Race, for most people, is a fundamental organizing principle in our society. People are divided and categorized into groups based on physical characteristics associated with different groups of people and assumed to be based on genetic difference. Although race does clearly have some relation to biology in reproducing superficial physical differences, it has been argued that race is primarily a sociopolitical construct created "by powerful groups for the purposes of maintaining and extending their own power" (Spickard, 1992: 13). Peter Li, a Canadian sociologist, has argued that the process of racial labeling is highly dependent on geographic, economic and social contexts that arise in different periods of history. Depending on particular contexts, "racialization" takes place, a process by which "groups are singled out for unequal treatment on the basis of real or imagined phenotypical characteristics" (Li, 7). The categories that exist today are largely a product of colonial times, during which a racial hierarchy was established to legitimize colonialism and institutions of racism. However, Spickard also notes that race can be a powerful tool for the self-actualization of minority groups who derive commonality from external and internal recognition of shared group identities (Spickard, 1992). Because race is such a fundamental ordering principle within society, mixed race people pose a dilemma for categorization; in which categories do multiracial people belong? In the past, multiracial people were often not permitted to delineate and assert their own identities and were often forced to accept externally imposed categorization. For example, laws of hypodescent in the United States dictated that individuals with even a slight trace of African heritage were classified as black. Today, in a nation that is confronted with the necessity of tolerance in the face of growing racial and ethnic diversity, mixed race people have the opportunity to reject socially constructed single categories of race. Their existence points to the tenuousness and irrelevance of the concept that people are biologically determined and separable into "pure" races; they pose a fundamental challenge to a social order defined on the basis of race.