Kolkata, July 25 (IANS) Genomic analysis of the Jarawas and Onge tribes of the Andaman and Nicobar islands has yielded "strong" evidence of existence of a new ancestor of humans, according to an international team of researchers.
In addition, the scientists have also shed light on the mystery of the short height of the Andamanese ethnic tribes.
"People have speculated that there could be more ancestors to the human and these ancestors are offshoots of the Heidelberg man," Partha Majumder, director National Institute of Biomedical Genomics (NIBMG), told IANS.
Neanderthals, Denisovans, and modern humans are all considered to have descended from Homo heidelbergensis (the Heidelberg man) that appeared around 600,000 years ago in Ethiopia.
"What we have been able to show is that there is strong possibility that there is at least one more ancestor and we have found the segments of this new ancestor, not found in either the Neanderthal or the Denisovan," Majumder said.
Published in the Nature Genetics journal on July 25, the work is a collaborative effort between the NIBMG Kalyani, an autonomous institution of India's Department of Biotechnology, and Institute of Evolutionary Biology (IBE), a joint centre of Pompeu Fabra University (UPF) and the Spanish National Research Council (CSIC).
Majumder stressed: "Remains of this extinct hominid have not yet been recovered, but our results provide definitive evidence that Homo heidelbergensis had given rise to multiple lineages, not just the Neanderthal and the Denisovan."
"And we have dated the segments of the genome and it goes back to about 40,000 years ago. That's the third group of ancestors from whom we have descended."
The current view of human evolution is that about 2 million years ago Homo erectus evolved in Africa. This species gave rise to a new species - Homo heidelbergensis. About 400,000 years ago, Homo heidelbergensis came out of Africa, and split into two lineages.
One of these lineages gave rise to Neanderthals after moving to Europe from Africa, through the Middle East. The other lineage gave rise to the Denisovans (a finger bone of this species was recovered from the Denisova cave in Russia).
Homo heidelbergensis also evolved into Homo sapiens in Africa about 200,000 years ago. Modern humans, Homo sapiens sapiens, evolved in Africa about 80,000 years ago.
"When comparing the DNA sequences of the Jarawas and the Onges with those of Neanderthals and Denisovans, we have found some notable differences. By exploring various possibilities that could have given rise to these differences, we have concluded that these DNA fragments belong to an extinct hominid that shares a common ancestor with the Neanderthal and the Denisovan but has a different history."
Further, the team sought to understand and identify the ancestral components in the genomes of the Andamanese by sequencing whole genomes of 60 individuals drawn from a carefully sampled set of diverse ethnic groups of mainland India and 10 Jarawas and Onges.
"For comparative purposes and for drawing more robust inferences, we also downloaded data available in the public domain pertaining to diverse human groups as also to primates. We have concluded that natural selection has favoured the retention of short height among the Jarawas and Onges," Majumder said.
The other authors of the paper are Mayukh Mondal (lead author), F. Casals, H. Zheng, GM Dall'Olio, M Pybus, Netea MG, D Comas, H Laayouni, Li Q, and J Bertranpetit.A
