Fat women in mediaeval times would be possibly thinner than an average Western woman now? Have you seen the fattest guy in the World from ~1900s picture he's large but he'd probably fit in an airline seat?

It's really hard to consider these things as "fatter" probably meant larger dowry (!), better survivability, healthier and by extension better for child-rearing. Whilst fatter in Western society now (anorexia, etc., aside) is almost certainly healthier, fitter for child-rearing and such.

Populations were lower and people moved around less, there was far less choice for mates.

But then choosing, rather than falling in love seems strange from where I am.

I’m not saying they were fatter, but that they preferred fatter. Fatness was a proxy for wealth, which meant that it was easier to be emaciated back then, which means people were less likely to be overweight.

Contrast to today where it is easy to be fat, so therefore not hip to be round anymore. That means we’d see more fatter people than in the past because it is easy now.

> As I stated at the end there's historical pretext to this: fat women used to be preferred by men.

Is there a citation? I've heard only the rich were 'plump' in ancient times, though not that it was ever sexually desirable.

> What about homosexual woman? If they both prefer someone taller how does that work?

Nature doesn't always fit our intuition or first hypothesis. IIRC, gay men strongly prefer very fit men, yet they cannot procreate. That struck me as counterintuitive, though if the cause is genetic there could be a variety of factors leading to such genes.

According to the "sneaky bisexual" theory, bisexuality is beneficial because of you can seduce the fit dude maybe he'll let you sleep with his mate, and if he's fit he probably has a high quality mate.

One hypothesis is that gayness is from an evolutionary point of view "too much bisexuality". Similar to how one sickle cell gene is beneficial, but two is deleterious. According to this theory, evolution favors bisexuals, and sometimes produces gays as a side effect of that.

There are probably many factors that determine preference ranging from genetic, enviromental, personal-history, cultural, that determine it either immediately or through some other mechanisms, but we just don't know that yet. In any case preference isn't comparable to an institution, for many reasons beyond the mechanics of preference.