But while Darwinists admit the perpetual _instability_ of specific forms and their _transmutation_, the illustrious professor of Cambridge believes in their _absolute immutability_. Upon this fundamental point he is in exact opposition to Darwin. In 1840, whilst proclaiming the unity of the human species, he admits that the diversity which it presents is the result of _original physical differences_. This is really nothing more than a mitigated polygenism; and, like every polygenistic doctrine, compels its author to place man in contradiction to general laws. In 1845, Agassiz himself accepted this consequence in a memoir upon the geographical distribution of animals and man. He attributed the diversities of both to the same causes. “But,” he adds, “whilst in every zoological province animals are of _different species_, man, in spite of the diversity of his _races_, always forms one and the same species.” The following year he declared his belief in “an indefinite number of primordial races of men created separately.” Agassiz has collected and developed all his theories in a memoir inserted at the beginning of the great polygenistic work entitled _Types of Mankind_. It is clear that Nott and Gliddon, the authors of this work, were perfectly aware of the real meaning of a doctrine which proclaims the specific unity of man, while at the same time admitting that the human races have been created separately with all their distinctive characters. We, also, must not be deceived, but recognise Agassiz as a true polygenist. I shall, therefore, be obliged to make all those objections to the theory of the eminent naturalist which have already been stated. Moreover, the singular association which he has endeavoured to establish between the _unity of species_ and the _original characterisation of races_, has led him into contradictions and consequences which are peculiar to him, and which it would scarcely be possible to pass by in silence. Agassiz, like the greater number of polygenists, gives no intimation of what he means by the word _race_. Yet he makes use of it incessantly and declares, for example, that he is ready to show that “the differences existing between human races are of the same nature as those which separate families, genera, and species of apes or other animals....” “The chimpanzee and the gorilla,” he adds, “do not differ from each other more than Mandingoes from the Negroes of Guinea; there is less difference between either of them and the orang, than there is between the Malay or the White and the Negro.”