An Intro To Renascent Igbo Religion: January 2017

Race

INTRODUCTION

Elderly Lakota (Sioux) Woman

The Lakota, also called Sioux, are a Native American people whose members live mainly in North Dakota and South Dakota in the United States.

Farrell Grehan/Photo Researchers, Inc.

Race, term historically used to describe a human population distinguishable from others based on shared biological traits. All living human beings belong to one species, Homo sapiens. The concept of race stems from the idea that the human species can be naturally subdivided into biologically distinct groups. In practice, however, scientists have found it impossible to separate humans into clearly defined races. Most scientists today reject the concept of biological race and instead see human biological variation as falling along a continuum. Nevertheless, race persists as a powerful social and cultural concept used to categorize people based on perceived differences in physical appearance and behavior.

Interest in defining races came from the recognition of easily visible differences among human groups. Around the world, human populations differ in their skin color, eye color and shape, hair color and texture, body shape, stature, limb proportions, and other physical characteristics. However, most anthropologists and biologists regard these differences between populations as largely superficial, resulting from adaptations to local climatic conditions during the most recent period of human evolution. Genetic analysis, which provides a deeper and more reliable measure of biological differences between people, reveals that overall, people are remarkably similar in their genetic makeup. Of the genetic differences that do exist, more variation occurs within so-called racial groups than between them. That is, two people from the same “race” are, on average, almost as biologically different from each other as any two people in the world chosen at random. This high degree of genetic diversity exists within populations because individuals from different populations have always intermingled and mated with each other. Given that populations have interbred for most of human history, most anthropologists reject the idea that “pure” races existed at some time in the distant past. Today, genetic analysis has replaced earlier methods of comparing color, shape, and size to establish degrees of relationship or common ancestry among human populations.

The term race is often misunderstood and misused. It is often confused with ethnicity, an ambiguous term that refers mostly, though not exclusively, to cultural (non-biological) differences between groups. An ethnic group derives its identity from its distinctive customs, language, ancestry, place of origin, or style of dress. For example, the Hispanic ethnic group comprises people who trace their ancestry to Spanish-speaking countries in the Western Hemisphere. Although some people assume Hispanics have a common genetic heritage, in reality they share only a language. Members of an ethnic group with a common geographic origin often do share similar physical features. But people of the same ethnic group may also have very different physical appearances, and conversely, people of different ethnic groups may look quite similar. People may also mistakenly use the term race to refer to a religion, culture, or nationality—as in the “Jewish race” or the “Italian race”—whose members may or may not share a common ancestry. The term race is also sometimes used to refer to the entire human species, as in the “human race.” In everyday language, the distinction between race and ethnicity has become blurred, and many people use the terms to mean the same thing.

Many people believe, falsely, that differences in physical appearance have something to do with differences in the behavior, attitude, intelligence, or intrinsic worth of people. These beliefs promote racism, prejudice or animosity against people perceived to belong to other races. At its worst, racism has inspired the abuse and extermination of enormous numbers of people. Recent historical examples included the near-extermination of Native Americans by European settlers of the Americas between the 16th and 20th centuries, the capture and export of Africans for use as slaves in the Americas from the early 17th to the mid-19th century, the extermination of Jews in Europe by German Nazis during World War II (1939-1945), and the system of apartheid perpetrated by Afrikaners against all nonwhite peoples in South Africa.

This article examines the concept of human races and explains why most scientists have discredited race as a biological concept. It also traces the history of attempts to classify people into races, from ancient times to the present. Finally, the article describes the principles of human biological variation and discusses race as a sociological concept.

PROBLEMS IN DEFINING RACES

Around the world, human populations differ in their skin color, eye color and shape, hair color and texture, body shape, height, limb proportions, nose and lip size and shape, and other physical characteristics. For example, peoples of the Arctic, such as the Inuit, differ significantly in body form and skin color from Aboriginal Australians. Likewise, Norwegians appear quite different from Nigerians in their skin color and hair color and texture. These easily visible differences between peoples led early scientists to attempt to define races based on outward physical appearance. Such observable traits make up a person’s phenotype. In more recent times, scientists have tried to define races based on genotype, the genetic makeup of individuals. Both methods have shortcomings that illustrate the fundamental problems of racial classification.

Based on Physical Appearance

Aboriginal Australians

The blond hair of some Aboriginal Australians posed a problem for early racial classifiers, who thought blond hair was restricted to the so-called Caucasian races. Anthropologists now know that all human populations have significant physical and biological variability, making it difficult to classify individuals into racial groups.

B. Wills/Hutchison Library

Interest in classifying races flourished in the 19th century and continued in the 20th century. But every anthropologist proposed a different list of races, with numbers varying from as few as 2 to as many as 60 or more. Racial taxonomists usually divided into two opposing camps: “lumpers,” who minimized the number of races; and “splitters,” who divided humans into many small, local races. Early racial classification schemes were based primarily on skin color. For example, many scholars once believed all people could be classified into one of three main races: (1) Caucasoid, or “white”; (2) Negroid, or “black”; and (3) Mongoloid, or “yellow.” These races corresponded roughly to the geographic areas of Europe, sub-Saharan Africa, and Asia, respectively.

However, some people did not fit neatly into any of these races. For example, the Aboriginal people of Australia have dark skin similar to tropical Africans. But some Aboriginal people have blond hair, unlike most Africans. Were they Negroid or Caucasoid? Some scholars added a new race, Australian, to avoid the problem. The peoples of southern India and Sri Lanka, who have dark skin like tropical Africans but facial features and hair like Europeans, posed a similar classification problem. Again, some scientists added an Indian race. One trait thought to be unique to Mongoloids was the epicanthic fold, a fold of skin across the inner part of the eye. But anthropologists soon discovered that certain African and Native American groups also have epicanthic folds. Should they also be classified as Mongoloid?

These examples show the difficulty in classifying races based primarily on a single physical trait: Populations that share the trait are subjectively lumped into the same race, without any scientific evidence that they are more closely related to each other than to other groups. In addition, the choice of trait is completely arbitrary. One could just as logically choose to classify races by nose shape as by skin color.

An alternative approach might classify races on the basis of particular combinations or clusters of external traits, rather than a single trait. But this approach reveals other problems. Traits that may seem uniform within a population actually vary widely between individuals, making it difficult to classify individuals into racial groups. Furthermore, physical traits are inherited independently of one another. For example, stature in a population may vary from very small to very tall and shows no relation to skin color. Each trait has a unique pattern of geographic distribution that may be unrelated to those of other traits.

Black or White?

In the United States, the children of a black person and a white person are usually regarded as black. The racial designation is arbitrary because the children share in each parent’s genetic heritage equally.

Photo Researchers, Inc.

Perhaps the greatest problem in racial classification involves determining the boundaries of the races. Populations from different continents or climates may differ profoundly in physical appearance, suggesting that the differences between peoples are sharp and discrete. But scientists now recognize that most human physical characteristics vary gradually and smoothly over large geographic areas. Anthropologists refer to this gradient of variation as a cline. For example, skin color is distributed as a cline, generally varying along a north-south line. Skin color is lightest in northern Europeans, especially in those who live around the Baltic Sea, and becomes gradually darker as one moves toward southern Europe, the Mediterranean, the Middle East, and into northern Africa and northern subtropical Africa. Skin is darkest in people who live in the tropical regions of Africa. The lack of clear-cut discontinuities makes any racial boundary based on skin color totally arbitrary. Similar continuity exists for most other physical traits. (For more information about skin color as an environmental adaptation, see the Variation and Environmental Adaptation section of this article.)

