 The ambiguities and confusion associated with determining the boundaries of racial categories have led to the widespread position that discrete or essentialist races are socially constructed, not biologically real. However, significant scholarly debate persists regarding whether reproductive isolation, either during human evolution or through modern practices barring miscegenation, may have generated sufficient genetic isolation as to justify using the term race to signify the existence of non-discrete human groups that share not only physical phenotypes but also clusters of genetic material. In addition, scholarly debate exists concerning the formation and character of socially constructed, discrete racial categories. For instance, some scholars suggest that race is inconceivable without racialized social hierarchies, while others argue that egalitarian race relations are possible. Finally, substantial controversy surrounds the moral status of racial identity and solidarity and the justice and legitimacy of policies or institutions aimed at undermining racial inequality.