Population Genetics, Race and Human Variation — UPSC Anthropology Optional Notes

1. Concepts and Definitions

Population genetics: the study of allele and genotype frequencies in populations and the forces that change them; it is the genetic basis of evolution, built by R.A. Fisher, J.B.S. Haldane and Sewall Wright in the 1920s and 1930s.

Mendelian population: Theodosius Dobzhansky defined it as a reproductive community of sexual and cross-fertilising individuals that share a common gene pool; in humans, endogamous castes and tribes approximate Mendelian populations.

Gene pool: the total of all alleles in a breeding population at a given time.

Allele (gene) frequency: the proportion of one allele among all alleles of that gene in the population; for two alleles, p + q = 1.

Evolution in genetic terms: a change in allele frequencies over generations; Dobzhansky called it a change in the genetic composition of populations.

2. The Hardy–Weinberg Law

Statement: G.H. Hardy, an English mathematician, and Wilhelm Weinberg, a German physician, independently showed in 1908 that in a large, randomly mating population with no mutation, migration or selection, allele and genotype frequencies remain constant from generation to generation.

Equation: if p is the frequency of allele A and q of allele a, genotype frequencies are AA = p², Aa = 2pq and aa = q², and p² + 2pq + q² = 1; equilibrium is reached in one generation of random mating.

Assumptions: very large population, random mating, no mutation, no migration, no selection, equal fertility and viability of genotypes, and no overlapping generations; real human populations violate several of these.

Uses: it serves as a null model; deviation from expected frequencies shows that an evolutionary force is acting; it also allows estimation of carrier frequency from disease frequency.

Worked example: if albinism (aa) occurs in 1 in 10,000 people, q² = 0.0001, so q = 0.01 and p = 0.99; carrier frequency 2pq = 2 × 0.99 × 0.01 = 0.0198, about 1 in 50, showing that most harmful recessive alleles hide in carriers.

Second example (sickle cell): if 4 percent of a tribal sample are HbSS, q² = 0.04 and q = 0.2, p = 0.8; carriers (HbAS) = 2 × 0.8 × 0.2 = 0.32, so 32 percent are expected to carry the trait, a level reported in some highly affected tribal groups.

3. Forces that Change Gene Frequencies

Mutation: a heritable change in DNA; the ultimate source of new alleles; human mutation rates are of the order of 10 to the minus 5 or 6 per gene per generation, too slow alone to change frequencies quickly, but recurrent mutation balances loss by selection (mutation-selection balance).

Natural selection: differential survival and reproduction of genotypes; fitness (w) and selection coefficient (s = 1 − w) measure it; types are stabilising (favours the average, as in birth weight studied by Mary Karn and Lionel Penrose, 1951), directional (shifts the mean, as with lactase persistence) and disruptive (favours extremes).

Migration or gene flow: movement of alleles between populations; it reduces differences between populations and adds new variation; change in frequency equals m (qm − q), where m is the migrant proportion; the spread of Rh-negative and B alleles across Eurasia reflects gene flow.

Genetic drift: random change in allele frequencies due to chance in small populations (Sewall Wright); it can fix or lose alleles regardless of fitness and is strongest in small isolated groups such as the Andamanese tribes.

Founder effect: a new population started by a few founders carries only part of the original variation; the high frequency of Ellis–van Creveld syndrome among the Old Order Amish of Lancaster County, Pennsylvania, and of some disorders among Ashkenazi Jews and Finns are classic examples.

Bottleneck effect: a sharp reduction in population size by disaster, epidemic or war leaves a random remnant; very small tribes such as the Great Andamanese, reduced to a few dozen people in the twentieth century, show this.

Dunker study: Bentley Glass (1952) studied the Dunkers, a small religious isolate in Pennsylvania, and found blood group frequencies different from both their German homeland and surrounding Americans, a classic demonstration of drift.

Isolation: geographic, ecological or social barriers to mating; caste and tribal endogamy in India have kept many groups genetically distinct for centuries, as shown by genome studies (Reich and colleagues, 2009; Moorjani and colleagues, 2013).

4. Genetic Polymorphism and Selection

Definition: E.B. Ford (1940) defined genetic polymorphism as the occurrence together in the same habitat of two or more discontinuous forms of a species in such proportions that the rarest cannot be maintained merely by recurrent mutation; in practice, a locus is polymorphic if the rarer allele exceeds about 1 percent.

Balanced polymorphism: maintained by selection, usually heterozygote advantage; A.C. Allison (1954) showed that HbAS carriers in East Africa resisted falciparum malaria, while HbSS homozygotes suffered anaemia and HbAA were vulnerable to malaria.

Other malaria-linked polymorphisms: thalassaemias, G6PD deficiency, HbE in north-east India and South-East Asia, and the Duffy-negative blood group (resistance to vivax malaria) in West Africa; J.B.S. Haldane first suggested (1949) that thalassaemia might protect against malaria.

Transient polymorphism: occurs while one allele is replacing another under directional selection, such as industrial melanism in the peppered moth.

Indian example: the sickle-cell gene is common in the central Indian tribal belt (Madhya Pradesh, Chhattisgarh, Odisha, Maharashtra, Gujarat, Jharkhand), where malaria has long been endemic, illustrating balanced polymorphism in an Indian setting.

5. Consanguinity, Inbreeding and Genetic Load

Consanguineous and non-consanguineous mating: consanguineous marriage is between persons related by descent from a common ancestor (usually second cousins or closer); non-consanguineous mating is between unrelated persons; positive assortative mating (choosing similar partners) also changes genotype frequencies without changing allele frequencies.

Inbreeding coefficient (F): Sewall Wright's measure of the probability that two alleles at a locus are identical by descent; F = 1/4 for brother-sister, 1/8 for uncle-niece, 1/16 for first cousins and 1/64 for second cousins.

Effect of inbreeding: it increases homozygosity (frequency of aa becomes q² + Fpq), so rare recessive disorders appear more often; it does not by itself change allele frequencies.

Indian context: cross-cousin and uncle-niece marriages are traditional among many communities of Tamil Nadu, Karnataka and Andhra Pradesh, as Dravidian kinship prescribes; NFHS data have shown consanguineous marriage to be far more common in south India than in the north, where clan exogamy and village exogamy discourage it.

Genetic effects observed: studies of consanguinity worldwide (summarised by Alan Bittles) report higher rates of stillbirth, infant death, congenital malformations and recessive disorders among offspring of first-cousin unions, though the absolute excess is modest (often estimated at a few percentage points).

Genetic load: H.J. Muller (1950, Our Load of Mutations) used the term for the reduction in average fitness of a population due to harmful alleles; types are mutational load, segregational (balanced) load, such as HbSS births from maintaining the sickle-cell polymorphism, and drift load.

Lethal equivalents: Morton, Crow and Muller (1956) estimated that each person carries a few lethal equivalents, harmful recessive alleles that would together cause death if homozygous.

6. Theory and Debates

Selectionists versus neutralists: Motoo Kimura's neutral theory (1968) argued that most molecular variation is selectively neutral and governed by drift, while selectionists stress adaptive polymorphism; both operate, and the balance is debated.

Consanguinity and policy: some argue that long-term inbreeding purges harmful alleles, so consanguineous communities may have lower risk than expected (debated); counselling rather than bans is the accepted approach.

Indian population structure: geneticists find that endogamy among Indian groups began roughly 2,000 years ago (Moorjani and colleagues, 2013), producing many founder events and group-specific recessive diseases.

7. Diagrams to Draw

Hardy–Weinberg Punnett square: a 2 by 2 grid with sperm alleles (p A, q a) across the top and egg alleles down the side, filled with p², pq, pq and q², summing to p² + 2pq + q².

