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File: Map of the migration of modern humans out of Africa, based on mitochondrial DNA. Colored rings indicate thousand years before present..jpg (274KB, 889x635px) Image search: [Google]

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Out of Africa
For the human journey to really get into its stride, our species had to leave the warm embrace of mother Africa. Researchers identify the Bab-el-Mandeb Strait on the Red Sea as the most likely departure point. This narrow stretch of water between the Horn of Africa and the Arabian Peninsula offered the shortest route to new continents. The strait would actually have been even less of a stretch than it is today (12 miles), because when Homo sapiens made the crossing some 60,000 to 70,000 years ago, sea levels were 230 feet lower due to the onset of ice age conditions that locked water up in vast polar ice caps. Given some kind of raft, and perhaps a few islands to hop between, such a crossing isn’t difficult to imagine.
There were probably earlier attempts. Modern human remains have been found at sites in the Middle East that are in excess of 100,000 years old. Yet these trailblazers likely left little or no genetic trace on humans living today, suggesting that either climate change forced them to double back or they died out.
Studies mapping human genetic diversity support the theory that modern humans emerged in Africa, and identify the Middle East as their gateway to the wider world. The so-called “multi-regional theory,” which envisions Homo sapiens interbreeding with archaic human species already living outside Africa, is challenged by the finding that genetic variation in today’s populations decreases with increased distance from Africa. The Middle East has a unique mixture of African, Asian, and European DNA markers, which indicates the ancestors of all non-Africans passed that way.

>>69187823
The Horn of Africa also offers clues to how our species might have spread swiftly along the coasts of Arabia, India, Southeast Asia, and all the way to Australia. Sites with garbage dumps filled with clam and oyster shells reveal that local inhabitants were familiar with coastal living and exploiting the sea long before any Red Sea crossings.
Australia
Archaeological evidence for the remarkably quick passage of modern humans to Australia, perhaps just a few millennia after leaving Africa, is backed by genetic analysis which ties Australian Aborigines to that first migration wave.
They must have improved their seafaring skills on the way, because getting from Asia to the continental landmass of which Australia was then a part would have meant navigating across a series of straits. Australia shared its prehistoric continent with present-day New Guinea, explaining why, genetically, at least, the island’s indigenous population shares genetic markers with Australian Aborigines. The two landmasses lost touch due to rising sea levels only about 8,000 years ago.
Europe
That modern humans should reach down under before setting foot in Europe seems remarkable given Europe’s closeness to the cradle of humanity. But whereas this glacial period enabled the first Australians to walk most of the way without getting wet feet, its impact in Europe was much less welcoming. Europe’s earliest occupiers didn’t show up until about 40,000 years ago.
Genetic evidence points to Europeans originating from a second migration wave from Africa that took a circuitous path via the Middle East into the steppes of Central Asia before swinging west. The challenges faced by these frostbitten pioneers are illustrated by the start-stop colonization of Britain. Britain’s first settlers were soon evicted by northern Europe’s fluctuating chills some 25,000 years ago.

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>>69187863
Evidence of more permanent occupancy isn’t found until around 12,000 years ago, when the retreating ice sheet and warmer conditions tempted back tribes from refuges in continental Europe, one in the southwestern and one in the southeastern part of the continent. Sea levels remained low enough for these hunter-gatherers to make the journey by land, lured by herds of reindeer and wild horse that had already made the crossing. Today, genetic patterns in European populations still retain traces of the time their ancestors overwintered the last ice age in the southern refugia.

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Cactus Hill, Virginia
At a site in Virginia called Cactus Hill, archaeologists have found an assemblage of artifacts that challenges scientific ideas about the first Americans. The conventional wisdom was that Native Americans are descended from a small band of people from northeast Asia who crossed over a now-vanished land bridge that extended between Siberia and Alaska between 12,000 and15,000 years ago.
But the artifacts at Cactus Hill dated back to 16,000 B.C. What’s more, stone spear points found at the site are reminiscent of those made by a Stone Age culture in southwest France,called the Solutreans, that ended 18,000 years ago.
Archaeologist Dennis Stanford has suggested that the first Americans were actually the Solutreans, who crossed the Atlantic in boats similar to ones used by Arctic Eskimos. According to this controversial idea, the Solutreans were among the first New World explorers and may have been the ancestors of another ancient American culture, the Clovis people, who lived about 13,000 years ago.
In recent years, the idea that there may have been multiple migrations to the Americas by several groups of people beginning as far back as 16,000 or 18,000 years ago appears to be supported by a growing body of genetic, linguistic, and physical evidence.

