Chapter 7 Outline

Introduction

• In 2018, Senator Elizabeth Warren publicized the results of a genetic ancestry test demonstrating that she had a small portion of Native American ancestry.
• President Trump and his allies dismissed her claims as “a scam and a lie” because it was such a small portion of her ancestry.
• This debate will likely continue in the political arena, but the underlining assumption that “Native American ancestry” can even be ascertained via a genetic test requires further investigation.
• Genetic tests that claim to reveal genealogical information have grown popular in the last several years. The tests measure variant alleles as compared to variants in reference populations whose data exist in genetic databases, producing statistical probabilities of relationship.
• But there are limits to these tests: they only look at a small portion of an individual’s DNA; the presence of variation is no guarantee that an individual is connected to the reference population; and the basis of comparison is very small.
• Most troubling, is the use of continents as a marker for genetic variation, which is typically a proxy for race and ethnicity. Race and ethnicity have nothing to do with any gene or genetic variation.
• Most anthropologists agree that these tests skew our understandings of our genetic make-up. The tests reinforce the erroneous idea that DNA shapers who we are and that racial and ethnic differences have something to do with DNA.
• What makes us human is not our genes but our social complexity, our cooperative ability, and our capacity to innovate and change.
• Nonetheless, there are important genetic and biological variations among humans, which leads us to ask the question at the heart of this chapter: How should we understand biological and genetic diversity among contemporary human populations? Embedded in this broader question are the following problems:
• In what ways do contemporary humans vary biologically?
• Why do human bodies look so different across the planet?
• Are differences of race also differences of biology?
• What biocultural consequences do discrimination and stress have on human bodies?
• Here we explore what biological anthropologists know about contemporary human biodiversity: the similarities and differences within and across human groups that have biological and biocultural dimensions.
• That knowledge challenges simplistic notions about the biological or genetic origins of racial differences and also demonstrates that cultural processes like racism and social stress can have important impacts on human biology.

In What Ways Do Contemporary Humans Vary Biologically?

• All humans share mostly identical genetic material—100% of the same genes and 99.9% of their variations—and have common physiological processes. Any differences are typically related to ancestral mutations or developmental processes that play out within an individual’s lifetime.
• The primary interest of anthropologists is not so much individuals as it is understanding species-wide patterns, which means focusing on how that biological diversity works at the population level.
• We examine four key dimensions of population-level human biodiversity:
• patterns of genetic variation;
• the role of gene flow in genetic variation;
• physiological differences;
• immune responses to disease.
• For most mammals, the typical pattern of genetic variation is one in which variation exists between different populations, and most individual populations are more genetically uniform.
• A population that remains separate from other populations can develop a specific genetic profile over time. In humans, this situation is reversed and almost all our species’ genetic variations are found within populations, not between them.
• In 1972, evolutionary biologist Richard Lewontin’s statistical analysis of the appearance across human populations of certain known genes led to his proposal that genetic variation exists between, not within, human populations.
• More extensive empirical evidence to support this proposal, however, took another quarter century to compile. A key contribution came from the Human Genome Project: an international scientific research project between 1990 and 2003 whose goal was to identify all the genetic material in humans. It clearly established that humans demonstrate relatively little genetic variation between populations.
• All of this research shows is that between 83 and 97 percent of genetic variation is found within human populations, and between 3 and 17 percent is found between populations.
• These numbers are quite surprising for a mammal like ours that is large-bodied and well- dispersed. As a simple comparison, there are greater genetic differences between white-tailed deer populations in North Carolina and Florida than between human populations from Central America, Central Asia, and Central Africa.
• One of the major reasons we find this pattern of genetic variation among humans is because of gene flow due to migration, as the example of the Culí from Central America demonstrates. The Culí genotype shows a much more complex pattern than anyone would have imagined.
• Genetic variation is not the only kind of biological variability among humans. There are also physiological variations—in blood factors, enzymes, organ functions, and so on—which powerfully shape how our bodies work. Any one of these physiological traits would provide a more valid basis for meaningful classification than a morphological feature such as the color of one’s skin, if there were any good reason to divide humans into biologically defined groups.
• One way to investigate human physiological diversity and can also help us understand certain human evolutionary dynamics is through the study of blood types: sets of proteins that coat the red blood cells, which serve a variety of functions in the human body, including delivering oxygen to tissues and producing antibodies as an immune response.
• Variability in blood types is likely due to mutation, natural selection, and gene flow. Gene flow between populations over the past 50,000 years or so, have left their marks on the distribution of some alleles across human populations.
• Diseases can directly shape our evolutionary trajectory. The other side of that equation is the complex adaptive response of the human immune system to disease pressures which aid survival.
• Our species’ immune system has responded with both flexibility and the ability to resist. We can see evidence of adaptive responses on two levels, the first a generalized one across our species endowing flexibility to deal with pathogens, and the second providing certain populations with resistance to specific diseases. A vital component of human immunity is the Human Leukocyte Antigen system (HLA): a series of proteins on the surface of white blood cells that recognize foreign particles or infectious agents.
• As a result of this HLA system, within any human population great variation exists in immune system response, and gives humans flexibility to handle different disease environments. This same variation makes organ transplants very difficult.
• Sickle cell disease is a blood disorder occurring in individuals in many human populations, but because of its negative impact on fitness it tends to be selected out of the population over time. The allele’s persistence is related to the presence of malaria in an environment, a mosquito-borne disease caused by a family of parasitic microorganisms. In areas where malaria is endemic, individuals with sickle cell disease usually do not get malaria, because sickled red blood cells interfere with the reproduction of the parasites.
• One theory about this capacity to resist malaria is that human activity increased breeding opportunities for mosquitoes, which in turn increased the likelihood that humans will contract the malarial parasite.
• Up to this point, we have been discussing human biodiversity mostly in terms of substances and processes—proteins, genes, cells, immune responses, etc.—that we can’t see. Next, we examine what biological anthropologists know about how and why humans look so different across the planet.

