Race

E

Racial Classification in the 20th Century

During the 20th century, scientists (mostly anthropologists) continued to devise a profusion of racial classification schemes and names for particular races. But by the 1940s, advances in genetics had led to a new understanding of human diversity and had begun to transform scientific views of race. One of the first scientists to argue against race as a biological concept was British-born American anthropologist Ashley Montagu. He published Man’s Most Dangerous Myth: The Fallacy of Race (1942) at a time when Nazi Germany was using the concept of racial superiority to justify the killings of millions of Jews.

In 1950 biologists and anthropologists met at a large scientific symposium in Cold Spring Harbor, New York, to discuss human origins, evolution, and race. Three American anthropologists who participated in this symposium—Joseph Birdsell, Carleton Coon, and Stanley Garn—defended the relevance of racial classification. They and other supporters of racial classification acknowledged that race was only a classificatory convenience and not a physical reality. Coon and Garn continued to advocate the use of racial taxonomies for many years. For instance, in the 1971 edition of his book Human Races, Garn identified nine major races corresponding to geographic regions: Amerindian, Polynesian, Micronesian, Melanesian, Australian, Asiatic, Indian, European, and African.

Between 1950 and the early 1970s the United Nations Educational, Scientific, and Cultural Organization (UNESCO) made a series of formal statements on race, which were jointly authored by anthropologists, sociologists, and geneticists. In these statements, UNESCO declared a goal of eliminating racism around the world and questioned the legitimacy of racial classification. In 1998 the American Anthropological Association also published a formal statement on race, in which it established its position against racial classification.

Today, the measurement and analysis of human variation at the genetic level provides convincing evidence that refutes the existence of distinct human races. This research shows that the visible physical variations among people are generated by minor genetic differences, that individual and not population differences account for most genetic variation, and that human physical variation does not fall into discrete categories. But racial classification continues to play an important role in many modern societies. For example, the United States census has included a question on race since the first census in 1790. All federal agencies, including the U.S. Census Bureau, must follow federal standards for collecting data on race and ethnicity. These standards define five basic racial categories: American Indian or Alaska Native; Asian; Black or African American; Native Hawaiian or Other Pacific Islander; and White. The standards also define two ethnic categories: Hispanic or Latino, and not Hispanic or Latino. The census form lists more detailed racial categories, which the Census Bureau later aggregates into the basic categories. Census respondents may also select more than one racial category. The U.S. government uses race figures from the census and other agencies to guide many aspects of public social and economic policy. For example, census racial data can affect legislation and funding for affirmative action policies, welfare programs, and educational programs for minority groups.

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IV

Explaining Human Biological Variation

Although most scientists today believe that the human species cannot be subdivided into biologically distinct races, the study of human biological variation remains important to science. Instead of trying to classify human diversity into discrete races, scientists focus on why variation occurs and on explaining specific biological traits. Among their questions: How did physical and genetic differences evolve between groups of people? Why do some people have light skin and others dark skin? What makes some populations more susceptible to certain diseases?

Many anthropologists have turned from a study of races to a study of local populations. Statistically, a population is a group of people defined in some unambiguous way, usually on the basis of geographic or political boundaries. For example, anthropologists might study the inhabitants of a village, a town, a city, or a nation. Populations may also be defined genetically. The simplest genetic model of a population is one in which mating takes place more or less randomly among individuals who are part of it. Researchers must be careful to clarify how they defined a population so that a study repeated on the same population can be compared to earlier studies.

A

Human Origins

The differences among modern human populations developed in the evolutionary past. Scientists believe that humans evolved from apelike ancestors beginning about 5 million years ago. The predecessor of modern humans, Homo erectus, lived in Africa and migrated to Asia and Europe 1 million to 2 million years ago. Scientists generally agree that anatomically modern humans, Homo sapiens, evolved within the last 200,000 years. However, anthropologists disagree about how and where modern humans evolved. There are two major hypotheses about how modern humans evolved: the out of Africa hypothesis and the multiregional hypothesis.