Inbreeding path diagram: a first-cousin marriage pedigree with the common ancestors at top, arrows along the paths to the inbred child, and F = 1/16 calculated by counting links (n links give (1/2) to the power n summed over paths).

Drift and founder diagram: a large population of mixed coloured dots with a few dots breaking off to found a new colony with a different colour mix.

Malaria-sickle cell map and fitness table: overlapping shading of malaria zones and HbS frequency in Africa and central India, with a table of fitness: HbAA lowered by malaria, HbAS highest, HbSS lowest.

8. Using it in the Exam

10-mark note on Hardy–Weinberg law: statement, equation, assumptions, one worked example and one line on why real populations deviate.

15 or 20-mark answer on factors changing gene frequency: define the equilibrium, then mutation, selection, migration, drift (founder, bottleneck), isolation and inbreeding, each with an example (preferably Indian), and conclude with genetic load and counselling.

Keywords: gene pool, Mendelian population, p² + 2pq + q², fitness, selection coefficient, balanced polymorphism, heterozygote advantage, founder effect, bottleneck, inbreeding coefficient, genetic load, lethal equivalents.

Definition to quote: Ford's definition of genetic polymorphism (1940) and Dobzhansky's definition of a Mendelian population as a reproductive community sharing a common gene pool.

1. Concepts and Definitions

Race (typological definition): E.A. Hooton described race as a great division of mankind whose members share a certain combination of morphological and metrical features, primarily non-adaptive, derived from common descent (paraphrase); this view treated races as fixed types.

Race (genetic definition): Dobzhansky defined races as Mendelian populations that differ in the frequencies of genes; W.C. Boyd (Genetics and the Races of Man, 1950) similarly used blood group frequencies.

Cline: a gradual change in a trait or allele frequency across geography; Frank Livingstone (1962) argued that there are no races, only clines, and C. Loring Brace supported this view.

Ethnic group: a group defined by shared culture, language, history or identity, not by biology; Ashley Montagu proposed replacing race with ethnic group in Man's Most Dangerous Myth: The Fallacy of Race (1942).

Racism: the belief that human groups have innate, hereditary differences in ability or worth that justify unequal treatment, and the practices built on it.

2. Racial Criteria: Non-metric and Metric Characters

Non-metric (descriptive) characters: skin colour, hair colour and form (straight or leiotrichy, wavy or cymotrichy, woolly or ulotrichy), eye colour and form (epicanthic fold), nose form, lip thickness, face shape, body hair, and shovel-shaped incisors.

Metric (measurable) characters: stature, cephalic index, nasal index, facial index, limb proportions and cranial capacity, measured with standard instruments (anthropometer, spreading and sliding callipers).

Cephalic index: maximum head breadth divided by maximum head length, multiplied by 100; dolichocephalic (long-headed) up to about 75.9, mesocephalic about 76 to 80.9, brachycephalic (round-headed) about 81 and above (on the living head).

Nasal index: nasal breadth divided by nasal height, multiplied by 100; leptorrhine (narrow) up to about 69.9, mesorrhine about 70 to 84.9, platyrrhine (broad) about 85 and above (on the living).

Serological and genetic criteria: ABO, Rh, MN, HLA and DNA markers came into use from Hirszfeld (1919) and Boyd (1950); unlike morphological traits they are not easily changed by environment and allow population genetic analysis.

3. Biological Basis of Variation: Heredity and Environment

Skin colour: determined by melanin and many genes; Nina Jablonski and George Chaplin (2000) explained its world distribution as a balance between protecting folate from strong ultraviolet radiation (dark skin near the equator) and allowing vitamin D synthesis under weak UV (lighter skin at high latitudes).

Gloger's rule: animals in warm, humid regions tend to be more heavily pigmented than those in cool, dry regions; human skin colour broadly follows this pattern.

Bergmann's and Allen's rules: body mass relative to surface area is greater in cold climates (Bergmann) and limbs are shorter in cold and longer in hot climates (Allen); Inuit stockiness and the tall, linear build of Nilotic peoples such as the Dinka illustrate them.

Nose form: Arthur Thomson and Dudley Buxton (1923) correlated narrow noses with cold, dry air, as narrow noses warm and moisten inhaled air.

Plasticity: Boas's study of children of immigrants in the United States (around 1910–1912) found changes in head form, and later studies (Gabriel Lasker on Japanese migrants, Harry Shapiro on Japanese in Hawaii, 1939) showed that stature and other metric traits respond to nutrition and environment; a reanalysis of Boas's data in 2002 produced a debate, but most scholars accept plasticity.

Secular trend: increases in stature and earlier menarche over the last century in many populations, including Indian urban groups, show that metric racial criteria are not fixed.

4. Racial Classification and Differentiation

Early schemes: Linnaeus (1758) described four varieties of humans by continent with prejudiced temperaments; J.F. Blumenbach (1795) gave five, Caucasian, Mongolian, Ethiopian, American and Malay, and coined Caucasian after a skull from the Caucasus.

Twentieth-century schemes: Hooton recognised three primary races (White, Negroid, Mongoloid) with subdivisions; Stanley Garn (Human Races, 1961) distinguished geographical races (nine), local races and micro-races; Carleton Coon's The Origin of Races (1962) claimed five subspecies evolved separately, which was widely criticised.

Risley's classification of India (1901 Census; The People of India, 1908): seven physical types, Turko-Iranian, Indo-Aryan, Scytho-Dravidian, Aryo-Dravidian, Mongolo-Dravidian, Mongoloid and Dravidian, based mainly on cephalic and nasal indices; he claimed that caste rank correlated inversely with nasal index (paraphrase), a claim now rejected.

Guha's classification (1931 and 1935): B.S. Guha proposed six main racial elements in India, Negrito, Proto-Australoid, Mongoloid, Mediterranean, Western Brachycephals (Alpinoid, Dinaric, Armenoid) and Nordic, with nine sub-types; it was based on measurements from the 1931 Census and remains the most cited Indian scheme.

Other Indian views: Haddon, Eickstedt and S.S. Sarkar proposed different schemes; Sarkar denied a separate Negrito element on the mainland, so the Negrito question is debated.

Genomic view of India: Reich and colleagues (2009) found most Indians descend from two ancestral groups, Ancestral North Indians (related to West Eurasians) and Ancestral South Indians (distinct, related distantly to Andamanese); Narasimhan and colleagues (2019) refined this into ancient Iranian-related, steppe-related and indigenous South Asian hunter-gatherer components.

Race crossing (admixture): Eugen Fischer's study of the Rehoboth Basters of Namibia (1913), descended from Dutch men and Khoikhoi women, and Harry Shapiro's study of the Pitcairn Islanders (1936), descended from the Bounty mutineers and Tahitians, found no biological deterioration; often heterosis (hybrid vigour) appeared; in India Anglo-Indians are an example of admixture.

5. Racism and Its Rejection

Scientific racism: Arthur de Gobineau's Essay on the Inequality of the Human Races (1853–55), skull measurement by Samuel Morton, eugenics, the Nazi Aryan myth leading to the Holocaust, and apartheid in South Africa (1948–1994) show how pseudo-science justified oppression.

UNESCO statements: UNESCO issued statements on race in 1950, 1951, 1964 and 1967 (the first drafted with Montagu and Lévi-Strauss among the contributors), declaring that race is a social myth more than a biological fact and that there is no proof of innate mental differences between groups.

Lewontin's finding: Richard Lewontin (1972) showed that about 85 percent of human genetic variation lies within local populations, about 8 percent between populations within a race and only about 6 percent between the conventional races; later genomic studies confirm that most variation is within groups.

