Much of the variation we see in genetic types is due to a random occurance in genetices known as crossover. It is when genes that are linked on one chain of a chromosome are severed and reconnect with the other side of that chromosome. This occurs in the formation of sex cells.

That one in a million births might create a moron or it might create a genius. What if there has been / is being manipulation that stops that process or makes sure that those rare individuals are weighted heavily toward the stupid scale? What would happen to humanity if the barriers were removed? How fast would change occur?