Humans exhibit biological variation. Humans also have a universal desire to categorize other humans in order to make sense of the world around them. Since the birth of the discipline of biological anthropology (or physical anthropology, as referred to back then), we have been interested in studying how humans vary biologically and what the sources of this variation are. Before we tackle these big problems, first consider this question: Why should we study human variation?
Not that Different: The Human Genome vs. The Concept of “Race”
There are certainly academic reasons for studying human variation. First, as we have seen already, it is important to consider the evolution of our species and how our biological variation may be similar to (or different from) that of other species. Second, anthropologists study modern human variation to understand how different biological traits developed over evolutionary time so we can make more accurate inferences about evolution and adaptation among our hominin ancestors, complementing our study of fossil evidence and the archaeological record. Third, it is important to consider that biological variation among humans has biomedical, forensic, and sociopolitical implications. For these reasons, the study of human variation and evolution has formed the basis of anthropological inquiry for centuries and continues to be a major source of intrigue and inspiration for scientific research conducted today.
An even-more-important role of the biological anthropologist is to improve public understanding of human evolution and variation. Terms such as race and ethnicity are used in everyday conversations and the division of humankind into smaller, discrete categories is a regular occurrence in day-to-day life. This can be seen regularly when governments acquire census data with a heading like “geographic origin” or “ethnicity.” Furthermore, such checkboxes and drop-down lists are commonly seen as part of the identifying information required for surveys and job applications. Race is very often understood as rooted in biological differences, ranging from familiar traits as skin color or eye shape to the genetic level. However, race is an “ideological construct” beyond biological and genetic bases at different times relating to our ethnicities, languages, religious beliefs, and cultural practices. Looking at human variation in terms of ‘race’ almost seems silly when compared to our actual biological variation as a species.
Some basics of genomics helps put this into perspective. In 2003, The Human Genome Project mapped out the entire human Genome, the entire set of ‘genetic instructions’ for our species. All humans are, genetically speaking, very much alike, sharing more than 99.9 percent of our DNA in common. However, people aren’t identical and genes do differ from one person to another. Phenotype refers to the expression of genes, such as height or hair color. Some phenotypic variation is not outwardly obvious, like blood type. DNA (deoxyribonucleic acid) is a complex molecule made up of only four “bases:” adenine, thymine, cytosine, guanine, and thymine—A, T, C and G for short. Just as zeros and ones make up the ‘code’ of current computer systems, these four letters form the basic ‘code’ of all life on earth. The bases are paired with one another—A with T and G with C—to form the rungs of the spiral ladder shape, or double helix, of the DNA molecule. The human genome, the complete set of genetic material, contains about 3 billion such pairs. That remaining 0.1% of our DNA accounts for the variation we see between people.
And where does that 0.1 percent (or one out of every thousand) come from? Occasionally when DNA replicates, a copying error or mutation occurs. These mutations occur randomly. With every child born, there are approximately 50 new mutations. Changes in a single base from one letter to another are called SNPs (“snips”) short for single nucleotide polymorphisms. SNPs are the most common form of genetic difference between people. Sometimes a change in one letter has no effect, other times, a SNP can affect a physical trait like eye color. And in rare cases, a SNP can lead to a debilitating disease like cystic fibrosis, sickle-cell anemia, or Huntington’s disease. SNP’s account for much of human variation. Two people chosen at random are likely to differ in 1 in every 1,000 nucleotide bases or 0.1 percent.
But any pair of individuals certainly seem to be more than one one-thousandth different from one another. This is because of how our ever-so-slight differences in DNA present in individuals. Sexually produced organisms inherit genes from both their parents. The genes you inherit from each parent may be slightly different. These variants of genes, called alleles, are sometimes either dominant or recessive. A dominant allele will mask the expression of the recessive allele. Sometimes, you need two copies of the recessive allele in order for some feature to be expressed. We will see how recessive alleles for certain disease get passed on in part because their presence in a ‘recessive’ state can actually be an advantage.
And so, from a biological perspective any two people are statistically more identical than they are different! At the same time ideas about ethnicity and race have huge social and political impacts, and have been part of the motivation behind various forms of racism and prejudice today, as well as many wars and genocides throughout history. Racism manifests in many ways—from instances of bullying between kids on school playgrounds to underpaid minorities in the workforce, and from verbal abuse to violent physical behaviors. Prejudice is negative views toward another group based on some perceived characteristic. Choosing which biological or nonbiological features to use when discussing race is always a cultural process. Race concepts have no validity to them unless people continue to use them in their daily lives.
