In a state of nature the weaklings perish.  If man interferes with this state of nature in the lower animals, he may make a selection and cultivate some particular attribute.  This is artificial selection, and is best exemplified in the experiments with pigeons.  Pasteur saved the silk industry of France, and perhaps of the whole world, by the application of this law of artificial selection.  The disease of silkworms, known as Pebrine, was spreading with ruinous rapidity in France.  Pasteur demonstrated that the germ of the disease could be detected in the blood of affected moths by the aid of the microscope.  He proved that the eggs of diseased moths produced unhealthy worms, and he advised that the eggs of each moth be kept apart, until the moth was examined for germs.  If these were found, the eggs were to be burned.  Thus the eggs of unhealthy moths were never hatched, and artificial selection of healthy stock stamped out a disease, and saved a great industry.

Each individual plant in the struggle for life has only itself to maintain.  In the higher forms of animal life, each animal has its offspring as well as itself to maintain.  In a state of nature, that is in a state unaffected by man’s rational interference, defective offspring and weaker brethren were the victims of the inexorable law of natural selection.  When Christ gave his reply to the question, “Am I my brother’s keeper?” the defective and the weakling became the special care of their stronger brother.  They constituted thenceforth The Fit Man’s Burden.  The work a man has to do during life, in order to support himself, is the unit of measurement of the burden he has to bear.  Many factors in modern times have helped to reduce that work to a minimum.  The invention of machinery has multiplied his eyes, his hands, his feet; and one man can now produce, for his own maintenance and comfort, what it took perhaps a score of men to produce even a century ago.  Man’s disabilities from incidental and epidemic disease have been immeasurably reduced by modern sanitation, and the teaching and practice of preventive medicine.  Agricultural chemistry has made the soil more productive, and manufacturing arts have aided distribution as well as production.

All the departments of human knowledge have been placed under contribution to man’s necessity, and longer life, better health, and more food and clothing for less work, are the blessings on his head to-day.

While the burden has been lessened by the industrial and scientific progress of the last half century, it has been augmented by the fertility of the unfit; and the maintenance in idleness and comfort of the great and increasing army of defectives constitutes the fit man’s burden.  The unfit in the State include all those mental and moral and physical defectives who are unable or unwilling to support themselves according to the recognised laws of human society.  They include the criminal, the pauper, the idiot and imbecile, the lunatic, the drunkard, the deformed, and the diseased.  We are now face to face with the startling fact that this army of defectives is increasing in numbers and relative fertility.