It’s a question that’s baffled evolutionary theorists for decades: if survival of the fittest is the rule, how have the genes that contribute to serious, debilitating mental disorders survived?
It’s been shown that people who suffer from schizophrenia, autism, anorexia and other disorders are less likely to have children. And yet, the genes that cause these disorders aren’t going away. In fact, some of the disorders appear to be becoming more common. Evolutionary theory wouldn’t predict that.
Scientists have a few theories that attempt to explain this paradox.
One is that the genetic mutations that cause these disorders occurred relatively recently, so not enough generations have passed to allow the evolutionary process to weed them out.
Another theory is that the genetic mutations that cause a disorder in one person somehow make that person’s sibling more likely to have children. In a situation like that, the mutation offers a net benefit to a person’s family.
by DAVID SCHULTZ, NPR