Why Do Human Bodies Look So Different Across the Planet?

• People across the planet vary, sometimes quite dramatically, in their looks. In areas of the United States where immigration levels are high, that variability is on display every day. Some view that display as a celebration of multicultural diversity, others see it as troubling or threatening. In many societies, powerful cultural judgments and prejudices are heaped onto bodily characteristics like skin pigmentation, hair, facial features, and body type.
• Biological anthropology holds these kinds of morphological variations as overemphasized and widely misunderstood, and less significant for everyday bodily function than genetic, physiological, and immunity issues.
• Because our bodies interact most directly with the natural environment, morphological traits can reflect evolutionary adaptations.
• One of the most widely misunderstood aspects of skin is the feature that most of us take for granted, its “color.” Skin does not have color, per se. What it does have, just under its outer layers, are cells called melanocytes that produce melanin: a complex polymer whose color is either black or brown.
• Melanin works as a pigment providing a protective tint from the rays of the sun for what lies underneath. The density and distribution of melanin, along with several other factors create variations in reflection and absorption of light in the skin, contributing to the perception that skin has “color”.
• Melanin is a natural sunscreen that evolved through natural selection. Through natural selection, early hominins almost certainly had high levels of melanin to regulate their UV exposure, and thus they had dark skin complexions. This adaptation was all the more important after humans lost their fur, which probably happened a million years ago.
• As these early hominins migrated out of Africa and into northern latitudes, new variation to skin pigmentation began to appear. The lower levels of UV in northern latitudes resulted in the loss or reduction of melanin pigmentation and skin complexions lightened.
• The variation we see today globally in skin pigmentation can be traced to the latitude where one’s ancestors spent the most time. Generally-speaking, darker-skinned populations either live in or can trace their ancestry to lower latitudes. There are obviously many exceptions, and the best we can say is only that skin pigmentation is not an accurate way to describe any population and that it only correlates in very general terms with latitude.
• Humans also vary greatly in body shape, stature, and size. Some groups of people are quite tall and slender, others may be short and somewhat stocky. The differences between different groups, not to mention the range of other bodily types seen globally, raise questions about the adaptive significance and biological dimensions of that variability for our species.
• These variations can be quantified with anthropometry: the measurement of body parameters that assess physical variation and the relative contributions of particular body parts to overall body shape.
• These measurements take the form of indices, such as the cormic index: standing height divided by sitting height, and the intermembral index: the ratio of arm length to leg length.
• While all of these variations may seem important, they pale in comparison to the variability among early hominins and members of the genus Homo who had even greater sexual dimorphism and differences in size and mass. This is because the ability of early humans to reduce environmental stresses on the human body through culture improved.
• When it comes to these kinds of patterns, it is difficult to get much beyond suggestive generalities. Migration may indicate that a population entered a climatological region too recently for evolutionary adaptations to have occurred. Bodies can also change within individual lifetimes. More importantly, people adapt to climate through cultural processes, including diet, activity patterns, and the use of clothing and shelter, which affect the ability to adapt to extreme climates no matter what the body shape, stature, or size.
• One of challenges of describing and explaining variations in how people look is just how much those variations can pass through and be shaped by cultural filters. The idea that it is possible to organize humans into definable biological groups based on their looks is a persistent and enduring belief.