Biological anthropology is crucial in the public sphere, because it debunks myths surrounding human variation. Rooted in scientific observations, our work can help non-anthropologists recognize how common ideas about “race” have no biological or genetic basis. Humans cannot actually be divided into discrete “races” because most traits vary on a continuous basis and human biology is, in fact, very homogenous compared to the greater genetic variation we observe in closely related species.
Instead, productive biological anthropology today is limited to discussing the presentation of biological traits among populations. While these traits like skin tone, build, or eye or nose shape often seem visually significant, it is important to keep in mind that the reason populations of humans vary as much as they do is that the most minor of changes in DNA can present as these physical differences. So far as physical differences in animals go, these are actually very slight. What makes them appear significant to us is the cultural significances we apply to them!
Populations Change Over Time
As early humans left Africa and spread across the globe, they faced numerous challenges related to their new environments. Beyond genetically influenced changes in physiology as a result of evolution, humans have developed lifestyle strategies to cope with and even thrive in a wide range of habitats. The ways populations of humans met such challenges, coupled with their geographic separation throughout the majority of the last two hundred thousand years, have led to the many forms of adaptation in our species. All organisms, including humans, must maintain a baseline of normal functions within their cells, tissues, and organs to survive. This constancy of internal functions is referred to as homeostasis. Homeostatic regulation, however, may be disrupted by a variety of both external and internal stimuli known as stressors. Within limits, all organisms have evolved certain physiological mechanisms to respond to stressors to maintain homeostasis. The range of changes in the physiology (function), morphology (form), and/or behavior of organisms in response to their environments and potential stressors is regulated by its phenotypic plasticity. Coping with these stressors led to the development of both adjustments (behavioral, acclimatory, and developmental) and adaptations, which are explained in detail in the following sections.
The term adjustment refers to an organism’s nongenetic way of coping with the stressors of its environment. Although adjustments themselves are nongenetic in nature, the ability of an organism to experience or develop an adjustment is based on its phenotypic plasticity, which is linked to its evolutionarily-guided genetic potential. Adjustments occur exclusively on the individual level. As such, different individuals within a population may experience a wide range of possible adjustments in response to a similar stressor.
In general, the three main forms of adjustment are: behavioral, acclimatory, and developmental. Behavioral adjustments are regarded as cultural responses to environmental stressors and must be constantly altered to meet novel situations posed by the environment. Acclimatory adjustments are temporary, reversible changes in an organism’s physiology in response to environmental stressors. The range of acclimatory adjustments that an organism is capable of producing is linked to its underlying phenotypic plasticity and the duration and severity of the stressor. A good example of this is the human response to varying ambient temperatures—vasoconstriction (flushing), vasodilation (blushing), shivering, or cooling by evaporation by producing sweat. Developmental adjustments occur only in individuals who spend their developmental period (i.e., childhood and adolescence) under specific environmental conditions, such as high-altitudes with low oxygen levels or with or without access to particular nutrients. Changes during development are directly related to underlying phenotypic plasticity as well as the amount of time during the crucial growth and development period that the individual resides within the challenging environment.
Behavioral, acclimatory, and developmental adjustments are all related to phenotypic plasticity; however, most adjustments are temporary and only affect individuals rather than populations. What if the physiological changes were permanent and affected an entire population? The long-term, microevolutionary (i.e., genetic) changes that occur within a population in response to an environmental stressor are referred to as an adaptation. From an evolutionary standpoint, the term adaptation refers to a phenotypic trait (i.e., physiological/morphological feature or behavior) that has been acted upon by natural selection to increase a species’ ability to survive and reproduce within a specific environment. Adaptations are traits that serve to restore homeostasis. The physiology-based interpretation of adaptations presumes that all traits serve a purpose and that all adaptations are beneficial in nature; however, this may be a fallacy, since some traits may be present without clear evidence as to their purpose.
We know that genetic mutations called SNPs are acted upon by natural selection to produce these adaptations. So, why do populations look different from others or have higher frequencies of certain SNPs than others? There are two important ways in which SNPs get distributed which should be familiar to you from our look at evolution in general: the founder effect and natural selection.