Racial classification has generally relied on the premise that each race can be defined by a certain set of physical features that are inherited and unchangeable. But scientists now know that a population’s phenotype (visible physical characteristics) can change without genetic change. For example, the average height of adult males in Japan increased an estimated 10 cm (4 in) in the span of only a few decades after 1950. This time span is too short to permit major genetic changes; changes in the Japanese diet account for the height increase. Given how rapidly some phenotypic traits can change in response to environmental conditions, they form a poor basis for defining fixed, biological races.

Race mixing highlights another problem in defining races. In the United States, the child of a white parent and a black parent is usually defined as black, because American society traditionally has not recognized intermediate racial categories. In biological terms, however, the child shares in each parent’s genetic heritage equally. Until the mid-20th century, many states defined a person as black if he or she had even a small fraction of black ancestry. Most state laws specified the fraction of black ancestry that made someone black as one-fourth or one-eighth. Thus, having one black great-grandparent was sufficient to define a person as black, but having seven white great-grandparents was insufficient to define the person as white. A Virginia law (overturned in 1967) went even further, defining as black “every person in whom there is ascertainable any Negro blood”—the so-called one-drop rule. These definitions were created as part of laws against miscegenation, which were designed to prohibit interracial marriage. Anthropologists today recognize that race is also culturally relative. A light-skinned African American considered black in the United States would be considered white by many dark-skinned populations of Africa. These examples show that race is socially and culturally constructed, not determined by biology.

A final argument against basing races on phenotype is that relatively few genes determine surface characteristics, such as skin color, hair color, and facial features. For example, fewer than ten genes determine skin color. Considered against the estimated 30,000 genes that make up the entire human genome (the total of all human genes), skin color and other external features represent a trivial source of biological variation. There are many other sources of human biological variation that we cannot see, such as variations in blood type and susceptibility to certain diseases. It is of course inevitable to be influenced by what we see, and this helps to explain why people attribute so much more importance to visible physical traits.

Based on Genetic Makeup

Distribution of O Allele

The distribution of the O allele (form) of the ABO blood group gene demonstrates the continuous nature of human biological variation. The frequency with which the allele appears in a population varies gradually across large geographic regions, a pattern of variation known as a cline. The lack of sharp discontinuities in patterns of human physical variation poses a problem for racial classifiers.

As scientists in the 20th century became aware of the many problems in defining races based on physical appearance, some turned to the field of genetics in an effort to define races more scientifically. Genetic analysis allows scientists to learn about differences between people at the level of the genotype—the structure of the molecular genetic material, deoxyribonucleic acid (DNA). Genes are segments of DNA that determine the inheritance of certain traits, or groups of traits. Genetic research provides much more consistent and verifiable information about human variation than do phenotypic studies, primarily because genes are much less susceptible to rapid changes produced by the environment. In addition, genetic studies can examine a much wider range of variable traits—including those not visible to the naked eye.

Scientists first learned about the human genotype through research on proteins—substances fundamental to the function and structure of the body. Proteins indirectly provide information about gene structure because they are the main product of genes. The human body contains tens of thousands of different proteins, most of which vary in form from person to person. Protein research has focused on variation in blood groups, hemoglobin (the protein that carries oxygen in red blood cells), red blood cell enzymes, blood-serum proteins, and human lymphocyte antigens (HLA) that affect individuals’ resistance to organ transplants.

The first attempts to classify races by genetic traits used the ABO system of blood groups. Blood groups determine whether any two people can successfully exchange blood through medical transfusion. All people belong to one of four blood groups (A, B, AB, or O), depending on which alleles (forms) of the ABO gene they inherited. The three major alleles of this gene, A, B, and O, are present in almost all populations of the world, but in different proportions. For example, the O allele reaches its maximum frequency among Native Americans, so much so that in South America almost all individuals have type O blood. In central Canada, type A blood is unusually frequent, type O somewhat less frequent, and types B and AB are rare or absent. On other continents one finds all blood groups, with some local variation. But the ABO blood group system lends itself very poorly as a way to distinguish races. Two populations that are remote both geographically and biologically (based on almost all other criteria), such as Germans and New Guineans, often show very similar ABO allele frequencies.

When scientists examine a large number of different genes, some distinctions between groups begin to appear more clearly. For example, one can usually find some degree of genetic differentiation between populations separated by geographic barriers, such as seas, mountains, and rivers. This occurs because geographic barriers tend to isolate populations from each other, although no barrier seems to completely prevent interbreeding of populations. The genetic differentiation observed between such populations is always extremely modest and not discernible without a thorough analysis. In most areas of the world, genetic traits, like phenotypic (external) traits, are distributed clinally—that is, they vary in a smooth, gradual pattern across geographic areas. For example, in Central Asia the transition from a European type to an East Asian type (as defined by gene frequencies) is almost continuous, making the task of drawing a boundary between “European” and “Asian” races impossible. Around the world, abrupt changes in gene frequencies are unusual between neighboring populations. The reason is that human groups, throughout history, have generally mixed and mated with one other, guaranteeing a constant flow of genes between populations.

By analyzing the data from a sufficiently large number of genes, one could identify hundreds of thousands of local populations at a minimum, each with a slightly different profile of gene frequencies. But this analysis would not answer the question of how many basic races there are. No reasonable multiplication of the list of races could cope with the observed continuity and complexity of genetic variation. Thus, most scientists have given up racial classification as a futile exercise.

The direct analysis of DNA, which became possible in the 1980s, has revolutionized the study of human variation. DNA research has shown that similarities among all people far outweigh any differences. On average, two randomly chosen individuals have 99.9 percent of their genetic material in common. Of the 0.1 percent variation that does exist, 85 percent exists within populations; only 15 percent exists between populations. In other words, almost all the genetic differences between any two people are due simply to the fact that they are different individuals. In comparison with the genetic variation observed among individuals, that between human groups, however defined, is almost negligible.

The human species has less genetic variability than many other animal species, including chimpanzees, the closest living relatives of humans. The reason is that the differentiation among humans living today probably began in the recent evolutionary past. Genetic studies suggest that all people alive today are descended from a relatively small group of humans in eastern Africa who began migrating out of Africa as recently as 50,000 years ago. For more information, see the Human Origins section of this article.

III

HISTORY OF THE CONCEPT OF RACE

Race is a social and cultural creation whose definition has varied over time. Until a few hundred years ago, most people had very little exposure to individuals who differed markedly from themselves in physical appearance or culture. Thus, the concept of race was absent in most early societies. In the 15th and 16th centuries, European explorers traveled to distant lands and encountered peoples who looked and behaved differently. The concept of race emerged as a way to categorize people on the basis of physical and cultural differences. Later, colonialists used the concept of race to justify unequal treatment, exploitation, and enslavement of supposedly inferior peoples.

