Genocide is neither spontaneous nor episodic. Emerging from biological sciences and from philosophies that encourage and reflect those perspectives, ideas accrete and culminate in racial policies and practices that often become genocidal. These biological and philosophical antecedents began in earnest in the late eighteenth century. By the time of the Nazi rise to power, established thought-patterns about racial hierarchies had come to the fore— as 'science"—in Europe and particularly in Britain and the United States. Biological race theory, which is the primary basis of modern genocide, came from within the scientific, medical, and academic communities—not from without as a political imposition by totalitarian governments. In the twentieth century, the members of the "doctorhood" that formulated, legitimized, and justified biological solutions to social and political problems not only thought, expounded, and wrote about their findings but also acted out their beliefs.