Usage Note: The notion of race is nearly as problematic from a scientific point of view as it is from a social one. European physical anthropologists of the 17th and 18th centuries proposed various systems of racial classifications based on such observable characteristics as skin color, hair type, body proportions, and skull measurements, essentially codifying the perceived differences among broad geographic populations of humans. The traditional terms for these populationsCaucasoid (or Caucasian), Mongoloid, Negroid, and in some systems Australoidare now controversial in both technical and nontechnical usage, and in some cases they may well be considered offensive. (Caucasian does retain a certain currency in American English, but it is used almost exclusively to mean ?white? or ?European? rather than ?belonging to the Caucasian race,? a group that includes a variety of peoples generally categorized as nonwhite.) The biological aspect of race is described today not in observable physical features but rather in such genetic characteristics as blood groups and metabolic processes, and the groupings indicated by these factors seldom coincide very neatly with those put forward by earlier physical anthropologists. Citing this and other pointssuch as the fact that a person who is considered black in one society might be nonblack in another, many cultural anthropologists now consider race to be more a social or mental construct than an objective biological fact.