Ancient Times

Herodotus

The 5th-century bc Greek historian Herodotus provided information about ancient Greece, North Africa, and the Middle East. Herodotus traveled extensively throughout the Mediterranean world, observing the different peoples he encountered and studying the military history of the region. Known as the father of history, Herodotus produced a narrative compilation of his findings, entitled History.

Hulton Deutsch

Since ancient times, explorers have traveled to foreign lands and written about the differences that exist among human populations. In these written accounts of their journeys, travelers often described the appearance and ways of life of the people they met in distant lands. In many cases, these accounts attempted to demonstrate the inferiority of other peoples.

The people of ancient Egypt had contacts with seafarers (often pirates) from other parts of the Mediterranean. Egyptian kings also financed expeditions to explore unknown lands. One expedition, sent by King Pepi II in about 2250 bc, encountered a group of Pygmies in southern central Africa. In contrast with Egyptians, who were tall and had light-brown skin, Pygmies were very short and dark-skinned. The Egyptians were fascinated by the diminutive Pygmies and by their performance of a variety of exuberant dances. Several carvings of dancing Pygmy figures found in the ruins of ancient Egyptian civilization provide evidence of the Egyptians’ early fascination with physical and cultural differences between themselves and other peoples.

The Greek historian Herodotus, who lived in the 5th century bc, described many peoples of Eurasia and Africa, including Pygmies and a people thought to be Mongols. He also described the customs of some of them—for example, the Scythians. Herodotus traveled widely, but never far south in Africa or to Mongolia, where the people he described lived. Instead, he heard reports about these peoples from other travelers. The accounts of Herodotus showed his fascination with differences among people in physical appearance, culture, and behavior.

The descriptions recorded by Herodotus and other ancient writers indicate the attitudes they had toward differences in other peoples. The Greeks referred to anybody who could not speak Greek as a barbarian (meaning “stammerer,” as when trying to speak Greek), an early historical example of racism. Pliny the Elder, a Roman writer and natural historian of the 1st century ad, described Africans as black-skinned with bristled hair. He decided they must have been burned by living too close to the sun.

In the 2nd century ad the Roman Empire reached its height, encompassing large territories in the Middle East, North Africa, and eastern Europe. The Romans established trade routes with India, while the empire of the Chinese Han dynasty established the Silk Road, which ran from eastern China to India, the Middle East, and Roman ports on the Mediterranean Sea. These trade routes established links among urban centers throughout Eurasia and North Africa, exposing people in many cultures to other peoples and cultures.

The Age of European Exploration

Marco Polo’s Journey

This medieval manuscript illustration shows Marco Polo—along with his father, Niccolò, and his uncle Maffeo—beginning their famous trip from Italy to China in 1271. Polo’s book, The Description of the World, for a long time was the only account of such places as China, Thailand (then Siam), Japan, Java, Vietnam, Sri Lanka (then Ceylon), Tibet, India, and Myanmar (then known as Burma). The book also served as a stimulus to Christopher Columbus’s journey to the New World in 1492. The colored illuminated manuscript here dates from 1375.

THE BETTMANN ARCHIVE/Corbis

In the 15th and 16th centuries, several western European countries—Portugal, Spain, The Netherlands, England, and France—began sponsoring expeditions to explore regions of the world that were then largely unknown to Europeans. Rulers financed these voyages with the hopes of establishing control over foreign lands for economic and political benefit—a practice known as imperialism. From the reports of voyagers, Europeans learned of cultures quite different from their own as well as of the physical appearance of non-European peoples. Europeans generally came to believe that what they saw as bizarre and exotic customs were somehow directly related to differences in skin color, hair color and texture, and body and face shape. Thus, the concept of race developed to include both physical and cultural differences among people.

In the 1200s Europeans had little exposure to the cultures of East Asia. Many found reports by Venetian explorer Marco Polo of his travels to China and the countries of South and Southeast Asia difficult to believe. Polo described urban populations in China of over a million people, much larger than any in Europe, and unfamiliar customs, such as the use of paper money for commerce, coal and oil for fuel, and engraved wooden blocks to print documents. He noted in many instances the dietary customs of Asians, such as the eating of dog and other animals not eaten in Europe. Although Polo recorded the skin color and appearance of the peoples he encountered, the concept of race is absent from his writings.

Regular contact between Europe and the Americas began in the late 15th century with the voyages of Italian-Spanish navigator Christopher Columbus. The first Native Americans Columbus encountered were the Arawak-speaking Taíno people of the islands of the Caribbean. In his descriptions of these people, Columbus recorded details of their olive- to copper-colored skin; thick, straight, and long black hair; and short, muscular bodies. He commented on their habits of going largely unclothed and bathing frequently. He also described their types of body adornment, including paints, gold piercings, and tattoos.

Soon after these first encounters, the Spaniards began to clash with and assert their authority over Native Americans. By the early 1500s, the Spaniards had enslaved and killed a great number of indigenous people, a pattern that would be followed for centuries by other Spanish, Portuguese, French, and British colonists of the Americas. White settlers and their financial backers in Europe justified the domination of Native Americans based in large part on notions of European racial superiority.

Europeans first came to know of most Pacific Ocean islands and their inhabitants in the 18th and 19th centuries. Archaeological and linguistic evidence suggests close connections among the many peoples of the Pacific Islands—known today as Micronesians, Melanesians, and Polynesians—although they can appear physically quite distinct. During the 1700s British navy officer Captain James Cook traveled widely in the South Pacific, meeting peoples such as the Maori of New Zealand, Tahitians, and Hawaiians. He treated these peoples with a respect uncharacteristic of other European explorers in the region.

The British established their first settlements in Australia in the late 1700s and early 1800s. The settlers soon met the Aboriginal hunter-gatherers indigenous to that continent (see Aboriginal Australians). In a manner very similar to that of European settlers in the Americas, the British colonists of Australia generally regarded Aborigines as an inferior race. Clashes on the frontiers of white settlement led to a massive number of Aboriginal deaths and the enslavement and displacement of most surviving indigenous Australians.

The Rise of Racial Classification

Carolus Linnaeus

Swedish physician Carolus Linnaeus was among the first to attempt to classify people into races, although he did not use that term. In the mid-1700s he divided humans into four main subspecies and two minor subspecies. He also ascribed temperaments and cultural traits to each subspecies that reflected his own social prejudices.

Culver Pictures

The science of biological classification uses a taxonomic hierarchy to indicate how any one type of organism is related to other types. Swedish botanist and physician Carolus Linnaeus developed the precursor to the modern classification system in the mid-1700s. In the first edition of Systema Naturae (1735), he set out a system for classifying plants, animals, and minerals. To any particular type of organism, Linnaeus gave two Latin names, the first of which identified its genus and the second its species. Linnaeus classified humans as animals, an unpopular idea at the time. He recognized that people belonged with monkeys and apes in the taxonomic order (a broader level of classification) Anthropomorpha, which he later renamed Primates. Linnaeus also recognized all humans as belonging to a common genus, Homo, and species, sapiens.