Are Differences Of Race Also Differences Of Biology?

• Most Americans have a worldview that assumes that race—a system that organizes people into hierarchical groups based on specific physical traits that are thought to reflect differences that are rooted in biological differences—is a natural and inevitable aspect of human society.
• The markers upon which racial distinctions are made are especially arbitrary, and they can and often do change.
• How race has been framed scientifically and how it connects to human biological variability, and recognition that there are no valid biological origins for grouping people into human races, is essential to understanding how race works.
• Biological anthropologists work with two concepts of race:
• The scientific concept of race: a population or group of populations within a species that has measurable, defining biological characteristics and low statistical measures of similarity.
• In biology this population within a population is known as a subspecies: a population that meets the criteria defined within the scientific concept of race.
• The other concept is a culturally-constructed concept of race: a set of cultural or ethnic factors combined with easily perceived morphological traits (e.g., skin reflectance, body shape, cranial structure) in an artificial “biologized” category.
• The culturally-constructed conceptions of race we take for granted today originated during the period of European colonial expansion from the fifteenth to the nineteenth centuries. Europeans explained and justified their dominance and control through colonialism by developing racial classifications that evaluated non-Europeans as less human or less civilized than themselves.
• Beginning in the eighteenth century, largely through the production of scientific theories, schemes, and typologies about human differences, these differences were naturalized: made part of the natural order of things.
• The early years of physical anthropology (roughly 1850-1950) focused on attempts to discover the biological basis for classifying humans into races, typically through various kinds of anthropometric measurements. Despite some countervailing research, the basic notion of race in humans was assimilated deeply by mainstream scientific studies about human differences. There is, of course, a fundamental problem inherent in attempting to categorize humans racially.
• Scientists came up with four general approaches to categorize human races.
• The trait-based approach isolates certain physical features, such as head size and shape, bodily structure, facial features, lip shape, eye folds, or skin pigmentation, to divide people into races according to what seems physically most typical of the group.
• The geographic origins approach, which classifies according to geography. The obvious weakness of this model is that political designations high levels of ethnic diversity are made into racial groups.
• The adaptational approach, which refers to the notion that people adapt to the environments in which they live and pass on those adaptations through inheritance. This point suggests only a very general correlation between biology and latitude, and does not translate neatly to the four or five commonly defined races.
• The fourth approach builds on advances in population dynamics since the 1950s, defining races as reproductively isolated breeding populations. This approach moved beyond trait- based and geography-based approaches by focusing on who mates with whom, and allows for the influence of cultural factors in the formation of racial groups. It also means the number of races grows to dozens because of so many separate breeding populations. In the extreme, it would also mean that every population qualifies as a race.
• The problem is that none of these typologies describe an actual individual, and none characterize whole groups of people. What seem like obvious “racial” differences come from a special way of sampling people, a process that isolates one or more arbitrarily-chosen visible traits and marks that trait as representative of a whole group of people. More troubling, that one trait can come to be representative of other characteristics, such as intelligence, aptitude, and personal character. Moreover, the categories themselves are just not that stable and they shift over time.
