“But,” say those writers who deny the reality of a distinction between species and race, “what man has done nature must be able to do also, for she governs space and time, and is therefore more powerful than man.” This form of argument rests upon a confusion of ideas and a strange neglect of the most ordinary facts. Most true, nature is more powerful than man in certain cases and for certain ends, but man also has his domain, in which he is much superior to nature. Natural forces act in virtue of blind and necessary laws, the result of which is constant. Now man has acquired the knowledge of these laws, he has made use of them to constrain and master the natural forces one after another, he now knows how to exaggerate some and to weaken others. In this manner he changes their resultants, and obtains products which nature herself could not realise. Give to the latter all the time and space that you will, she would never be able either to produce or preserve potassium or sodium in a metallic form; in spite of the physico-chemical forces, or rather by directing them, man has obtained and preserved these two metals, as he has obtained and preserved the Ægilops triticoïdes, which is destroyed by the inflexibility of natural forces as soon as it is exposed to their action. VIII. The infertility, or, if you will, the restricted and rapidly limited fertility between species, and the impossibility of natural forces, when left to themselves, producing series of intermediary beings between two given specific types, is one of those general facts which we call a _law_. This fact has an importance in the organic world equal to that rightly attributed to attraction in the sidereal world. It is by virtue of the latter that the celestial bodies preserve their respective distances, and complete their orbits in the admirable order revealed by astronomy. The _law of the sterility of species_ produces the same result, and maintains between species and between different groups in animals and plants all those relations, which, in the palæontological ages, as well as in our own, form the marvellous whole of the _Organic Empire_.