In later editions of Systema Naturae, Linnaeus subdivided humans into four main subspecies (he did not refer to them as races): Homo sapiens americanus, for peoples of the Americas; Homo sapiens europaeus, for Europeans; Homo sapiens asiaticus, for Asians; and Homo sapiens afer, for Africans. He provided no systematic method for determining these divisions. Linnaeus also identified two other subspecies: Homo sapiens monstrosus, which included people with deformities, mythological giants, and the Hottentots (see Khoikhoi) people of southern Africa; and Homo sapiens ferus, which described wild children found abandoned in forests. The taxonomic divisions of the human species developed by Linnaeus resembled later racial characterizations in that he associated different temperaments and cultural traits with each subspecies. For example, he identified the Asian subspecies as melancholy, stiff, and greedy, whereas the European subspecies was described as gentle, optimistic, and inventive. Linnaeus’s classification of humans was not based on scientific evidence and reflected his own European social prejudices.

Central to Linnaeus’s scheme was the idea of the Great Chain of Being, referred to as the scala naturae. During the 18th century, Christian scholars assumed that all aspects of the world could be arranged in a hierarchy of worth consisting of a series of discrete levels. At the top of the hierarchy was God, representing perfection. Below God were living things, with humans at the top and other animals ranked lower. At the bottom of the Chain of Being were inorganic materials, such as metals. Although Linnaeus did not explicitly rank humans, his attribution of temperaments to subspecies implied a ranking of Europeans first, followed by Asians and Americans, with Africans at the bottom.

Linnaeus’s contemporary, French naturalist George-Louis Leclerc, Comte de Buffon, took a different approach to describing human diversity. Buffon rejected racial classification and instead sought merely to describe the variety of forms and behaviors among human populations. In 1749 he was the first to use the term race to refer to a local population. He remarked that as diverse as humans might appear physically, any man and woman could successfully reproduce. Thus, he believed all people belonged to one biological group. Like others of his time, Buffon believed differences in human populations resulted directly from prevailing environmental conditions and circumstances, mainly diet, climatic temperature, and the evils of enslavement. These factors could make a person change form or, in his words, degenerate. According to this thinking, changes in conditions could change people physically over a few generations.

In the late 1700s German physician Johann Blumenbach developed one of the most influential and enduring racial classification systems. He proposed five human races, which he called varieties: Caucasian, Mongolian, Malayan, Ethiopian, and American. These races corresponded approximately to the geographic regions of Europe, Asia, Australia and Oceania, Africa, and the Americas, respectively. Later, Blumenbach’s divisions were popularized as the white, yellow, brown, black, and red races, terms that continued to be used into the 20th century. Blumenbach rejected Linnaeus’s grouping of humans with the apes and instead placed them in separate orders, reflecting his belief that humans were dramatically different from all other animals.

Blumenbach, a pioneer in the field of comparative anatomy and a collector of human craniums, based his racial classification scheme primarily on observed differences in skull size and shape as well as in skin color. Blumenbach proposed that all people descended from an original human type, and that the people of Georgia, in the Caucasus Mountain region of eastern Europe (now considered part of western Asia), were the closest living representatives of this original type. Thus, Blumenbach used the term Caucasian to describe a race of white European peoples. He believed the other races had “degenerated” from Caucasians. According to some accounts, he developed this theory after deciding that a skull of a Georgian woman was the most beautiful he had ever seen. Implicit in Blumenbach’s classification scheme was that the original humans were created in God’s image, making Caucasians closer to divine perfection and superior to other races.

“Scientific” Racial Studies in the 19th Century

Measurement of Head Shape

Scientists in the 1800s and early 1900s used craniometry, the measurement of head dimensions, in an attempt to document uniform differences among human races. Researchers proposed that each human race had a particular head shape, measured as a ratio of the length to the width of the skull. By the 1930s, anthropological research had instead demonstrated that this measurement could also vary widely among people who shared a common heritage.

The Image Bank

In the 1830s Belgian statistician Adolphe Quételet attempted to make racial classification into a mathematical science. He suggested that within human populations, many traits, when plotted on a graph, could be shown to fall into what is known as a bell curve or normal distribution. Using stature as an example, this means that a graph of the heights of many people would always contain very few extremely short and extremely tall people, more somewhat short and somewhat tall people, and many people near the average height. Quételet believed that by plotting curves of physical and intellectual traits, one could arrive at a profile of the so-called average person of each race. Based on this theory, scientists tried to establish how the average white European person looked and behaved as compared with the average person of any darker-skinned population. In these efforts, scientists were merely trying to confirm the existence of already established racial categories.

During the 19th century, many scholars turned away from what they considered subjective and anecdotal methods of describing races. They devised techniques to measure the physical attributes of people, a practice known as anthropometry. Scientists became especially interested in craniometry (the measurement of head shape and size), inspired partly by the popularity in the early 1800s of phrenology, the study of the link between head shape and mental abilities. One of the first people to systematically measure skulls was American physician Samuel G. Morton. In the 1830s and 1840s Morton conducted various measurements, including cranial capacity, of more than 1,000 skulls. Based on these studies, Morton concluded that the various human races did not share a common ancestor and were probably unrelated to one other. This view, known as polygenism, opposed the prevailing doctrine of monogenism, the belief that races are a single species with a common origin. The popularity of monogenism stemmed from its compatibility with the biblical idea that all people descended from Adam and Eve. After Morton’s death in 1851, some of his associates used his work to justify the institution of slavery in the American South, arguing that blacks were distinctly different from whites and biologically inferior. Morton also influenced French anthropologist Paul Broca, who elaborated on polygenic theory and developed new instruments to measure the skull. Modern critics of Morton’s work argue that his measurements contained errors that reflected an unconscious racial bias.

In the 1840s Swedish physician Anders Retzius developed one of the most influential craniometric techniques, the cephalic index—the ratio between the width and length of the head. Retzius used precision calipers to measure the heads of people from different backgrounds. He generally classified peoples as having one of two characteristic head shapes—brachycephalic (broad-headed) or dolichocephalic (long-headed). People with intermediate head shapes were assigned to a third type, mesocephalic. Soon after its development, the cephalic index gained popularity in Europe and the United States as a way to classify individuals into races based on similar measurements. As a measure of racial differences, however, the cephalic index proved problematic. For example, Germans were largely dolichocephalic, but so were many West African tribes.

In the 1850s British naturalist Charles Darwin developed the theory of natural selection and the modern concept of biological evolution. Unlike most of his contemporaries, Darwin thought that human variation did not lend itself to taxonomic organization because the differences among people do not fall into distinct categories. In his book The Descent of Man (1871) he wrote, “Every naturalist who has had the misfortune to undertake the description of a group of highly varying organisms, has encountered cases ... precisely like that of man; and if of a cautious disposition, he will end by uniting all the forms which graduate into each other, into a single species; for he will say to himself that he has no right to give names to objects that he cannot define.” Supporters of polygenism, meanwhile, rejected Darwin’s evolutionary theory and persisted in believing that races were fixed, unchanging entities.

In 1911 German-born American anthropologist Franz Boas mounted the most convincing challenge against the classification of races based on the cephalic index or any other anthropometric measurements. Boas demonstrated that the stature and head shapes of children born and raised in the United States differed from those of their parents from Europe. He thus showed that skull shape was significantly influenced by the environment (the basis for this influence remains unknown), undermining the use of the cephalic index as a racial marker. Nonetheless, scientists continued to use this and other anthropometric measurements as bases for racial classification well into the mid-20th century.

