Zoologist Desmond Morris wrote a book about this, called "The Human Zoo". When immersed in "diversity," people experience as much stress as tribesmen plunked down in another (rival) tribe. In the Stone Age, this would routinely lead to you getting killed. These stress hormones, says Morris, lead to sickness, cancer and early death. Malcolm Gladwell wrote about this in his book "The Outliers". It's called "The Roseto Effect". In mono-racial, homogeneous societies there was no heart-disease, crime or welfare. The inhabitants of the town [Roseto] were medical outliers because of their cohesive community. This lasted for decades . . . until diversity was introduced. Crime spiked, social cohesion broke down and their disease rates started to match surrounding "diverse areas".

• Footnote: Desmond Morris did a social experiment. He paid an actor to pretend to collapse in a diverse city. No one came to help him. The only interaction the white actor had was when a black man saw him as vulnerable and mugged him. They then re-enacted this social experiment in a homogeneous setting [in Malta]. People immediately ran to his aid and helped him. You can watch this on a BBC documentary: https://www.youtube.com/watch?v=nsU4WRVpS-k&t=779s (Fast forward to around the 7:30 mark)