Professional statements: the American Association of Physical Anthropologists (1996) and the American Association of Biological Anthropologists (2019) stated that race does not accurately describe human biological variation.

Racism in India: discrimination against people from the north-east led the Ministry of Home Affairs to set up the M.P. Bezbaruah Committee (2014) after the death of Nido Taniam in Delhi; colour prejudice in marriage advertisements and colonial ideas linking caste to race are other examples; caste discrimination is not race but is sometimes discussed alongside it.

6. Theory and Debates

Does race exist biologically? Splitters argue that clusters of allele frequencies correspond roughly to continental ancestry and are useful in medicine and forensics; lumpers argue that clines, overlap and within-group variation make races arbitrary; most anthropologists now speak of populations and ancestry rather than race.

Race as social reality: even if biologically weak, race is socially real because people act on it, so its study belongs to social anthropology as much as to biology.

Indian race debates: the Aryan-Dravidian racial theory of colonial writers has been replaced by genomic evidence of complex, layered admixture without discrete racial units.

7. Diagrams to Draw

Cephalic index diagram: a top view of the head with maximum length (glabella to opisthocranion) and maximum breadth (between euryons) marked, with the formula and the three class ranges.

Cline map: a sketch of the Old World with shading of skin pigmentation darkest at the equator and lighter toward high latitudes, labelled with UV gradient.

Variation pie chart: Lewontin's figures, about 85 percent within populations, about 8 percent between populations in a race and about 6 percent between races.

Risley and Guha table: two columns listing Risley's seven types and Guha's six elements for quick comparison.

8. Using it in the Exam

10-mark note on racial criteria or race crossing: definition, metric and non-metric examples with formulas, one study (Rehoboth or Pitcairn), and a line on the modern view.

15 or 20-mark answer on race and racism: concept and its evolution, criteria, heredity-environment evidence, classifications (world and Indian), genomic critique (Lewontin, clines), racism and UNESCO statements, Indian examples, and a conclusion that human variation is real but races are not discrete.

Keywords: typology, cline, cephalic index, nasal index, Bergmann and Allen, Gloger, plasticity, admixture, heterosis, Lewontin, UNESCO statements, ANI and ASI.

Quotation: Livingstone's phrase that there are no races, there are only clines (1962).

1. Concepts and Definitions

Genetic marker: a trait or DNA variant that is inherited in a simple, known way, is polymorphic in populations, can be reliably identified and is little affected by environment; classical markers are blood groups, serum proteins and enzymes, modern ones are DNA markers (STRs, SNPs, mtDNA, Y-chromosome).

Why markers matter in anthropology: they help trace origins and migrations, estimate admixture, study selection and disease association, and identify persons (paternity, forensics).

First anthropological use: Ludwik and Hanna Hirszfeld (1919) tested soldiers of many nationalities on the Salonika front and found ABO frequencies varying regionally; they proposed a biochemical race index (ratio of A to B), with B rising from western Europe toward Asia.

2. ABO and Rh Blood Groups

ABO system: discovered by Karl Landsteiner (1900; Nobel Prize 1930), with group AB found by Decastello and Sturli (1902); controlled by three alleles (IA, IB, i) on chromosome 9; antigens on red cells and naturally occurring antibodies in plasma.

World distribution: group O is highest among Native Americans (near 100 percent in some South American groups) and Australian Aborigines; A is relatively high in parts of Europe and among some Aboriginal Australians and Sami; B is highest in Central Asia and north India and nearly absent in Native Americans and Aboriginal Australians.

India: B is relatively frequent in north India (often around 30 percent or more in some groups), and the B allele frequency generally falls from north to south and among some tribal groups; O is the most common group overall in India.

Disease associations: group O has higher risk of peptic ulcer and severe cholera, group A of stomach cancer; group O may protect against severe falciparum malaria; these associations are statistical, not deterministic.

Rh system: discovered by Landsteiner and Alexander Wiener (1940) using rhesus monkey blood; the D antigen is the most important; Rh-negative (dd) frequency is about 15 percent in Europeans, highest among the Basques (often above 30 percent), low in India (around 5 percent) and very low among East Asians, Africans and Native Americans.

Rh incompatibility: an Rh-negative mother carrying an Rh-positive foetus can form anti-D antibodies, damaging later Rh-positive foetuses (haemolytic disease of the newborn, erythroblastosis foetalis); anti-D immunoglobulin given after delivery prevents it.

Other blood groups: MN (Landsteiner and Levine, 1927) shows codominance; Duffy-negative (Fy a− b−) is near universal in West and Central Africa and protects against vivax malaria; Diego positive is found among Native Americans and East Asians and indicates Mongoloid-related ancestry.

3. HLA, Serum Proteins and Red Cell Enzymes

HLA (human leucocyte antigen): the major histocompatibility complex on chromosome 6, the most polymorphic system in humans; it presents antigens to the immune system, decides transplant compatibility and is used in paternity testing and population studies; Jean Dausset described the first HLA antigen (1958, Nobel 1980).

HLA and disease: HLA-B27 is strongly associated with ankylosing spondylitis (present in about 90 percent of patients of European descent), HLA-DR3 and DR4 with type 1 diabetes, and HLA-B*1502 with severe drug reactions to carbamazepine in some Asian populations.

Haptoglobin (Hp): a serum protein that binds free haemoglobin; Oliver Smithies (1955) discovered its variants (Hp1-1, Hp2-1, Hp2-2) using starch gel electrophoresis; the Hp1 allele is common in Africa and parts of South America and lower in India and South-East Asia.

Transferrin (Tf): the iron-transport protein in serum; TfC is common everywhere, while variants such as TfD occur among Africans, Australian Aborigines and some Indian tribes, and TfB in Europeans; useful as a population marker.

Gm system: genetically determined antigenic variants (allotypes) of the heavy chain of immunoglobulin G, discovered by Rune Grubb (1956); Gm haplotypes differ sharply between Caucasoid, Mongoloid and Negroid populations, making Gm one of the best markers of admixture.

Red cell enzymes: G6PD (glucose-6-phosphate dehydrogenase) deficiency is X-linked, common in malarial regions (including parts of India, among Parsis and some tribal and coastal groups), and causes haemolysis with fava beans (favism) or drugs like primaquine; other polymorphic enzymes include acid phosphatase, phosphoglucomutase (PGM), adenylate kinase and esterase D.

Haemoglobin variants: HbS (sickle cell) in Africa, the Mediterranean, the Middle East and central India; HbE in north-east India, Bangladesh and South-East Asia; HbD (Punjab) in Punjab; these are both markers and evidence of malaria selection.

4. Age, Sex and Population Variation

Age: blood pressure rises with age in industrial societies but much less in some foraging and pastoral societies (for example studies among the !Kung and Yanomami), showing lifestyle influence; haemoglobin and lung capacity decline in old age.

Sex: men have higher average haemoglobin (WHO cut-off for anaemia is 13 g/dl in men, 12 g/dl in non-pregnant women and 11 g/dl in pregnant women), greater muscle mass and vital capacity; women have higher body fat percentage.

Population: marker frequencies differ between populations because of founder effects, drift, selection and admixture, so they reveal history, for example West Eurasian-related Gm and Y-chromosome markers in north Indian upper castes and Austro-Asiatic-related Y markers among Munda tribes.

5. Physiological Characteristics in Different Groups

Haemoglobin level: shaped by altitude (higher in Andean highlanders), nutrition, parasites and genes; NFHS-5 (2019–21) found anaemia in 57.0 percent of Indian women aged 15–49 and 67.1 percent of children aged 6–59 months, with higher levels among poorer and Scheduled Tribe households.

