Race and Human Variation — Study Notes (2nd Edition)

Learning Objectives

Illustrate the troubled history of “race” concepts and how they have been used to classify humans.
Explain human variation and evolution as the thematic roots of biological anthropology as a discipline.
Critique earlier “race” concepts based on contemporary understandings of human genetic variation and how it is distributed.
Explain how biological variation in humans is distributed clinally and in accordance with isolation-by-distance and Out-of-Africa models.
Identify phenotypic traits that reflect selective and neutral evolution.
Extend this nuanced view to contemporary research, biomedical implications, forensic anthropology, and related social/political concerns.
Recognize that humans are biologically similar overall yet vary in distribution of traits due to evolutionary and demographic processes.

Why Study Human Variation?

Humans exhibit biological variation, and there is a universal tendency to categorize others.
The discipline investigates how biological variation arises, its sources, and what it implies about evolution and adaptation.
Goals include: understanding evolution, improving public understanding of human diversity, and addressing social/political concerns linked to race concepts.
Public discourse often conflates race with biology; anthropologists aim to debunk myths and show the actual distribution of human variation (Figure 13.1 exemplifies cultural vs. genetic diversity).

What Counts as Race? Race as Social Construct and Biological Reality

Race concepts have historical roots in census practices, social organization, and political power.
Race can be studied as an ideological construct tied to ethnicity, languages, religions, and cultural practices, not only biology.
Racism manifests in many forms, from microaggressions to structural oppression, and has real social and political consequences.
Advances in molecular genetics show remarkable genetic similarity across humans with relatively few differences between populations; biological races as discrete categories do not reflect the true pattern of human variation.
Anthropologists play a public-facing role in debunking myths, tracing the history of race concepts, and promoting a more accurate understanding of variation.

The History of “Race” Concepts (Overview)

Race concepts have evolved through multiple historical phases, often aligned with social and political contexts.
Early classification systems varied by place and era and often linked to observable traits like skin color or geography but lacked rigorous scientific grounding.
The emergence of racial typologies often reflected social hierarchies and justified domination and exploitation.
The field has moved from typological thinking toward population-based approaches that emphasize continuous variation and gene flow.

Race in the Classical Era and Early Taxonomy

Ancient Egyptians depicted groups (Aamu/Asiatics, Nehesu/Nubians, Reth/Egyptians, Themehu/Libyans) in ways that reflected beliefs about difference rather than biology.
Biblical narratives framed humanity via descendants of Noah (Shem, Japheth, Ham), which historically intersected with ideas about human groups but were not scientific explanations of variation.
The Great Chain of Being (Plato, Aristotle) placed humans in a hierarchical order, often justifying inequality.
Modern conclusions reject these hierarchies as explanations of biological variation; human traits are polygenic and distributed along continua rather than discrete races.

Linnaeus and the Rise of Typology (18th Century)

Carl Linnaeus (Systema Naturae, 1758) introduced binomial nomenclature and placed humans among primates in a typological system.
He subdivided humans into four varieties with overtly racial and behavioral attributions to skin color and classically charged categories.
These typologies reflected essentialist thinking (a set of necessary traits) and supported contemporary social hierarchies and imperial expansion.

Race and the Dawn of Scientific Racism (19th–early 20th centuries)

The period between the 1800s and mid-1900s saw increased use of “science” to justify racial hierarchies (scientific racism).
Polygenism (multiple origins for different groups) gained prominence over a single-origin view.
Craniometry and measurement of physical traits were used to argue for racial differences and infer superiority.
Samuel George Morton and Paul Broca advanced craniometric claims linking skull size/capacity to cognitive ability and behavior, often aligned with racist ideologies.
Visualized hierarchies reinforced European colonial dominance and justified exploitation, slavery, and segregation.
By mid-20th century, essentialist and eugenic ideas faced strong critique and were increasingly rejected by the scientific community.