Founder effect happens when a small group of people establish a population, bringing with them a limited about of genetic variation. The founding group is then isolated from others. Sometimes the founders bring with them chance mutations, and so subsequent generations are more likely to have those mutations as well. As an example, on the Micronesian atoll of Pingelap, about one in ten people is totally colorblind, seeing only black and white. It is thought that a typhoon wiped out most of the population in 1775. The king, who was thought to have carried the defective gene, survived and passed it on to his many descendants. The colorblindness also makes people very sensitive to the sun, and they can’t see very well at all during the daytime. One solution has been to fish for flying fish at night, which the Pingelap excel at.
In natural selection, a trait has some advantage in a particular environment that causes individuals with that trait to survive and reproduce at a higher rate than individuals without the trait. Unlike founder effect, traits confer some advantage to the organism. Recall that, the mutations occur at random, but natural selection acts upon those random mutations. The same process has shaped the human phenotype, from lactose tolerance (or “lactase persistence”), to disease resistance, to skin color.
Human babies can digest lactose until about the age of 4 to 6, then the ability shuts down and people become lactose intolerant. In this case, the gene does not code for a protein but switches on and off the gene that produces lactase. In some populations, SNPs arose such that the ability to digest lactose never switches off and adults can drink milk freely—called lactose persistence. Not too surprisingly, populations that can drink milk are those where herding animals are important or were important to their ancestral populations. This is a good example of how a cultural trait, herding, led to the selection of a biological trait, lactose tolerance. In fact, humans are the only mammal that can do this. Shaping our biology as a result of culture is called gene-culture co-evolution. The ability to digest milk, even if it conferred a small advantage, would have led to most people being lactose tolerant.
Different mutations led to lactose tolerance in different populations. Different SNPs account for lactose tolerance in Europe, Africa, and the Middle East. The same SNP accounts for lactose tolerance on Europe and India, indicating a common origin. In northern Europeans, lactose tolerance is a result of just one SNP, a mutation in a single base pair. The Masai cattle herders of Tanzania and other sub-Saharan Africans, however, have a different mutation that also results in lactose tolerance. These mutations popped up randomly—and separately—but were acted on through natural selection in each case because they were advantageous in cultures with domesticated animals that could be milked (convergent evolution). It is likely these mutations likewise occurred in populations without milk-producing livestock, but, in these cases, the mutation didn’t offer any particular benefit and therefore was not acted upon by natural selection.
Distribution of adults who can digest lactose in the indigenous population of Africa, Eurasia, and Oceania. Dots represent sampled populations. [Source: Joe Roe via Wikimedia Commons]
Another example of natural selection in humans is the sickle cell trait. A disease called sickle cell anemia is caused by a variant of a gene that produces hemoglobin. The variant is caused by a single SNP from adenine to thymine. Sickle cell anemia is a painful disease that can result in shortened lifespan if left untreated. The normal variant of the gene is designated as S and the affected gene as s. Individuals inherit alleles each from their mother and father. If a person has SS (called homozygous dominant), then they do not have the disease. If a person has the variants Ss (heterozygous), then they do not have the disease but are a carrier. Two copies of the variant ss (homozygous recessive) causes sickle cell anemia causing red blood cells to become sickle shaped, preventing them from transporting oxygen.
Why would such a harmful mutation become so common in a population rather than fade away? The answer is natural selection. People with the variants Ss, who are carriers for the disease, are also resistant to malaria, a zoonotic disease transmitted by mosquitoes. Those with the SS variants are not resistant and so the Ss variants survive at a greater rate than SS. The sickle cell trait is prevalent in those areas where malaria is common like Western Africa, the Arabian Peninsula, and southern India. Because western Africans were brought to the United States as slaves, sickle cell anemia is prevalent among African Americans as well. Today, blood tests can determine if someone is a carrier and ascertain the likelihood of transmitting the disease to offspring.
Top Left: Diagram showing two carrier parents (heterozygous) and their three potential type of offspring. Note that the likewise heterozygous offspring (Ss) is actually twice as likely as either homozygous offspring (SS or ss) [Source: Luke Konkol, CC0]. Top Right: A comparison of typical red blood cells (left) and sickle cells (right) [Source: modified from public domain image via Wikimedia Commons]. Bottom: Comparison of malaria distribution (left) and sickle cell trait distribution (right) [Source: Anthony Allison, CC0 via Wikimedia Commons].
