Did Humans Colonize the World by Boat?

Research suggests our ancestors traveled the oceans 70,000 years ago.

By Heather Pringle|Tuesday, May 20, 2008

Jon Erlandson shakes out what appears to be a miniature evergreen from a clear ziplock bag and holds it out for me to examine. As one of the world’s leading authorities on ancient seafaring, he has devoted much of his career to hunting down hard evidence of ancient human migrations, searching for something most archaeologists long thought a figment: Ice Age mariners. On this drizzly late-fall afternoon in a lab at the University of Oregon in Eugene, the 53-year-old Erlandson looks as pleased as the father of a newborn—and perhaps just as anxious —as he shows me one of his latest prize finds.

The little “tree” in my hand is a dart head fashioned from creamy-brown chert and bristling with tiny barbs designed to lodge in the flesh of marine prey. Erlandson recently collected dozens of these little stemmed points from San Miguel Island, a scrap of land 27 miles off the coast of California. Radiocarbon dating of marine shells and burned twigs at the site shows that humans first landed on San Miguel at least 12,000 years ago, and the dart head in my hand holds clues to the ancestry of those seafarers. Archaeologists have recovered similar items scattered along the rim of the North Pacific, and some have even been found in coastal Peru and Chile. The oldest appeared 15,600 years ago in coastal Japan. To Erlandson, these miniature trees look like a trail left by mariners who voyaged along the stormy northern coasts of the Pacific Ocean from Japan to the Americas during the last Ice Age. “We haven’t published the evidence for this hypothesis yet, and I’m kind of nervous about it,” he says. “But we are getting very close.”

Until recently most researchers would have dismissed such talk of Ice Age mariners and coastal migrations. Nobody, after all, has ever unearthed an Ice Age boat or happened upon a single clear depiction of an Ice Age dugout or canoe. Nor have archaeologists found many coastal campsites dating back more than 15,000 years. So most scientists believed that Homo sapiens evolved as terrestrial hunters and gatherers and stubbornly remained so, trekking out of their African homeland by foot and spreading around the world by now-vanished land bridges. Only when the Ice Age ended 12,000 to 13,000 years ago and mammoths and other large prey vanished, archaeologists theorized, did humans systematically take up seashore living—eating shellfish, devising fishing gear, and venturing offshore in small boats.

But that picture, Erlandson and others say, is badly flawed, due to something researchers once rarely considered: the changes in sea level over time. Some 20,000 years ago, for example, ice sheets locked up much of the world’s water, lowering the oceans and laying bare vast coastal plains—attractive hunting grounds and harbors for maritime people. Today these plains lie beneath almost 400 feet of water, out of reach of all but a handful of underwater archaeologists. “So this shines a spotlight on a huge area of ignorance: what people were doing when sea level was lower than at present,” says Geoff Bailey, a coastal archaeologist at the University of York in England. “And that is especially problematic, given that sea level was low for most of prehistory.”

Concerned that evidence of human settlement and migration may be lost under the sea, researchers are finding new ways of tracking ancient mariners. By combining archaeological studies on remote islands with computer simulations of founding populations and detailed examinations of seafloor topography and ancient sea level, they are amassing crucial new data on voyages from northeast Asia to the Americas 15,000 years ago, from Japan to the remote island of Okinawa 30,000 years ago, and from Southeast Asia to Australia 50,000 years ago. New evidence even raises the possibility that our modern human ancestors may have journeyed by raft or simple boat out of Africa 60,000 to 70,000 years ago, crossing the mouth of the Red Sea. “If they could travel from Southeast Asia to Australia 50,000 years ago, the question now is, how much farther back in time could they have been doing it?” Bailey asks. “Why not the Red Sea?”

Our new understanding of climate and sea-level change sheds light on something that has long puzzled archaeologists: How did modern humans colonize the far reaches of the globe so quickly after their exodus from Africa? If Erlandson and his colleagues are right, it was a series of sea voyages and river crossings that brought our ancestors to alien lands, launching the greatest biological invasion of all time.

