources without further encouraging reproduction.

It almost certainly is an evolutionary dead end. That is why it is equally almost certainly not determined genetically.

That logic doesn't add up, regardless of your, or anyone's, position.

There are many genes that are expressed naturally, or through mutation, that would remove from reproductive ability.

How about genetic disorders that kill the individual in their infancy thus guaranteeing they will not pass on the gene? Homosexuals are technically able to reproduce should they insist on it.

Kind of throws a spanner in you lack of logic... Do you think this inability to reach a valid conclusion based on a set of inputs is a choice or genetic?

I don't think it's a good comparison, because those genetic disorders are usually single gene mutations, and much rarer than homosexuality. In many cases we know the exact enzyme that's broken and how it causes the disease. In the case of homosexuality, there are genetic markers that are statistically associated with it, but no clear proof of genetic causation. The genetic aspect could be indirect, by changing susceptibility to environmental factors.

> it is equally almost certainly not determined genetically

The point of the now almost flagged comment I was replying to (quoted above to make it easier to follow) is that being unable to reproduce is proof that the condition is not genetic. Whether it's one gene or a collection, that they are rare or common, that we know the mechanism in detail or not, becomes irrelevant in this context.

The inability to reproduce "proves" only that you are unable to reproduce. There is no conclusion that one can draw from this regarding the cause: genetic mutation, accident, etc. Unless you (or the serial downvoters who most likely didn't bother to understand what I said) can prove the connection implied by the poster above, I see no argument to contradict my statement.

The correct response is that "disease" doesn't carve reality at the joints. The sort of people that would call homosexuality a disease are doing it so they can then conclude "therefore, it must be cured". They're taking a noncentral example of "disease" and wildly generalizing.

See also: "MLK was a criminal and therefore was bad/should be locked up", "Taxation is theft and therefore bad", etc etc

Very good point. I studied a lot of Philosophy in college, and the postmodernist movement drove me nuts, but Foucault had a very good point in his paper on mental illness, that mental illness is socially constructed. The way I'd formulate the definition of a disease is that it's an atypicality that has a significant negative impact. What's a negative impact though? That's a value judgment, and most everyone has a value system that agrees in cases like cancer, but not on homosexuality. It's even situationally dependent. There is evidence that soldiers that measure higher on measures of psychopathy are more effective in conventional combat because they do not hesitate to kill.

Too bad you won't reproduce. You seem like an intelligent specimen of the human race.

Mate, we're humans. If zeta wants offspring, zeta has myriad ways of producing zeta-derived offspring.

Indeed, but you left your point unstated.

What if homosexuality is a naturally occurring trait that arises more frequently in the presence of environmental pollutants (say endocrine disruptors or whatever causes allergies)?

This is not implausible; in fact I’d be surprised if it weren’t probable (that enviromental pollutants affect human brain development and therefore sexuality)

What are the consequences or the course of action -if any - that should be taken?

Yes, I did leave out my point.

I have come across this before when I was a biologist many years ago. Homosexuality does not look like a genetic trait. It looks remarkably like a disease state - even an infectious one at that. But the first and last time I discussed this with other biology students, the reaction was very bad.

Research like this may get interpreted politically, and therefore ignored or even suppressed and the researchers lose credibility.

I do not know what you would interpret as natural, but homosexuality is detrimental for the persistence of a species. It is entirely a dead-end. The correct action to be taken is to prevent and/or counter the agent that causes this.

> homosexuality is detrimental for the persistence of a species. It is entirely a dead-end.

How do you state this with such confidence? In an overpopulated world, homosexuality may be beneficial for the survival of our species. Homosexuals who do not reproduce potentially provide nanny-power to family units, or parenting power to orphans. It is in no way clear cut that "the correct action to be taken is to prevent and/or counter the agent that causes this." This is crazy talk.

well, given that this article in particular is saying that increased inflammation signaling is associated with male traits, it'd be better suited for arguing that straight males (and possibly homosexual women) are the diseased ones. Not that that's any better.

Inflammation is not a disease, contrary to the countless blog posts by non-doctor bloggers. It is a somewhat natural reaction of the human body that is there to make things better. Like any bodily function it can go awry.

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