But lactose persistence and the sickle cell trait are largely invisible biological features rarely (if ever) used to culturally distinguish individuals. Race, today’s Western student might say, is about skin color. Human variation in skin tone likewise has a biological basis first better understood in terms of variation by natural selection rather than in the cultural terms it has been applied today.
All primates have ability to produce melanin, in part a natural sunscreen, in their skin. Skin color depends on the type of melanin produced in skin cells called melanocytes. Melanin also affects what eye color you have. Blue eyes derive from a mutation in a genetic “switch” for a certain gene. The switch reduces the ability of the gene to produce melanin (brown) in the eye resulting in blue. Melanin also colors hair/fur and bird feathers. But why does human skin color differ?
Closeup cutaway view of the skin showing malanocytes (the cells which produce melanin) and the melanin produced. [Source: National Cancer Institute via Wikimedia Commons]
Ultraviolet radiation damages DNA in the skin and disrupts cells’ processes. Dark skin protects against ultraviolet radiation and the damage it can cause. Melanin acts as a barrier between the ultraviolet rays and the nucleus of the skin cell, which houses the DNA. As a result, melanin protects DNA and helps prevents skin cancers. Those with dark skin in high UV regions have a selective advantage over lighter skinned people. Dark skin also conserves folate, which is destroyed by ultraviolet-B sunlight (UVB). Folate is essential, because low folate in pregnant women can result in severe birth defects as demand for folate increases during pregnancy. These advantages would quickly make dark skin universal in areas of high UV. Because folate is destroyed by sunlight, pregnant women take folic acid or eat foods high in folate to prevent neural tube defects. In the United States today, many foods like cereals, breads, and pasta, are supplemented with folic acid for this reason.
We can then ask, why do some people have lighter skin? Lighter skin is a liability in the tropics, but those with lighter skin are able to better synthesize vitamin D (a hormone necessary for absorption of calcium) in more northerly climates. Melanin greatly slows the production of vitamin D. A dark-skinned person can take six times as long to produce the same amount of vitamin D as a light-skinned person. Nutritional rickets, a deforming bone disease, can develop in the presence of vitamin D deficiency. Women with rickets have reduced pelvic openings, and have difficulty delivering babies, making the selective factors for light skin stronger in some areas. Some of the first c-sections in the U.S. were on enslaved African American women who suffered from pelvic deformities, likely brought about by vitamin D deficiencies. Similar to folate, foods are now enriched with vitamin D to prevent deficiencies (in the past, kids took cod liver oil). Vitamin D deficiencies are now being recognized as having other effects including a weakened immune system and an association with cancers. Like dark skin in the tropics, light skin is naturally selected for in areas of lower ultraviolet radiation.
There are still other skin phenotypes that are the product of natural selection. The ability to tan is also an adaptive trait based on genetic and environmental interaction. Tanning is the ability to increase melanin production when needed. In some areas of the world, such as the Mediterranean, the amount of sunlight varies considerably from one season to the next. Local populations have physiological mechanisms to darken their skin during yearly seasons of high sunlight. In other areas of the world, such as the British Isles, cloudy conditions prevail even during summer seasons and very little tanning ability has evolved.
Natural selection plays a significant role in the determination of the shape and size of the human body. The most significant thermodynamic mechanism of heat loss from the body is radiation; however, the efficiency of radiation is correlated to the overall body shape and size of the individual. There is a direct correlation between the ratio of an object’s surface area to mass and the amount of heat that may be lost through radiation. In regions where temperatures are consistently cold, the body shape and size of individuals indigenous to the area tend to be more compact. These individuals have a relatively higher body mass to surface area (i.e., skin) than their counterparts from equatorial regions where the average temperatures are considerably warmer. Individuals from hot climates, such as the Fulani of West Africa, have limbs that are considerably longer than those of individuals from cold climates, such as the Inuit of Greenland. Evolutionarily, the longer limbs of individuals from equatorial regions provide a greater surface area (i.e., lower body mass to surface area ratio) for the dissipation of heat through radiative processes. In contrast, the relatively short limbs of Arctic-dwelling people, such as the Inuit, allows for the retention of heat because there is a decreased surface area through which heat may radiate away from the body.
