The natural effect of slavery has been a selection of two sorts of individuals along the lines of the survival of the adapted.  It has tended to perpetuate in the breed the qualities of the strong which would make them stronger, and certain qualities in the weak which would increase their weakness.  For parasitism and likewise slavery infallibly entail the degradation of certain structures and an overgrowth of others by the law of use and disuse.  The type of organ which would function normally, were not its possessor parasitic in that function, invariably degenerates or disappears.  Parasitic insects lose their wings.  An entire anatomical system may even be lost.  So the tapeworm, which feeds upon the digested food present in the intestines of its host, has no alimentary canal of its own because it needs none.  On the other hand, the organs of attack and combat grow by a constant use into the most remarkable of efficient weapons.

In human society the process continues.  Out of the tapeworm nature, the tiger nature, the wolf nature, the simian nature, human nature evolves.  Repeated episodes of subjugation and suppression mixed with countless incidents of predaceous cupidity and rapacity have made Man what he is today.  Indeed, by a sort of instinct, society has constructed its institutions upon empirical observations and assumptions agreeing with this principle.  The deductions concerning human nature and human traits that an interplanetary visitor would draw from a study of our common law would be at least slightly humiliating to our incorrigible pride.  Law courts, codes of civil contract and criminal procedure, the systems of subordination in armies and navies, castes and classes, men and women, employers and employees, teachers and pupils, parents and children, are based upon the fundamental, the conservative axiom that man, especially the common plain man (Lincoln’s phrase), is a being incurably lazy, stupid, dishonest, muddled, cowardly, greedy, restless, obsessed with a low cunning and a selfish callousness and insensibility to the sufferings of his fellow creatures, animal and human.

Why is it that Man, the noblest creature of creation, made in the image of God, capable of the flights of attainment that distinguish a Christ, a Caesar, a Plato, a Shakespeare, a Shelley, a Newton, is so described, not alone by hopeless pessimists like Koheleth, Swift, and Mark Twain, but by the common law, the common opinion, the common assumptions of mankind?  Because the development of slavery and parasitism in human society, the subjection of the weak to the strong, the dull and base to the clever and headstrong, set up a vicious cycle:  the liberation of more energy for the making of more and more slaves and the propagation of slaves and slave qualities in a geometrically increasing proportion.