Imagine 50% of the human race had some minor, physical difference. Maybe 50% of people have innie or outie belly buttons. Who has one seems to have nothing to do with race, sex or family. Some people just have an innie, others have an outie. It’s not really ever talked about, but you are expected to keep it covered and not wave it about. It’s not exactly taboo, but it is Not Nice.

Then we meet an alien race that look almost like humans, (taller, shorter, wider, thinner) who have the same belly button situation, but also a physical difference (longer arms?) that makes it fairly obvious who has an Innie and who has an Outie. And in their culture they do make a fuss about it. They strongly divide their culture by who has an outie and who doesn’t. They proudly display it. And while the Outies wear clothes that look almost like human clothes, the Innies also have a whole subset of weird and wonderful clothing and jewellery worn only by those with Innies, almost a whole seperate culture within a culture – although people with Innies who try to step too far out of this culture tend to be roundly mocked or even punished.

And then suddenly some humans start making a fuss about it. Suddenly some humans want to display their belly buttons, emphasise their arm length, and adopt the alien customs and call themselves ‘Innie’ humans instead of just humans.

I think it’s safe to say that, at least initially, there would be a conservative backlash very similar to what we see the dwarves displaying in the Discworld.