Body fat: measured by skinfold callipers, BMI and waist-hip ratio; it varies with diet, activity and climate; South Asians tend to have more body fat and central obesity at a given BMI (the thin-fat Indian phenotype described by C.S. Yajnik), which raises diabetes risk.

Pulse rate and blood pressure: resting pulse is lower in physically active people such as hunters, pastoralists and athletes; urbanisation, salt intake and stress raise blood pressure in migrant and urban groups.

Respiratory functions: vital capacity and lung volumes are larger in high-altitude natives (Andeans, Sherpas, Ladakhis) and in physically active groups, and are reduced by indoor smoke from biomass fuel, common in rural and tribal homes.

Basal metabolic rate: higher among the Inuit and other cold-adapted groups, linked to diet and climate.

Sensory perception: the ability to taste PTC (phenylthiocarbamide), discovered by Arthur Fox (1931), is controlled mainly by the TAS2R38 gene, with non-tasters about 30 percent in Europeans and fewer in many Asian, African and Native American groups; R.H. Post (1962) proposed that colour blindness is rarer among hunter-gatherers because of selection (relaxed in agricultural and industrial societies).

Culture and perception: Segall, Campbell and Herskovits (1966) found that people in carpentered (rectangular-built) environments were more susceptible to the Müller-Lyer illusion, showing that perception is shaped by environment and culture.

Socio-economic differences: stature, weight, haemoglobin and growth differ by class, caste and region in India (for example tribal children show higher stunting in NFHS data), showing that physiological traits are not fixed racial markers but reflect inequality.

6. Theory and Debates

Markers and race: marker frequencies vary clinally and overlap widely, supporting the population and cline concept rather than discrete races; Boyd's blood group races (1950) are now historical.

Classical versus DNA markers: blood groups and proteins have largely been replaced by DNA markers, but classical markers remain cheaper and are still used in fieldwork, blood transfusion and some forensic work.

7. Diagrams to Draw

ABO inheritance table: six genotypes (IAIA, IAi, IBIB, IBi, IAIB, ii) matched to four phenotypes, with antigens and antibodies.

Rh incompatibility sequence: first pregnancy (Rh-positive foetus, sensitisation at delivery), anti-D formation, second pregnancy (antibodies cross the placenta), and prevention by anti-D injection.

World map of B allele: shading highest over Central Asia and north India and lowest in the Americas and Australia.

Electrophoresis sketch: starch gel lanes showing Hp1-1 (one band), Hp2-1 and Hp2-2 (multiple bands) to explain how protein markers are typed.

8. Using it in the Exam

10-mark note on a marker (ABO, Rh, HLA, Hp, Gm, G6PD): discoverer and year, genetics, world and Indian distribution, one disease association, anthropological use.

15 or 20-mark answer on physiological variation: define, then Hb, body fat, pulse, respiration and sensory perception with data and Indian examples (NFHS-5, thin-fat phenotype, biomass smoke), and conclude that variation reflects gene-environment-culture interaction.

Keywords: polymorphism, codominance, biochemical race index, erythroblastosis foetalis, MHC, allotype, favism, PTC tasting, carpentered world, thin-fat phenotype.

Quotation or fact to cite: the Hirszfelds' finding (1919) that ABO frequencies differ by nationality, the first anthropological use of a genetic marker.

1. Hardy–Weinberg Law, Genetic Polymorphism and Inbreeding

Example 1 (UPSC 2026, 10 marks): Genetic polymorphism and natural selection

Paper and question: Paper I, Q1(d)

Approach: Define genetic polymorphism, show how natural selection maintains it (balanced) or changes it (transient), with human examples, and note neutral polymorphism.

Genetic polymorphism, as defined by E.B. Ford (1940), is the occurrence in the same population of two or more discontinuous genetic forms in such proportions that the rarest cannot be maintained by recurrent mutation alone; by convention the rarer allele has a frequency above 1 per cent.

Selection maintaining polymorphism: in balanced polymorphism the heterozygote is fitter than either homozygote. A.C. Allison (1954) showed that sickle-cell carriers (HbAS) resist falciparum malaria, while HbSS homozygotes suffer severe anaemia and HbAA people die of malaria more often; hence HbS stays common in malarial belts of Africa and among tribes of central India. Thalassaemia, HbE in north-east India and G6PD deficiency show the same pattern.

Selection changing polymorphism: in transient polymorphism directional selection replaces one allele by another, as with the spread of lactase persistence among dairying peoples, or the decline of HbS among African Americans living without malaria.

Many DNA polymorphisms are selectively neutral and vary through drift, so selection explains only part of human polymorphism.

Example 2 (UPSC 2023, 15 marks): What assumptions must be met for a population to be in genetic equilibrium ? Explain the importance of genetic equilibrium.

Paper and question: Paper I, Q7(b)

Approach: State the Hardy-Weinberg principle, list and explain each assumption, then explain the importance of equilibrium as a null model with a worked example, and conclude.

The Hardy-Weinberg principle, stated independently by G.H. Hardy and Wilhelm Weinberg in 1908, holds that in an ideal population allele and genotype frequencies remain constant from generation to generation. With two alleles of frequencies p and q (p + q = 1), genotype frequencies are p² : 2pq : q², and this equilibrium is reached after one generation of random mating.

Assumptions: (i) a very large population, so that chance (genetic drift) does not alter frequencies; (ii) random mating, without inbreeding or assortative mating; (iii) no mutation; (iv) no migration or gene flow; (v) no natural selection, so all genotypes have equal survival and fertility; (vi) non-overlapping generations and equal allele frequencies in both sexes.

Importance: (i) it is the null model of population genetics; departure from it shows that an evolutionary force is acting, for instance an excess of homozygotes points to inbreeding; (ii) it allows estimation of carrier frequencies: if albinism affects 1 in 20,000, q² = 0.00005, q is about 0.007 and carriers (2pq) are about 1 in 70, which guides screening and counselling; (iii) it explains why dominant traits do not automatically spread and recessive ones do not vanish; (iv) it underlies forensic DNA probability calculations.

Real populations rarely meet every assumption, but the law remains the yardstick for measuring evolution.

Example 3 (UPSC 2022, 10 marks): Balanced and transient genetic polymorphism.

Paper and question: Paper I, Q5(a)

Approach: Define both types of polymorphism, explain the mechanism of each, and give human examples.

Genetic polymorphism is the stable coexistence of two or more alleles at a locus with the rarer above about 1 per cent (E.B. Ford). Depending on whether frequencies are stable or changing, it is balanced or transient.

Balanced polymorphism: allele frequencies are held at equilibrium by opposing selective forces. The main mechanism is heterozygote advantage: HbAS carriers resist falciparum malaria (Allison, 1954), so HbS persists despite the lethality of HbSS, as among Bhil, Gond and other tribes of central and western India. Thalassaemia, G6PD deficiency and HbE in Assam behave similarly. Frequency-dependent selection, as for some immune genes, also balances alleles.

Transient polymorphism: two alleles coexist only temporarily while directional selection replaces one with the other. Examples are industrial melanism in the peppered moth, the spread of lactase persistence, and the falling HbS frequency among African Americans removed from malaria.

Balanced polymorphism is stable over many generations; transient polymorphism ends in fixation.

Example 4 (UPSC 2022, 20 marks): Discuss the role of evolutionary forces in creating human diversity.

Paper and question: Paper I, Q7(a)

Approach: Introduce human diversity as the product of evolutionary forces acting on gene frequencies, then take mutation, natural selection, genetic drift, gene flow and non-random mating in turn with human and Indian examples, and conclude on their interaction.

