The genetic origins of the Andaman Islanders

Abstract

Mitochondrial sequences were retrieved from museum specimens of the enigmatic Andaman Islanders to analyze their evolutionary history. D-loop and protein-coding data reveal that phenotypic similarities with African pygmoid groups are convergent. Genetic and epigenetic data are interpreted as favoring the long-term isolation of the Andamanese, extensive population substructure, and/or two temporally distinct settlements. An early colonization featured populations bearing mtDNA lineage M2, and this lineage is hypothesized to represent the phylogenetic signal of an early southern movement of humans through Asia. The results demonstrate that Victorian anthropological collections can be used to study extinct, or seriously admixed populations, to provide new data about early human origins.

Figure 1

Map of the Andaman Islands showing the distribution of the known communities of 1858. The two clades (black and white) are defined by linguistic affinities. The term “Jarawa” is here extended to the inhabitants of Sentinel Island, on the basis of their similar phenotype and a similarity in language. The Greater Andamanese practiced body tattooing, whereas the Onge and Jarawa did not. There were also differences in material culture.

Figure 2

Median joining network (after Kivisild et al. 1999b) showing the known components of the M2 and M4 mtDNA lineages belonging to Asian haplogroup M in mainland India and the Andaman Islands. Substitution positions minus 16,000 are shown and are relative to the CRS (Anderson et al. 1981). The reticulation is shown with equal weighting, although the higher mutation rate of 311 and the date of coalescence for M4 favor the assignment of these three variants to M2. The diameters of the nodes are an approximate indication of the population totals inferred from sampling to date. The “starlike” radiations of M4, M2a, and M2b are consistent with late Pleistocene population expansion events (17,000–32,000 years ago). The linear nature of M2 prior to these demographic signatures suggests a greater antiquity, confirmed by dates modeled on the coalescent process (63,000±6,000 years ago compared with 32,000±7,500 years ago for M4).

Figure 3

Distribution map for mtDNA lineages and haplogroups present in India and the Andaman Islands. The noncaste populations are considered individually, whereas the figures for castes are separated north/south along the borders of Goa, Karnataka, and Andhra Pradesh. The upper pie charts depict the percentage of M versus non-M haplotypes, whereas the lower ones indicate the percentage of M2 and M4 expressed as a proportion of all M haplotypes. The figures for ethnic populations from West Bengal and Tamil Nadu have been conflated in each case for the purposes of clarity, although they do conceal the fact that neither the Irula or Kota samples contained any M2. Despite this, the average of M2 in the total noncaste population (n=169) exceeded 20%, compared to ∼10% for caste populations (n=598). New data sets for additional Indian ethnic groups confirm these distributions (n=528, M2=23% [P. Majumder, personal communication]). This asymmetry is not reflected in the data for M4, which displays a more even distribution (Kivisild et al. 1999b).