Eugenics, Race, and Public Policy (20th Century)

Francis Galton and Earnest A. Hooton and others promoted eugenics as a policy framework (restricting marriage, sterilization, and social control of certain groups).
The Immigration Act of 1924 in the U.S. restricted immigration of certain groups; similar ideologies influenced policies elsewhere.
Nazi Germany exemplified the misuse of biology to justify extreme racism and genocide.
After World War II, physics of biology shifted away from biological race concepts, but social and political misuse persisted in various forms (immigration policy, surveillance, and discriminatory medicine).

The New Physical Anthropology (Mid-20th Century): A Population Perspective

Wollcoming shift toward evolutionary explanations for variation, rather than typologies of races.
Key figures: Sherwood Washburn, Theodosius Dobzhansky, Julian Huxley.
Emphasis on populations as units of analysis rather than racial types; populations defined by geographic proximity, language, culture, interbreeding potential, and shared histories.
The modern synthesis reconciled Darwinian evolution with Mendelian inheritance, showing how populations can exchange genes and how polygenic traits can produce continuous variation.
The field began to emphasize the complexity of mechanisms (gene flow, drift, selection) shaping variation rather than fixed racial categories.

Modern Population Concepts and Nonconcordance

Many human traits are nonconcordant: genetic variants for one trait do not reliably predict another trait.
Notions like skin color, brain function, or temperament cannot be cleanly predicted from a single trait or a small set of traits.
Variation in humans is clinal and continuous rather than discrete; there is no single boundary separating populations into distinct races.

Nonconcordance; Clines; and Continuous Variation

Nonconcordance: Traits vary independently; knowing someone’s height says little about skin color, lactose tolerance, or ABO blood type.
Clinal distribution: Traits vary gradually across geography; not discrete. A classic example is skin color: darker near the equator, lighter at higher latitudes.
Some traits show clines due to natural selection (e.g., skin pigmentation) or neutral processes (gene flow, genetic drift, serial founder effects).
Height is an example of continuous variation that does not align neatly with geography alone; skin color demonstrates a more recognizable geographic cline.

Mechanisms Producing Clinal Patterns

Natural selection: Explains global clines like skin color, where UV radiation selects for pigmentation levels.
Lactase persistence: Variation tied to dairy consumption histories; geographically distributed according to cultural practices.
Malaria and sickle cell trait: Malaria prevalence correlates with certain alleles (sickle cell) in a geographic cline.
Cultural practices can influence mate choice and thereby contribute to clinal variation.
Neutral processes: Gene flow, genetic drift, and founder effects can also create clinal patterns independent of local adaptation.

Global Patterns of Genetic Variation and Population Models

Out-of-Africa model: Modern human origins trace to sub-Saharan Africa, with serial founder events as populations migrated globally.
Isolation-by-distance: Genetic similarity decreases with geographic distance; populations closer geographically are more similar.
Analyses of neutral markers reveal that most global genetic variation occurs within populations rather than between traditional race groups.
Approximately 93–95% of global genetic variation is found within populations; only about 3–5% accounts for differences among major population groups. $93 ext{-}95 ext{ extperthousand} ext{ of global genetic differences are within populations; } 3 ext{-}5 ext{ extperthousand} ext{ among groups.}$
These results support the conclusion that distinct biological races do not exist, though clusters or groups can be identified due to history and geography.
Sub-Saharan Africa contains the greatest genetic variation; variation decreases with distance from Africa due to serial founder effects.

Data Illustrating Population Structure

Rosenberg et al. (2002, 2005) used neutral genetic markers to examine population structure, showing that most variation is within populations and that clusters are arbitrary and shaped by study design.
Kanitz et al. (2018) demonstrate isolation-by-distance and Out-of-Africa models together: genetic similarity correlates with geographic distance, and the distance from Africa predicts allele sharing across populations.
We should avoid interpreting clusters as discrete ancestral populations; they reflect history, gene flow, migration, and demographic events.

