Context: https://www.astralcodexten.com/p/how-are-the-gay-younger-brothers
"Real" means there's at least a 1% difference in likelihood betwen youngest and oldest sibling in a family of any size. Includes any combination of genders.
I think I give it 30%.
One heuristic investigation that might be fun is testing this in some of the SSC surveys as Scott collected data on it there, or in Aella's giant dataset if she collected data on it there. From "to be evaluated whenever stronger evidence comes in", it sounds like this wouldn't be sufficient for resolving it, but it would still be interesting for making bets.
It does in scott's survey i think?
An alternate hypothesis could bring in weird immune stuff, like that thing where people with more older brothers are more likely to be gay because of maternal immunoreactivity to the Y chromosome (which my survey replicates, by the way). But this is a huge stretch and I don’t even know if people are sure this explains the homosexuality results, let alone the birth order ones.