34 Indian Population Structure
Dr. Jyoti Ratan Ghosh
Contents of This Unit
1. Introduction
A. Criteria for the classification of human population
B. Factors that determine the genetic structure
C. Population structure
2. Indian population structure A. Race and ethnicity
B. Sir H.H. Risley’s (1915) classification
C. Linguistic classification
D. Classical genetic markers as a criteria for population structure
E. Blood Groups
F. Protein Polymorphism
G. Enzyme Polymorphism
H. Dermatoglyphics
I. Abnormal Haemoglobins
J. Other Genetic Traits
K. DNA as a criteria for population structure
Learning objectives
- What is population structure?
- What is race and ethnic group?
- What criteria should be used for the classification of human population?
- Classical genetic markers as a criteria for population structure
- DNA as a criteria for population structure
1. Introduction
Traditionally, physical anthropologists were concerned with describing and interpreting the patterns of geographical variety which are found to be so striking in the human species. The variables that first examined were anthropometric and somatoscopic, such as head and body dimensions, skin colour, hair form including hair colour and texture, eye colour, lip and ear form, etc. Many of these characters demonstrated geographical variations in its distribution and populations were differentiated on a broad continental basis. These patterns of variations were widely used for racial taxonomies. The objective of these racial taxonomies was not only the classification of human population like that of Darwinian principle, where similarities indicated phylogenetic affinity. Rather, these racial taxonomies were attempted to study the evolutionary histories of the mankind. Because, understanding of this evolutionary history is one of the primary objective of the physical anthropology. However, the available anthropometric and somatoscopic characteristics that were used initially for these racial taxonomies had a number of limitations. For example, some of these variables are subjective and thus interpretation of the data was difficult. Moreover, these variables are influenced by the environmental factors in which the individual grows. Thus, the similarities and differences are to some extent determined by environmental factors which are not reliable to establish the evolutionary relationship (Harrison, 1977).
A. Criteria for the classification of human population
In 1940, Boyd proposed some requirements for the variables that are to be used for the classification of human population, which are as follows:
- The criteria must be objective.
- They must not be subject to too much modification by the environment.
- They must be determined by one, or a small number of genes.
- They must be non-adaptive; that is, they must not have any great selective value in evolution.
- They must not mutate at too high a rate.
However, the situation changed with the discovery of so-called marker genes which show discrete variation within and between populations. The marker genes can be classified into four main classes namely the blood groups, the plasma proteins, the red cell enzymes and haemoglobins, and the histocompatibility antigens (Mourant, 1977). These characters are not affected by immediate environmental factors, their mode of inheritance, responsible allele and locus are known, moreover they are easy to identify and interpretation. Additionally, the variations of these characteristics often reach polymorphic proportions within populations. These genetic markers can be used to characterize populations and also to compare among populations in terms of gene frequencies.
However, these genetic markers demonstrated less distinct geographical variation in comparison with most of the quantitative traits, but, their frequency shows clinal distribution with rarely close similarities in the distribution of the different characters. Interestingly, the results of taxonomic studies in man demonstrated agreement in broader sense in the distribution of polymorphic genetic markers and anthropometric traits. Moreover, the genetic marker traits also demonstrated broad continental patterns in its distribution (Harrison, 1977).
B. Factors that determine the genetic structure
It has long been recognized that the forces determining the genetic structure are mutation (change in genetic materials), gene flow (the exchange of genes between populations), genetic drift (changes in allele frequencies, produced by random factors), recombination (produce different combinations of genes) and natural selection (operates through genetically determined differences in fertility and mortality).Genetic structure of a population is also influenced by the social structure of that population through the prescribed mating system.
C. Population structure
Population structure is simply the understanding of population composition. A population structure may be heterogeneous i.e. the population is made up of genetically different subgroups or it may be homogenous i.e. the population is made up of genetically similar individuals. However, by population structure, population geneticists mean that, instead of a single, simple population, populations are subdivided in some way.On a genetic level, population structure is defined as the relationship of gene and genotype frequencies within a population, or set of subpopulations. This distribution is essentially a reflection of a population’s mating structure. Hence, the study of population structure offers an ideal focus for anthropological investigations of genetic variation. Population structure has often been defined in terms of assessing deviations from panmixia (Relethford and Lees, 1982).Studying population structure helps to understand the ways individuals and populations adapt, or fail to adapt, to their environments, priorities for attending change. Moreover, the knowledge about the structure of human populations also helps to understand the evolutionary history. However, changes in population structure can be studied by historical data, because historical populations provide the opportunity to investigate changes in the rates of inbreeding, migration, and genetic drift and their effect (Mielke and Swedlund, 1993).
