"It will be seen at a glance," Dr. Penrose writes, "that early in the history of the Malone family these indications of degeneracy were absent; but they began in the fourth generation and rapidly increased afterward until they culminated by the presence of five idiots in one family. The original stock was apparently excellent, but the present state of the descendants is deplorable."
Now three generations of emigration from a little community, which even to-day has only 1,000 inhabitants, would naturally make quite a difference in the average eugenic quality of the population. In almost any population, a few defectives are constantly being produced. Take out the better individuals, and leave these defectives to multiply, and the amount of degeneracy in the population will increase, regardless of whether the defectives are marrying their cousins, or unrelated persons. The family of five idiots, cited by Dr. Penrose, is an excellent illustration, for it is not the result of consanguineous marriage—at least, not in a close enough degree to have appeared on the chart. It is doubtless a mating of like with like; and biologically, consanguineous marriage is nothing more.
Honesty demands, therefore, that consanguineous marriage be not credited with results for which the consanguineous element is in no wise responsible. The prevailing habit of picking out a community or a strain where consanguineous marriage and defects are associated and loudly declaring the one to be the cause of the other, is evidence of the lack of scientific thought that is all too common.
Most of the studies of these isolated communities where intermarriage has taken place, illustrate the same point. C. B. Davenport, for example,