A while back, I wrote an essay that showed that androphilic Male-To-Female transwomen had a greater Fraternal Birth Order Effect (FBOE) than gay men as populations. This is evidence that gender atypical androphilic males are more likely to have a FBOE etiology than more gender typical androphilic males. But I saw pushback from some in the transgender community that didn’t understand the science, didn’t understand that there could be, and is strong evidence that there are, other etiological factors that can cause gender atypical androphilia in males. There was anecdotal comments about, and even a long list of, first born androphilic transwomen (at least one included me), as “proof” that the FBOE had nothing to do with androphilic transwomen’s etiology.

Sigh…

This reminds me of the type of argument that goes like this, “I had a large lunch today… so clearly there is no hunger problem in the world.”

But, in any event, we now have evidence that the underlying cause of the FBOE can and has operated in some first born androphilic males, including transwomen. One of the chief hypothesis of the cause of the FBOE is the ‘Maternal Immune Response’ in which key proteins in male only development during a pregnancy enters the mother’s blood stream where the mother’s immune system creates antibodies to fight off a mistaken “infectious agent”… the male child. This in turn passes back to the male fetus where it interferes with normal male sexually dimorphic brain development, leading to a feminized brain. The FBOE effect would then come about because each male pregnancy increases the amount and strength of the immune response. Each male pregnancy increases the chances of the next male pregnancy resulting in an androphilic gender atypical male child, including the chance of an androphilic MTF transkid.

We now have what may be the ‘smoking gun’ and at the same time strong evidence that it may also operate in first born males, not just subsequent male children. Testing for a specific antibody suspected to be the cause has shown that mothers of gay sons have more than those who have had only straight sons. What’s more interesting, is that mothers of only first born gay sons and androphilic MTF transkids showed the same effect, as this graph shows, though not as strong as those mothers of gay sons who had older brothers… indicating a progressive effect leading to the progressive FBOE.

Let me state that again, the underlying cause of the FBOE can and does operate in some first borns !

So, Please. No more bad logic regarding potential FBOE etiologies in androphilic transwomen?

Further Reading:

Essay on FBOE being a stronger effect in androphilic transwomen

Reference:

Bogeart, et al, “Male homosexuality and maternal immune responsivity to the Y-linked protein NLGN4Y” (2018)

https://doi.org/10.1073/pnas.1705895114