2. Indian population structure
The Indian population is characterized by a vast assemblage of peoples with different morphology, genetics, culture and language. Thought larger portion of this variability is native, a sizeable fraction of it has been introduced through Large-scale migrations into India in the past. From an evolutionary point of view, it is very important to quantify the biological variation in human populations, to understand the biological affinities and to relate observed patterns of distribution with cultural, linguistic and demographic histories of the Indian populations (Majumder, 1998). Such efforts are intended to shed light on the population structure of India.
A. Race and ethnicity
During the early part of the twentieth century the systems of classification of Indian people were typological and based on anthropometric and somatoscopic characters.The data collected in these early studies provided ample evidence of vast anthropometric and somatoscopic variation among different Indian populations. This typological variations were used to classify the peoples of India into a number of ‘‘racial’’ types. However, now a day the term ‘ethnic group’ is most commonly used and preferred instead of ‘race’. Because, if races are defined as geographically delimited con specific populations characterized by distinciveregional phenotypes, then human races do not exist now and have not existed for centuries (Cartmill, 1999).
Race is a concept. All men living today belongs to a single species i.e. Homosapiens sapiens. But there is variation in different groups or populations, each differing from other. Each of this population constituting the species Homo sapiens were considered as race. According to Hooton, race is a grate division of mankind, the members of which, though individually varying are characterized as a group by certain combinations of morphological and material features, principally, non-adaptive, which have been derived from their common descent.
B. Sir H.H. Risley’s (1915) classification
A number of racial classifications of Indian populations have been reported in the literature. The first attempt for systematic classification of Indian population was made by Sir H.H. Risley in 1915. He classified the Indian population in to seven types.
- The Turko-Iranian Type: Represented by theBaluchis, Brahuis, Afghans and North-Western Frontier Province (characterized by fair skin, wavy to curly hair form with medium brown to black in colour, broad head, tall stature, etc).
- The Indo-Aryan Type: represented by the Rajputs, Khattris and Jats (characterized by fair skin, wavy to curly hair form with brown to black in colour, long head, tall stature, long nose etc.).
- The Scytho-Dravidian Type: Represented by the Western India including the Maharashtrian Brahmins and Kunbis (characterized by fair skin, wave to curly hair with dark brown to black in colour, medium to broad head, medium stature an nose, etc.).
- The Aryo-Dravidian Type: Represented by the peoples of Uttar Pradesh and some parts of Rajputana, Behar and Sri Lanka (Ceylon) as well as higher caste and lower caste people (characterized by light brown to dark skin coloue, wavy to curly hair with dark brown to black in colour, long head with a tendency towards medium, short to medium stature with medium to broad nose, etc.).
- The Mongolo-Dravidian Type: Represented by the people of lower Bengal and Orissa, particularly the Bengali Brahmins and Kayastha and Mohammedans (characterized by darkskin, wavy black hair, broad to medium hair, short to medium stature with medium to broad nose, etc.).
- The Mongoloid Type: Represented by the Kannets of Lahul, Kulu, Lepchas, Limbus, Murmis and Gurangs of Nepal and Bodos of Assam and Burmese (characterized by dark with yellowish skin, straight and dark hair, broad head, presence of epicanthic fold, broad face, short to below medium stature, etc.).
- The Dravidian Type: Represented by the people from the valley of the Ganges to Sri Lanka (Ceylon) including the whole of Madras, Hyderabad, Central Province and Chota Nagpur (characterized by very dark skin and hair colour, curly hair, long head, short stature with broad nose.