The individual on the left is typical of one adapted to a cold environment where the conservation of heat in the body’s core is of critical importance.The individual on the right could be adapted to a tropical environment where the rapid dispersal of heat is necessary to maintain homeostasis. Credit: Greenland 1999 (01) by Vadeve has been designated to the public domain (CC0).
To better describe the trends related to the general shape and size of human bodies in relation to the thermal conditions, we turn to a couple of general principles that are applicable to a variety of species beyond humans. Bergmann’s Rule predicts that as average environmental temperature decreases, populations are expected to exhibit an increase in weight and a decrease in surface area. Also, within the same species of homeothermic animals, the relative length of projecting body parts (e.g., nose, ears, and limbs) increases in relation to the average environmental temperature. This principle, referred to as Allen’s Rule, notes that longer, thinner limbs are advantageous for the radiation of excess heat in hot environments and shorter, stockier limbs assist with the preservation of body heat in cold climates.
These organisms are representative of Bergmann’s rule. The animal on the left depicts an ungulate from a cooler environment with increased body weight and decreased surface area, compared to the slender ungulate on the right. Credit: Bergmann’s Rule (Figure 14.16a) original to Explorations: An Open Invitation to Biological Anthropology by Mary Nelson is under a CC BY-NC 4.0 License.These animals are representative of Allen’s rule. The rabbit on the left comes from a cooler environment and is compact with short limbs and ears. The rabbit on the right comes from a warm environment and has long and lanky limbs and ears. The rabbit in the middle has ears and limbs that are in-between the other two. Rabbits do not sweat like humans; heat is dissipated primarily through their ears. Credit: Allen’s Rule (Figure 14.16b) original to Explorations: An Open Invitation to Biological Anthropology by Mary Nelson is under a CC BY-NC 4.0 License.
Nasal shape and size is another physiological feature affected by our ancestors’ environments. The selective role of climate in determining human nasal variation is typically approached by dividing climates into four adaptive zones: hot-dry, hot-wet, cold-dry, and cold-wet. A principal role of the nasal cavity is to warm and humidify ambient air prior to its reaching the lungs. Given this function of the nasal cavity, it is anticipated that different nasal shapes and sizes will be related to varying environments. In cold-dry climates, an individual’s nasal cavity must provide humidification and warmth to the dry air when breathing in through the nose, conserve moisture, and minimize heat loss when the individual exhales through the nose. Conversely, in hot-wet environments, there is no need for the nasal cavity to provide additional moisture, nor a need to warm the air or to preserve heat within the nasal cavity. As with most human morphological elements, the shape and size of the nasal cavity occurs along a cline (a gradient). Due to the environmental stressors of cold-dry environments requiring the humidification and warming of air through the nasal cavity, individuals indigenous to such environments tend to have taller (longer) noses with a reduced nasal entrance (nostril opening) size. Individuals indigenous to hot-wet climates tend to have nasal shapes which are shorter with broader nasal entrances.
So, does variation mean race? The short answer is no. Variation only means variation. Race is what we make of it.
Concepts of “Race”
The earliest classification systems used to racially describe human variation are evidenced by ancient manuscripts, scrolls, and stone tablets recovered through archaeological, historical, and literary research. The Ancient Egyptians had the Book of Gates (between 1550 BCE and 1077 BCE). In one part of this tome dedicated to depictions of the underworld, scribes used pictures and hieroglyphics to illustrate a division of Egyptian people into the four categories known to them at the time: Asiatics, Nubians, Egyptians, and Libyans. The Ancient Egyptians believed that each of these groups were made of a distinctive category of people, distinguishable by their skin color, place of origin, and even behavioral traits.
The Jewish Bible (the Old Testament of the Christian Bible) writes that all humankind descends from one of three sons of Noah: Shem (the ancestor to all olive-skinned Asians), Japheth (the ancestor to pale-skinned Europeans), and Ham (the ancestor to darker-skinned Africans). Similar to the Ancient Egyptians, these distinctions were based on behavioral traits and skin color. More recent work in historiography and linguistics suggest that the branches of “Hamites,” “Japhethites,” and “Shemites” may also relate to the formation of three independent language groups some time between 1000 and 3000 BCE. With the continued proliferation of Christianity, this concept of approximately three racial groupings lasted until the Middle Ages and spread as far across Eurasia as crusaders and missionaries ventured at the time.
