This is when evolution kicks in. Those that can pair up and have children are more likely to be selected for in future generations

Medicine has improved such that it is far less of an evolutionary pressure. I imagine psychological well being, and wealth are more of an issue. It would be interesting to look at the correlation between mental health and wealth, or if there’s a key point between them.

Or there could be a selection pressure for more social groups of humans, a eusocial society, I can’t remember who suggested that.