Racial Classification in the 20th Century

Example of Racial Classification Scheme

For many years, scientists devised lists of human races that they believed represented biologically distinct groups of people. One popular classification scheme, shown here, divided humanity into nine major races corresponding to geographic regions. Today, most scientists recognize that human biological variation does not fall into discrete categories and that racial classification schemes are arbitrary.

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.

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.

Human Origins

Routes of Human Migration

It is widely agreed upon that original routes of human migration began with emigrations from Africa into the Mideast, Asia, and Europe, and only much later from Asia to the Americas. Exactly when and how migrations occurred is highly debated. Nonetheless, it is clear that people encountered and overcame substantial geographic and climactic barriers, including deserts, mountain ranges, bodies of water, and glaciers (especially during periodic Ice Ages).

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.

Tree of Human Evolution

Fossil evidence indicates that the first humans evolved from ape ancestors at least 6 million years ago. Many species of humans followed, but only some left descendants on the branch leading to Homo sapiens. In this slide show, white skulls represent species that lived during the time period indicated; gray skulls represent extinct human species.

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.

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.

Mutation

DNA Strands

Nucleic acids are complex molecules produced by living cells and are essential to all living organisms. These acids govern the body’s development and specific characteristics by providing hereditary information and triggering the production of proteins within the body. This computer-generated model shows two strands of deoxyribonucleic acid (DNA) and the double-helical structure typical of this class of nucleic acids.

Ken Eward/Photo Researchers, Inc.

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.

Natural Selection

Natural selection is the principal way that organisms adapt to their environment. It is the very basis of the evolution of all living organisms. In natural selection, a trait that provides individuals with greater evolutionary fitness (reproductive success) will increase in frequency over generations, and one that makes individuals less fit will decrease. An initially rare gene resulting from a single mutation will become common in a population if it produces an effect that enables individuals to better adapt to their environment. Those with the beneficial gene will survive longer and produce more offspring than those without the gene. Offspring who inherit the favorable gene will also leave more offspring, and individuals with the gene will soon outnumber those without it.

Natural selection thus automatically sorts out and preserves useful changes in the gene pool, the total of all genes in a population. Successful genes—or more specifically, certain alleles—become widespread in the gene pool of a population, and therefore the characteristics of individuals with successful genes also spread. How quickly an adaptive trait spreads through a population depends on the magnitude of the difference in fitness between individuals with the trait and those without it.

Scientists have shown that many of the differences in human populations—such as skin color, body type, and susceptibility to specific diseases—evolved through natural selection as adaptations to local environmental conditions. These adaptations are explained in the Variation and Environmental Adaptation section of this article.

Random Genetic Drift

Pitcairn Island

Steep cliffs line Bounty Bay on the northern coast of Pitcairn Island in the Pacific Ocean. In 1790 mutineers of the British merchant ship HMS Bounty, accompanied by a small group of Polynesian men and women, settled on the island, which was then uninhabited. Subsequent generations of islanders faced reduced genetic diversity because they all descended from a small number of original settlers, a phenomenon known as the founder effect.

Wolfgang Kaehler/Corbis

Besides mutation and natural selection, pure chance factors may change the frequencies of genes present in a population. Most genes occur in two or more forms, or alleles. For each gene, an individual inherits one allele from the mother and one from the father. Even though a parent may have two different alleles of the gene, only one will be passed down to a child. Which allele is passed down is determined entirely by chance at the time of conception. Random genetic drift refers to the change in a population’s gene frequencies resulting from this chance factor. Due to genetic drift, certain alleles will disappear from a population—even if they confer evolutionary fitness—simply because they occur in very low frequencies. At the same time, other alleles will become widespread because they occur in higher frequencies.

Random genetic drift does not usually have a major effect on a population’s gene pool if the size of the population is large. If the population is small, however, genetic drift can dramatically influence gene frequencies. The founder effect illustrates this phenomenon well. The founder effect refers to the founding of a new settlement by a small group of individuals. The sudden establishment of a small, isolated population, whether intentional or accidental, creates a situation in which the alleles of a very few individuals will become predominant as the population grows. For example, in 1790 the Pacific Ocean island of Pitcairn, which had previously been uninhabited, was occupied by a few mutineers from the British merchant ship HMS Bounty, along with a small group of Polynesian men and women whom the sailors had brought from Otaheite (now Tahiti) and other islands. This low number of settlers passed on a very small sample of genetic variation to the next generations of Pitcairn islanders—a strong founder effect. The genes of these settlers—including alleles that were formerly very rare—would have a high likelihood of passing on to large numbers of descendants, becoming more prevalent in each new generation. In a similar way almost all island populations have unusually high frequencies of certain genes.

Epidemic diseases, wars, and destructive natural events, such as volcanic eruptions, earthquakes, and floods, can create a similar situation, known as a population bottleneck. The calamity leaves a reduced population in which the genes of only a few survivors remain.

Gene Flow and Migration

Another source of genetic change in human populations is gene flow, the exchange of genes between populations. Gene flow occurs directly when individuals from one population mate with members of another population, thereby introducing their genes into the population. Increased gene flow between populations generally makes them more alike than they had been previously. Gene flow also occurs indirectly. For example, if population A interbreeds with population B, and population B interbreeds with population C, some genes from population A will pass to population C. In this way, gene flow occurs across vast geographic regions and connects distant populations. In fact, global gene flow maintains the unity of the human species, ensuring that people from any two populations in the world can successfully mate. If a human population became isolated and no longer shared gene flow with other populations, it might, over hundreds of thousands of years, lose the ability to breed successfully with other human populations. At that point the isolated population would be considered a new species.

In humans, gene flow often occurs as a result of migration. Migrations most frequently occur on a small scale, as when individuals or families move to a neighboring village, town, or city. Small-scale migration usually takes place at short distances and is reciprocal—that is, members of neighboring populations each migrate to the region of the other population. Large-scale or mass migrations occur when a large group of people moves to a new region, often because of the effects of war or natural disaster.

Mass migration and major population resettlements dramatically increase gene flow. For example, Africans who were brought to the United States as slaves, as well as their descendants, intermixed with white populations. Today the gene pool of those who identify themselves as African American is intermediate between that of American whites and African blacks. On average, African Americans in the United States have 30 percent European ancestry. Those African Americans in the northern United States may have up to 50 percent European ancestry while those in the Southern states—where laws and cultural values long prohibited racial mixing—may have as little as 10 percent European ancestry. This difference illustrates the power that psychological and cultural barriers can have in decreasing gene flow. People who feel deeply rooted in a particular racial or ethnic group may have some animosity toward the mating of people with different physical appearances or from different cultural backgrounds. Religious and socioeconomic differences can also act as barriers to gene flow. However, people are highly social by nature. Even with the effects of racism and ethnocentrism (a belief in the superiority of one’s own social or cultural group), people have always intermarried and interbred with members of neighboring groups.

Historically, natural barriers such as large rivers, seas, deserts, and mountain ranges have prevented migration and reduced gene flow between certain regions. Geographic distance also impeded migrations; people preferred to migrate only short distances. Over the course of the past several centuries, technological improvements in transportation have reduced the influence of geography and distance. For instance, people now can travel easily from one side of the world to the other within a day by airplane. In general, however, populations tend to be more similar to their neighbors and more different from populations that live far away.

