Skin color is the primary physical criterion by which people have been classified into groups in the Western scientific tradition. From the earliest classifications of Linnaeus, skin color labels were not neutral descriptors, but connoted meanings that influenced the perceptions of described groups. In this article, the history of the use of skin color is reviewed to show how the imprint of history in connection with a single trait influenced subsequent thinking about human diversity. Skin color was the keystone trait to which other physical, behavioral, and culture characteristics were linked. To most naturalists and philosophers of the European Enlightenment, skin color was influenced by the external environment and expressed an inner state of being. It was both the effect and the cause. Early investigations of skin color and human diversity focused on understanding the central polarity between “white” Europeans and nonwhite others, with most attention devoted to explaining the origin and meaning of the blackness of Africans. Consistently negative associations with black and darkness influenced philosophers David Hume and Immanuel Kant to consider Africans as less than fully human and lacking in personal agency. Hume and Kant's views on skin color, the integrity of separate races, and the lower status of Africans provided support to diverse political, economic, and religious constituencies in Europe and the Americas interested in maintaining the transatlantic slave trade and upholding chattel slavery. The mental constructs and stereotypes of color-based races remained, more strongly in some places than others, after the abolition of the slave trade and of slavery. The concept of color-based hierarchies of people arranged from the superior light-colored people to inferior dark-colored ones hardened during the late seventeenth century and have been reinforced by diverse forces ever since. These ideas manifest themselves as racism, colorism, and in the development of implicit bias. Current knowledge of the evolution of skin color and of the historical development of color-based race concepts should inform all levels of formal and informal education. Awareness of the influence of color memes and race ideation in general on human behavior and the conduct of science is important.
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