One Migration from Siberia Peopled the Americas: Study
A single Siberian migration about 23,000 years ago later branched into today's distinct native American groups.
Native American ancestors reached the New World in a single, initial migration from Siberia at most 23,000 years ago, only later differentiating into today's distinct groups, DNA research revealed Tuesday.
Most scientists agree the Americas were peopled by forefathers who crossed the Bering land and ice bridge which connected modern-day Russia and Alaska in Earth's last glacial period.
And it is known through archaeological finds that humans were already present in the Americas 15,000 years ago.
But there was a long list of outstanding questions.
When did the migration take place? In one or several waves? And how long did these early pioneers spend in Beringia - the then-raised land area between Asia and America?
On Tuesday, analysis of Native American and Siberian DNA, present-day and ancient, sought to fill in some of the blanks with two studies carried simultaneously in the journals Science and Nature.
The first, led by the Center for GeoGenetics at the University of Copenhagen and published in Science, found there was only one initial migration, no more than 23,000 years ago.
This ancestral pool split into two main branches about 13,000 years ago, coinciding with glacier melt and the opening of routes into the North American interior, researchers found.
These became the groups which anthropologists refer to as Amerindians (American Indians) and Athabascans (a native Alaskan people).
Previous research had suggested that Amerindian and Athabascan ancestors had crossed the strait independently.
"Our study presents the most comprehensive picture of the genetic prehistory of the Americas to date," said Maanasa Raghavan, one of the study's lead authors.
"We show that all Native Americans, including the major sub-groups of Amerindians and Athabascans, descend from the same migration wave into the Americas."
This was distinct from later waves which gave rise to the Paleo-Eskimo and Inuit populations, she added.
Given that the earliest evidence for the presence of humans in the Americas dates to 15,000 years ago, the first ancestors may have remained in Beringia for about 8,000 years before their final push into the New World, the team said.
This is much shorter than the tens of thousands of years of isolation theorized by some earlier research.
But diversification into the distinct tribes we know today, happened only after arrival in the Americas, not before.
The second study showed that, surprisingly, some Amazonians descend from forefathers more closely related to the indigenous peoples of Australia, New Guinea and the Andaman Islands than present-day fellow Native Americans.
"Present-day groups in South America have a small but distinct genetic link to Australasians," co-author Pontus Skoglund of the Harvard Medical School told AFP of the research published in Nature.
This may explain a long-standing riddle: why, if Native Americans came from Eurasia, do some early American skeletons share traits with present-day Australasians?
But how and when this forefather came to the Americas remains "an open question," said the study.
These are rock drawings made by early Native Americans.
Back in the Beginning
To put a human face on our ancestors, scientists from the Senckenberg Research Institute used sophisticated methods to form 27 model heads based on tiny bone fragments, teeth and skulls collected from across the globe. The heads are on display for the first time together at the Senckenberg Natural History Museum in Frankfurt, Germany. This model is Sahelanthropus tchadensis, also nicknamed "Toumai," who lived 6.8 million years ago. Parts of its jaw bone and teeth were found nine years ago in the Djurab desert in Chad. It's one of the oldest hominid specimens ever found.
With each new discovery, paleoanthropologists have to rewrite the origins of man's ancestors, adding on new branches and tracking when species split. This model was fashioned from pieces of a skull and jaw found among the remains of 17 pre-humans (nine adults, three adolescents and five children) which were discovered in the Afar Region of Ethiopia in 1975. The ape-man species, Australopithecus afarensis, is believed to have lived 3.2 million years ago. Several more bones from this species have been found in Ethiopia, including the famed "Lucy," a nearly complete A. afarensis skeleton found in Hadar.
Meet "Mrs. Ples," the popular nickname for the most complete skull of an Australopithecus africanus, unearthed in Sterkfontein, South Africa in 1947. It is believed she lived 2.5 million years ago (although the sex of the fossil is not entirely certain). Crystals found on her skull suggest that she died after falling into a chalk pit, which was later filled with sediment. A. africanus has long puzzled scientists because of its massive jaws and teeth, but they now believe the species' skull design was optimal for cracking nuts and seeds.
The skull of this male adult was found on the western shore of Lake Turkana in Kenya in 1985. The shape of the mouth indicates that he had a strong bite and could chew plants. He is believed to have lived in 2.5 million years ago and is classified as Paranthropus aethiopicus. Much is still unknown about this species because so few reamins of P. aethiopicus have been found.
Researchers shaped this skull of "Zinj," found in 1959. The adult male lived 1.8 million years ago in the Olduvai Gorge of Tanzania. His scientific name is Paranthropus boisei, though he was originally called Zinjanthropus boisei -- hence the nickname. First discovered by anthropologist Mary Leakey, the well-preserved cranium has a small brain cavity. He would have eaten seeds, plants and roots which he probably dug with sticks or bones.
This model of a sub-human species -- Homo rudolfensis -- was made from bone fragments found in Koobi Fora, Kenya, in 1972. The adult male is believed to have lived about 1.8 million years ago. He used stone tools and ate meat and plants. H. Rudolfensis' distinctive features include a flatter, broader face and broader postcanine teeth, with more complex crowns and roots. He is also recognized as having a larger cranium than his contemporaries.
The almost perfectly preserved skeleton of the "Turkana Boy" is one of the most spectacular discoveries in paleoanthropology. Judging from his anatomy, scientists believe this Homo ergaster was a tall youth about 13 to 15 years old. According to research, the boy died beside a shallow river delta, where he was covered by alluvial sediments. Comparing the shape of the skull and teeth, H. ergaster had a similiar head structure to the Asian Homo erectus.
This adult male, Homo heidelbergensis, was discovered in in Sima de los Huesos, Spain in 1993. Judging by the skull and cranium, scientists believe he probably died from a massive infection that caused a facial deformation. The model, shown here, does not include the deformity. This species is believed to be an ancestor of Neanderthals, as seen in the shape of his face. "Miquelon," the nickname of "Atapuerca 5", lived about 500,000 to 350,000 years ago and fossils of this species have been found in Italy, France and Greece.
The "Old Man of La Chapelle" was recreated from the skull and jaw of a Homo neanderthalensis male found near La Chapelle-aux-Saints, in France in 1908. He lived 56,000 years ago. His relatively old age, thought to be between 40 to 50 years old, indicates he was well looked after by a clan. The old man's skeleton indicates he suffered from a number of afflictions, including arthritis, and had numerous broken bones. Scientists at first did not realize the age and afflicted state of this specimen when he was first discovered. This led them to incorrectly theorize that male Neanderthals were hunched over when they walked.
The skull and jaw of this female "hobbit" was found in Liang Bua, Flores, Indonesia, in 2003. She was about 1 meter tall (about 3'3") and lived about 18,000 years ago. The discovery of her species, Homo floresiensis, brought into question the belief that Homo sapiens was the only form of mankind for the past 30,000 years. Scientists are still debating whether Homo floresiensis was its own species, or merely a group of diseased modern humans. Evidence is mounting that these small beings were, in fact, a distinct human species.
Bones can only tell us so much. Experts often assume or make educated guesses to fill in the gaps in mankind's family tree, and to develop a sense what our ancestors may have looked like. Judging from skull and mandible fragments found in a cave in Israel in 1969, this young female Homo sapien lived between 100,000 and 90,000 years ago. Her bones indicate she was about 20 years old. Her shattered skull was found among the remains of 20 others in a shallow grave.