Here is an interesting article from Unz Review that argues that maladaptive genetic changes have become more common due, ironically, to the technological improvements made possible by the industrial revolution. Basically, in the past, those children with poor genes that were divergent from the norm tended to die off early on and thus would be less likely to reproduce and pass those adaptations on to the next generation.
Until the Industrial Revolution, we were under harsh conditions of Darwinian Selection, meaning that about 40% of children died before they reached adulthood. These children would have been those who had mutant genes, leading to poor immune systems and death from childhood diseases. But they would also have had mutant genes affecting the mind. This is because the brain, home to 84% of the genome, is extraordinarily sensitive to mutation, so mental and physical mutation robustly correlate. If these children had grown up, they might have had autism, schizophrenia, depression… but they had poor immune systems, so they never had the chance.
Under these conditions, prevalent until the nineteenth century, we were individually selected for but we were also “group selected” for. Ethnic groups are simply a genetic extended family and some groups fared better against the environment and enemy groups than others did, due to the kind of partly genetic psychological adaptations they developed.