The “Great Chain of Being,” conceived by ancient Greek philosophers like Plato (427‒348 BCE) and Aristotle (384‒322 BCE) also played a key role in laying early foundations of empirical sciences. Observations of things were made with the aim of creating taxonomic categories. Aristotle describes the Great Chain of Being as a ladder along which all objects, plants, animals, humans, and celestial bodies can be mapped in an overall hierarchy (in the order of existential importance, with humans placed near the top, just beneath divine beings). When he writes about humans, Aristotle expressed the belief that certain people are inherently more instinctive rulers, while others are more natural fits for the life of a worker or enslaved person.
The Great Chain of Being from the Rhetorica Christiana by Fray Diego de Valades (1579). Credit: Great Chain of Being by Didacus Valades (Diego Valades 1579), print from Rhetorica Christiana (via Getty Research), is in the public domain.
Based on research by biological anthropologists, we currently recognize that these early systems of classification and hierarchization are unhelpful in studying human biological variation. Both behavioral traits and physical traits are coded for by multiple genes each, and how we exhibit those traits based on our genetics can vary significantly even between individuals of the same population. But this style of thinking survived from Aristotle, through the Scientific Revolution, and even, sadly, into the work of early ‘anthropologists.’
The 1400s to 1600s saw the beginnings of the Scientific Revolution in Western societies. While by no means the first or only scholars globally to use observation and experimentation to understand the world around them, early scientists living at the end of the medieval period in Europe increasingly employed more experimentation, quantification, and rational thought in their work. This is the main difference between the work of the ancient Egyptians, Romans, and Greeks and that of later scientists such as Isaac Newton and Carl Linnaeus in the 1600s and 1700s.
Linnaeus classified (typified) all plants and animals under the formalized naming system known as binomial nomenclature in which all organisms are placed into groups according to how they are similar or different to others under study. What was most anthropologically notable about Linnaeus’s typological system was that he was one of the first to group humans with apes and monkeys, based on the anatomical similarities between humans and nonhuman primates. However, Linnaeus viewed the world in line with essentialism, a problematic concept that dictates that there are a unique set of characteristics that organisms of a specific kind must have and that would remove organisms from taxonomic categorizations if they lacked any of the required criteria. As a result, Linnaeus subdivided the human species into four varieties, with overtly racist categories based on skin color and “inherent” behaviors.
Most European scientists during this period were not aware of their own biases skewing their interpretations of biological variation; others deliberately worked to shape public perceptions of human variation in ways that established “otherness” and enforced European domination and the subordination of non-European people. During the so-called Age of Discovery, the superiority of European cultures over others was a pervasive idea throughout people’s social and political lives. Although much of Eurasia was linked by spice- and silk-trading routes, the European colonial period between the 1400s and 1700s was marked by many new and unfortunately violent encounters overseas. When Europeans arrived by ship on the shores of continents that were already inhabited, the Indigenous peoples looked, spoke, and behaved differently from peoples with whom they were familiar. Building on the idea of species and “subspecies,” ‘natural historians’ of this time invented the term race, from the French rasse meaning “local strain.”
Between the 1800s and mid-1900s, an increased use of scientific methods to justify racial schemes developed in scholarship. Classification systems after 1800 became more polygenetic (all people having separate origins) rather than monogenetic (all people having a single origin). There was increased support for the notion that each race was created separately and with different attributes (intelligence, temperament, and appearance).
The 1800s was when the scientific measurement of human physical features (anthropometry) became popularized. However, empirical studies in the 1800s pushed even further the idea that Europeans were culturally and biologically superior to others. Samuel George Morton (1799‒1851) was a scholar who had a large role in perpetuating 1800s scientific racism. By measuring cranial size and shape, he calculated that “Caucasians,” on average, have greater cranial volumes than other groups he referred to collectively as “Negros.” Today, we know that cranial size variation depends on such factors as Allen’s and Bergmann’s rules, which give a more likely explanation. The leading figures in craniometry during the 1800s instead were linked heavily with powerful individuals and wealthy sociopolitical institutions and financial bodies. Theories in support of hierarchical racial schemes using “scientific” bases certainly helped continue the exploitative and unethical trafficking and enslavement of Africans between the 1500s and 1800s. Morton went on to write a number of views that fit with a concept called biological determinism: that an association exists between people’s physical characteristics and their behavior, intelligence, ability, values, and morals. If the idea is that some groups of people are essentially superior to others in cognitive ability and temperament, then it is easier to justify the unequal treatment of certain groups based on outward appearances.
