Question for all you biologists/geneticists/sociologists amongst us: Is there a possibility that because of polarised wealth distribution and the classification of humans an increased rate of birth defects or fertility problems would arise when someone from a historically high-caste breeds with someone from a historically low-caste?

I am curious because it seems weird that with seven billion humans heavily discriminating against each other there wouldn't be some sort of niche segregation.

Curious to hear your thoughts.