According to the out of Africa hypothesis, modern humans originated in Africa in the last 200,000 years and spread from there to the rest of the world, including the Americas and Australia. This migration out of Africa to the rest of the world took place within the last 100,000 years and may have begun as recently as 50,000 to 70,000 years ago. Based on this hypothesis, the differences among modern humans today originated relatively recently—mostly after the great dispersal out of Africa, although some differences may have formed in Africa. According to the competing multiregional hypothesis, modern humans developed in parallel in Africa, Europe, and Asia over 1 million or 2 million years from existing populations of Homo erectus. In this scenario, differences between human populations originated in the distant past.

The original support for the multiregional hypothesis derived from fossil evidence that suggested continuity of evolution between archaic humans in Europe, known as Neandertals, and modern Europeans. Certain fossils suggested similar continuity between archaic and modern humans in East Asia. The out of Africa hypothesis was first proposed based on genetic studies of a type of DNA known as mitochondrial DNA, which is inherited through the maternal line. Since then, studies of the Y chromosome, which is inherited through the paternal line, have confirmed the results of mitochondrial DNA studies. These studies show that living African populations have more genetic diversity than any other human groups, and that this diversity has been accumulating for perhaps 100,000 to 200,000 years. This finding implies that all modern humans are descended from a small population of Homo sapiens that lived in Africa 100,000 to 200,000 years ago. Analysis of mitochondrial DNA from a Neandertal fossil found in Germany also suggests that Neandertals did not contribute DNA to modern Europeans. Thus, evidence has been accumulating that modern humans are not descended from Neandertals living outside of Africa. Today, many geneticists and physical anthropologists see the balance of the evidence as strongly favoring the out of Africa hypothesis. For more information on the evolution of modern humans, See Human Evolution: Theories of Modern Human Origins and Diversity.

Another important finding is that human genetic variation between groups, however defined, is small compared to that within groups. The data strongly support the idea that all living humans originated recently from a relatively small population—on the order of thousands or tens of thousands of individuals. All people share a strong genetic heritage, and are much more alike than different.

B

Factors of Genetic Change

Genetic variation is essential to the long-term survival of many species, including humans. It allows a species to adapt to changes in the environment. Within a population that has a high amount of genetic variation, some individuals may have traits that allow them to survive even major fluctuations in environmental conditions. For instance, certain alleles (variants) of genes make animals or plants resistant to disease-causing microorganisms, which can cause severe damage and even extinction to the species they attack. If not for the existing amount of genetic variation among humans, diseases such as plague or smallpox—which have infected or killed millions of people in the past—could have easily wiped out entire populations, or possibly the human species as a whole.

Population genetics is the study of genetic variation in populations. For many years, scientists have known that gene frequencies—the frequency with which specific genes appear in a given population—change over time. That is, some genes become more common and others less common. The factors that influence genetic change in populations are well understood. There are four basic factors: (1) mutation, (2) natural selection, (3) random genetic drift, and (4) gene flow and migration.

B

1

Mutation

Mutations are rare, random changes that occur to the genes of an individual during a lifetime and that are transmitted directly to offspring. Mutations occur at the level of the molecular genetic material, DNA (deoxyribonucleic acid). A DNA strand is made of substances called nucleotides, joined one to the other. Within each nucleotide is one of four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). Their sequence on the strand is responsible for the specific biological information carried by DNA, just as the order of letters in a book forms meaningful words and sentences carrying information. Mutations are replacements of one nucleotide base by another (for example, A by T or G or C) or the loss or addition of one or more nucleotides in specific positions.

The effect of a mutation can be inconsequential, advantageous, or disadvantageous to the individual carrying it. Most have no effect. An advantageous mutation increases an individual’s success in reproducing offspring and may allow an individual to adapt to changing environmental circumstances. An advantageous mutation might, for example, make an individual able to withstand changes in climate or to digest new and plentiful sources of food. Through the process of natural selection, described below, an advantageous mutation will likely spread to all the individuals of a population over successive generations, usually taking many thousands or even millions of years.

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