In elaborating his racial classification, Linnaeus departed from his botanical expertise and turned anthropological, even amaeurishly psychological. He told his readers that temperament and character systematically vary from one race group to the next. This essentialism—the idea that there are characteristics that any member of a given race must possess—imprinted public consciousness in ways we still struggle to overcome. Race, more or less as we know it today, entered the scientific canon as a fact of nature.
Kenneth Prewitt, What is Your Race? The Census and Our Flawed Efforts to Classify Americans (Princeton, N.J.: Princeton Univ. Press, 2013), ch. 2