Human diversity, visible in skin colour, stature and blood groups and hidden in DNA, results from evolutionary forces that disturb Hardy-Weinberg equilibrium and change gene frequencies across populations and time.

Mutation: the ultimate source of new variation, arising from errors in DNA replication or from radiation and chemicals. The sickle-cell mutation (a single base change in the beta-globin gene) and the lactase persistence mutations are examples; mutation alone changes frequencies slowly.

Natural selection: differential survival and reproduction shapes adaptive diversity. Skin pigmentation tracks ultraviolet radiation, balancing protection of folate against vitamin D synthesis (Jablonski and Chaplin, 2000); HbS, thalassaemia and G6PD deficiency persist in malarial zones; EPAS1 variants help Tibetans at high altitude; lactase persistence spread among herders.

Genetic drift: random change in small populations. In the founder effect, a few founders carry unusual alleles, as with Ellis-van Creveld syndrome among the Old Order Amish; in a bottleneck, survivors of a disaster pass on a skewed gene pool, as with achromatopsia on Pingelap atoll after a typhoon. Small isolated groups such as the Andamanese, and many endogamous Indian communities with strong founder events (Reich and colleagues, 2009), show the effects of drift.

Gene flow: migration and intermarriage reduce differences between populations, as in the African ancestry of the Siddis of Gujarat and Karnataka, or the gradual clines of ABO frequencies across Eurasia.

Non-random mating: caste and tribal endogamy subdivide the gene pool, and consanguineous marriages common in parts of South India raise homozygosity and recessive disorders without changing allele frequencies directly.

These forces act together: mutation supplies variation, drift and endogamy create local differences, selection fits populations to environments and gene flow connects them, producing the clinal and largely continuous diversity of humankind.

Example 5 (UPSC 2020, 10 marks): Genetic drift

Paper and question: Paper I, Q5(b)

Approach: Define genetic drift, explain its forms (founder effect, bottleneck) and consequences, with human examples.

Genetic drift, emphasised by Sewall Wright, is the random change in allele frequencies from one generation to the next due to chance sampling of gametes. Its effect is strongest in small, isolated populations.

Forms: (i) founder effect (Ernst Mayr): a new population started by a few individuals carries only part of the parent gene pool; the Old Order Amish of Pennsylvania have a high frequency of Ellis-van Creveld syndrome traced to one founding couple; (ii) bottleneck: a sharp fall in numbers leaves a skewed gene pool, as on Pingelap atoll, where after a typhoon in the 1770s about 5 to 10 per cent of the people now have complete colour blindness (achromatopsia).

Classic study: Bentley Glass (1952) found that the Dunkers, a small religious isolate in Pennsylvania, differed in ABO and MN frequencies from both their German homeland and surrounding Americans.

Consequences: loss of heterozygosity, fixation or loss of alleles and differentiation of isolates, as in many endogamous Indian groups and tribes such as the Andamanese.

Example 6 (UPSC 2020, 15 marks): How do marriage rules impact the gene pool of populations ?

Paper and question: Paper I, Q7(c)

Approach: Explain how each marriage rule (endogamy, consanguinity and cross-cousin or uncle-niece marriage, exogamy, assortative mating, polygyny, hypergamy) alters genotype frequencies and population structure, with Indian examples and the inbreeding coefficient.

Marriage rules decide who mates with whom, so they break the random-mating assumption of the Hardy-Weinberg law and shape the gene pool of a population.

Endogamy: marriage within caste, sub-caste or tribe divides a population into many breeding isolates. Genetic studies (Reich and colleagues, 2009; Nakatsuka and colleagues, 2017) found that many Indian groups have experienced strong founder events and have been endogamous for up to two to three thousand years, leading to high frequencies of particular recessive disorders, such as butyrylcholinesterase deficiency among the Vysya of Andhra Pradesh.

Consanguinity: cross-cousin and uncle-niece marriages, common in parts of South India, raise homozygosity. The inbreeding coefficient (F) is 1/16 for first-cousin and 1/8 for uncle-niece marriages; offspring show more recessive disorders, stillbirths and child deaths. Inbreeding changes genotype frequencies, not allele frequencies.

Exogamy and other rules: clan and village exogamy among the Gond, Munda and north Indian Hindus spread genes more widely and reduce inbreeding; assortative mating for stature or education increases homozygosity for related traits; polygyny lets some men father more children, reducing effective population size; hypergamy carries women’s genes up the caste hierarchy.

Thus social rules are evolutionary forces: they govern genetic structure, disease burden and the success of carrier screening.

Example 7 (UPSC 2019, 15 marks): Differentiate between transient and balanced genetic polymorphism. Illustrate your answer with suitable examples from human populations.

Paper and question: Paper I, Q4(c)

Approach: Differentiate the two types of polymorphism on mechanism, stability and outcome, then illustrate each with human examples, ending with a comparative statement.

Genetic polymorphism is the coexistence of two or more alleles at a locus, the rarer exceeding about 1 per cent, at frequencies too high to be explained by recurrent mutation (E.B. Ford). It may be balanced or transient.

Differences: (i) mechanism: balanced polymorphism is maintained by opposing selective forces, chiefly heterozygote advantage or frequency-dependent selection, whereas transient polymorphism occurs while directional selection favours one allele; (ii) stability: balanced polymorphism reaches a stable equilibrium frequency, transient polymorphism is a passing phase; (iii) outcome: balanced keeps both alleles indefinitely, transient ends in fixation of the favoured allele.

Human examples of balanced polymorphism: sickle-cell haemoglobin, where carriers resist falciparum malaria (Allison, 1954), keeping HbS frequent in Africa and among tribes of central India such as the Gond and Bhil; beta-thalassaemia in the Mediterranean and India; HbE in north-east India and South-East Asia; G6PD deficiency; and highly diverse HLA genes, favoured because rare alleles help resist pathogens.

Human examples of transient polymorphism: the rise of lactase persistence alleles among pastoral peoples over the last several thousand years; the decline of HbS among African Americans and Afro-Caribbeans in malaria-free environments; and the spread of skin-lightening alleles in northern latitudes.

Thus balanced polymorphism reflects stable adaptation to a constant pressure, while transient polymorphism records evolution in progress.

Example 8 (UPSC 2018, 20 marks): Explain the mechanisms of human variation in gene frequencies.

Paper and question: Paper I, Q6(a)

Approach: Take the Hardy-Weinberg equilibrium as the baseline and explain each mechanism that changes gene frequencies (mutation, selection, drift, gene flow, non-random mating), with mathematical sense and human examples, then conclude.

Under the Hardy-Weinberg law, allele frequencies stay constant in a large, randomly mating population free of disturbing forces. Human variation in gene frequencies arises because these conditions are never fully met.

Mutation: changes one allele into another at a low rate (about 1 in 100,000 per gene per generation for many loci), slowly creating new variants such as HbS, HbE and the many beta-thalassaemia mutations found in India. Recurrent mutation balances selection against harmful alleles (mutation-selection balance).

Natural selection: alleles that raise survival and fertility increase. It may be directional (lactase persistence), stabilising (birth weight around an optimum, as Karn and Penrose showed in 1951), or balancing (HbS and malaria). Climate-related selection explains clines in skin colour, and selection by disease explains the high diversity of HLA alleles.

Genetic drift: random sampling in small populations changes frequencies unpredictably and can fix or eliminate alleles. Founder effects (the Amish, Ellis-van Creveld syndrome), bottlenecks (Pingelap) and the Dunkers study of Bentley Glass (1952) show it; small tribes such as the Onge and Jarawa are especially affected.

