Accord and discord between organs and acts.--Tarses and sacred scarab.--The hand of man.--Mediocre fitness of sexual organs for copulation.--Origin of "luxuria."--The animal is a nervous system served by organs.--The organ does not determine the aptitude. --Man's hand inferior to his genius.--Substitution of one sense for another.--Union and rôle of the senses in love.--Man and animal under the tyranny of the nervous system.--Wear and tear of humanity compensated by² acquisitions.--Man's inheritors. Translator's Postscript Bibliography: Practical Works Consulted THE NATURAL PHILOSOPHY OF LOVE CHAPTER I THE SUBJECT OF AN IDEA Love's general psychology.--Love according to natural laws.--Sexual selection.--Man's place in Nature.-- Identity of human and animal psychology.--The animal nature of love. This book, which is only an essay, because its subject matter is so immense, represents, nevertheless, an ambition: one wanted to enlarge the general psychology of love, starting it in the very beginning of male and female activity, and giving man's sexual life its place in the one plan of universal sexuality. Certain moralists have, undeniably, pretended to talk about "love in relation to natural causes," but they were profoundly ignorant of these natural causes: thus Sénancour, whose book, blotted though it be with ideology, remains the boldest work on a subject so essential that nothing can drag it to triviality. If Sénancour had been acquainted with the science of his time, if he had only read Réaumur and Bonnet, Buffon and Lamarck; if he had been able to merge the two ideas, man and animal into one, he, being a man without insurmountable prejudices, might have produced a still readable book. The moment would have been favorable. People were beginning to have some exact knowledge of animals' habits. Bonnet had proved the startling relationships of animal and vegetable reproduction; the essential principle of physiology had been found; the science of life was brief enough to be clear; one might have ventured a theory as to the psychological unity of the animal series.