England and Normandy, at that time, hence it is obvious that the theoretical number has been greatly reduced in every generation by consanguineous marriages, even though they were between persons so remotely related that they did not know they were related. C. B. Davenport, indeed, has calculated that most persons of the old American stock in the United States are related to each other not more remotely than thirtieth cousins, and a very large proportion as closely as fifteenth cousins.
Fig. 41.—A living individual who was a lineal descendant of George Washington might well take pride in the fact, but genetically that fact might be of very little significance. The above chart shows graphically how small a part any single ancestor plays, a few generations back. A general high average of ability in an ancestry is much more important, eugenically, than the appearance of one or two distinguished individuals.
At any rate, it must be obvious that the ancestors of any person of old American stock living to-day must have included practically all the inhabitants of England and Normandy, in the eleventh century. Looking at the pedigree from the other end, William the Conqueror must have living to-day at least 16,000,000 descendants. Most of them can not trace back their pedigrees, but that does not alter the fact.