Humans: Homogeneity Relative to Other Species

Humans are 99.9% identical at the genome level; the remaining 0.1% accounts for observed variation.
Compared to chimpanzees and other great apes, humans show far less average genome-wide heterogeneity, despite vast geographic and phenotypic diversity.
The relatively young age of our species (roughly 150,000–300,000 years) and significant historical population moves explain much of the pattern of variation.

Phenotypic Traits: Neutral Evolution vs Natural Selection

Phenotypic traits reflect different evolutionary histories:
- Neutral evolution: Traits distributed by drift, gene flow, and founder effects without strong selective pressures (e.g., certain cranial features, some dental traits).
- Natural selection: Traits shaped by environmental pressures (e.g., skin pigmentation, lactase persistence, resistance to malaria traits).
Contemporary analyses using larger samples and more informative measurements show most cranial variation occurs within populations and decreases with distance from Africa, consistent with neutral population history rather than discrete racial categories.
Pelvis shape, teeth, and inner ear (bony labyrinth) also show similar within-population variation and a gradient with distance from Africa.

Skin Color and Other Trait Variations

Skin color variation is a notable example of a cline that reflects adaptive changes to UV radiation exposure.
Quantitative studies show global skin color variation is largely explained by genetic differences between populations, with a smaller contribution from variation within populations. In one analysis, roughly:
- $87.9\%$ of global skin color variation is attributed to between-population differences,
- $3.2\%$ among local populations within regions,
- $8.9\%$ within local populations.
This distribution contrasts with many other markers, like ABO blood group alleles, which show different geographic patterns due to historical demography and drift.
Researchers like Nina Jablonski have advanced quantitative methods to study pigmentation, though some populations remain under-studied, underscoring the need for broader sampling.

Other Phenotypic Traits Reflecting Neutral and Selection Histories

Cranial variation, pelvis shape, dental traits, and the bony labyrinth all show variation shaped by migration and demography with a strong component of neutral evolution.
Skeletal traits tend to be continuous and nondiscrete across populations; their distribution can reflect migration patterns, not discrete races.
While many traits are determined by complex polygenic networks, the overall picture is that most variation is not aligned with racial categories.

Social and Ethical Implications

The public understanding of race impacts health, medicine, forensics, and social policy.
Medical racism and disparities in care arise partly from misapplications of race concepts and from biases in healthcare, epidemiology, and clinical trials.
Forensic anthropology debates whether ancestry estimation should be used; many argue for a focus on population affinity and probabilistic inference rather than discrete racial categorization.
The Black Lives Matter movement highlights how racialized systems produce social and health inequities; anthropologists advocate for EDI (equity, diversity, inclusion) in institutions.
Dorothy Roberts argues that race as a biological concept is scientifically unfounded but socially consequential; caution is needed in the use and portrayal of ancestry information in medicine, policy, and law enforcement.
In pharmacogenomics and medicine, population-specific biology is crucial for accurate diagnosis and treatment, but typological races are not scientifically valid proxies for health outcomes.
Public communication should emphasize similarities, while acknowledging real social effects of racialized policies and biases.

Forensic Anthropology and Population Affinity

In the past, some forensic anthropologists labeled ancestry based on skull morphology; now many scholars argue against rigid ancestry assignments because of the substantial overlap among populations and the limitations of skeletal data.
Ancestry estimations should be framed probabilistically, with transparent methodology and recognition of uncertainty.
The field increasingly emphasizes neutral or selective causes of variation and questions the validity of discrete racial categories in skeletal analysis.

Lewontin’s Apportionment of Human Diversity (The Classic Result)

Richard Lewontin (1972) evaluated how genetic variation is distributed using 17 genetic markers across global populations. He introduced the fixation index $F<em>{ST}$ to quantify genetic differentiation. $F</em>{ST} = \frac{V<em>{ ext{between}}}{V</em>{ ext{total}}}$ where Vbetween is the genetic variance among subpopulations and Vtotal is the total genetic variance.
Lewontin reported that about $85.4\%$ of genetic variation is within local subpopulations, with only $8.3\%$ between populations within continental groups, and $6.3\%$ attributable to traditional continental races.
This work laid the groundwork for rejecting biological race as a meaningful taxonomic unit, while acknowledging that some structure exists due to geography and demography.
Later work refined these numbers and reinforced the central claim: most genetic variation is shared within populations rather than partitioned among them.

