The discovery promises to shed light on one of the most enigmatic periods in early human history, when the first people colonised the world, eventually leading to Homo sapiens becoming the only species to dominate every corner of the globe.
Locks of hair stored at Cambridge University for the past 90 years have revealed DNA evidence to link the inhabitants of the remote Andaman Islands with the first anatomically modern humans to migrate across Asia.
The Andamanese were living a stone-age existence whenWestern explorers in the 19th century made contact. An analysis of their genetic makeup indicates they could be a lost tribe that has remained isolated from other humans for many thousands of years.
DNA analysis has shown that in spite of the wide variation in the physical features of ethnic groups today, we are more closely related to each other than most other species of mammals.
Scientists believe only a small number of our ancestors - perhaps no more than a few thousand - crossed the Sinai peninsula to populate Asia, Europe, Oceania and the Americas.
The genetic "bottleneck" caused by having so few ancestors resulted in humans today being relatively inbred. Studies into the sequence of "letters" in the genetic code of different ethnic groups - analysed from blood samples - have nevertheless been able to guide scientists to the most ancient lineages of DNA that date back to this early period of human history.
Dr Erika Hagelberg, a geneticist at Cambridge University, and Dr Carlos Lalueza Fox, from the University of Barcelona, have extracted enough DNA from the hair of 42 people to compare the genetic relationship of the Andamanese with other ethnic groups around the world.
One particular mutation, where a tiny stretch of DNA is deleted, shows that the Andamanese, who live in the Bay of Bengal south of Burma, do not share their pattern of inheritance with other Asians.
"The significance of this mutation is that it seems to be associated with the more recent population explosions linked with the development and spread of agriculture about 6,000 to 8,000 years ago," said Dr Hagelberg.
"It looks like the Andamanese are the descendants of a much earlier hunter-gathering group of humans who did not have any later contact with the agricultural people and who were therefore not part of the subsequent population explosion out of Africa and across the Asian continent."
Agriculture is a recent innovation in human history, with the earliest indications of it appearing in the fertile crescent of the Middle East about 10,000 years ago. It is widely assumed that the agricultural revolution spread across the rest of Europe and Asia either by hunter-gathering communities dying out, or by their conversion to farming.
The Andamanese may prove to be one of the few people alive today with a truly ancient genetic lineage dating directly to the earliest human migrations across Asia.
The Andaman islanders may owe their unique genetic makeup to their fierce reputation and to geographical isolation. They live in densely forested mountains and have a history of killing any foreigners who stray into their territory.
The Andamanese traditionally live by hunting wild pigs, fishing and collecting fruit, berries and nuts. One of their most unique cultural features is that they had no method of making fire. Their language is also unique, having no relationship with the tongues of neighbouring populations.
Their only indigenous weapon is the bow, which the Andamanese use for both hunting and fishing from dug-out canoes. They have no traps and have never discovered how to make fishhooks.
Anthropologists have long been unable to classify the Andamanese - their physical appearance is neither caucasian nor mongoloid - and gave them the name "negrito" because of their dark skin and pygmy stature.
The Andamanese hair samples at Cambridge are part of the Duckworth collection made by the great explorer and early anthropologist, AR Radcliffe-Brown, one of the first Western scholars to study the islanders.
Dr Hagelberg said the hair samples represented a unique genetic resource because they date to a period just after the islanders were contacted and therefore had not suffered any "genetic dilution" resulting from intermarriage with outsiders.
"Our results indicate that the Andamanese are the descendants of one of the earliest expansions of anatomically modern humans. They appear more closely related to southern African pygmies than to other Asian groups. They are, in effect, the descendants of the earliest migrations of Homo sapiens out of Africa," she said.
The present-day Andamanese are in decline, being highly susceptible to illnesses to which they have no immunity, and from pressure on their native forests from logging companies.