[Sidenote: Belief in the blighting effect of incest may have helped to institute the forbidden degrees.] Thus the belief that incest or sexual crime in general has power to blast the fruits of the earth is widespread and probably goes back to a very remote antiquity; it may long have preceded the rise of agriculture. We may conjecture that in its origin the belief was magical rather than religious; in other words, that the blight was at first supposed to be a direct consequence of the act itself rather than a punishment inflicted on the criminal by gods or spirits. Conceived as an unnatural union of the sexes, incest might be thought to subvert the regular processes of reproduction, and so to prevent the earth from yielding its fruits and to hinder animals and men from propagating their kinds. At a later time the anger of spiritual beings would naturally be invoked in order to give a religious sanction to the old taboo. If this was so, it is possible that something of the horror which incest has excited among most, though by no means all, races of men, sprang from this ancient superstition and has been transmitted as an instinct in many nations long after the imaginary ground of it had been forgotten. Certainly a course of conduct which was supposed to endanger or destroy the general supply of food and therefore to strike a blow at the very life of the whole people, could not but present itself to the savage imagination as a crime of the blackest dye, fraught with the most fatal consequences to the public weal. How far such a superstition may in the beginning have operated to prevent the union of near kin, in other words, to institute the system of prohibited degrees which still prevails among the great majority of mankind, both savage and civilised, is a question which deserves to be considered by the historians of marriage.[408]
[Sidenote: Explanation of the seeming contradiction in the foregoing customs.] If we ask why it is that similar beliefs should logically lead, among different peoples, to such opposite modes of conduct as strict chastity and more or less open debauchery, the reason, as it presents itself to the primitive mind, is perhaps not very far to seek. If rude man identifies himself, in a manner, with nature; if he fails to distinguish the impulses and processes in himself from the methods which nature adopts to ensure the reproduction of plants and animals, he may leap to one of two conclusions. Either he may infer that by yielding to his appetites he will thereby assist in the multiplication of plants and animals; or he may imagine that the vigour which he refuses to expend in reproducing his own kind, will form as it were a store of energy whereby other creatures, whether vegetable or animal, will somehow benefit in propagating their species. Thus from the same crude philosophy, the same primitive notions of nature and life, the savage may derive by different channels a rule either of profligacy or of asceticism.