Since Risley’s classification in 1915, a number of scholars were also tried to classify Indian population into different racial groups. They are, Giuffrida-Ruggari in 1921, Haddon in 1924, Roy in 1934 – 1938, v. Eickstedt in 1934, 1952, Guha in 1935, 1937, Sarkar in 1958, Biasutti in 1959, Roginskij and Levin in 1963, Buchi in 1968 and Bowles in 1977, Abe and Tamura in 1983, Mourant in 1983 and Abe in 1985.
Figure 1. Distribution of various racial strains present in the people of India (Source: Bhasin, 2006)
Linguistic classification
An attempt has also been made to classify Indian population on the basis of language. The people of India display a high degree of diversity in their languages and dialects. It has been acquired through a long process of peopling of the sub-continent by heterogeneous ethnic groups drawn from the adjacent regions of Asia. According to the 1961 Census of India there were 187 languages spoken by different sections of our society. The languages spoken by the people of India belong to the following four language families (Bhasin 2006):
- The Austro-Asiatic Language Family (Nishada),
- The Tibeto-Chinese Language Family (Kirata),
- The Dravidian Language Family (Dravida), and
- The Indo-European Language Family (Aryan).
D. Classical genetic markers as a criteria for population structure
However, after 1950s with the introduction of blood grouping techniques and, subsequently, electrophoretic techniques for detecting polymorphisms in genetic markers at serum protein and red-cell enzyme loci, there was a major chance in the pattern of understanding human variation, which yielded much valuable insight into the biological structure of Indian populations. Surveys conducted next three to four decades were dominated by blood groups and electrophoresis markers along with anthropometry for studying the evolutionary relationships within and between different populations. These studies also revealed marked regional and ethnic differences in the distribution of blood groups and other genetic markers. For example,
E. Blood Groups
Table 1. Distribution of “A” gene of ABO blood group system
| Population | % |
| TelangiKumbharand Nandiwala (Maharashtra) | 4.17 |
| Onge tribe (Andaman) | 50.62 |
| Dhodia, Konkani and Worli tribes (Dadra & Nagar Haveli) | 28.96 |
| Kurumba and Yarava (Karnataka) | 30.07 |
| Mala Kuruvan, Mala Vedan, Muthuvan, Paniyan (Ketala) | 25.48 |
(Source: Singh et al., 1994)
Table 2. Distribution of “B” gene of ABO blood group system
| Population | % |
| Brahmin, Ezhava, Hurchiar, Nair (Kerala) | 14.73 |
| Oraon (Andaman) | 30.25 |
| Onge (Andaman) | 4.97 |
| Bhotia (U.P.) | 33.18 |
(Source: Singh et al., 1994)
Table 3. Distribution of “O” gene of ABO blood group system
(Source: Singh et al., 1994)
| Population | % |
| Bhotia (U.P.) | 43.26 |
| Nicobarese and Shompen (Andaman and Nicobar) | 90.24 |
| Nandiwala (Maharastra) | >70.00 |
| Pulayan (Kerala) | >60 |
(Source: Singh et al., 1994)
Table 4. Distribution of “M” gene of MN system
| Population | % |
| Dhodia, Konkana and Worli (Dadra and Nagar Haveli) | 42.26 |
| Grate Andamanese, Nicobarese and Onge (Andaman) | 88.49 |
| Manne (Andhra Pradesh) | 88.12 |
| Dogra (Jammu and Kashmir) | 76.42 |
| Riang (Tripura) | 89.00 |
(Source: Singh et al., 1994)
Table 5. Distribution of “MS Haplotype” of MNSs system
| Population | % |
| Chetri, Limboo, Rai, Tamang (Sikkim) | 8.71 |
| Brahmin and Meitie (Manipur) | 7.60 |
| Sikh (West Bengal) | 29.24 |
| Khasi (Meghalaya) | 9.60 |
| Onge (Andaman) | 7.25 |
(Source: Singh et al., 1994)
Table 6. Distribution of “Ms Haplotype” of MNSs system
| Population | % |
| Muslims (Orissa) | 64.10 |
| Kota, Toda (Tamil Nadu) | 57.81 |
| Nicobarese (Andaman) | 70.80 |
| Rajbanshi (West Bengal) | 55.02 |
| Bhotia, Lepcha (Sikkim) | 59.27 |
(Source: Singh et al., 1994)
F. Protein Polymorphism
Table 7. Distribution of “Hp1 gene” of Haptoglobin system
| Population | % |
| Santal (West Bengal) | 0.89 |
| Ladakhi (Jammu and Kashmir) | 27.40 |
| Siddi and Jenu-Kurumba (Karnataka) | 22.50 |
| Ezhava (Kerala) | 20.51 |
(Source: Singh et al., 1994)
Table 8. Distribution of “Gc1” gene of Group specific component system
