The First Odyssey- did humans leave Africa by sea?

Swahili outrigger canoe, Tanzania

Around 100,000 years ago, give or take a few tens of thousands of years, modern humans traveled out of Africa. But how? The answer seems obvious- we walked. Surprisingly, fossils, artifacts and our DNA tell a different story. Instead of traveling by foot, modern humans may have left Africa by sea, on primitive rafts or boats.

        Our species originated in Africa. Human beings’ closest relatives, the chimps and gorillas, live there, and human DNA and languages are most diverse there, suggesting a long period of evolution in Africa, and recent arrival elsewhere. Then there are fossils of early humans, from ape-like Ardipethecus all the way to primitive Homo sapiens, recording our evolution on the African continent.

       We weren’t the first humans to leave Africa. Modern Homo sapiens are one of many waves of migration out of Africa, taking place over millions of years. Those migrants gave rise to multiple species: Homo floresiensis in Indonesia, H. georgicus in the Caucasus, H. erectus in Indonesia again, Homo antecessor in Europe. A later migration produced two species - Neanderthals in Europe and the Middle East, then Denisovans in Asia. Then, primitive Homo sapiens migrated into the Levant and southern Europe. They’re represented by the Skhul and Qazfeh people in the Middle East, and the Apidema skull in Greece. Often called “anatomically modern Homo sapiens” these people might be better described as “nearly modern” H. sapiens. They resembled us in details of their teeth and skulls, but had Neanderthal-like brow ridges and a  primitive brain shape. They were probably a sister lineage that split off a hundred thousand years or more before we evolved.

The human evolutionary tree shows multiple “Out-of-Africa” dispersals (red). Modern H. sapiens (blue) is just the last of these.

        The fossils suggest perhaps seven waves of dispersal. The precise number is unclear, as it depends on how you draw the evolutionary tree- but there were lots of waves of migration, and others probably remain undiscovered. Modern humans were just the last, and most successful- wiping out  all the others.

        The other human species, so far as we know, simply walked out of Africa. But modern Homo sapiens apparently did something very different— we may have traveled by water.

        The ancestors of modern Homo sapiens evolved perhaps 250,000 years ago. That estimate is based on DNA; comparisons of human gene sequences imply hundreds of thousands of years of evolution produced the different gene sequences we see today. Depending on which analysis you look at, modern humans go back anywhere from a recent (in evolutionary terms) 200,000 years ago to perhaps 260,000-350,000 years ago.

        Human diversity is highest in Africa’s south, in terms of genes and language, suggesting we originated there. Specifically, our direct ancestors may have lived in the  Okovango Delta region in Botswana. Over hundreds of thousands of years, these early Homo sapiens spread through Africa, giving rise to modern groups- Bushmen in South Africa and Namibia, Pygmies in central Africa, Hadza in Tanzania. Other groups, some now extinct, spread north, west and east Africa. Finally, one lineage, related to the peoples of eastern Africa, left.

        These people were the ancestors of all non-African peoples- Aborigines and Andamanese, Indians and American Indians, Chinese and Polynesians, Arabs, Greeks, Romans, Russians, French, Celts, Scots and soforth. We can call them the “Out-of-Africa People”. The low diversity of their genes and language compared to Africans suggests they left Africa relatively recently, likely in a single wave. Exactly how is debated.

         The simplest way out was to cross the Sahara, moving up the green Nile Valley, making use of the river’s water and game drawn to it. From the Nile Delta, one can then go east overland from Egypt into the Sinai, then the Levant (Israel, Palestine, Jordan, Lebanon, Syria). In science, the simplest hypothesis that fits the facts is usually correct. The problem is that as we’ve gotten more facts, this simple explanation doesn’t seem to fit the facts anymore.

         If humans left Africa using an overland route, then fully modern Homo sapiens should first appear in the Levant. But that’s not the case. Fossils show the Levant was first occupied not by modern humans, but by primitive, near-modern sapiens- the Skhul and Qazfeh people, with those brow ridges and weird skull shapes- around 100,000 years ago. These near-modern peoples were then replaced by Neanderthals 50-60,000 years ago, who invaded to retake these lands. The oldest modern Homo sapiens in Israel- people without the brow ridges, and a more modern brain shape- date to just 55,000 years ago.