Variation and Environmental Adaptation

The differences among people most easily and commonly noticed include those in skin color, body shape, the shape of the face and facial features, and hair color and texture. Many of these variations evolved as simple adaptations to the environments in which our ancestors lived. As discussed earlier, current research supports the idea that the modern human species, Homo sapiens, evolved first in Africa within the last 200,000 years and that all living people are descended from a relatively small population. This original population shared a similar climate, and its members probably looked very similar to each other. However, within the last 100,000 years, humans expanded out of Africa and eventually settled a wide range of climates, from hot, humid rainforests to frigid tundras. In order to survive, populations were forced to adapt to extreme conditions both biologically, by the process of natural selection, and culturally, by producing innovations such as clothing.

Variations due to climatic adaptation generally affect exposed parts of the body rather than internal structures. The reason involves a basic fact about the human body: its temperature must stay very close to 37ºC (98ºF), regardless of the external temperature. Overheating of the body to above 42ºC (105ºF) is especially dangerous for the brain and may cause death. Thus, people have evolved a variety of external physical characteristics that work to increase or decrease the exchange of heat between the interior and the exterior of the body. For instance, people indigenous to the Arctic have short, stout bodies adapted to retain heat, while people indigenous to equatorial savannas have tall, lean bodies adapted to dissipate heat. However, these physical distinctions do not mean that all Arctic peoples or all equatorial savanna peoples have identical bodies. To the contrary, the same feature can and often does vary broadly among members of the same population.

Because climatic adaptations affecting skin color and body shape are outwardly visible, populations that evolved in the same type of climate tend to appear similar, and populations that evolved in different climates tend to appear different from each other. However, genetic research has shown that the seemingly large amount of physical variation among people has resulted from very few biological changes. All people differ very little biologically.

Although most scientists agree that variation in physical features most often results from environmental adaptation, other factors may also contribute to differences. Darwin suggested that a type of natural selection known as sexual selection accounts for some of the differences we observe among human populations. According to this hypothesis, some physical traits evolved the way they did because of competition among individuals for mates; traits that provided an advantage in attracting a mate tended to persist. Others believe that a certain amount of variation in human traits is nonadaptive—that is, some human features simply occur in a broad range of variation for no particular reason.

Skin Color

Skin color, perhaps the most conspicuous human trait, is determined largely by the amount of the pigment melanin in the skin. People with large amounts of melanin have dark skin, and those with little melanin have light skin. The function of melanin is to absorb ultraviolet radiation from the sun. Thus, many scientists have proposed that dark skin, with its high amount of melanin, is an environmental adaptation that evolved to protect people in areas of high solar radiation from sunburn and skin cancer.

In support of this argument, many populations of tropical areas—where solar radiation is most intense—do have dark skin. For example, indigenous people in tropical Africa, Australia, and parts of India and the South Pacific have very dark skin. However, inhabitants of tropical Central and South America have much lighter skin than these populations. Although the reason for this difference is debated, native Central and South American populations usually live in forest areas, where shadows from trees considerably reduce their exposure to solar radiation. Moreover, forests are very humid, a factor that also decreases the intensity of ultraviolet light. Thus, African Pygmies and, to a lesser extent, other Africans who also live in forest areas are lighter in skin color than Africans who live in unforested areas. Darker skin is more often observed in tropical savannas and deserts.

Ultraviolet light has another effect on the human body—it converts certain molecules in the skin to vitamin D, a nutrient necessary for absorption of calcium into the bones. Too little vitamin D leads to rickets, a debilitating disease that causes bones to soften and deform. As African populations migrated north into Europe, where the level of ultraviolet radiation is lower than at tropical latitudes, darker-skinned people would have developed rickets if their diet did not contain enough vitamin D. Women with rickets would have suffered deformation of the pelvis and a high risk of death during childbirth. The European diet of 5,000 to 10,000 years ago, prevalent in wheat and other cereals produced by agriculture, was very poor in vitamin D. But their diet contained a precursor of vitamin D that could be converted to vitamin D through exposure to ultraviolet radiation. Over time, therefore, natural selection favored lighter-colored skin, which maximizes absorption of whatever sunlight is available so that the body can produce enough vitamin D.

Two other observations support the idea that skin color is an adaptation to the level of ultraviolet radiation. First, people with darker skin have a lower incidence of certain types of skin cancer that are most likely produced by exposure to ultraviolet light. In addition, the existence of sun tanning, which darkens skin when it is exposed to ultraviolet radiation, demonstrates the importance of having darker skin in areas of intense solar radiation.

Body Build

Adaptation to Cold

Inuit people, who live in the extreme cold of the Arctic, tend to have short, stout bodies that conserve heat.

B and C Alexander/Photo Researchers, Inc.

Body size and shape also vary with climate. In hot, arid regions, a tall, slender body with long extremities increases body surface area relative to volume, which helps to dissipate heat by allowing large areas of skin to sweat. For example, pastoral (animal-herding) peoples who live in the hot, arid savannas of eastern Africa, such as the Masai, tend to have this body shape. In hot, humid climates, where sweat cannot evaporate and therefore is not a very efficient cooling mechanism, smaller bodies achieve the same result of increasing body surface area relative to volume, helping to dissipate heat more efficiently. In addition, a smaller body requires less muscular work for movement and decreases the body’s internal heat production. Pygmy groups in central Africa epitomize this type of adaptation.

Adaptation to Heat

Masai people, who live in the arid lands of eastern Africa, tend to have tall, lean bodies that disperse heat well.

Bildarchiv Okapia/Photo Researchers, Inc.

Bigger, rounder bodies are beneficial in cold climates. This type of build conserves heat in the core of the body, preventing dangerous drops in the temperature of internal organs. Arctic peoples, such as the Inuit, tend to have this body type.

Larger size, more compact shape, and shorter limbs are favored in colder climates, and the opposite structure is favored in warmer ones. These are well known general evolutionary rules, observed also when comparing similar animal species living in different climates.

Facial Features

Certain facial features may also have evolved different forms in response to differences in climate. For instance, most people indigenous to the Arctic have thin eye openings padded with fat that can protect against freezing winds. Cold climates seem to favor small noses, to decrease the chance of the nose freezing, and small nostrils to warm the air more easily when it is inhaled. Nostrils seem to be largest where air is warm and humid, as in tropical forests. If nose shapes did arise as climatic adaptations, they have less significance today, when people in industrialized nations spend much of their time indoors in temperature-controlled environments.

Lung Capacity

Some physical adaptations seem to result not from natural selection but rather from the body’s ability to adjust to its immediate environment. For example, people who live at high altitudes, such as the Quechua of the South American Andes and the Sherpas of Nepal, have greater lung capacity than their lowland counterparts. This allows them to take in more air, compensating for the low amount of oxygen in the air at high altitudes. Studies of the Quechua show they also have more red blood cells and larger capillaries than lowland natives, adaptations that help to transport oxygen more efficiently in the body. A child born in the lowlands but raised at high altitudes will develop the same adaptations. This fact suggests that these adaptations arise from the plasticity of the human body, not from long-term evolutionary forces.