• Biological traits and genetic features never vary in neat and easily defined ways, or in ways that correspond to the “racial” categories Americans recognize. Historical movement, intermingling, and gene flow, human genetic and biological variations occur in a continuous fashion. Anthropologists call such variations clinal: a type of variation in which change is gradual across groups and that traits shade and blend into each other.
• Genetic and biological traits also tend to vary independently of each other. There is no connection between skin pigmentation and any other supposed “racial” trait, such as certain facial features, cranial size, or body shapes. There is also absolutely no physiological parallel or relationship between these traits and the biological and social phenomena we call character and intelligence.
• Anthropological skepticism about the utility of race for understanding human variation runs deep in the discipline’s history.
• See Classic Contributions: Ashley Montagu and “Man’s Most Dangerous Myth”
• Where does this all leave the scientific concept of race? To test the hypothesis that modern humans can be categorized according to the scientific concept of race, we just need to identify the biological characteristics that define a subspecies within Homo sapiens and then assess how those characteristics map onto human variations. We need evidence.
• There is no genetic evidence. The genetic differentiation needed to classify a population or group as a subspecies in non-human animals simply doesn’t exist in humans. The variation levels are well below the statistical limits biologists use. No single genetic marker can be used to sort people into races.
• See “Anthropologist as Problem-Solver: Jada Benn Torres and Reparational Genetics in the Caribbean”
• There is no morphological evidence. For this, we must rely on forensic analysis: the identification and description of dead people.
• Forensic experts often use cranial measurements to sort people into populations, and can frequently classify a skull’s race about 80 percent of the time. This does not mean these categories are biologically-based. Health, nutrition, and evolutionary factors like gene flow create cranial variation between individuals. In humans, levels of cranial variations are similar to the levels of variation in our DNA. About 80 percent of any variations in cranial shape would be found within a human population, and about 20 percent between populations.
• Forensic scientists are able to classify skulls into culturally-constructed racial categories based on how the crania are classified, and how many categories there are for classification. Differences in skull measurements between individuals in a given group comes from differences in their health and nutrition across time, as well as gene flow, especially if any of these individuals had some ancestors from other parts of the planet.
• When we look at skull measurements indicating “Black” in the United States, and compare them with crania from African continent, with all its human diversity, they don’t match up. Cranial measurement used to identify “racial” groups is not specific or unique to any of the culturally-constructed racial categories. Because the cranial measurements for each group are based on averages and ranges, any specific cranium will usually diverge from the “correct” range. As a result, forensic experts can’t always place crania in the “correct” category.
• All of this evidence indicates that race is a powerful cultural and scientific construction. Any certainties about it have to be actively built around a set of assumptions that anthropology shows are flawed when applied to humans. Despite this, many people, including many scientists, still believe that erroneous racial classifications are real. This is largely because they do not understand how processes natural selection, population genetics, and human variation work. It is important to recognize that even if the origins of racial groups are not genetically or biologically-determined, and that race can become biology by shaping peoples’ biological outcomes.