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Dhofar, Oman
The recent discovery of over a hundred sites in the Sultanate of Oman, located in the southeastern corner of the Arabian Peninsula, could change how scientists think about the ancient migration of our ancestors out of Africa.
According to one idea, called the coastal expansion hypothesis, early modern humans left Africa about 60,000 years ago and spread throughout Europe and Asia by following the coastline. But stone spear points and other artifacts discovered at Oman that date to about 106,000 years ago suggest that a “Nubian Middle Stone Age” culture once thrived in southern Arabia.
The spear points appear to have been created using a technique similar to one used by a nomadic hunter-gatherer society from Africa’s Nile Valley known as the “Nubian Complex.” According to archaeologist Jeffrey Rose, the evidence from Oman provides a “trail of stone bread crumbs” left by early humans who migrated out of Africa and into Arabia by following a network of rivers inland. The climate in Arabia was tropical during the time the Stone Age humans lived there, scientists say, and would have been home to abundant freshwater and plentiful game such as gazelles and antelopes.

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In 1996, a 9,300-year-old skeleton was accidentally discovered along the Columbia River in Kennewick, Washington, during a hydroplane race. The U.S. Army Corps of Engineers initially turned the skeleton over to a coalition of Native American tribes, who claimed Kennewick Man as their ancestor and who wanted to bury him according to tribal tradition. But scientists filed a federal lawsuit to gain permission to study the skeleton, and in 2004, a federal judge decided to grant the request after determining that the tribes could not prove a direct cultural affiliation with Kennewick.
An analysis of the skeleton in 2005 determined that Kennewick Man was purposefully buried and had suffered various physical traumas before dying in his mid-to-late 30s. He was a well-built individual, and his right arm was larger than his left, which likely resulted from frequent use of an atlatl, or spear thrower, which he and his contemporaries could use to hurl a spear up to the length of a football field to kill prey.
Some of the scientists who studied the Kennewick Man skeleton suggested his facial features were European, while others argue that his skull shape is most similar to a Japanese group called the Ainu. National Geographic Explorer-in-Residence and Genographic Project founder Spencer Wells says Kennewick is typical of other early (pre-8,000 years ago) American skulls in this regard; most of them exhibit features more typical of European populations than later remains.

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Monte Verde, Chile
The Monte Verde archaeological site is located in the low mountains of southern Chile and has been dated to more than 14,000 years old. Artifacts discovered at the site include mastodon bones, charcoal-filled hearths, and wooden posts that once supported huts. Its discovery in the late 1970s suggested humans had not only arrived in the Americas a lot earlier than expected, but that they had also traveled a lot farther than anyone thought.
In 2008, archaeologists discovered bits of chewed up seaweed at the site that may have been used for food and medicine and which corroborate the dating of other artifacts at the site. Several different species of seaweed were discovered, which suggests that early Americans possessed a fairly sophisticated knowledge of coastal ecosystems.
Based on this evidence, some researchers have suggested that ancient humans spread across the Americas through a slow coastal migration down the Pacific Coast, instead of dispersing along strictly inland routes as had been traditionally thought. Archaeologist Tom Dillehay speculates that people could have moved in a “zigzag” pattern—taking inland detours to follow “thousands of temptations” along the way before returning back to the coast to continue their southward migration.

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Meadowcroft Rockshelter, Pennsylvania
Located near Pittsburgh, Pennsylvania, the Meadowcroft Rockshelter site is a rock ledge overhang that was used as a campsite by prehistoric hunters and gatherers some 16,000 years ago. Discovered in 1955, Meadowcroft Rockshelter is the oldest known site of human habitation in North America and its existence lends credence to the idea that humans arrived in the Americas earlier than traditionally thought. The site has yielded nearly two million artifacts, including ancient tools made of stone or bone, pottery fragments, and hundreds of fire pits. Animal and plant remains—including fruits, nuts, and seeds—have also been discovered at the site.

