You wouldnt need full BP or Schizophrenia to justify this -- if partial traits to partial degrees confer advantage, then the full constellation of them may be dysfunctional in an individual but worth preserving for net benefits. Evolution does not operate at the level of individuals, so most in practice, are often dysfunctional in many respects.

As for schizophrenia, see it is an exageration of rule-seeking and pattern-seeking behaviour, an over-imparting of consciousness and intention to the world, a (disregulated) sense of significance. But each of these are vital for survival and procreation in less extreme degrees.

As for BP, hypomania seems plainly adaptive in some cases (eg., esp. having sex a lot, working a lot, ...); and "hypo-depression" likewise (eg., low opporunitites for winter work, retreating, conserving, less risk takign, etc.).

It also seems adaptive that we would swing between these, so we can better explore the mood-space of motivation.

You just extremize that and you get disfunction

Someone posted an article a while ago that claimed the ratio of people with ADHD, autism, etc. lined up with Dunbar’s number (the theoretical preferred size of a social group) so that there would be about one individual per group with these traits. The article then went on to theorize that this was an evolutionary adaptation against total conformity. Even if everyone else doesn’t see the landslide in the distance the one weirdo might.

I can’t find the article after searching on hn.algolia.com but IIRC there was no real evidence for this, it was just a theory.

Don't know much about BPD, know a little more about schizophrenia. The genes that make you predisposed to schizophrenia seem to positively impact creativity and certain types of creative output. A gene doesn't necessarily have to have a good outcome for everybody with that gene, so long as it results in enough good outcome to make up for it.

I think of this with homosexuality. What is the possible evolutionary advantage to homosexuality? Well there's lots of reasons why we would want humans to be attracted to both men and women, so they're reproduce, and it's not hard to see how genes that cause that could make people gay.

Religion.

"It's not paranoia when they're really out to get you"