PUB: James, Michael. "Race." STANFORD ENCYCLOPEDIA OF PHILOSOPHY May 28, 2008.

The concept of race signifies the grouping of individual humans by some set of perceived physical characteristics, often called “phenotypes,” which are thought to be inherited through some blood-born factor. Which specific set of perceived, shared physical characteristics constitute a race varies historically, geographically, socially, and politically. Indeed, there is no biological or genetic foundation for the grouping of individual humans into a racial group. Instead, humans themselves choose (consciously or unconsciously) which physical characteristics constitute a racial group. Consequently, racial groups are presently thought to be social constructions, or a category created not by biological nature but by human invention. However, from its origins in the early modern era until the twentieth century, race was not considered a social construction but a real, biological distinction transmitted from one generation to the next. Thus, racial identity was thought to be something fixed and imposed genetically. As a result of this biological conception, racial groupings are typically thought of as discrete, meaning that the boundaries between them are determinate. Where one racial group ends, a distinct other racial group begins. If human phenotypes are simply considered to be gradual variations in things like skin color, hair texture, or bone structure, then one cannot really speak of distinct human races. Rather, such differences would simply reflect variations in physical traits, such as the variation between very straight versus very curly hair. To speak of race, then, requires classifying humans into discrete groupings based upon a set of putatively inherited physical characteristics. Note that the discrete character of racial groups holds even when we speak of “mixed race” people, since this term implies that a “mixed” individual has ancestry from two or more discrete racial groups. Determining the boundaries of discrete races has proven to be the most vexing problems for those thinkers who sought to classify humans according to race, and led to great variations in the number of human races believed to be in existence. Thus, some thinkers categorized humans into only four distinct races (typically white or Caucasian, black or African, yellow or Asian, and red or Native American), and downplayed any phenotypical distinctions within racial groups (such as those between Scandavians and Spaniards within the white or Caucasian race). Other thinkers, drawing boundaries around different physical traits, classified humans into many more racial categories, for instance arguing that those humans “indigenous” to Europe could be distinguished into discrete Nordic, Alpine, and Mediterranean races. The ambiguities and confusion associated with determining the boundaries of discrete racial categories has over time provoked a widespread scholarly consensus that that race is socially constructed, while advances in the understanding of human genetics has undermined scholarly belief in the biological foundations of discrete races. However, significant scholarly debate persists regarding the relationship between racial groupings and social or political processes. For instance, some scholars suggest that race is inconceivable without racialized social hierarchies, such that racial identities are always organized so that some races are portrayed as superior while others are inferior. In addition, scholars dispute whether racial categories are defined only by members of superior racialized groups or whether subordinate groups themselves contribute to and maintain racial categorization. Finally, there is some controversy as to whether some real genetic differences may validly be used to categorize individual humans into breeding populations, even though these categorizations do not fit the socially constructed racial groups that may be recognized within any given society. . . . Read the rest here: http://plato.stanford.edu/entries/race/.