Ancient island-hoppers
Erlandson never bought the long-held assumption among archaeologists that our distant ancestors were the ultimate land lovers. He grew up near the ocean, surfing and snorkeling as a boy in Southern California and Hawaii and earning the nickname Shredded Coconut for his sun-bleached hair. He could not fathom anyone’s resisting the call of the sea.

Erlandson began actively questioning the received wisdom while still an undergraduate. After reading about simple reed boats that the Chumash people once paddled along the California coast, he and a few friends decided to make a replica. They dried tule reeds, lashed them together in bundles, and coated them with tar to make a 17-foot-long vessel capable of carrying three people plus cargo. Then they launched it off the Santa Barbara coast. Paddling effortlessly from kelp forest to kelp forest, Erlandson once voyaged 14 miles in an afternoon. “The boat soaked up a lot of water, but it was unsinkable,” he recalls. “So it doesn’t take that much ingenuity and complex technology to make a pretty sound boat that can get you across a fairly substantial strait.”

By the 1980s, coastal archaeologists were beginning to mull over some remarkably early finds in Australia. A series of excavations by Jim Bowler, Alan Thorne, and others in the continental interior revealed that ancient humans had fished and collected freshwater mussels along the shores of the Willandra Lakes 50,000 years ago, possibly earlier. How on earth had humans managed to arrive down under so early? Even then Australia was an island continent, and some researchers reported that its indigenous inhabitants, the Aborigines, historically lacked oceangoing boats. It did not seem possible that their ancestors had arrived by watercraft.

Points found on the Channel Islands in California
Image courtesy of Jon Erlandson

What’s more, detailed studies of the Southeast Asian coastline of 50,000 years ago showed that an 800-mile-long stretch of islands and at least eight ocean straits separated the island continent from the Asian mainland. “By any route, you have to island-hop to Australia, with one water crossing greater than 44 miles,” Erlandson says. “So it is a real exercise to get across, and the magnitude of that is illustrated by the fact that, before anatomically modern humans made the leap, no large-bodied animal ever got all the way across.”

But modern humans possessed the wherewithal to paddle to Australia. With stone knives they could have felled Asia’s giant bamboo and then tied the canes together to make a raft large enough to carry several passengers. Moreover, they could have navigated by sight for most of the journey. As they set out from one island to the next, they could generally have spied at least a smudge of land on the far horizon.

Even where land lay beyond view, ancient mariners could have deduced its presence from natural indicators such as cloud formations that tend to gather over islands, mats of drifting land vegetation, and the flight paths of land-roosting seabirds. Traditional navigators in the Caroline Islands, northeast of New Guinea, make use of such signs today, and many researchers believe that our modern human ancestors possessed the cognitive skills both to perceive the significance of these indicators and to communicate them to potentially fearful passengers.

“It looks like seafaring capabilities and seafaring technology have a much greater antiquity than conventional wisdom among archaeologists would lead one to expect,” says James O’Connell, an archae­ologist at the University of Utah.

“I think water crossing goes with modern language and with modern art,” says Geoff Irwin, an expert on ancient seafaring at the University of Auckland in New Zealand. “I think they are a package.”

Genes and tools around the Pacific rim
In the wake of the Australian finds, archaeologists are looking long and hard at other major migrations of ancient humans. For decades researchers have promoted the idea that the first Americans were clans of Siberian big-game hunters who trekked hundreds of miles on foot over a vast land bridge (where the Bering Strait is now) and came south from Alaska some 13,000 years ago. But were these Siberian hunters the first to explore the Americas? Or could they have been beaten there by skilled mariners exploring ice-choked northern coasts?

