On average Black people have a lower IQ and and higher testosterone than White people. On average White people have a lower IQ and higher testosterone than Asians.

High testosterone is associated with violence.

There is a similar birth curve where black people on average have more babies but fewer survive than white and white more and fewer survive than Asian.

This explains birth rate differences and why mixing populations causes strange social effects.

These are provably correct but any discussion about it is considered taboo and controversial.