Sickle-Cell Trait and Resistance to Malaria

Sickled Blood Cell

The curved, crescent-shaped blood cell (bottom, left) signals the presence of sickle-cell anemia, a genetic disorder that affects 72,000 people in the United States, primarily African Americans. Caused by a defective gene, this anemia results from abnormal hemoglobin, the oxygen-carrying component of red blood cells, which distorts the shape of blood cells after they have released oxygen. The misshapen, or sickled, cells cannot pass smoothly through tiny blood vessels. The resulting blockages cause intense pain and serious deficiencies of oxygen and other blood nutrients throughout the body.

Omikron/Science Source/Photo Researchers, Inc.

The incidence of certain genetic diseases can differ among human populations as a result of environmental adaptation. One such case is the high occurrence of sickle-cell anemia among peoples of sub-Saharan Africa compared to other groups. This disease can lead to severe infections, damage to the internal organs, and death. Sickle-cell anemia is caused by a mutated gene that produces an abnormal form of hemoglobin, a protein that transports oxygen in the bloodstream. The abnormal hemoglobin, called hemoglobin S, deforms red blood cells from their normal disc shape into the shape of a crescent, or sickle. Not every person with the sickle-cell gene, however, suffers from sickle-cell anemia. Only individuals who inherit two copies of the sickle-cell gene, one from their father and one from their mother, contract the illness. People who inherit one sickle-cell gene and one normal hemoglobin gene have what is known as the sickle-cell trait. These people generally do not have any health problems, but they can pass the abnormal gene to their children.

Because people with sickle-cell anemia often die before reaching reproductive age, scientists initially wondered why the forces of natural selection had not eliminated the sickle-cell gene from human populations. The answer, proved by experiments in the 1950s and by later observations, is that having one copy of the sickle-cell gene makes an individual resistant to the most common form of malaria (Plasmodium falciparum malaria), a deadly disease caused by parasites and transmitted by mosquitoes. In malarial areas such as sub-Saharan Africa, carriers of one sickle-cell gene have a survival advantage over individuals with normal hemoglobin genes, who lack resistance. Individuals with protection from malaria will live longer and produce more children, so natural selection maintains the sickle-cell gene. However, whenever two carriers of the sickle-cell gene mate, by chance some children will inherit the gene from both parents and will suffer from sickle-cell anemia.

Malaria and Sickle-Cell Trait

Traits associated with racial differences often relate to environmental adaptations. A genetic mutation to the hemoglobin gene, which affects the development of red blood cells, is most common in parts of Africa where malaria is prevalent. Individuals who carry one copy of this mutation, known as the sickle-cell gene, are less susceptible to the most common form of malaria than people without the gene. Those who inherit two copies of the sickle-cell gene usually develop sickle-cell anemia. In the United States, this disease is most prevalent among African Americans, many of whom have ancestry in regions of endemic malaria.

The frequency of the sickle-cell gene in a population depends on the intensity of malaria where that population lives. If environmental conditions change and affect the malaria rate, the frequency of the sickle-cell gene can also change. For example, many African Americans whose ancestors came from tropical sub-Saharan Africa are carriers of the sickle-cell gene, and therefore the incidence of sickle-cell anemia is somewhat higher among African Americans than among other groups in the United States. Over time, however, this difference will decrease in magnitude because malaria is almost unknown today in North America. Natural selection should slowly wipe out the sickle-cell gene in African Americans because in the absence of malaria, it has no adaptive properties, only the potential to cause sickle-cell anemia.

At one time medical authorities viewed sickle-cell anemia as a marker of race, because the disease occurs primarily in people of African ancestry. Today, scientists understand that the presence of the sickle-cell trait merely indicates that a person is descended from a population that lived in a malarial area. Populations in the Mediterranean, the Middle East, and India also carry the sickle-cell gene, although at lower frequencies.

Besides the sickle-cell trait, many other genetic conditions confer some degree of resistance to malaria and are frequent in areas where malaria is widespread. Thalassemia is a blood disorder that can cause mild to severe anemia. Thalassemia results from the inheritance of certain mutated genes that produce an abnormal form of hemoglobin. Like the sickle-cell gene, people can carry thalassemia genes without suffering from the disease, and carriers are partially resistant to malaria. The thalassemia genes are present in many populations, especially of Mediterranean origin, but also elsewhere. Other genes provide resistance to malaria without causing health problems. The Duffy gene makes a protein present at the surface of red blood cells. This protein helps one variety of malarial parasite, Plasmodium vivax, to enter into the red cell. But individuals with an allele of the gene known as Duffy-zero lack this protein and are resistant to infection by the parasite. Having the Duffy-zero allele in one or two copies involves no known disease or disability. Not surprisingly, in Central and West Africa, where the parasite is frequent, almost all individuals have two copies of the Duffy-zero allele (also known as the Duffy negative trait). But outside this area the frequency of the gene decreases rapidly, and it is practically unknown outside of Africa.

RACE AND SOCIETY

Based on years of research into human variation, the majority of anthropologists and biologists now reject race as a biological concept. However, the idea that people belong to different races remains deeply embedded in many societies. People continue to classify themselves and others as members of particular races, usually based on skin color, hair, and facial features. More importantly, race continues to define how many people think about and behave toward one another. Many people are treated unfairly or discriminated against because of their perceived race. Thus, race remains very important as a social concept—one that social scientists must take into account to understand society and human behavior.

In many societies, a dominant group of people exercises greater influence over government, business, and culture than do other groups. Minority groups differ from the dominant group in some way, and they often suffer from discrimination and have less political power. Traditionally, racial minority groups are defined on the basis of physical differences from the dominant group, and ethnic minority groups on the basis of cultural differences, such as language or religion. In practice, however, many minority groups are defined by both physical and cultural differences. Examples of minority groups in the United States include African Americans, Asian Americans, Native Americans, Hispanic Americans or Latinos, and Jews. Statistically, many minorities have a lower average socioeconomic status than the dominant group in their society. Minorities also often face barriers in education and employment. For these reasons, race and racial discrimination have become important political issues in countries with diverse populations.

Prejudice, Racism, and Discrimination

“Whites Only” Waiting Room

A black man is ordered out of a “whites only” waiting room. Separate facilities for blacks and whites were maintained throughout the South from the end of the 19th century until the 1960s.

Express Newspapers/Archive Photos

Prejudice refers to preconceived attitudes or opinions about other people. Prejudices may be favorable or unfavorable, but the term usually refers to negative attitudes held toward others based solely on their membership in a specific group. Racism is a form of prejudice based on perceived physical differences and usually refers to unfavorable or hostile attitudes toward people perceived to belong to another race. Racism usually results in a belief in the superiority of one’s own race. One cause of prejudice and racism is the human tendency to form stereotypes, generalized beliefs that associate whole groups of people with particular traits. Racial stereotypes are exaggerated or oversimplified characterizations of the appearance, personality, and behavior of a group of people. For example, at one time or another, certain racial groups have been described as lazy, stupid, athletic, dishonest, violent, or miserly.