Erlandson has been examining this possibility since the late 1990s, when he read of a dig on the island of Okinawa, some 1,000 miles southwest of Tokyo. Poring over archaeological reports from the region, he learned that Japanese researchers had unearthed the 32,000-year-old bones of a child on Okinawa in the 1950s. He also examined studies of ancient sea levels and a detailed bathymetric map showing the depth of the seafloor between the islands of Okinawa and Japan. Some 32,000 years ago, a coastal plain joined Japan to the Asian mainland, allowing travelers to tramp back and forth by foot. But they could not have trekked to Okinawa, a distant island even then. “Several sea voyages would have been required to reach it from Japan,” explains Erlandson, “including one crossing roughly 46 miles long.” Intrigued, he delved further into Japanese archaeological reports. Other ancient mariners, he discovered, had ventured into stormier waters to the north: Some 21,000 years ago, people had paddled boats across 30 miles of choppy water from Honshu to Kozushima Island to fetch shiny black obsidian, a type of volcanic glass, for stone tools.

Almost certainly these voyagers traveled in small, sturdy boats—perhaps a type of kayak—and possessed sufficient seafaring skill to avoid spills that would lead to hypothermia and death. With such experience, the mariners and their children could well have headed northward at least 16,000 years ago. Crossing the straits by boat and walking the beaches, they could have gradually explored the coasts of the Kuril Islands, the Kamchatka Peninsula, and the Bering Land Bridge until finally reaching the west coast of the Americas, a journey of several thousand miles. A trail of distinctively shaped points and a telltale pattern of genes support this hypothesis.

Last November an international team of geneticists out of University College London and the University of Michigan at Ann Arbor published a key new study of genetic diversity among Native Americans. The researchers examined repetitive stretches of short DNA sequences known as micro­satellites in DNA samples taken from 422 individuals, ranging geographically from Chipewyan and Cree individuals in northern Canada to Guarani and Huilliche people in South America. What they discovered was that genetic diversity decreased from north to south and was higher among tribal groups living along the Pacific coast than among those residing in the continent’s interior. This suggested to the team that the first Americans migrated down the west coast of the Americas; only later did smaller bands—with less genetic diversity—move inland. Moreover, another new genetic study by Brazilian researchers pegs the date for that coastal migration somewhere between 18,000 and 15,000 years ago.

Taken together, the genetic and archaeological evidence now strongly suggests that ancient mariners from northeast Asia could well have explored the coast of the Americas at least 12,000 or 13,000 years ago, and conceivably earlier. Erlandson has found two stone tools and a bone bead on San Miguel Island that may be 18,000 years old, but he has yet to confirm the date via further excavation. “We need to know more,” he says.

Just what drew ancient seafarers from northeast Asia to California remains a puzzle. As they ventured along the southern coast of the Bering Land Bridge, which was an arid grassland at that time, they could have pursued both terrestrial and marine prey. Then, as they moved into coastal North America after ice sheets there began retreating around 16,000 years ago, they could have continued to dine on a wealth of coastal foods.

Erlandson believes that kelp forests—rich oases of seaweed—were key to their success all along the route. Giant kelp grows nearly two feet a day, reaching lengths of 150 feet in the water. Kelp forests teem with abalone, rockfish, and other seafood delicacies. Furthermore, the fronds of kelp are edible, and its stemlike stipe can be cut to create fishing lines, making it possible to catch fish that live outside the kelp beds, such as halibut and cod.

Ice Age migrants journeying from kelp forest to kelp forest, Erlandson says, would have had no need to adjust to strange new ecosystems or devise brand-new hunting technologies as they pushed along the rim of the North Pacific. “I think they were just moving along and exploring,” he muses. “It was like a kelp highway.”

Out of Africa—By boat
As the evidence for Ice Age mariners mounts in Australia, Asia, and the Americas, researchers are now peering further and further back in time for traces of seafarers. When and where, they ask, did humans first journey over the water? One highly controversial piece of evidence surfaced a decade ago during an excavation at Mata Menge on the island of Flores in Indonesia. There Michael Morwood, an archaeologist at the University of New England in Australia, recovered several stone tools as well as the bones of crocodiles and stegodonts—extinct elephantlike animals—beneath a layer of volcanic ash. Geologists dated the finds to some 800,000 to 880,000 years ago—a time when early humans known as Homo erectus wandered parts of Southeast Asia. To Morwood, the remains at Mata Menge pointed to a remarkable human journey. More than 800,000 years ago, he theorized, H. erectus crossed 12 miles of ocean to reach Flores.

