Human variation, historically a topic of much opinion, debate, and fallacy, is ruled today by deoxyribonucleic acid (DNA) technology that was absent from early classification systems. Before the onset of European exploration in the late 15th century, it was believed that humans were descended from a single pair and should not be placed into different categories as other animals were. However, the discovery of diverse cultures on different continents prompted scientists such as Linneaus, Buffon, Blumenbach, and Cuvier to distinguish Homo sapiens by physical and cultural characteristics. Carolus Linneaus, the first of these scholars, added temper, behavior, and dress to the already traditional division of skin color. Comte de Buffon, the next scientist to describe the human “race,” did so by categorizing different peoples by their geographic location. However, Buffon did not separate people into different species as Linneaus did. In 1781, Johann Friedrich Blumenbach moved away from cultural traits altogether in his classification system and the limited set of physical characteristics he described were assumed to be finite for five varieties of people. Baron Georges Cuvier condensed these groups even further into basic “white,” “yellow,” and “black.” As one of the last classification scholars, Cuvier moved to eradicate the “Great Chain of Being,” which placed humans (unsurprisingly, Europeans) at the top of the animal hierarchy.
In the mid-19th century, scientists and anthropologists began to use a different approach to the question of human variation by quantifying observed physical characteristics. This was done through anthropometry, the measuring of the body and body parts, particularly skulls, and noting variation between supposed ethnic groups. Samuel Morton measured skulls, and his conclusions are now believed to reflect his own stereotypes about certain groups of people. The cephalic index, a construct of Anders Retzius, was also used to compare different groups of people by cranial measures, which placed them into two categories: dolichocephalic and brachycephalic. However, one of the problems with craniometric analyses is that people from extremely different geographic locales may show similarities, giving questionable basis for division.
The number of “types” of people, however, lingers in a state of disagreement over characteristics that define a “race.” Thus, there have been many different definitions of the race concept. One of the broadest and currently accepted of these definitions was suggested by Huxley and Haddon in the 1930s and is the replacement of the word race with the term ethnic groups. The most conclusive definitions emphasize that the human species is polytypic, with different features loosely corresponding to certain geographic areas. There are three main ways that these differences come about: environmental adaptations, population genetics, and migration.
First, there are adaptive environmental traits unique to certain locales. Perhaps the best documented of these is sickle-cell anemia, an inherited disease in which red blood cells that are normally disk shaped are crescent shaped. The sickle-cell gene is common in Africa because it serves a distinct selective purpose. Those who carry one copy of the gene are resistant to malaria, a mosquito-borne illness. Those who carry two copies of the gene, however, have sickle-cell disease (SCD) and rarely live to reproductive age. Because of the pressures malaria places on those who live in high-risk areas such as Africa, populations in those environments have adapted and now possess a genetic trait indicative of their ancestry.
Sickle-cell anemia is an environmental adaptation that cannot be observed externally. The largely misinterpreted concept of skin color, however, can be. The rate in which melanin (a skin pigment) is produced varies with different skin types. Melanin levels are higher in darker-skinned people and lower in fairer-skinned people, and this variation is found latitudinally. Those living in lower latitudes have darker skin, where the abundance of melanin helps block harmful ultraviolet radiation. The lighter skinned are found in higher latitudes, where a lack of melanin allows more sunlight to be absorbed. More sunlight means greater processing of vitamin D, a vitamin necessary for strong bones.
Along with environmental adaptations, population genetics is another way to explain human variation. In all organisms, the foremost means of achieving variation is through genetic mutation, specifically point mutation. Point mutations occur when a single nucleotide base is added, deleted, or replaced. If the mutation is advantageous to the organism, it will be passed on via natural selection. The aforementioned example of sickle-cell anemia is one such instance. It is probable that a human cell thousands of years ago underwent a mutation that produced the sickle-cell gene, consequently providing malarial immunity. Those individuals without a copy of the sickle-cell gene may have contracted malaria and died without producing their full potential of offspring at a higher rate than those that did have a copy of the gene. In contrast, people with one copy of the sickle-cell gene did not die of malaria and probably still retained full reproductive abilities, thus passing the gene on to offspring. Over thousands of generations (and malaria outbreaks), the frequency of the sickle-cell gene increased.
Finally, the third means of producing variation in humans is through migration and genetic drift. Over time, humans have always traveled, taking their varied gene pools with them. This means that people mated with people from other populations with different sets of genes, increasing genetic variation. The opposite, genetic isolation, can occur as well. A product of catastrophe or new habitation, isolation produces less variability within, but more variation between, populations.
Therefore, although there are several mechanisms in which human variation occurs, overall they are insignificant. During the recent mapping of the human genome, it was found that the DNA between any two individuals is about 99.9 percent identical. Hence, the concept of “race” based on individual physical variation has been rendered inaccurate, and scientists have in essence given up on a once popular notion.
References:
- Gould, S. J. (1981). The mismeasure of man. New York: Norton Press.
- Harrison, G. A., Tanner, J. M., Pilbeam, D. R., & Baker, P. T. (1988). Human biology: An introduction to human evolution, variation, growth, and adaptability. Oxford: Oxford University Press.
- Marks, J. (1995). Human biodiversity: Genes, race, and history. New York: Aldine de Gruyter Press.
- Molnar, S. (2002). Human variation: Races, types, and ethnic groups. New Jersey: Pearson Education.
- Moran, E. F. (2000). Human adaptability. Boulder, CO: Westview Press.
- Scupin, R. (2002). Race and ethnicity: An anthropological focus on the United States and the world. Upper Saddle River, NJ: Prentice Hall.
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