Whereas prejudice and racism refer to beliefs or attitudes about people, discrimination refers to actual behavior based on these attitudes. For example, racial discrimination takes place when an African American couple is denied a bank loan for a house that a similarly qualified white couple would have received. In the United States prior to the 1960s, a lack of federal laws permitted discrimination against black Americans in housing, employment, education, public accommodations, voting, and access to the judicial system. These forms of discrimination led to the civil rights movement in the United States, a movement by black Americans to achieve racial equality. Today, federal laws and government policies have outlawed most forms of racial discrimination. Some policies are designed to redress the effects of past discrimination. For example, affirmative action programs are designed to favor racial minorities in hiring and promotion, college admissions, and the awarding of government contracts. See Discrimination: Racial Discrimination.

Apartheid Tensions

Under apartheid, South Africa’s policy of racial segregation, tensions ran high between the black population and supporters of apartheid. These black South Africans read a newspaper account of a 1973 clash between police and black miners that resulted in 11 deaths.

UPI/Corbis

Much of human suffering throughout history has resulted directly from racism and racial discrimination. For example, beginning in the 17th century, Europeans sailed to West Africa and imprisoned people to be sold into slavery in the Americas. Millions of Africans were taken as slaves. In South Africa in the 20th century, a system of enforced racial segregation known as apartheid caused blacks and so-called Coloured people to suffer severe mistreatment, violence, and even death at the hands of a ruling white population. During the 1920s and 1930s, the Nazi Party of Germany believed in the superiority of the “Aryan race.” The Nazi party conducted a horrific campaign of racial extermination, known as the Holocaust, against Jews and other people who were believed to belong to inferior races. Millions of Jews were killed.

In some cases, the mistreatment of a group of people is based primarily on cultural differences but also involves prejudice based on racial stereotypes. The term ethnic conflict refers to strife among people who differ more culturally than physically. One example of a serious ethnic conflict is the wars among Serbian, Croatian, Bosnian Muslim, and Albanian ethnic groups in the former Yugoslavia during the 1990s (see Yugoslav Succession, Wars of). Another is the mass genocide of ethnic Tutsis by ethnic Hutus in the African country of Rwanda in 1994.

Race and Intelligence

Although cultural differences among peoples may not be rooted in biology, such differences often coincide with differences in physical appearance. Therefore the two types of variation can appear to be somehow related. It can be particularly difficult to determine whether differences in behavior—such as in basic temperament, styles of communication, or forms of ritual—have any genetic basis. Thus, many people tend to associate the behavioral and cultural differences among peoples with the physical differences among them, often unconsciously. These kinds of associations can be difficult to avoid, even though scientific evidence does not support them.

The problems of presuming that human physical variation corresponds with cultural variation have become clear in many attempts to draw links between race and intelligence. Numerous studies find a difference in average intelligence test (IQ) scores among racial groups. For instance, the average IQ of white Americans exceeds that of black Americans by about 15 points. Some people have interpreted this difference, on the basis of totally inadequate scientific evidence, as due to genetic differences. These people believe that whites are innately more intelligent than blacks. However, this conclusion fails to consider two important facts. First, cultural and environmental factors undoubtedly have a strong influence on the skills measured by IQ tests. Because of years of prejudice and discrimination, black Americans are more likely than white Americans to live in poverty, to have less access to good education, and to encounter prejudices in the classroom—all factors likely to affect IQ scores. Second, the comparison between “blacks” and “whites” reflects socially constructed racial categories, not genetic ones. According to genetic studies, two whites or two blacks picked at random are almost as different genetically, on average, as a black person and a white person. In addition, a substantial portion of the “black” gene pool was contributed by whites.

Most scientists agree that environmental factors alone are sufficient to account for group differences in IQ scores. However, research on this topic has yet to identify the exact causes of these differences, and some theorists continue to promote a genetic hypothesis. See Intelligence.

Race and Disease

Scientists have noticed that certain diseases occur with higher incidence in various racial and ethnic groups. For example, about 1 in 25 people of northern European ancestry is a carrier of a gene that can cause cystic fibrosis, about ten times the rate seen among people of African or Asian descent. Likewise, African Americans are more likely to carry the gene that can cause sickle-cell anemia. Many population-specific predispositions to disease probably evolved as the result of adaptations to historical environmental conditions. Some scientists believe that the cystic fibrosis gene spread in northern European populations because it conferred greater resistance to an infectious disease such as tuberculosis or influenza. The higher incidence of sickle-cell anemia among African Americans reflects their African ancestors’ adaptation to malarial conditions. The sickle-cell trait, however, is not an indicator of race—not all people of African descent carry the sickle-cell gene, and not all people who carry the gene are of African descent.

Ethnic groups with a higher incidence of certain diseases are usually small and rather specific. Often the higher frequency of disease results from the founder effect or a population bottleneck at some point in history, in which many people are descended from just a few. For instance, researchers have found that the founder effect accounts for the high prevalence of Ellis-van Creveld syndrome (which causes heart defects, dwarfism, and extra fingers or toes) among the Amish people of Pennsylvania. Some researchers have suggested a similar explanation for the high incidence among Ashkenazic Jews (Jews of eastern European descent) of the gene causing Tay-Sachs disease, a lethal brain disorder. Tay-Sachs is not a “Jewish” disease; Jews not of eastern European descent carry the gene at the same frequency as the general population. The gene also occurs in somewhat higher frequencies among non-Jewish French Canadians and among Cajuns in Louisiana (Cajuns derive in part from French Canadians). Other genetic diseases, rare elsewhere, have an unusually high frequency in Ashkenazic Jews, indicating that this group experienced a strong population bottleneck some centuries ago.

Knowing that a certain population, however defined, has a statistically higher incidence of a specific disease can be of great value in the prevention and diagnosis of the disease. For example, African American couples may choose to undergo genetic screening to determine their risk of having a child with sickle-cell anemia. Physicians can make better-educated diagnoses with the knowledge that a person may have an elevated risk of contracting a specific disease. Therefore, medical researchers continue to examine how disease risk varies across racial and ethnic groups.

Unfortunately, medical authorities and researchers too often accept socially defined racial categories, such as those used by the U.S. Census Bureau, as if they were scientifically meaningful. By reporting results of studies in terms of differences between races, researchers may inadvertently perpetuate the idea that races are biologically distinct and that observed differences in risk are due to innate racial differences. For example, many studies have shown that hypertension (high blood pressure) is about twice as common among black Americans as it is among white Americans. For many years medical authorities cited this difference as evidence of genetic differences between the races. But researchers who compared blacks from the United States and West Africa found extremely low rates of hypertension among rural West Africans—less than half the rate of hypertension among white Americans. The researchers concluded that environmental, not biological, factors accounted for the increased rates of hypertension in African Americans—factors such as diet, exercise, and the stresses associated with racial discrimination. Because of the potential for misinterpretation of findings, some public health experts have called on the scientific community to abandon the use of racial labels in medical research.

In contrast to race-based disease research, the study of relatively small populations that are isolated either geographically (for example, on islands) or socially offers unusually good opportunities to understand genetic diseases or the genetic variation of medically important traits. For example, researchers can learn about a population’s degree of sensitivity to a particular drug. Knowledge about diseases in such well-defined populations is of potential importance for the members of that population and for medical genetics in general. But these populations bear no resemblance to the races listed by the U.S. census or to those identified in old-fashioned classifications.

Contributed By:
Luigi Luca Cavalli-Sforza

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