Gene flow: migration and admixture move alleles between populations and reduce differences, as in the mixed ancestry of most Indian groups from Ancestral North and South Indian sources, or the European admixture of African Americans.

Non-random mating: inbreeding (consanguineous marriages in South India) and assortative mating alter genotype frequencies and expose recessive alleles to selection; caste endogamy keeps groups genetically distinct.

In combination these mechanisms produce the patterned, mostly clinal variation of human gene frequencies, with each population carrying a unique history of mutation, drift, selection and contact.

Example 9 (UPSC 2017, 10 marks): Hardy-Weinberg law

Paper and question: Paper I, Q5(a)

Approach: State the law with its formula, assumptions and a worked example, and note its significance.

The Hardy-Weinberg law, formulated independently by the mathematician G.H. Hardy and the physician Wilhelm Weinberg in 1908, states that in a large, randomly mating population, in the absence of mutation, migration, selection and drift, allele and genotype frequencies remain constant over generations.

Formula: for two alleles A and a with frequencies p and q (p + q = 1), genotype frequencies are AA = p², Aa = 2pq and aa = q², so p² + 2pq + q² = 1. Equilibrium is restored in a single generation of random mating.

Worked example: if 16 per cent of a population are non-tasters of PTC (tt), q² = 0.16, so q = 0.4 and p = 0.6; homozygous tasters are 0.36 and heterozygous tasters 0.48 (48 per cent).

Significance: it is the baseline for detecting evolutionary change, estimating carrier frequencies for genetic counselling (for thalassaemia or sickle-cell trait), measuring inbreeding and calculating forensic DNA probabilities.

Example 10 (UPSC 2015, 15 marks): Define genetic polymorphism. Give details of its types with suitable examples.

Paper and question: Paper I, Q8(b)

Approach: Define genetic polymorphism (Ford), then describe its types (balanced, transient, neutral; and by level: morphological, serological, biochemical, DNA), each with human examples.

E.B. Ford (1940) defined genetic polymorphism as the occurrence together in the same population of two or more discontinuous forms of a species in such proportions that the rarest of them cannot be maintained merely by recurrent mutation. In practice a locus is polymorphic when its commonest allele has a frequency below 99 per cent.

Types by mechanism: (i) balanced polymorphism, maintained by heterozygote advantage or frequency-dependent selection, as with HbS and malaria (Allison, 1954), beta-thalassaemia, G6PD deficiency and HbE in north-east India; (ii) transient polymorphism, a temporary phase as one allele replaces another under directional selection, as with lactase persistence or declining HbS in malaria-free America; (iii) neutral polymorphism, alleles of equal fitness whose frequencies change by drift, as with most non-coding DNA variants, as Motoo Kimura’s neutral theory (1968) proposed.

Types by level of detection: morphological (PTC tasting, ear-lobe attachment, colour vision); serological (ABO, Rh, MN, Duffy blood groups, HLA); biochemical (haemoglobin variants, haptoglobin, transferrin and red cell enzymes such as acid phosphatase); and DNA polymorphisms (RFLPs, microsatellites, SNPs, mitochondrial and Y-chromosome haplogroups).

Polymorphisms are the raw material of population studies, disease association, paternity testing and forensic identification.

Example 11 (UPSC 2014, 20 marks): Discuss the factors affecting gene frequencies among human populations.

Paper and question: Paper I, Q7(a)

Approach: Begin from Hardy-Weinberg equilibrium and discuss the factors that alter gene frequencies, grouped as those changing allele frequencies (mutation, selection, drift, gene flow) and those changing genotype frequencies (inbreeding, assortative mating), with Indian and world examples and a short worked calculation.

Gene frequency is the proportion of a particular allele among all alleles at a locus in a population. The Hardy-Weinberg law predicts that it will stay constant unless disturbed; the factors that disturb it are the forces of evolution.

Factors changing allele frequencies: (i) mutation introduces new alleles, such as the sickle-cell and HbE mutations, but at low rates; (ii) natural selection favours alleles that raise fitness: HbS carriers survive falciparum malaria, so the allele reaches high frequencies among tribes of central India and in tropical Africa, while lactase persistence spread among herders in Europe and north-west India; (iii) genetic drift alters frequencies by chance in small populations, through founder effects and bottlenecks, as among the Amish and Pingelap islanders, and in small isolated Indian tribes; (iv) gene flow through migration and intermarriage homogenises populations, as in the African ancestry of the Siddis and the admixture of Ancestral North and South Indian components in most Indians.

Factors changing genotype frequencies: inbreeding, as in cross-cousin and uncle-niece marriages of South India, raises homozygosity by the inbreeding coefficient F (1/16 for first cousins), increasing recessive disorders; assortative mating for traits such as stature has a similar effect for those genes; endogamy subdivides the population into many small gene pools.

Worked illustration: if the frequency of an allele is 0.1, random mating gives 1 per cent homozygotes; with first-cousin marriage (F = 1/16) homozygote frequency becomes q² + Fpq, or about 1.6 per cent.

Cultural factors such as differential fertility, polygyny, warfare, famine and medical care also act as agents of selection. The gene frequencies of any population are therefore the outcome of biology and culture together.

2. Race and Racism

Example 12 (UPSC 2023, 10 marks): Race and Ethnicity

Paper and question: Paper I, Q1(c)

Approach: Define race and ethnicity, contrast them on basis, boundaries and change, with Indian and world examples, and conclude on current usage.

Race traditionally meant a division of humankind sharing inherited physical traits such as skin colour, hair form and head shape, as in the schemes of Linnaeus, Blumenbach and, for India, Risley and B.S. Guha (1931). Ethnicity refers to a group’s shared cultural identity, based on common descent claims, language, religion, customs and history.

Differences: race was claimed to be biological and fixed, ethnicity is cultural and learnt; racial boundaries were drawn by outside observers, ethnic boundaries are maintained by members themselves, as Fredrik Barth (Ethnic Groups and Boundaries, 1969) showed; ethnicity changes and can be mobilised politically.

Examples: the Naga, Bodo, Santal and Tamil are ethnic groups, whereas Guha classed Indians into races such as Proto-Australoid and Mongoloid.

Since the UNESCO statements on race (1950 onwards), and Ashley Montagu’s suggestion to replace race with ethnic group, anthropologists treat race as a social construct, while ethnicity remains a central analytical concept.

Example 13 (UPSC 2021, 10 marks): Is race a valid and biologically meaningful concept ?

Paper and question: Paper I, Q5(c)

Approach: State the traditional concept, present the genetic evidence against discrete races (within-group variation, clines, discordance) and the counter-argument about population structure, and give a balanced conclusion.

The traditional concept held that humankind could be divided into a few discrete races, such as Caucasoid, Mongoloid and Negroid, each with a fixed set of inherited traits.

Against biological validity: (i) Richard Lewontin (1972) found that about 85 per cent of genetic variation lies within populations and only about 6 per cent between so-called races, a result confirmed by later DNA studies; (ii) human traits vary gradually across space as clines, so Frank Livingstone (1962) wrote that there are no races, only clines; (iii) traits are discordant: skin colour, blood groups and sickle-cell frequencies do not vary together; (iv) many racial traits, such as head form, are plastic, as Boas showed in 1912.

Counter-view: genome studies (Rosenberg and colleagues, 2002) can cluster individuals by continental ancestry, which matters for medicine and forensics.

Conclusion: ancestry and population structure are real, but race as discrete, ranked, biologically bounded units is not meaningful, as the American Association of Biological Anthropologists’ statement (2019) affirms.