| Population | % |
| Karbi (Assam) | 67.34 |
| Brahmin, Chetri and Pradhan (Sikkim) | 85.51 |
| Madiga (Andhra Pradesh) | 83.10 |
| Langia-Saora (Orissa) | 84.40 |
| Brahmin (Karnataka) | 81.31 |
(Source: Singh et al., 1994)
G. Enzyme Polymorphism
Table 9. Distribution of “G6PD” deficiency
| Population | % |
| Naga-Angami (Nagaland) | 27.06 |
| Rajput (Himachal Pradesh) | 14.86 |
| Gond and Oraon (Madhya Pradesh) | 13.28 |
| Santal (West Bengal) | 14.03 |
| Adi, Apatani and Nishi (Arunachal Pradesh) | 16.78 |
(Source: Singh et al., 1994)
Table 10. Distribution of “PGM 1 ” variants of Phosphoglucomutase system
| Population | % |
| Oriya and SaoraLangia (Orissa) | 85.90 |
| Lingayat and Vokkaliga (Karnataka) | 79.81 |
| Bagdi, Kaibarta and Kaora (West Bengal) | 80.26 |
| Bhil and Meena (Rajasthan) | 83.72 |
| Nadar, Reddiar and Thevar (Tamil Nadu) | 76.95 |
(Source: Singh et al., 1994)
H. Dermatoglyphics
Table 11. Distribution of “finger pattern”
| Population | Pattern | % |
| Gurung (Uttar Pradesh) | Loops | 41.37 |
| Brahmin (Karnataka) | Loops | 64.21 |
| Oraon (West Bengal) | Whorls | 56.97 |
| Brahmin (Karnataka) | Whorls | 32.49 |
| Tibetan (Orissa) | Arches | 0.40 |
| Gujjar, Oswal and Rajpur (Rajasthan) | Arches | 7.00 |
(Source: Singh et al., 1994)
Table 12. Distribution of “total ridge count (TRC)”
| Population | TRC |
| Gaddi (Himachal Pradesh) | 125.30 |
| SonowalKachari (Assam) | 178.40 |
| Chamar (Uttar Pradesh) | 124.90 |
| Rajbanshi (Assam) | 157.40 |
(Source: Singh et al., 1994)
I. Abnormal Haemoglobins
Table 13. Distribution of abnormal haemoglobin traits
| Population | trait | % |
| Panka (Madhya Pradesh) | Sickle cell | 24.28 |
| Kachari (North East region) | Haemoglobin E | 50.59 |
| In West Bengal and Sikkim | Haemoglobin E | <6.00 |
(Source: Singh et al., 1994)
J. Other Genetic Traits
Table 14. Distribution of “non-taster gene (t)” of PTC taste ability
| Population | % |
| Ladhakhi (Jammu and Kashmir) | 23.79 |
| Adi Karnataka (Karnataka) | 78.17 |
| Nags-Angami (Nagaland) | 24.49 |
| Gond (Madhya Pradesh) | 75.60 |
(Source: Singh et al., 1994)
Table 15. Distribution of “non-secretor allele” ABH Secretion
| Population | % |
| Onge (Andaman) | 14.10 |
| Khond (Orissa) | 78.10 |
| Nair (Kerala) | 66.96 |
| Iyer, Kallan and Mudaliar (Tamil Nadu) | 23.71 |
(Source: Singh et al., 1994)
K. DNA as criteria for population structure
In the last two decades, however, new methods with elaborate statistics and biometry along with the molecular genetic techniques have added new dimension to the study of Indian population structure, which yielded much appreciated understanding into the biological structure of human populations in India. For example, a study by Basu et al., (2003) using 58 DNA markers {mitochondrial (mt), Y-chromosomal, and autosomal} and sequence data of the mtHVS1 from a large number of ethnically diverse populations of India demonstrated that there was an underlying unity of female lineages in India, indicating that the initial number of female settlers may have been small. The tribal and the caste populations were highly differentiated. The result also revealed that Austro-Asiatic tribals were the earliest settlers in India (as they possess the highest frequencies of the ancient east-Asian mtDNA HG-M and exhibit the highest HVS1 nucleotide diversity. They also have the highest frequency of sub HG M2). It showed that a major wave of humans entered India through the northeast and the Tibeto-Burman tribals shared considerable genetic similarities with the Austro-Asiatic tribals, supporting the hypothesis that they may have shared a common habitat in southern China, but the two groups of tribals can be differentiated on the basis of Y-chromosomal haplotypes. The study also demonstrated that the Dravidian tribals were possibly widespread throughout India before the arrival of the Indo-European-speaking nomads, but retreated to southern India to avoid dominance. Moreover the analysis of DNA markers also demonstrated that the upper castes showed closer genetic affinities with central Asian populations, although those of southern India were more distant than those of northern India.
