questions, rather than proximate or "how?" questions. "How?" questions are more directly tackled by behavioral genetics research, which aims to understand how genes and environment impact behavior. The search for biological origins of psychological phenomena has long involved debates about the importance of race, and especially the relationship between race and intelligence. The idea of white supremacy and indeed the modern concept of race itself arose during the process of world conquest by Europeans. Carl von Linnaeus's four-fold classification of humans classifies Europeans as intelligent and severe, Americans as contented and free, Asians as ritualistic, and Africans as lazy and capricious. Race was also used to justify the construction of socially specific mental disorders such as "drapetomania" and "dysaesthesia aethiopica"—the behavior of uncooperative African slaves. After the creation of experimental psychology, "ethnical psychology" emerged as a subdiscipline, based on the assumption that studying primitive races would provide an important link between animal behavior and the psychology of more evolved humans. Psychologists take human behavior as a main area of study. Much of the research in this area began with tests on mammals, based on the idea that humans exhibit similar fundamental tendencies. Behavioral research ever aspires to improve the effectiveness of techniques for behavior modification. Early behavioral researchers studied stimulus–response pairings, now known as classical conditioning. They demonstrated that behaviors could be linked through repeated association with stimuli eliciting pain or pleasure. Ivan Pavlov—known best for inducing dogs to salivate in the presence of a stimulus previously linked with food—became a leading figure in the Soviet Union and inspired followers to use his methods on humans. In the United States, Edward Lee Thorndike initiated "connectionism" studies by trapping animals in "puzzle boxes" and rewarding them for escaping. Thorndike wrote in 1911: "There can be no moral warrant for studying man's nature unless the study will enable us to control his acts." From 1910–1913 the American Psychological Association went through a sea change of opinion, away from mentalism and towards "behavioralism", and in 1913 John B. Watson coined the term behaviorism for this school of thought. Watson's famous Little Albert experiment in 1920 demonstrated that repeated use of upsetting loud noises could instill phobias (aversions to other stimuli) in an infant human. Karl Lashley, a close collaborator with Watson, examined biological manifestations of learning in the brain. Embraced and extended by Clark L. Hull, Edwin Guthrie, and others, behaviorism became a widely used research paradigm.