Modern Conclusions: Populations, Not Races

Today we describe human variation in terms of populations rather than races, defined by geography, language, culture, and ancestry estimates with statistical probability.
The concept of a fixed racial hierarchy is scientifically unsupported; variation is continuous and shaped by multiple evolutionary processes.
Genetic distances correlate with geographic distances, reflecting isolation by distance and historical migration, rather than discrete race boundaries.
Societal implications remain: populations with different ancestries may have different disease risks or drug responses, but these are population-level patterns, not indicators of discrete racial groups.
The ethical mandate is to report ancestry probabilistically, avoid essentialist claims, and communicate uncertainty clearly to the public.

Review Questions (Key Points to Remember)

How is human genetic variation distributed worldwide?
Which evolutionary processes produce genetic/phenotypic variation within and between populations?
Should we attribute value to race concepts pre-1950s given current understanding?
How should scientists communicate findings about human variation to non-specialists?

Key Terms (Glossary Highlights)

Age of Discovery: Late 1400s–late 1700s, European exploration and colonial expansion.
Ancestry: Biogeographical information about an individual derived from genome, skeletal traits, or forensic/archaeological evidence; probabilistic estimates used by anthropologists.
Binomial nomenclature: Linnaeus’s system naming species with two Latin names, e.g., $Homo~sapiens$ .
Biological anthropology: The study of human origins, evolution, variation, and adaptation.
Biological determinism: The erroneous idea that biology alone fixes behavior, abilities, or social outcomes.
Cline: A gradient of trait frequency or allele frequency across geography.
Clinal variation: Gradual changes in a trait across geographic space.
Continuous variation: Variation that does not fall into discrete categories.
E.g., lactose tolerance, skin color, or height variation across populations.
Gene flow: The transfer of genes between populations.
Genetic drift: Random changes in allele frequencies over generations.
Heterogeneity: Genetic diversity within a population.
Homo- and heterogeneity: terms describing genetic uniformity or diversity.
Isolation-by-distance: Model predicting greater genetic distance with increased geographic distance.
Monogenetic vs polygenetic origins: One origin vs multiple origins; current evidence supports a single origin of Homo sapiens in Africa (Out-of-Africa).
Mutation: Random genetic changes contributing to variation.
Natural selection: Differential survival/reproduction shaping trait frequencies.
Nonconcordance: Traits do not co-vary predictably; independence of trait inheritance.
Out-of-Africa model: Modern humans originated in Africa and dispersed globally.
Population: A local interbreeding group with some degree of isolation from others.
Polymorphism: A genetic variant occurring with frequency >1% in a population.
Population bottlenecking: Sharp reduction in population size causing loss of genetic variation.
Race: Sociocultural category with historical misuse; not a biological reality.
Racialism: Beliefs that assign fixed, discrete biological races; scientifically unsupported.
FST (Fixation Index): A measure of population differentiation due to genetic structure. $F_{ST} ext{ values range from } 0 ext{ to } 1.$
Population affinity vs ancestry: Probabilistic estimates of geographical origin or genetic background, especially in forensic contexts.

Connections to Broader Themes

The history of race concepts reveals how science has been entangled with social power; modern biology rejects race as a biological category but acknowledges the social consequences of racial classifications.
Contemporary research in biological anthropology emphasizes continuous variation, population history, and adaptive as well as neutral processes shaping human diversity.
Knowledge of population structure has real-world implications for medicine, public health, forensics, and policy; ethical communication and rigorous statistics are essential in translating research to society.