The mental functions, which are indispensable to organic and to animal life properly so called, quickly attained the degree of development without which the species would have disappeared. On the contrary, the highest “fundamental dispositions” of our nature remained latent for a long time, and only manifested themselves by degrees. But if their development has been slow, it is, in return, continuous and indefinite. And these dispositions tend to preponderate, although the “inversion” of the primitive economy can never become complete. Humanity emerges progressively from animality. The highest civilization is then, at bottom, entirely in conformity with nature: for it is only the manifestation more and more marked of the most characteristic properties of our species. In this sense, our social solution must be understood “as the extreme term of a progression continued uninterruptedly throughout the whole living kingdom from the most simple forms of vegetable life, the predominance of the organic functions becoming less and less exclusive, in order in the first place to make room for the predominance of the animal functions properly so called, and finally for that of the intellectual and moral functions, whose development is the very definition of humanity.”[208] Thus, the chain of being is uninterrupted. But Comte, as we know, did not accept Lamarck’s hypothesis. He believed in the fixity of species. Undoubtedly he admits in a measure which science will some day fix, acquisitions slowly incorporated into organisms by heredity. But he does not think that they will go so far as to transform species. The whole evolution of man must then be explained by its original constitution. Indeed, Comte here maintains, as everywhere in nature, the perfect correspondence between the statical and the dynamical point of view. The case of man cannot be an exception to this encyclopædic law, which is verified in all the orders of phenomena from the most simple to the most complex. As the whole line of the curve corresponds to the equation, so the whole development of humanity must correspond to the “fundamental nature” of man. On this condition alone is sociology possible as a science. Now positive sociology exists: therefore the postulate is justified. II. The theory of the relation between man and animals thus finds itself deduced from the general principles of positive philosophy. But it can also be verified _a posteriori_, through the criticism of the arguments of the adverse theory by means of observation and experience.