teristic will reappear in certain of their progeny (that is, some of their children will be feeble-minded) although the characteristic may have been latent for several generations. Obviously, parents who both come from feeble-minded stock are more apt to possess this determinant than parents of diverse stock: hence we see the feeble-mindedness reappearing strikingly in certain cases of consanguineous marriages. The situation with regard to other weaknesses is similar. Marriage of cousins produces a significant number of deaf, or color-blind, or otherwise defective children because these defects were latent in the stock and are brought out by being transmitted through both parents. If the parents in such a case had each married persons not carrying the “determinant” of the defect in question, the defect might not have appeared, but (and this is the consideration which must not be forgotten), the determinant would have been transmitted to a certain proportion of their progeny, to reappear or produce the defect, in later generations when the conditions were favorable.
With regard to points of strength, the situation is the same as with points of weakness. High intelligence and longevity are actualized in the progeny of parents who both possess the determinant, whereas the determinant is in a large pro-
