Page:Popular Science Monthly Volume 71.djvu/87

Rh of those possessing traits making for success. It probably means selectional disadvantage, owing to the heavy incidence of reproductive selection on "successful" families.

International migration to a new country is another case of selective dissociation. The American colonists were undoubtedly, on the whole, men of superior initiative and independence of character. Their coming to America made possible the multiplication of their descendants and their kind. Even our present-day immigrants are rather superior in point of energy to those of the same economic condition who remain behind, and they come to an environment presenting greater opportunities.

Urban migration is a notable example of selective dissociation. According to the indications of anthropological and other evidence, it is the more energetic element that migrates from country to city. Under conditions prevailing down into the nineteenth century, cities could not maintain their population by natural increase. Migration to the city then meant subjection to an unusually severe incidence of lethal selection. Our modern sanitary improvements have not yet entirely removed the disadvantage of the city as compared with the country.

We have mentioned selection by society as possible, but not a very important fact. The execution of criminals and their imprisonment, so far as it prevents reproduction, are cases of such selection. In crueller ages, with numerous capital crimes and many executions a year, this may have been an important mode of selection. Now it amounts to little. Perhaps public opinion, also, puts certain members of society under some selective disadvantage.

Francis Galton has proposed that society deliberately undertake the improvement of the human stock. He would have certificates of fitness issued and suggests the giving of marriage portions to girls of superior personal qualities and good family. Such a program of "eugenics" would operate through reproductive selection. It is an interesting proposition, if not very practical. Hitherto the method of evolution has been essentially negative, that is, primarily the elimination of the unfit. Will any human society ever be wise enough positively to map out the line which further evolution shall take? The definition of what is undesirable is much simpler than the definition of what is most desirable.

In the above brief review of the incidence of selection in man, it has been the intention of the writer merely to give examples illustrative and suggestive of the applicability and importance of the