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Stone Age India
After first leaving Africa, modern humans may have veered east to settle India some 76,000 years ago—tens of thousands of years before they are thought to have arrived in Europe. According to paleoanthropologist Michael Petraglia, who is developing the theory, early modern humans may have wiped out another human species,Homo heidelbergensis, which scientists think left Africa about 800,000 years ago and who was already living in India.
The scenario Petraglia envisions is eerily similar to what some scientists think happened in Europe about 30,000 years ago, with modern humans driving their close cousins the Neanderthals to extinction. The modern humans who colonized India may also have been responsible for the disappearance of another species,Homo floresiensis(aka “the hobbits”), whose fossilized bones have been discovered on the Indonesian island of Flores, Petraglia says.

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Peking Man
In 2008, Chinese archaeologists claimed that a newly unearthed skull that dated back 80,000 to 100,000 years belonged to an early modern human. China’s government-run press hailed the discovery as “the greatest discovery in China after Peking Man”—a subspecies of AsianHomo erectusthat was discovered in the 1920s and which for a time caused some anthropologists to suggest that China was the original homeland of humanity. (That idea was later discounted by discoveries in Africa.)
If the new skull did indeed belong to a modern human, it would have forced a radical rethink of theories about when our ancestors first left Africa because it would have indicated a very early dispersal of modern humans eastward from Africa and the Middle East. But other experts have discounted this idea, saying the Chinese skull resembles Peking Man more than it does modern humans.

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>>69189067
How and when humans first came to the Americas has long been a topic of intense debate. Theories to explain the colonization of the New World—the last great habitable landmass to be occupied by humans—focus on the Bering land bridge, or Beringia, which emerged between Siberia and Alaska during the last ice age. Rising from seas drained by the water-locking effect of spreading ice caps, Beringia is said to have given passage to the forebears of Native Americans anywhere between 40,000 and 15,000 years ago.
The earliest date, based on a footprint left in volcanic ash in Mexico, might be wildly off track, according to recent studies that put the migration at the opposite end of the timescale. While older archaeological evidence exists, 13,000 years is the date put on the oldest known human remains. This fits with the findings of DNA studies that indicate that the genetic ancestors of the Native Americans consisted of a few dozen individuals from eastern Siberia who ventured across Beringia less than 20,000 years ago.
The gap between their departure and arrival (the length of this time gap varies depending on the study) is explained by the presence of two massive ice sheets, the Laurentide and Cordilleran, that blocked entry to North America. The hunter-gatherers waited out the ice age in Beringia. (A significant landmass, if a temporary one, Beringia supported large herds of mammoth, reindeer, and other substantial prey.) When conditions eventually warmed, and the glaciers began to melt, the migrants were up and running again.

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>>69190010
Or were they? Another debate centers on the migrants’ mode of transport. Some researchers believe Beringia was flooded by rising sea levels before its inhabitants had the chance to cross into Alaska. Challenging the idea that the land bridge was the only route in, they say groups must have ferried themselves in boats at least part of the way. This seafaring theory is supported by evidence of human occupation in Chile by 14,500 years ago. Such rapid progress from the Arctic, all the way down through South America, is difficult to explain if the colonizers had to wait for corridors to open up in the ice sheets that overlaid the land route through Canada. Southward excursions down the Pacific Coast by boat would have been a much quicker way of covering the distance.

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>>69190050
Or were they? Another debate centers on the migrants’ mode of transport. Some researchers believe Beringia was flooded by rising sea levels before its inhabitants had the chance to cross into Alaska. Challenging the idea that the land bridge was the only route in, they say groups must have ferried themselves in boats at least part of the way. This seafaring theory is supported by evidence of human occupation in Chile by 14,500 years ago. Such rapid progress from the Arctic, all the way down through South America, is difficult to explain if the colonizers had to wait for corridors to open up in the ice sheets that overlaid the land route through Canada. Southward excursions down the Pacific Coast by boat would have been a much quicker way of covering the distance.

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Backing for this argument has been found in the form of ancient DNA extracted from a 10,300-year-old tooth from Alaska’s Prince of Wales Island. Researchers found that only one percent of modern indigenous people they sampled matched the tooth’s genetic markers, but those who did lived primarily along the Pacific Coast, between Chile and California.
Such findings haven’t helped the pioneer reputation of the Clovis people, long feted as the earliest occupiers of America. A culture characterized by fluted stone spear points, often found with the bones of bison and other large animals, the Clovis people are described from sites dating back 13,000 years in New Mexico and Colorado. But that’s too recent, and too far inland to retain their claim as founders of the New World.