Example 14 (UPSC 2020, 10 marks): Racism and Eugenics

Paper and question: Paper I, Q5(a)

Approach: Define racism and eugenics with their origins, show how they fed each other (scientific racism, sterilisation laws, Nazism, colonial India), the anthropological critique, and present-day relevance.

Racism is the belief that humans are divided into biologically distinct races with inherent differences in ability and worth, and the discrimination built on that belief. Arthur de Gobineau’s Essay on the Inequality of Human Races (1853–55) and craniometric ranking by Samuel Morton gave it a pseudo-scientific form.

Eugenics, a term coined by Francis Galton in 1883, aimed to improve the hereditary quality of a population by encouraging the fit to reproduce (positive eugenics) and preventing the unfit (negative eugenics). Linked to racism, it produced compulsory sterilisation laws in the USA (upheld in Buck v. Bell, 1927), restrictive immigration acts and, at its extreme, Nazi racial hygiene and genocide.

In India, Risley’s use of the nasal index to rank castes echoed racial thinking.

Boas, Montagu and the UNESCO statements (1950) refuted both. Concerns now arise over genetic testing, embryo selection and racial profiling, so the lessons remain relevant.

Example 15 (UPSC 2019, 20 marks): With reference to the somatoscopic and morphometric characteristics commonly used for racial classification, make critical comments as to whether 'Race' is a valid concept.

Paper and question: Paper I, Q4(a)

Approach: Describe the somatoscopic (observational) and morphometric (measured) criteria used in racial classification with their categories, then critically evaluate whether they support race as a valid concept, using plasticity, clines, discordance and genetic evidence.

Classical physical anthropology, from Blumenbach to Risley, Guha and Coon, classified races by visible and measurable bodily traits, assuming that these were stable, inherited and concordant.

Somatoscopic characteristics (observed): skin colour (graded by colour charts such as von Luschan’s scale); hair form, straight (leiotrichy), wavy (cymotrichy) or woolly (ulotrichy); hair and eye colour; eye form, including the epicanthic fold; nose form and profile; lip thickness; facial prognathism; and body hair.

Morphometric characteristics (measured): stature; the cephalic index (head breadth/length × 100), classing heads as dolichocephalic (below about 76), mesocephalic (about 76 to 81) or brachycephalic (above about 81); the nasal index, classing noses as leptorrhine (below 70), mesorrhine (70 to 85) or platyrrhine (above 85); facial index; and limb proportions. Risley ranked Indian castes partly by nasal index.

Critique: (i) these traits vary continuously, so category boundaries are arbitrary; (ii) they are discordant, since skin colour, head form and nose form do not vary together; (iii) many are environmentally plastic: Boas (1912) showed changed cephalic index among immigrants’ children, and Harry Shapiro (1939) found Japanese migrants in Hawaii differing from their relatives in Japan; (iv) many are climatic adaptations, such as nose shape (Thomson’s rule), body build (Bergmann’s and Allen’s rules) and pigmentation tracking ultraviolet radiation, so similarities can reflect convergence rather than kinship; (v) genetic data show that most variation lies within populations (Lewontin, 1972) and that variation is clinal.

Assessment: somatoscopic and morphometric traits describe adaptation and local population history, but do not divide humanity into discrete races. Race is thus not a valid biological concept, though the study of human variation through populations and clines remains valuable.

Example 16 (UPSC 2018, 10 marks): Race is a Myth. Justify its Present Day Relevance.

Paper and question: Paper I, Q5(d)

Approach: Explain why race is called a myth (Montagu, genetic evidence), then justify its present-day relevance as a social reality (racism, Indian cases, medicine and forensics), and conclude.

Ashley Montagu called race Man’s Most Dangerous Myth (1942) because the idea of discrete, ranked biological races has no scientific basis: about 85 per cent of genetic variation lies within populations (Lewontin, 1972), traits vary in clines and do not vary together, and humans share about 99.9 per cent of their DNA.

Present-day relevance: although biologically a myth, race is a powerful social reality. Racial discrimination persists, as global protests after George Floyd’s killing in 2020 showed. In India, people from the north-east face racial slurs and violence; after the death of Nido Taniam in Delhi in 2014 the Bezbaruah Committee recommended legal and social remedies. African students have faced attacks in Indian cities.

Race also matters in medicine, where ancestry rather than race helps predict disease risks and drug responses, and in forensic identification of skeletal ancestry.

Studying race critically thus remains necessary to fight racism while using ancestry responsibly.

Example 17 (UPSC 2017, 10 marks): Concept of race

Paper and question: Paper I, Q5(c)

Approach: Define race through classical and genetic definitions, outline major classifications (world and India), and give the modern critique.

Classically, a race was defined as a large group of people sharing a combination of inherited physical traits, such as skin colour, hair form, head and nose shape, that distinguish it from other groups. In genetic terms, Theodosius Dobzhansky defined races as populations that differ in the frequencies of some genes.

Classifications: Linnaeus (1758) and Blumenbach (1795, five races) ranked humanity by appearance; Coon, Garn and Birdsell (1950) related races to adaptation.

In India, H.H. Risley (The People of India, 1908) proposed seven types and B.S. Guha (1931, 1935) six main races: Negrito, Proto-Australoid, Mongoloid, Mediterranean, Western Brachycephals and Nordic.

Critique: human variation is continuous and clinal, traits are discordant, most genetic variation lies within groups (Lewontin, 1972), and racial labels have served racism. Hence modern anthropology prefers population, ancestry and ethnic group, treating race as a social construct.

Example 18 (UPSC 2016, 15 marks): Explain the role of heredity and environment in the formation of races.

Paper and question: Paper I, Q6(b)

Approach: Explain population differentiation as the joint result of heredity (mutation, drift, isolation, gene flow, sexual selection) and environment (natural selection by climate, disease, altitude; developmental plasticity), with examples and the ecological rules.

Whatever term is used, the formation of geographically distinct human populations results from the interaction of heredity, which supplies and transmits variation, and environment, which selects and moulds it. Coon, Garn and Birdsell (Races, 1950) and Dobzhansky treated race formation as a population-genetic process.

Heredity: mutation creates new alleles; genetic drift and isolation, as in island and forest groups such as the Andamanese, fix distinctive frequencies; gene flow blends neighbouring groups, producing clines; and sexual selection and cultural preference may reinforce some traits.

Environment through natural selection: skin pigmentation correlates with ultraviolet radiation, dark skin protecting folate in the tropics and light skin aiding vitamin D synthesis at high latitudes (Jablonski and Chaplin, 2000); body form follows Bergmann’s rule (larger, stockier bodies in cold climates, as among the Inuit) and Allen’s rule (shorter limbs in cold, long limbs among East African Nilotes); Thomson and Buxton’s nose rule links narrow noses to cold, dry air; malaria selected HbS and thalassaemia; high altitude selected EPAS1 variants in Tibetans.

Environment through plasticity: Boas’s immigrant head-form study, Shapiro’s Japanese migrants in Hawaii and the secular rise in stature show that nutrition and climate alter phenotype within a generation without genetic change.

Thus population differences are neither purely hereditary nor purely environmental; they are adaptations and histories written jointly by genes and environment.

3. Genetic Markers and Physiological Variation

Example 19 (UPSC 2025, 20 marks): What are genetic markers ? Discuss their applications in understanding population variation, disease association and forensics.

Paper and question: Paper I, Q6(a)

Approach: Define genetic markers and their essential properties, classify classical and molecular markers, then discuss applications in three blocks (population variation, disease association, forensics) with examples, and close with ethical cautions.

