Why Have the Peninsular “Negritos” Remained Distinct?

Unravelling the genetic history of Negritos and indigenous populations of Southeast Asia

Indigenous populations of Malaysia known as Orang Asli (OA) show huge morphological, anthropological, and linguistic diversity. However, the genetic history of these populations remained obscure. We performed a high-density array genotyping using over 2 million single nucleotide polymorphisms in three major groups of Negrito, Senoi, and Proto-Malay. Structural analyses indicated that although all OA groups are genetically closest to East Asian (EA) populations, they are substantially distinct. We identified a genetic affinity between Andamanese and Malaysian Negritos which may suggest an ancient link between these two groups. We also showed that Senoi and Proto-Malay may be admixtures between Negrito and EA populations. Formal admixture tests provided evidence of gene flow between Austro-Asiatic-speaking OAs and populations from Southeast Asia (SEA) and South China which suggest a widespread presence of these people in SEA before Austronesian expansion. Elevated linkage disequilibrium (LD) and enriched homozygosity found in OAs reflect isolation and bottlenecks experienced. Estimates based on N_e and LD indicated that these populations diverged from East Asians during the late Pleistocene (14.5 to 8 KYA). The continuum in divergence time from Negritos to Senoi and Proto-Malay in combination with ancestral markers provides evidences of multiple waves of migration into SEA starting with the first Out-of-Africa dispersals followed by Early Train and subsequent Austronesian expansions.

Time and place in the prehistory of the Aslian languages

The Aslian language family, located in the Malay Peninsula and southern Thai Isthmus, consists of four distinct branches comprising some 18 languages. These languages predate the now dominant Malay and Thai. The speakers of Aslian languages exhibit some of the highest degree of phylogenetic and societal diversity present in Mainland Southeast Asia today, among them a foraging tradition particularly associated with locally ancient, Pleistocene genetic lineages. Little advance has been made in our understanding of the linguistic prehistory of this region or how such complexity arose. In this article we present a Bayesian phylogeographic analysis of a large sample of Aslian languages. An explicit geographic model of diffusion is combined with a cognate birth-word death model of lexical evolution to infer the location of the major events of Aslian cladogenesis. The resultant phylogenetic trees are calibrated against dates in the historical and archaeological record to infer a detailed picture of Aslian language history, addressing a number of outstanding questions, including (1) whether the root ancestor of Aslian was spoken in the Malay Peninsula, or whether the family had already divided before entry, and (2) the dynamics of the movement of Aslian languages across the peninsula, with a particular focus on its spread to the indigenous foragers.

Concluding remarks: what's in a name? "Negritos" in the context of the human prehistory of Southeast Asia

The "negrito" hypothesis posits that various indigenous groups throughout Island and Mainland Southeast Asia have a shared phenotype due to common descent from a putative ancestral population, representing a pre-agricultural substrate of humanity in the region. This has been examined and tested many times in the past, with no clear resolution. With many new resources to hand, the articles in this volume reexamine this hypothesis in a range of different ways. The evidence presented in this double issue of Human Biology speaks more against the category of "negrito" than for it. While populations with the negrito phenotype form a small proportion of all contemporary populations in this region, they have remained a persistent presence. And without a fascination about their origins, there would not be such a depth of knowledge about the human biology of this region more broadly as there is now.

Introduction: revisiting the "negrito" hypothesis: a transdisciplinary approach to human prehistory in southeast Asia

The "negrito" hypothesis predicts that a shared phenotype among various contemporary groups of hunter-gatherers in Southeast Asia--dark skin, short stature, tight curly hair--is due to common descent from a region-wide, pre-Neolithic substrate of humanity. The alternative is that their distinctive phenotype results from convergent evolution. The core issues of the negrito hypothesis are today more relevant than ever to studies of human evolution, including the out-of-Africa migration, admixture with Denisovans, and the effects of environment and ecology on life-history traits. Understanding the current distribution of the negrito phenotype dictates a wide-ranging remit for study, including the articulation of the relationship between foragers and farmers in the present, the development of settled agriculture in the mid-Holocene, and terminal Pleistocene population expansions. The consensus reached by the contributors to this special double issue of Human Biology is that there is not yet conclusive evidence either for or against the negrito hypothesis. Nevertheless, the process of revisiting the problem will benefit the knowledge of the human prehistory of Southeast Asia. Whether the term negrito accurately reflects the all-encompassing nature of the resulting inquiry is in itself questionable, but the publication of this double issue is testament to the enduring ability of this hypothesis to unite disparate academic disciplines in a common purpose.

Making friends in the rainforest: "negrito" adaptation to risk and uncertainty

The so-called negritos adapt not just to a tropical forest environment but also to an environment characterized by perturbations and fluctuations. As with other hunter-gatherers in the region and, indeed, throughout the world, they use both social and ecological methods to enhance their chances of survival in this changing environment: socially, they have developed networks of trading and marriage partners; ecologically, they maintain patches of key resources that are available for future harvesting. As evidenced in the case of the Batek (Orang Asli), patterns of forest structure and composition are sometimes direct outcomes of intentional resource concentration and enrichment strategies. While little of the above is controversial anthropologically, what has drawn some debate is the nature of the relationship with partner societies. Conventional wisdom posits relations of inequality between foragers and "others": foragers and farmers are often construed as hierarchical dyads where foragers supply products or labor to farmers in exchange for agricultural harvests and other trade goods. This kind of adaptation appears to be one of divergent specialization. However, there are cases, such as in the relationship between Batek and Semaq Beri, where both societies follow a roughly similar mode of adaptation, and specialization has not materialized. In sum, while not denying that hierarchy and inequality exist, I suggest that they have to be contextualized within a larger strand of relationships that includes both hierarchy and egality. Further, such relationships are part of the general portfolio of risk reduction strategies, following which access to widely scattered environmental resources, and passage from one location to another, is enhanced not by competing with and displacing neighbors but by maintaining a flexible regime of friendly exchange partners.

Kinship matters: structures of alliance, indigenous foragers, and the Austronesian diaspora

The study of kinship systems has direct relevance for the field of human genetics and the study of microevolution in human populations. Some types of postmarital residence rules--rules requiring a married couple to live with or near relatives of the husband or wife--will have consequences for the distribution of mitochondrial DNA and Y chromosome lineages. Rules that proscribe or encourage marriage with close kin will also have consequences for allele frequency. A preference for marrying at a distance, both socially and geographically, creates alliances that can have survival value for individuals and groups in an environment of periodic or unpredictable scarcity. This article considers the nature of early contact between the indigenous foraging populations of the Philippines and Austronesian speaking settlers who began arriving ~4,500-4,000 BP. It argues that when the first Austronesians arrived they brought with them a kinship system based on symmetrical exchange between descent-based groups. It considers why such a system was gradually changed into the bilateral kinship systems that characterize the various peoples of the Philippines today, "negrito" and non-negrito alike.