Wednesday, April 6, 2011

Human migration: Early humans did not settle down in India immediately after out of Africa migration

Syed Akbar
Hyderabad: Early human beings did not settle down in India immediately after their famous migration out of Africa. They took nearly 40,000 years before they settled down in India.

According to a new hypothesis on the migration of human beings from Africa and their settling down in Europe and Asia, the divergence among different Eurasian populations occurred more than 40,000 years after their divergence with Africans. Scientists from the University of Utah and the Human Genome Sequencing Centre, Houston, based their observations after re-analysing the genetic material obtained from three castes (Brahmin, Yadava and Mala/Madiga) and one tribe (Irula) from Andhra Pradesh.

The divergence time estimates among the major population groups suggest that Eurasian populations diverged from Africans during the same time frame, about 90,000 to 1,10,000 years ago. But the divergence among different Eurasian populations occurred more than 40,000 years after their divergence with Africans.

"Genetic studies of populations from the Indian subcontinent are of great interest because of India’s large population size, complex demographic history, and unique social structure. Despite recent large-scale efforts in discovering human genetic variation, India’s vast reservoir of genetic diversity remains largely unexplored," one of the researchers Lynn B Jorde said.

According to the researchers, several Indian populations, such as  Yadava, Mala/Madiga, and Irula, have nucleotide diversity levels as high as those of HapMap African populations. "Our data also support a delayed expansion hypothesis in which an ancestral Eurasian founding population remained isolated long after the out-of-Africa diaspora, before expanding throughout Eurasia," he pointed out.

The high diversity and the deep mitochondrial lineage in India support the hypothesis that Eurasia was initially populated by two major out-of-Africa migration routes. Populations migrating along an early “southern-route” originated from the Horn of Africa,
crossed the mouth of the Red Sea into Arabian Peninsula, and subsequently migrated into India, Southeast Asia, and Australia. Later, populations migrated out of Africa along a “northern route”
from northern Africa into the Middle East and subsequently populated Eurasia.

"Overall, these results support a scenario in which the ancestors of the Indian, European, and East Asian individuals left Africa in one major migration event, and then diverged from one another more than 40,000 years later," the research report said.

Regardless of caste affiliation, genetic distance estimates with mitochondrial markers showed a greater affinity of south Indian castes to East Asians, while distance estimates with Y-chromosome markers showed greater affinity of Indian castes to Europeans.

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