Genetic affinities of Sri Lankan populations
Human Biology, by Kshatriya, Gautam Kumar
The population of Sri Lanka is heterogeneous and is composed of diverse ethnic groups (Table 1). (Table omitted) It is evident that the Sinhalese are numerically dominant, accounting for 72% of the total population. Next in order of preponderance are the Tamils, who constitute approximately 20% of the total population. Among other groups that inhabit Sri Lanka are the Burghers, Christians, Moors, and Malays--the descendants of culturally, religiously, and ethnically diverse groups who colonized the island from time to time (Table 2). (Table omitted) Finally, there are the Veddahs, the original inhabitants of Sri Lanka, who constitute less than 1% of the total population.
Sri Lankan populations and the legendary origin of the Sinhalese have generated considerable interest among anthropologists to study and examine mythological and historical records in light of genetic evidence.
Kirk (1976) and Saha (1988) studied the genetic composition of the population of Sri Lanka to determine the validity of Ceylonese mythology regarding the legendary origin of the Sinhalese people. Although Kirk (1976) found the Sinhalese to be genetically closer to Bengalis and to Indian Tamils to a lesser extent, Saha (1988) failed to recognize any genetic characteristics in the present-day Sinhalese population that are distinct from those of Sri Lankan Tamils. Later, however, Tay and Saha (1989) undertook a more detailed study on gene differentiation and genetic admixture among the Sinhalese and Sri Lankan Tamils and found that the Sinhalese have a stronger genetic contribution from the Bengalis of India than from the Sri Lankan Tamils.
These earlier studies, which focused mainly on the Sinhalese and Tamil population, have oversimplified the historical and mythological records of Sri Lanka. Therefore the degree and the magnitude of foreign admixture might have been compromised. In light of this, the genetic affinities of the Sri Lankan population have been studied after considering a detailed ethnohistorical account of Sri Lanka.
Materials and Methods
The present-day Sinhalese, Sri Lankan Tamil, and Veddah populations are considered admixed populations. A number of population groups from northwestern, eastern, and southern India have contributed genes in varying proportions to the contemporary Sri Lankan populations. In addition, many more populations, such as Arabs, Persians, Portuguese, Dutch, and English, enroute along seaways or from India, have also admixed with the local populations at different periods of time. The available information on genetic data of these most likely contributory gene pools is presented in Table 3. (Table omitted) The selection of the populations was made in light of the mythological and ethnohistorical background of Sri Lanka.
After careful scrutiny two data sets were selected, and a genetic distance analysis was performed: first, on the basis of 11 population groups
Sinhalese, Sri Lankan Tamils, Veddahs, Indian Tamils, South Indian Muslims (Andhra Pradesh, Kerala), Gujaratis, Punjabis, West Indian Muslims (Gujarat, Bombay), Bengalis, populations of the Middle East (Saudi Arabia, Kuwait, Jordan, and Iran), and populations of Europe (United Kingdom, Holland, Denmark) with 40 alleles controlled by 13 polymorphic loci and, second, on the basis of 8 population groups (Sinhalese, Veddahs, Indian Tamils, South Indian Muslims, Gujaratis, Punjabis, West Indian Muslims, and Bengalis) with 43 alleles controlled by 15 polymorphic loci.
Genetic distances among these populations were computed by Nei`s standard genetic distances (Nei 1972) and their standard errors (SE) using Nei and Roychoudhury`s (1974) method. To determine the significance of genetic distances among the different populations, I compared the gene frequency data pairwise using the chi-square statistic (Nei and Roychoudhury 1974). The distance matrix was then used to construct a phylogenetic tree based on the unweighted pair group method with arithmetic mean (UPGMA) (Li, personal communication, 1988).
The contribution (%) of ancestral populations to the hybrid populations (Sinhalese and Sri Lankan Tamils) was calculated using the method of Chakraborty (1985, 1986), with each population considered the product of admixture of three parental populations. The parental populations for the Sinhalese have been considered to be the Bengalis, the Indian Tamils, and the Veddahs of Sri Lanka, and the parental populations for the Tamils are considered to be the Sinhalese of Sri Lanka, the Bengalis, and the Indian Tamils.
