The invocation of heredity in problems of this kind is always hazardous. We only throw the difficulty of explanation further back. At what point of the world's history was the morbid taste acquired? If none but tainted individuals are capable of homosexual feelings, how did these feelings first come into existence? On the supposition that neuropathy forms a necessary condition of abnormal instinct, is it generic neuropathy or a specific type of that disorder? If generic, can valid reasons be adduced for regarding nervous malady in any of its aspects (hysteria is the mother, insanity is the father) as the cause of so peculiarly differentiated an affection of the sexual appetite? If specific, that is, if the ancestors of the patient must have been afflicted with sexual inversion, in what way did they acquire it, supposing all untainted individuals to be incapable of the feeling? At this moment of history there is probably no individual in Europe who has not inherited some portion of a neuropathic stain. If that be granted, everybody is liable to sexual inversion, and the principle of heredity becomes purely theoretical. That sexual inversion may be and actually is transmitted, like any other quality, appears to be proved by the history of well-known families both in England and in Germany. That it is not unfrequently exhibited by persons who have a bad ancestral record, may be taken for demonstrated. In certain cases we are justified, then, in regarding it as the sign or concomitant of nervous maladies. But the evidence of ancient Greece or Rome, of what Burton calls the "sotadic races" at the present time, of European schools and prisons, ought to make us hesitate before we commit ourselves to Krafft-Ebing's theory that hereditary affliction is a necessary predisposing cause.[24]