Another such problematic thinker was Paul Broca (1824‒1880) (after whom that region of the frontal lobe related to language use is named). Influenced by Morton, Broca claimed that internal skull capacities could be linked with skin color and cognitive ability. He went on to justify the European colonization of other global territories by purporting it was noble for a biologically more “civilized” population to improve the “humanity” of more “barbaric” populations. Today, these theories of Morton, Broca, and others like them are known to have no scientific basis.
In the early 20th century, we saw a number of new figures coming into the science of human variation and shifting the theoretical focus within. Most notably, these included Aleš Hrdlička and Franz Boas. Hrdlička (1869‒1943) was a Czech anthropologist who moved to the United States. As part of his work and the scope of the journal, he differentiated “physical anthropology” from other kinds of anthropology. Franz Boas (1858‒1942) was a German American anthropologist who established the four-field anthropology system in the United States and founded the American Anthropological Association in 1902. He argued that the scientific method should be used in the study of human cultures and the comparative method for looking at human biology worldwide. One of Boas’s significant contributions to biological anthropology was the study of skull dimensions with respect to race concluding that, “There is no reason to believe that one race is by nature so much more intelligent, endowed with great willpower, or emotionally more stable than another, that the difference would materially influence its culture.” This conclusion directly contrasted with the theories of the past that relied on biological determinism and biological anthropologists today have found evidence that corroborates Boas’s explanations.
But the first half of the 1900s also involved essentialist research focused on proving racial determinism. Anthropologists like Francis Galton (1822‒1911) and Earnest A. Hooton (1887‒1954) created the field of eugenics as a way of “dealing with” criminals, diseased individuals, and “uncivilized” people. Eugenicists recommended prohibiting non-superior portions of the population from being married or sterilizing these members of society so they could no longer procreate. In the 1930s, Nazi Germany used this false idea of there being “pure races” to highly destructive effect. The need to be protected against admixture from “unfit” groups was their justification for their blatant racism and purging of citizens that fell under their subjective criteria.
Eugenicist ideas were popularly discussed around the world. The Immigration Restriction Act of 1924 was passed in the United States, with the explicit aim of reducing the country’s “burden” of people considered inferior. In the early 1900s, Chinese scientists and politicians showed great interest in eugenic ideologies influencing their medicine and laws. In 1950s apartheid South Africa, interracial marriages and sexual relations were banned by law. We still see the continuation of eugenics-based logic today around the world—in exclusionary immigration laws, cases of incarcerated prison inmates being forcibly sterilized, and the persistence of intelligence testing as a form of measuring people’s “fitness” in a society.
Shortly after World War II and the Nazi Holocaust, the full extent of essentialist, eugenicist thinking became clear. Social constructions of race, and the notion that one can predict psychological or behavioral traits based on external appearance, had become unpopular both within and outside the discipline. It was up to those in the field of physical anthropology at the time to separate physical anthropology from race concepts that supported unscientific and socially damaging agendas. This does not mean that there are no physiological or behavioral differences between different members of the human species. However, going forward, several physical anthropologists saw human biological variation as more complicated than simple typologies could describe.
Genetics and Variation
All traits are genetic. Even if you spend hours at the gym and are totally ripped, that is still a genetic trait because genes produce chemicals that respond to all that work. But all traits are also environmental. For example, height has a genetic component, but diet, temperature, and elevation also play roles in how tall you will be by affecting whether genes will be expressed or not. Genes and environment can’t be separated; instead they interact to produce traits. Some traits, however, are more heritable than others, which means that environment plays a lesser role in its expression. Rather than the tired phrase “nature versus nurture”, it is more accurate to speak of “nature through nurture,” so even the most basic elements of human variation we might think of as ‘purely genetic’ are much more complicated than that.