Figure 2. Frequencies of Y-chromosomal haplogroups among ethnic populations. (Source: Basu et al., 2003)
Figure 3: Neighbor-joining tree depicting genetic affinities among Indian ethnic populations based on (A) mitochondrial RS haplotype frequencies, (B) Y-Haplogroup frequencies, (C) Y-STRP frequencies, and (D) autosomal markers. The social [(UC) upper caste, (MC) middle caste, (LC) lower caste, (TR) tribal] and linguistic [(AA) Austro-Asiatic, (DR) Dravidian, (TB) Tibeto-Burman, (IE) Indo-European] background of each population is color-coded; the key to the color codes is given on the top right-hand corner (Source: Basu et al., 2003).
Another study by Indian Genome Variation Consortium (2008) using data on 405 SNPs observed high levels of genetic divergence between groups of populations that cluster largely on the basis of ethnicity and language. Indian populations not only overlap with the diversity of Hap-Map populations, but also contain population groups that are genetically distinct.
Figure 4. Grouping of Indian populations by SStr (a) System Structure analysis reveals five major groups depicted by different colour schemes. The relative fuzzy memberships of populations in each group are depicted by horizontal bars. (b) Representation of system structure-derived membership information on the linguistic map of India. Blue, brown, green and pink backgrounds indicate regions where languages of predominantly IE, DR, AA and TB lineages are spoken, respectively. A key to the group colour based on typicality membership is given. The pie-charts represent fuzzy membership information for each population inferred from SStr analysis (Source: Indian Genome Variation Consortium, 2008)
Figure 5. Spatial frequency maps depicting distribution of minor allele frequencies of selected keystone SNPs. Minor allele frequency distribution is plotted for SNPs of: (a) FCGR2A (rs1801274; p.R131H), (b) OPRM1 (rs1799971; p.D102N) and (c) CYP1B1 (rs1056827; p.A119S). The colour gradient below each map depicts the range of observed frequency from minimum to maximum (Source: Indian Genome Variation Consortium, 2008).
A study by Kashyap et al., (2006) in 54 endogamous Indian populations (representing all major ethnic, linguistic and geographic groups) based on autosomal microsatellite markers detected no evidence of general clustering of population groups based on ethnic, linguistic, geographic or socio-cultural affiliations. However, genetic sub-structuring was observed among populations originating from northeastern and southern India, which was reflective of their migrational histories and genetic isolation, respectively.
Figure 6. Alleles with significant distribution among the different groups of India for the studied microsatellite markers. ‘❍’represents alleles occurring at a high frequency and ‘ם’ denotes unique alleles present in a population.(Source: Kashyap et al., 2006)
However, Indian population experienced several waves of immigrants at different periods of history. These immigrants entered into the ethnic composition of the population at different levels from a very early phase of human civilization. The invasions of these people with several racial elements have left the strains of various developed races together with their ethnic and cultural substratain the land, thus representing the elements of all the main divisions of mankind. Thus, the Indian population is consisting of almost all the primary ethnic strains, including Proto-Australoid (skin colour-dark)
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