Also changes eye shape over time, causing vision issues, etc.. Longer you're up there the more starts to go wrong. We were built to fight off gravity. I think its worth considering that it may be fundamentally impossible for humans to reproduce/gestate babies/live entire lifetimes/generations in low gravity conditions.

Well there's a world of difference between micro-gravity (where there have been problems with nice) and low gravity like on the moon (where there's been no experiments)

If you did have viable babies in low (not zero) gravity situations though, would you in fact be starting a new species.

It's not clear when a new specie is different from the previous one, but you probably need:

* Like 100.000 years, probably more. (From the split of us from chimps 5.000.000 I counted like 30 species in https://en.wikipedia.org/wiki/Human_evolution , but the number depends a lot on who count them.)

* Isolate the populations so they can't interbreed (first because they can't meet and later becuse the dna is incompatible)