Brian Hanley
Jan 7, 2018 · 5 min read

Many transgender and gay people are dual sex chimeras

So what’s a chimera? It’s the opposite of twins in one way. It’s also when you are your own twin. Instead of your brother or sister being born with you, the two of you smoosh together, and you’re born as one child. In other words, sometimes two embryos merge one.

We know this happens.We don’t know exactly how often it happens, but it happens. Most people don’t get tested to find out if they are a chimera. Boklage set the upper limit for this kind of chimerism at 60%. But it’s probably 10%-15% of the population.

Do the math on it, and about half the time, there should be a brother-sister pair of twins that merge into one person. So probably 5% to 8% or so of all births should be mixed-sex people. That’s a lot.

What happens when two separate embryonic blastocysts merge into one? Based on what we think we know, most of the time, one of those wraps around the other, and becomes the ectoderm (outer layer) and the other becomes the endoderm (inner core). There’s also a mesoderm layer. What happens with that is anybody’s guess. So, here’s the really interesting part. Gonads (testicles and ovaries), internal organs like liver, intestines, and the heart are made from endoderm.

Guess what is made from ectoderm? The brain and nervous system. The brain starts as a fold in the ectoderm. Skin should also be made from ectoderm.

Now, the obvious question from here is whether it stays that way, or should the brains and gonads of mixed-sex people be a patchwork of cells from both? Except in very rare cases, no, individual organs will be from one twin or the other. There will be a little infiltration. But, in the brain, we have more than just nerves.

The brain also has glial cells (astrocytes, oligodendrocytes, and microglia), and these outnumber neurons. Astrocytes may even be part of the brain’s communications network, or have their own, parallel net. Microglial cells have immune system functions. Whether all these cell types start from the the same ectoderm as the nerves do I don’t know. They might not. So we might have brains that have a mix of male and female, where the nerves are one sex and other cell types are the opposite sex.

How many people are born with a male brain in a female body? Based on the numbers above, it should be around 2.5% to 3.5%. And similar numbers for female brains in male bodies. Those numbers are pretty darn close to what surveys show for homosexuality and transgender people.

I don’t think that every gay or trans person is a chimera. But I think that the majority are, probably the vast majority.

This popular format article you are reading comes from a paper I published 6 years ago in 2011. I am writing it because someone asked me to write it. Like most things, this really started years before 2011. I had thought of this before 2000. In grad school I talked about writing the paper, or trying to study it further. But I was discouraged from doing so by everyone I talked to. There may be acceptance of such studies in the humanities department on most campuses. And, some campuses might be willing to consider it. But I was counseled strongly to leave it alone— it would be a “career killer” in biology. So I left it during grad school.

I kept expecting someone else would publish a similar paper because it seemed so obvious. But nobody did. So I guess I am the originator of this theory of transgender and homosexuality. I think it probably explains most of what we see.

I haven’t exactly been embraced by LGBTQ groups so far. I’ve had a number of transgender people write to me, and also gay men. But in the academic LGBTQ community there is a strong aversion to the “biology is destiny” idea. There are a lot of LGBTQ folk who also reject that idea because to them it feels like they are not their biology.

I understand why biological determinism has been rejected when gay and trans folk are indistinguishable physically from anybody else sharing their gross physical biological gender. Only by using difficult and recent laboratory methods is this possible. People that look biologically male or female, but act the opposite seems to many people to be obvious evidence of weirdness. That generates bullying, mockery, hurtful jokes and more.

Around the world are laws and religious dictates that in some cases have capital punishment for gay and transgender folk. There is widespread harassment and even the nice people have programs to set make gay and transgender people straight.

I think, though, that if this understanding of how chimerism works can be accepted, that it should go a long way toward acceptance.

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