Although the Mata Menge discoveries attracted much media attention, there is no conclusive evidence that Flores was even an island at the time. Moreover, archaeologists have yet to find any other strong evidence of island-hopping by H. erectus. Instead, Erlandson and others believe that coastal voyaging began with our modern human ancestors, Homo sapiens. Current research shows that H. sapiens evolved in Africa some 200,000 years ago and soon took an intense interest in the sea. At Pinnacle Point, a coastal site in South Africa that borders the Indian Ocean, Arizona State University archaeologist Curtis Marean and his colleagues found table scraps from humans’ feasting 164,000 years ago. The favorite item was the brown mussel, which is exposed in large numbers during low spring tides. “People think that shell­fish are easy to capture, that it’s a no-brainer,” Marean says. “It’s not that way at all. There are optimal times to get shellfish, and going into the water when it’s roaring in the intertidal zone can easily be fatal.”

Along the Semliki River in Congo, wandering bands began fishing in earnest 80,000 years ago. To catch catfish lurking at the bottom of the river, they devised a lethal new weapon—a composite harpoon tipped with a beautifully manufactured, symmetrical barbed point carved from bone. No earlier hominin had ever created such a specialized technology for systematic fishing. “Those harpoons,” Erlandson says, “are not like anything the Neanderthals or archaic humans ever produced. They are extraordinary.” With such creative abilities, ancient water-loving Africans could well have devised a new technology for fishing deep waters: the raft.

It is even possible, say some seafaring experts, that H. sapiens spread out of Africa by watercraft 60,000 to 70,000 years ago. Until recently, most scientists assumed that our modern human ancestors migrated to Asia on foot via the Sinai Peninsula and the eastern shore of the Mediterranean. But current genetic research suggests that they took a more southerly route, crossing from the African coast of the Red Sea to the Arabian Peninsula and then following the coast to India. Mitochondrial DNA studies conducted by Lluís Quintana-Murci of the Pasteur Institute in Paris and a team of international researchers reveal, for example, that humans migrated from East Africa to western India more than 50,000 years ago.

Today a 20-mile stretch of choppy water separates Africa from the Arabian Peninsula. Locals call this strait Bab el Mandeb, or “Gate of Tears,” but it was not always so formidable. University of York archaeologist Geoff Bailey recently led a major study of the ancient Red Sea coastline. Between 90,000 and 10,000 years ago, the strait got as narrow as 2.5 miles across. For Bailey and other coastal archaeologists, this raises a fascinating question. Could our modern human ancestors have rafted out of Africa, crossing the mouth of the Red Sea 60,000 years ago to reach Saudi Arabia? Bailey reflects on this question a moment. “I think it’s entirely possible,” he says.

Still, many researchers want more evidence of seafaring. At the Natural History Museum in London, for example, Chris Stringer, an expert on modern human origins, continues to lean toward a terrestrial migration route out of Africa. He believes that boats did not become necessary until modern humans had already left Africa on foot and confronted coastal mangrove swamps and great river mouths in southern Asia. Even so, Stringer is looking at the new evidence carefully, noting that he is keeping an open mind on the subject.

Twenty years ago, most archaeologists would simply have laughed at the idea of Ice Age mariners colonizing the globe. These days, as minds are opening to the possibility, Erlandson and others are beginning to receive major grants that will speed up the pace of research. “Now that people are thinking about coastal migration,” Erlandson says, “we have a truly golden opportunity.”

Right, from top: An Aleutian man fishes for cod in an 1872 drawing by Henry Wood Elliott; a replica of a 9,000-year-old dugout, the world’s oldest known boat (the original is now on view at the Drents Museum in the Netherlands); islanders in the Torres Strait (between Australia and New Guinea) pose aboard a bamboo raft in a 1906 photo. Below: Points? found on the Channel Islands in California.

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