A genetic marker is a heritable, polymorphic character with a known mode of inheritance and chromosomal location, which can be reliably identified and used to trace individuals, families and populations. A good marker is simply inherited, polymorphic, environmentally stable and easily typed.

Types: classical markers include blood groups (ABO, Rh, MN, Duffy, Diego), serum proteins (haptoglobin, transferrin), red cell enzymes (G6PD, acid phosphatase), haemoglobin variants, HLA antigens and traits such as PTC tasting. Molecular markers include RFLPs, VNTRs (minisatellites), STRs (microsatellites), SNPs, mitochondrial DNA (maternal line) and Y-chromosome markers (paternal line).

Population variation: the Diego antigen is frequent in Mongoloid and Native American populations but nearly absent in Europeans; the Duffy-null allele is almost fixed in West Africa; mtDNA traced recent African origin (Cann and colleagues, 1987). In India, deep mtDNA lineages among the Andamanese and the Ancestral North and South Indian components (Reich and colleagues, 2009) revealed population history, and Y-haplogroup studies traced male-mediated migrations.

Disease association: HLA-B27 with ankylosing spondylitis; HLA-DQ2 with coeliac disease; blood group A with stomach cancer and O with duodenal ulcer (Aird and colleagues, 1953); HbS with malaria resistance; and GWAS SNPs mapping susceptibility to type 2 diabetes and heart disease.

Forensics: DNA fingerprinting, developed by Alec Jeffreys (1984), first solved a double murder in England (the Colin Pitchfork case, 1988); today STR profiles at standard loci identify suspects, victims of disasters and parentage. In India Lalji Singh pioneered DNA fingerprinting at the Centre for Cellular and Molecular Biology, and the Centre for DNA Fingerprinting and Diagnostics in Hyderabad performs forensic work.

Ethical cautions: informed consent from communities, privacy of DNA databases and avoidance of misuse in racial profiling must accompany these uses.

Example 20 (UPSC 2024, 10 marks): Hemoglobin in health and disease

Paper and question: Paper I, Q1(e)

Approach: Describe haemoglobin’s structure, types and genes and its normal role, then the haemoglobinopathies (structural variants and thalassaemias) with Indian distribution, and close with significance.

Haemoglobin is the iron-containing protein of red blood cells that carries oxygen from the lungs to tissues. It is a tetramer of four globin chains, each holding a haem group. Adult haemoglobin HbA is α2β2, HbA2 is α2δ2 (about 2.5 per cent), and foetal HbF (α2γ2), with higher oxygen affinity, predominates before birth.

Alpha-globin genes lie on chromosome 16 and the beta-globin cluster on chromosome 11; switching from gamma to beta chains after birth replaces HbF by HbA.

Disease: haemoglobinopathies are the commonest single-gene disorders worldwide. Structural variants include HbS (glutamic acid replaced by valine at position 6 of the beta chain), which makes red cells sickle and causes painful crises; HbE, very frequent in north-east India; HbD Punjab; and HbC in West Africa. Thalassaemias reduce production of alpha or beta chains, causing severe anaemia in beta-thalassaemia major.

HbS is common among tribes of central and western India, and carriers are protected against falciparum malaria. Screening, counselling and hydroxyurea treatment, under the 2023 sickle-cell mission, address this burden.

Example 21 (UPSC 2022, 15 marks): What do you understand by blood group systems ? How is HLA system different from those based on red cell antigens ?

Paper and question: Paper I, Q8(b)

Approach: Define a blood group system with examples of red cell systems, then explain the HLA system and contrast it with red cell antigen systems point by point (location, genetics, polymorphism, antibodies, function, clinical use, disease association).

A blood group system is a set of red cell surface antigens controlled by alleles at a single locus or closely linked loci, inherited in a Mendelian manner. Over 40 systems are now recognised, the best known being ABO (Landsteiner, 1900), Rh (1940), MN, Duffy, Kell and Diego.

The HLA system (human leucocyte antigens), first identified by Jean Dausset in the 1950s, is the human major histocompatibility complex on chromosome 6p21. Class I antigens (HLA-A, B, C) occur on almost all nucleated cells and present peptides to cytotoxic T cells; class II antigens (DR, DQ, DP) occur on antigen-presenting cells.

Differences: (i) location: red cell antigens are on erythrocytes, HLA on white cells and most tissues; (ii) polymorphism: ABO has three main alleles, while HLA is the most polymorphic system in humans, with thousands of alleles; (iii) inheritance: HLA genes are tightly linked and inherited as a haplotype from each parent; (iv) antibodies: anti-A and anti-B occur naturally, whereas HLA antibodies arise only after sensitisation; (v) clinical use: red cell typing guides transfusion, HLA matching guides organ and bone-marrow transplantation; (vi) disease association is far stronger for HLA, as with HLA-B27 and ankylosing spondylitis, and DR3 and DR4 with type 1 diabetes.

Both serve as population markers, but HLA is the more powerful tool for population and disease studies.

Example 22 (UPSC 2016, 10 marks): Rh-Blood Group

Paper and question: Paper I, Q5(a)

Approach: Give the discovery, genetics (genes, nomenclature, inheritance), clinical importance (haemolytic disease) and population distribution of the Rh system.

The Rh blood group was discovered by Karl Landsteiner and Alexander Wiener in 1940, using antibodies raised against rhesus monkey red cells.

Genetics: two closely linked genes on chromosome 1, RHD and RHCE, control it. Fisher and Race described three linked loci with alleles C/c, D/d and E/e (the CDE notation), while Wiener proposed multiple alleles at one locus. Clinically, the presence of the D antigen makes a person Rh positive (DD or Dd), while Rh negative people (dd) lack the RHD gene product, so Rh positive behaves as dominant.

Clinical importance: an Rh negative mother carrying an Rh positive foetus can be sensitised at delivery, and her anti-D antibodies may destroy foetal red cells in later pregnancies, causing haemolytic disease of the newborn. Anti-D immunoglobulin given after delivery prevents this.

Distribution: Rh negative frequency is about 15 per cent among Europeans, highest among the Basques, about 5 per cent in India and very low in East Asians and Native Americans.

Example 23 (UPSC 2015, 15 marks): What do you understand by Immunogenetics? Explain with suitable examples.

Paper and question: Paper I, Q8(c)

Approach: Define immunogenetics, then explain its main areas with examples: blood group immunology, HLA and transplantation, immunoglobulin genes and allotypes, inherited immune disorders and resistance to infection, ending with anthropological relevance.

Immunogenetics is the study of the genetic basis of the immune system: how inherited variation shapes antigens, antibodies and immune responses, and how these vary between individuals and populations.

Areas and examples: (i) blood group immunology: ABO antigens and naturally occurring antibodies explain transfusion reactions, and Rh incompatibility causes haemolytic disease of the newborn; (ii) the HLA system on chromosome 6, the most polymorphic human gene complex, determines graft acceptance and is matched for kidney and bone-marrow transplants; HLA-B27 is associated with ankylosing spondylitis and DR3/DR4 with type 1 diabetes.

(iii) Antibody diversity: Susumu Tonegawa (Nobel Prize, 1987) showed that recombination of V, D and J gene segments generates millions of antibodies; inherited variants of immunoglobulin chains, the Gm and Km allotypes, differ among populations and serve as genetic markers. (iv) Inherited immune disorders: severe combined immunodeficiency (including adenosine deaminase deficiency) and X-linked agammaglobulinaemia. (v) Resistance to infection: the CCR5-Δ32 deletion protects against HIV; Duffy-negative people in West Africa resist Plasmodium vivax.

Immunogenetics thus links genes, disease and population history, and is central to transplantation, vaccine response studies and medical anthropology.