Charles Darwin in his famous book "On the Origin of the Species" made it very clear that it is an arbitrary number of categories used to divide up the human species. Some authorities will claim two races, some three, some four, and so on. In addition, Darwin points out the problem of degrees or gradations between the arbitrary number of categories used, which includes many exceptions to any rule.
Since the 1940s, some evolutionary scientists have rejected the view of race according to which any number of finite lists of essential characteristics could be used to determine a like number of races. For example, the convention of categorizing the human population based on human skin colors has been used, but hair colors, eye colors, nose sizes, lip sizes, and heights have not. Many social scientists think common race definitions, or any race definitions pertaining to humans, lack taxonomic rigour and validity. They argue that race definitions are imprecise, arbitrary, derived from custom, have many exceptions, have many gradations, and that the numbers of races observed vary according to the culture examined. They further maintain that "race" as such is best understood as a social construct, and they prefer to conceptualize and analyze human genotypic and phenotypic variation in terms of populations and clines instead.
Many scientists, however, have argued that this position is motivated more by political than scientific reasons. Others also argue that categories of self-identified race/ethnicity or biogeographic ancestry are both valid and useful, that these categories correspond to clusters inferred from multilocus genetic data, and that this statistical correspondence, not necessarily a proven cause and effect, implies that genetic factors somehow contribute to unexplained phenotypic variation among groups.
Answering questions on race is challenging given that most anthropologists regard race as a cultural concept rather than a biological reality. In the biological sciences, the term race has historically been used to describe a distinct population in which all the members share a suite of biological traits. Today, most anthropologists agree that there is no adequate way to divide the world's human population in the cut and dry manner that the definition of race traditionally requires.
Although anthropologists thus no longer classify populations in terms of races, they do recognize that human populations exhibit diverse phenotypes. Different traits are, for example, very useful in the field of forensic anthropology. A forensic anthropologist must extract as much information as possible to assist in the identification of an individual. Part of that job requires identifying that individual's ancestral phenotype. Ancestral phenotypes are suites of traits that are associated with geographic populations. At first, this sounds a lot like a synonym for race; however, the difference lies in the lack of distinct divisions. The task simply relies on the idea that any given individual may have characteristics known to be common in a particular geographic area. Determining ancestry comes from familiarity with the clinal distribution of phenotypic characteristics.