Across our history, humans have developed the cultural practice of racial classification. This involves assigning humans to categories based on phenotype, especially traits that are outwardly apparent. Sadly, some of the worst work in this area was done by early ‘physical anthropologists’ who claimed to be classifying humans ‘scientifically.’ In the recent past, American children were taught that there are ‘five great races of the world’—a taxonomy that was hierarchical. This was the essentialist view of race—that there are discrete groups with large gaps between them. Under this view, “Caucasians” were the most ideal form, and everyone was of degenerate form of human. (Note: “Caucasian” or “Caucasoid” referred to the ‘race’ of people named for the Caucasus region in Eurasia from whom fair-skinned individuals were thought to have originated. This view was mistaken. Despite its continued use as synonymous with “white” in U.S. census data and elsewhere, this historical baggage makes it problematic.)
The essentialist view of race runs into immediate problems in light of the continuous nature of traits, especially skin, hair, and eye color. Skin color and eye color are not straightforward SNPs like lactose tolerance or sickle cell trait. Rather, they are influenced by several different genes, more than 15 for skin and 16 or more for eye color. Skin color is not an essentialist category, but rather a continuum. If skin color is meant to reflect deeper qualities of a person or a person’s wider genotype, what do we make of siblings, even fraternal twins, who are considered different races based on their skin color? And how does a single individual who shares perceived features of different races—like dark skin and blonde hair— get categorized? For instance, blonde hair arose independently in Europe and Melanesia and from different mutations. Which trait is considered more important to race, and why? People decide, culturally, whether someone belongs to a race or not.
German anthropologist Johann Friedrich Blumenbach developed the notion of the ‘five great races.’ During Blumenbach’s time, nothing was known of genetics. The Augustinian friar Gregor Mendel (1822–1884), who began the study of genetics by working out the inheritance of pea plants, had not even been born. Instead Blumenbach based his categories on his perception of phenotype and his own biases. Many today assume still that racial categories correspond to deep underlying genetic differences. They do not.
With the Human Genome Project results, we know more about the genotypes of human populations. We now know that the genetic variation between any two individuals is about one tenth of one percent. Most genetic variation are found within populations around the world. As writer Malik Kenan in Why Both Sides are Wrong in the Race Debate writes, “Imagine that some nuclear nightmare wiped out the entire human race apart from one small population—say, the Masai tribe in East Africa. Almost all the genetic variation that exists in the world today would still be present in that one small group.” The differences between human populations are purely statistical, not essential or absolute. Populations are more likely to contain certain alleles, but not everyone has them. And statistical differences are found between virtually any two populations. If we decided that those categories would be useful and productive for society or science, there would be hundreds or thousands of races based on genetics. If you’re looking for statistical genetic differences between populations, you will find them. Even if there are genetic differences between populations they are influenced by likely hundreds of genes as well as the environment. We always have to decide which criteria, whether phenotypic or genotypic, to base our categories as well as why (and if) these categories are needed.
Human Variation: Our Story Continues
From the time that the first of our species left Africa, we have had to adjust and adapt to numerous environmental challenges. The remarkable ability of human beings to maintain homeostasis through a combination of both nongenetic (adjustments) and genetic (adaptations) means has allowed us to occupy a remarkable variety of environments, from high-altitude mountainous regions to the tropics near the equator. From adding piquant, pungent spices to our foods as a means of inhibiting food-borne illnesses due to bacterial growth to donning garments specially suited to local climates, behavioral adjustments have provided us with a nongenetic means of coping with obstacles to our health and well-being. Acclimatory adjustments, such as sweating when we are warm in an attempt to regulate our body temperature or experiencing increased breathing rates as a means of increasing blood oxygen levels in regions where the partial pressure of oxygen is low, have been instrumental in our survival with respect to thermal and altitudinal environmental challenges. For some individuals, developmental adjustments that were acquired during their development and growth phases (e.g., increased heart and lung capacities for individuals from high-altitude regions) provide them with a form of physiological advantage not possible for someone who ventures to such an environmentally challenging region as an adult. Genetically mediated adaptations, such as variations in the pigmentation of our skin, have ensured our evolutionary fitness across all latitudes.
Will the human species continue to adjust and adapt to new environmental challenges in the future? If past performance is any measure of future expectations, then the human story will continue as long as we do not alter our environment to the point that the plasticity of our behavior, physiological, and morphological boundaries is exceeded. In the following chapters, you will explore additional information about our saga as a species. From the concept of race as a sociocultural construct to our epidemiological history, the nuances of evolutionary-based human variation are always present and provide the basis for understanding our history and our future as a species.
