On the other hand, every species comprises, independently of the individuals which have preserved their primitive characters, all those which compose the primary, secondary and tertiary, etc., races, derived from the fundamental type. In other words the _species_ is the _unit_ and the _races_ are the _fractions_ of this unit. Or again, the _species_ is the _trunk of the tree_, of which the _several series of races_ represent the _principal_ and _lesser branches_ and the _twigs_. The general unity and relative independence of the trunk and the branches of the tree represent in an obvious manner the connections existing between the species and its races. CHAPTER IV. NATURE OF VARIATIONS IN ANIMAL AND VEGETABLE RACES; APPLICATION TO MAN. I. The meaning of the question stated above is now intelligible. We have to discover whether the human groups, which we know to be distinguished by characters which are often very marked, are fractions of a single unit, branches of the same tree, or so many units of different value, so many trees of various nature. Historical documents are absolutely incapable of solving this problem. On the other hand, man being the subject of the problem, it is evident that the solution must be sought elsewhere. Where then must we turn in order to obtain a definite answer to this question which concerns us so closely? Clearly to naturalists and to naturalists alone. The Species and the Race have, for more than two centuries, been the subject of their studies; they have amassed observations, multiplied experiments. They have, in their studies, been guided by a scientific spirit alone, and from being placed beyond the reach of controversy, have preserved all their freedom of judgment. The results thus acquired, deserve the greatest confidence, and supply reliable data for the application of our anthropological method. Anyone really desirous of forming an opinion upon the unity or multiplicity of the human species, should therefore discover what are the facts and phenomena which characterise race and species in plants and animals; then turn to man and compare the facts and phenomena there presented with those which botanists and zoologists have observed in the other kingdoms. If the facts and phenomena which distinguish the human groups are those which, in other organised and living beings differentiate _species_, he will then legitimately infer the multiplicity of human species; if, however, these phenomena and facts are characteristic of race in the two inferior kingdoms, he must conclude in favour of specific unity. It is the pursuance of this course which has convinced me of monogenism, and I am certain the result will be the same with anyone who will follow it.