Results and Discussion
Table 4 shows the allelic frequencies of 40 alleles in 11 populations and 43 alleles in 8 populations. (Table omitted)
Average heterozygosity and genetic differences along with their standard errors among the 11 population groups were estimated using Nei`s standard genetic distance among all pairs of populations (Table 5). (Table omitted) The average heterozygosity varies between 27.4% (Bengalis) and 32.6% (Veddahs). The genetic distances show no significant differentiation, as examined pairwise by the chi-square statistics (Table 6). (Table omitted) However, the dendrogram generated from the genetic distance matrix (Figure 2) reveals an absorbing pattern of clustering. (Figure omitted) It can be seen that the Sinhalese, the Sri Lankan and Indian Tamils, and the South Indian Muslims form one cluster, whereas the Gujaratis, the Punjabis, and the west Indian Muslims form another cluster. These two clusters are distinct and do not show much affinity with the Bengalis, the Veddahs, or the populations of the Middle East and Europe. In fact, the Veddahs are far apart from all the populations.
The results of a more detailed analysis on the basis of 43 alleles in 8 population groups for average heterozygosity and the genetic distance among all the pairs of populations together with their standard errors are presented in Table 7. (Table omitted) The average heterozygosity varies between 27.9% (Sinhalese) and 32.2% (Veddahs). The genetic distances do not reveal significant differentiation, as examined pairwise by the chi-square statistic (Table 8). (Table omitted) Nevertheless, the dendrogram produced from the genetic distance matrix (Figure 3) and the clustering obtained further strengthen earlier observations. (Figure omitted) It can be seen that the Sinhalese, the Indian Tamils, and the South Indian Muslims form one cluster, whereas the Gujaratis, the Punjabis, and the west Indian Muslims form another, an almost identical clustering to the one observed in Figure 2. Here, too, the Bengalis and the Veddahs are farthest from the Sinhalese.
Both dendrograms reveal close similarities between the Sinhalese and the Sri Lankan Tamils, between the Sinhalese and the Indian Tamils, and between the Sri Lankan Tamils and the Indian Tamils.
Table 9 presents the estimated values of admixture for the two hybrid populations (the Sinhalese and the Tamils) based on 13 polymorphic loci, fitting a trihybrid model using the ancestral frequencies shown in Table 10. (Tables 9 and 10 omitted)
The Bengalis, the Tamils, and the Veddahs are considered parental populations for the Sinhalese. The Bengali contribution is 25.41%, the Tamil (India) contribution is 69.86%, and the Veddah contribution is only 4.73%. Thus the Sinhalese have a predominantly Tamil (India) contribution followed by the Bengalis and the Veddahs. The fusion of the Veddahs and the Sinhalese was recorded in the ancient chronicles of Sri Lanka (Dipavamsa and Mahavamsa) as early as 543 B.C., but the Veddahs were subsequently pushed to the inhospitable dry zone for a long period of time under pressure from early colonizers.
By studying the Sri Lankan Tamils, one can see that the Sinhalese, the Bengalis, and the Indian Tamils can be considered ancestral populations. The contribution of the Sinhalese to the Sri Lankan Tamils is 55.20%. Similarly, the Bengali contribution is 28.17% and that of the Indian Tamils is 16.63%. The results indicate a predominant influence of the Sinhalese (who already have a high contribution from the Indian Tamils) and the Bengalis to a lesser extent.
In conclusion, the original inhabitants of Sri Lanka were the Veddahs, who have had little admixture with the Sinhalese and possibly none with the Tamils. The Veddahs are distinct because they were confined to inhospitable dry zones and were hardly influenced by the neighboring inhabitants. Furthermore, the Sinhalese and the Sri Lankan Tamils are an admixed population genetically. The Sinhalese, who first came from northwest India under the leadership of Prince Vijaya in 543 B.C., have received and exchanged a substantial amount of their genes with the populations of northeastern and southern India. The Sinhalese and the Tamils have no contribution from the population groups of northwest India. In fact, the contribution made by Prince Vijaya and his small band of 700 companions to the original pool of the Sinhalese must have been eliminated by the long-standing contribution (over 2000 years) of the population groups of northeastern and southern India.
Furthermore, although there is a noteworthy contribution from the Bengalis (northeast India) to the present-day Sinhalese, the Tamil (South India) contribution predominates. The contribution from the populations of northeast India were diluted, probably because the Indian influence on the Sinhalese after the eighth century A.D. became predominantly South Indian (Raghavan 1964). Thus the Sinhalese of Sri Lanka are genetically more similar to the Tamils of Sri Lanka and India, who were always in close proximity with each other historically, linguistically, geographically, and culturally.
Acknowledgments: I am extremely grateful to Ranajit Chakraborty (University of Texas, Houston), w...