 Modern European philosophers played a key role in the development of the concept of race as a way to characterize, and rank, differences among human groups (Bernasconi 2018; Valls 2005; Ward and Lott 2002; Bernasconi and Lott 2000). Philosophers in the modern era (roughly from 1600 to 1900) often disagreed on the nature of race, the source of racial differences, and the correlations between race and non-physical characteristics. Kant, Rousseau and Mill, for example, disagreed over the critical issue of whether racial differences were mutable (Kant 2012; Elden and Mendieta 2011; Boxill 2005). Defining race in terms of underlying biological features emerged well after the language of race had become familiar. The biology of race continues to elicit controversy over whether it has explanatory value (Kitcher 2007; Spencer 2015,  ; Glasgow et al. 2019).