According to Ernst Cassirer, Immanuel Kant was “the man who introduced anthropology as a branch of study in German universities.” And anthropologist W. E. Mühlmann calls Kant “the founder of the modern concept of race.”
All humans are members of the same species, Kant argues, since members of the different races are capable of interbreeding. Nonetheless, there are important sub-divisions — Kant believes there are four main races: white, copper-red, black, and olive-yellow. Yet within the races there are distinctive characteristics of various nationalities — e.g., French, English, German, Italian, and so on. Kant hypothesizes about the source of these differences: “it is here a question of innate, natural character which has, so to speak, its seat in the composition of the human blood.”
Spaniards, for example, must be of mixed blood: “as shown by bull-fights, his character is cruel, which is proved by the auto-da-fé of former times and this shows that his origin lies in part outside of Europe.”
Further afield from Europe, Kant’s method becomes increasingly speculative, as he never left the Königsberg area his whole life. A sample hypothesis about Negroes:
“We know now, for example, that human blood turns black (as is to be seen in blood coagulum) when it is overloaded with phlogiston. Now the strong body odor of the Negroes, not be avoided by any degree of cleanliness, gives reason to suppose that their skin absorbs a very large amount of phlogiston from the blood, and that nature must so have designed this skin that in them the blood can dephlogisticate [sic] itself through the skin to a far greater degree than is the case with us in whom the latter function is mostly performed by the lungs.”
Turning to breeding policy in particular: despite the fact that Kant believes we’re all members of the same species, he opposes reproduction across racial lines:
“The mingling of stocks (due to great conquests), little by little erodes the character and it is not good for the human race in spite of any so-called philanthropy.”
That general proposition was applied by Kant in a letter that he wrote to the governor of Mexico. The Spanish Crown was encouraging a policy of interbreeding and had ordered the Mexican governor to comply. The governor had, however, opposed the order, and Kant wrote this in congratulations:
“[Of the idea that] nature would develop new and better races of produce them through the commingling of two races there is little ground for hope in as much as nature has long since exhausted the forms appropriate to soil and climate, whilst cross-breeding (for example of the American with the European or of these with the Negro) has debased the good without raising proportionately the level of the worse — hence the governor of Mexico wisely rejected the order of the Spanish Court to encourage interbreeding.”
Kant’s account of race also includes the assumption that human perfection can be achieved only by the white race and that the others will become extinct. For details, see Wulf D. Hund’s “‘It must come from Europe’ The Racisms of Immanuel Kant,” which begins and ends with this disturbing quotation from Kant:
“All races will become exterminated …, except for the whites.”
 Cassirer quoted here.
 Mühlmann, quoted in Léon Poliakov, The Aryan Myth: A History of Racist and Nationalist Ideas in Europe (Meridien, 1977), p. 171. A more recent edition.
 Kant, in Poliakov, p. 171.
 Kant, in Poliakov, p. 172.
 Kant, quoted in John Greene, “Some Early Speculations on the Origin of Human Races,” American Anthropologist (1954), 56:31-41, p. 6. Greene gives the source as Kant’s 1785 Bestimmung des Begriffs einer Menschenrace, Gesammelte Schriften (Berlin, 1912), 8: 89-107.
 Kant, in Poliakov, p. 172.
 Kant, in Poliakov, p. 353.
 Wulf D. Hund, “‘It must come from Europe’ The Racisms of Immanuel Kant,” 2011, p. 91.