Galton's eugenics to his theory of races, Vacher de Lapouge's "selectionism" aimed first at achieving the annihilation of trade unionists, considered to be a "degenerate"; second, creating types of man each destined to one end, in order to prevent any contestation of labour conditions. His "anthroposociology" thus aimed at blocking social conflict by establishing a fixed, hierarchical social order. The same year, William Z. Ripley used identical racial classification in The Races of Europe (1899), which would have a great influence in the United States. Other scientific authors include H.S. Chamberlain at the end of the 19th century (a British citizen who naturalized himself as German because of his admiration for the "Aryan race") and Madison Grant, a eugenicist and author of The Passing of the Great Race (1916). Madison Grant provided statistics for the Immigration Act of 1924, which severely restricted immigration of Jews, Slavs, and Southern Europeans, who were subsequently hindered in seeking to escape Nazi Germany. Human zoos Human zoos (called "People Shows"), were an important means of bolstering popular racism by connecting it to scientific racism: they were both objects of public curiosity and of anthropology and anthropometry. Joice Heth, an African-American slave, was displayed by P.T. Barnum in 1836, a few years after the exhibition of Saartjie Baartman, the "Hottentot Venus", in England. Such exhibitions became common in the New Imperialism period, and remained so until World War II. Carl Hagenbeck, inventor of the modern zoos, exhibited animals beside humans who were considered "savages". Congolese pygmy Ota Benga was displayed in 1906 by eugenicist Madison Grant, head of the Bronx Zoo, as an attempt to illustrate the "missing link" between humans and orangutans: thus, racism was tied to Darwinism, creating a social Darwinist ideology that tried to ground itself in Darwin's scientific discoveries. The 1931 Paris Colonial Exhibition displayed Kanaks from New Caledonia. A "Congolese village" was on display as late as 1958 at the Brussels' World Fair. Theories about the origins of racism Evolutionary psychologists John Tooby and Leda Cosmides were puzzled by the fact that in the US, race is one of the three characteristics most often used in brief descriptions of individuals (the others are age and sex). They reasoned that natural selection would not have favoured the evolution of an instinct for using race as a classification, because for most of human history, humans almost never encountered members of other races.