In Piedmont Carolina down to 1900, the members of any church married other members of the same congregation 3 times out of 4. In the mountain counties of western N. Carolina, the inhabitants were divided into small isolates chiefly by topography; the young people generally marrying some one along the creek on which they lived. The opportunity to select a mate, before the automobile era was confined to a dozen or so individuals of the opposite sex. Human mating is one of the most selective activities in the whole world and, as applied to uncommon recessive pathological traits, there is no such thing as random mating in this population.