What Biocultural Consequences Do Discrimination and Stress Have on Human Bodies?

• One of the criticisms of the idea that race is a myth or is culturally-constructed is that it might give the impression that race is not “real”. Race is very real because racial groupings are accompanied with and supported by marginalization, exploitation, and stigma for some, and privilege for others. Race becomes a potent force and an objective reality when manifested through racism: the repressive practices, structures, beliefs, and representations that uphold racial categories and social inequality.
• Racism works through the prejudice that people express against people who are different from them, and discrimination: negative or unfair treatment of a person because of his or her group membership or identity.
• From a biocultural perspective, these processes powerfully shape a community’s exposure to factors that create certain kinds of embodied health outcomes, including sickness, long-term chronic disease, stress, and suffering. Studying these helps us see how cultural processes can contribute to the production of biological variation in human populations.
• One illustration of Ashley Montagu’s concerns about the dangers of race comes from the field of eugenics: the study of genetics with the notion of improving human biology and biological potential; often associated with simplistic, erroneous assumptions about the relationship of behavior or cultural traits with simple genetic systems.
• Early geneticists sought to improve humanity by making it more disease resistant and smarter, and understood social, cultural, and racial differences among peoples to be the result of genetic differences. They promoted selective mating and sterilization programs in an effort to protect and promote “good genes” and eliminate “bad genes” from the population.
• At the time, these ideas were viewed as progressive and were supported by prominent social reformers, philanthropists, and government agencies. But the track record of eugenics included numerous human rights abuses and was based on a totally incorrect way of thinking about genetics. Eugenicists believed that inheritance was a simple function of dominant and recessive genes: you simply get one thing from dad and one from mom, and the one that is dominant becomes your phenotype. This allowed them to claim that certain groups of social undesirables had low intelligence based simply on the belief that they inherited certain dominant traits in high amounts.
• Eugenics lost its social legitimacy following World War II when it became clear that the Nazis in Germany had used their own eugenicist ideology to identify and standardize their ideas about the superiority of Nordic and Aryan racial types and rationalize the holocaust.
• Many different nation-states and individual states within a nation—including Vermont—sanctioned eugenics as official state-supported ideology. As the example of eugenics shows, when aligned with powerful social institutions, racist ideologies can have profound biocultural consequences on ordinary people’s lives.
• Another context in which we can examine these biocultural consequences is by understanding racial inequalities in health. The existence of these inequalities has become an important area of biological and cultural research among anthropologists. Anthropological research lends support to a more a complex view that human health results from biocultural factors and is subject to phenotypic plasticity and epigenetic effects.
• Epidemiological studies in the United States indicate well-defined differences between racial groups in terms of morbidity and mortality, which refer to incidence of disease and life expectancy.
• Race is not the cause of these health inequalities. Rather, these health inequalities are the result of race, or more specifically, of racism and the complex environmental influences racism creates on human biology. Residential segregation by racial group has been shown to produce inequalities in health because it constrains opportunities such as access to education, certain occupations, and quality health care. It can also create social environments that influence the spread and distribution of disease, poor diets, illegal drug use, gang violence, and gunshot wounds. All of these problems are linked to poverty and social marginalization, not the biology of the populations affected.
• Discrimination has also been shown to have bodily consequences on individuals, producing a range of effects from high blood pressure to lower birth weights. Although they are still not understood very well, these conditions can also have epigenetic dimensions, in other words, producing lingering effects throughout childhood and well into adulthood of the next generation.
• This work shifts attention toward the lived experiences of racism known as embodiment: a concept that refers to how people literally incorporate, biologically, the material and social worlds in which they live, from conception to death.
• Embodied inequalities reinforce racialized understandings of human biology. Recognizing how biological variations are produced through social processes has been a productive avenue for biocultural research beyond the study of racial inequalities.
• If we want to understand human biological variation, it is necessary to take into account the role of that social relationships and cultural attitudes— such as those that produce discrimination and psychosocial stress—play in shaping biological processes and health outcomes. The importance of biocultural research lies in challenging long disproved reductionistic biological and genetic perspectives that reproduce the same myths of separate human races, while recognizing that race does have certain kinds of objective realities.

Conclusion

• Even though many Americans believe that race matters less in this country than it ever has, race and racially-based discrimination have not disappeared from American life. The unequal health outcomes between whites and blacks and other racialized minorities are but one expression of the ongoing problem.
• Racial inequalities persist because they emerge out of a worldview that interprets visible signs of human variation as expressions of fundamental biological and genetic differences.
• Anthropologists have demonstrated over and over again how wrong this worldview is, showing that:
• There is much less genetic variation between populations than within them;
• There is no single gene that codes for race;
• In scientific terms humans are a single race;
• There are never clearly definable lines between physical traits in an actual population because variation is clinal;
• Racial differences are culturally-constructed upon arbitrary and shifting physical markers;
• The construction of racial typologies comes from a special way of sampling people, and rarely describe an actual individual or group;
• Morphological differences in humans are typically expressions of adaptability, not inferiority;
• Any biologically-more relevant ways to group humans, others such as blood type or immunity, are much more consequential in terms of bodily function.
• In spite of the fact that race has no biological or genetic origins, race can become biology through the embodiment of inequalities, dangerously reinforcing racialized understandings of human biology.