Social selection weeds out the unfit, the murderer, the most unsocial man, and says to him: "You must die"; natural selection seeks out the most fit and says: "You alone are to live." The difference is important, for it marks a prime series of distinctions, when the conceptions drawn from biology are applied to social phenomena; but for the understanding of variations we need not now pursue it further.

The contrast may be put, however, in a sentence: in organic evolution we have the natural selection of the fit; in social progress we have the social suppression of the unfit.
Given social variations, therefore, differences among men, what becomes of this man or that?
We see at once that if society is to live there must be limits set somewhere to the degree of variation which a given man may show from the standards of society.

And we may find out something of these limits by looking at the evident, and marked differences which actually appear about us.
First, there is the idiot.

He is not available, from a social point of view, because he varies too much on the side of defect.

He shows from infancy that he is unable to enter into the social heritage because he is unable to learn to do social things.