One of my good friends discovered her biological half-brother on 23andMe who she had never been told about. They met up, and got along remarkably well, and have actually remained pretty close since! These things do happen. Glad you got something out of it, too.

Yeah, these experiences may or may not be rare. I was positing that they might be rare mostly to try to meet the person I was responded to halfway and because I don't actually have evidence one way or the other

While perhaps not as immediately "positive" an experience, there was a bunch of press last year about how consumer DNA tests were uncovering that incest was much more common than previously believed:

https://www.theatlantic.com/health/archive/2024/03/dna-tests...

That’s definitely interesting to learn you are the great great son of an incest !

Did you find out your cousin was gay through 23 and me or from him?

IIRC, his first and last name were visible to me in 23 and me, so I googled him and saw that we was a therapist with a focus on the LGBT community, so then I messaged him through 23 and me, told him a bit of my story and asked him if he was gay.

This is not the sort of thing a genetic test can determine

Give it time...

It might not happen. Fingerprints are partly heritable – immigration delay disease, for example, has an identifiable point mutation – but you'd be laughed out of the room if you tried to suggest that given time, we would eventually be able to predict fingerprints from genomes.

Non-heterosexual behaviour can be observed in most social amniotes, even those without fingerprints. Genetically-identical twins do not have identical sexual proclivities. There's no a priori reason to believe there's even a "gay gene" to find.

I looked it up, and twin studies say sexual orientation is party genetic, but it's far from the only factor.

So at most a perfect genetic test could give a percentage chance of someone being gay/straight.

I guess that's pretty much what you said.

And either gayness is evolutionarily beneficial (kin selection?), or it's so fundamental to amniote psychology that evolution can't get rid of it. (Or both, I guess.)

So you're saying they aren't born that way but it's learned? DSM2 called and something something something.

That is very much not what is being said.