Hence it is not correct to assert that the natural selection caused by the struggle for existence assures the survival of the _best_; in fact, it assures the survival of the best _fitted_.
This is a very great difference, alike in natural Darwinism and in social Darwinism.
The struggle for existence necessarily causes the survival of the individuals best fitted for the environment and the particular historical period in which they live.
In the natural, biological domain, the free play of natural (_cosmiques_) forces and conditions causes a progressive advance or ascent of living forms, from the microbe up to Man.
In human society, on the contrary, that is to say, in the super-organic evolution of Herbert Spencer, the intervention of other forces and the occurrence of other conditions sometimes causes a retrograde selection which always assures the survival of those who are best fitted for a given environment at a given time, but the controlling principle of this selection is in turn affected by the vicious conditions--if they are vicious--of the environment.
Here we are dealing with the question of "social selection," or rather "social selections," for there is more than one kind of social selection. By starting from this idea--not clearly comprehended--some writers, both socialists and non-socialists, have come to deny that the Darwinian theories have any application to human society.
It is known, indeed, that in the contemporaneous civilized world natural selection is injuriously interfered with by _military_ selection, by _matrimonial_ selection, and, above all, by _economic_ selection.[21]
The temporary celibacy imposed upon soldiers certainly has a deplorable effect upon the human race. It is the young men who on account of comparatively poor physical constitutions are excused from military service, who marry the first, while the healthier individuals are condemned to a transitory sterility, and in the great cities run the risk of contagion from syphilis which unfortunately has permanent effects.
Marriage also, corrupted as it is in the existent society by economic considerations, is ordinarily in practice a sort of retrogressive sexual selection. Women who are true degenerates, but who have good dowries or "prospects," readily find husbands on the marriage market, while the most robust women of the people or of the middle class who have no dowries are condemned to the sterility of compulsory old-maiddom or to surrender themselves to a more or less gilded prostitution.[22]