Scientists were surprised to find fragments of DNA of extinct human species in 35 people living in islands off New Guinea in Melanesian tribes.
The DNA was traceable to two early human species: Denisovans, whose remains were found in Siberia, and Neandertals, first discovered in Germany.
D. Andrew Merriwether, a molecular anthropologist at Binghamton University, collected the modern-day blood samples used in the study about 15 years ago in Melanesia. This is the first time full genomes from those samples have been sequenced.
"Substantial amounts of Neandertal and Denisovan DNA can now be robustly identified in the genomes of present-day Melanesians, allowing new insights into human evolutionary history," said a team of international anthropologists who studied the DNA and compared it with ancient DNA samples. "As genome-scale data from worldwide populations continues to accumulate, a nearly complete catalog of surviving archaic lineages may soon be within reach."
These tribes have been there for at least 48,000 years but remained aloof and in isolation from the rest of the human race.
Earlier studies have revealed some genetic overlap of about 2 percent between Neandertals and non-African populations, and little or no Neandertal and Denisovan ancestry among Africans.
This new research suggests Neandertals and modern human ancestors intersected at least three times. It also found an overlap of between 1.9 and 3.4 percent in the genetic codes of Denisovans and modern-day Melanesians.
Skepticism about the new findings is entirely appropriate, said Merriwether, who specializes in reconstructing the past using samples from contemporary populations and ancient DNA from the archaeological record.
"Ancient DNA is always damaged and broken into small pieces," he explained. "You only need one molecule of modern DNA to outperform all the ancient DNA."
The human genome contains about 3 billion "letters".
Studies like this one may enable scientists to answer big questions about human migrations and evolution thousands of years ago.
The finding of the study were published in the journal Science.[tags, ancient dna, melanesian tribes, denisovans, neandertal dna sample, living neandertal dna, mutant dna]
D. Andrew Merriwether, Binghamton University.