One will first establish that for manifestations of instinct and for those of intelligence, there is no essential difference between man and animals. The life of all men, quite as well as that of all animals, is based on instinct, and doubtless there is no animal who can not give signs of spontaneity, that is to say, of intelligence. Instinct seems anterior because in all animals except man the quantity and especially the quality of instinctive facts greatly surpasses the value and number of intellectual facts. This is so, but in admitting this hierarchy, if one thereby explain with considerable difficulty, the formation of intelligence in man and in the animals which show more or less perceptible gleams of it, one also renounces by so doing, all later attempts that might furnish some notions as to the formation of instinct. If the bee makes his combs mechanically, if this act is as necessary as the evaporation of warmed water, or the crystallization of freezing water, it is useless to search any further: one is in the presence of a fact which will never yield anything else. If, on the contrary, one consider intelligence as anterior, the field of investigation stretches out to infinity and instead of one problem radically insoluble, one has a hundred thousand or more, as many as there are animal species, and of these problems none is simple, none absurd. This manner of looking at it, brings, I admit, grave consequences. One must then look at matter as a simple allotropic form of intelligence, or, if you prefer, consider intelligence and matter as equivalents, and admit that intelligence is merely matter endowed with sensibility, and that its power of extremely diversifying itself finds impassable limits in the very forms which clothe it. Instinct is the proof of these limits. When acts have become instinctive, they have become invincible. A specie is a group of instincts whose tyranny becomes, one day, deaf to all attempts at movement. Evolution is limited by the resistance of what is, striving against what might be. There comes a moment when a specie is a mass too heavy to be moved by intelligence: then it remains in its place; this is death, but is compensated by the steady arrival of other species; new forms assumed by the inexhaustible Proteus. One will add nothing, here, to this theory, save a few facts favourable to it, and a handful of objections.