        Astonishingly, traces of modern humans appear long before this as far away as Australia. Here, signs of human habitation- ground stone axes, ochre pigment, other artifacts- date to 65,000 years ago. Charcoal in sediments also suggests increased frequency of fire in Australia 70,000 years ago. Fire is a signature of Homo sapiens, since hunter-gatherers typically used controlled burns to manage their landscapes.

         Other tools and fossils fit this pattern, where humans first show up east of the Levant. In Sumatra, fossils of modern humans date to ~68,000 years ago. In China, modern human teeth from a cave date to over 80,000 years ago. Tools show Homo sapiens in India by 80,000 years ago. Finally, advanced stone tools in the Arabian Peninsula, apparently made by modern humans, date to 125,000 years ago. These tools resemble technology from eastern Africa- not the Levant- suggesting technology and people spread between East Africa and Arabia.

        Taken together, the evidence suggests modern humans skipped North Africa entirely. Instead, we took a southern route from east Africa to Arabia, then rapidly moved along the coast of the Indian Ocean into India, Southeast Asia, and finally Australia. Only later did humans move west overland into the Levant, invading North Africa from the east. North Africans- Berbers and later Arabs- represent ”into-Africa” dispersals.

Map tracing the dispersal of Homo sapiens out of southern Africa and into territories occupied by Neanderthals, Denisovans, and archaic Homo sapiens.

        Interpreting migration patterns from the DNA is a complicated business and there’s currently no consensus about what this data shows. However, at least some genetic evidence supports this southern coastal route. A high diversity of mutations in mitochondrial DNA, which traces maternal descent, occurs in the Arabian peninsula and south-central Asia, suggesting humans have been in this region longer than the Levant.

        In isolation, no piece of evidence- stone tools, fossils, or genes- allows us to confidently support or reject any particular scenario- a northern land route, a southern coastal route, or a multiple dispersal scenario using both. But when all evidence is considered together, it’s striking how these different lines of evidence tend to fit a single story: humans migrated from East Africa across the Red Sea into Asia and Australia, and later moved west into Israel, North Africa, and Europe. So how did they cross?

        Sea levels were lower at the time, because Earth was in the grips of the Ice Ages. So much water was locked up in glaciers and icecaps that sea levels dropped 100 meters or more. The Red Sea was too deep to dry up completely, but it narrowed dramatically. At its narrowest point- Bab al Mandeb, the “Gate of Tears”, where the Red Sea enters the Indian Ocean- it was just a few kilometers across.

The shallow mouth of the Red Sea narrowed to a few kilometers across during the last Ice Age- but didn’t dry up.

        You could have easily stood on African soil and looked across, and wondered what was on the other side. Around 125,000 years ago, someone decided to find out.

        The distance was short enough that it was possible to swim it. It was impossible for a whole tribe to swim across, however, because these people would have had children, toddlers and infants, who couldn’t swim. Since they would no more have abandoned their children than we would, they must have found some way to ferry everyone over. And from that, we can conclude the Out-of-Africa people must have used some sort of watercraft.

        We have no archaeological traces of ancient watercraft, and modern watercraft used along the coast of East Africa today- outrigger canoes and dhows- are clearly recent inventions imported into Africa, with the dhow coming from Arabia or India, and the outrigger from Indonesia. Instead, the Aborigines of Australia may provide some insight into the kinds of technology around at the time. Since no land connection existed between Australia and Asia, even when seas fell during the last ice age, Australia’s people must have arrived by boat.

Even at the height of the ice ages, water separated Australia from Asia. Australia’s colonization by aboriginal peoples could only have been accomplished by water, and required more than one crossing. Boats must have been invented before 65,000-70,000 years ago, when Australia was first peopled (Wikipedia).

        After arriving in Australia, humans existed in near-isolation for around 70,000 years. With little cultural exchange to import new innovations from elsewhere, their technological traditions are likely to be relatively conservative, potentially offering a glimpse of the kinds of technology available to the first people out of Africa. By contrast, the far more sophisticated outrigger canoes and sailboats used in places like Indonesia, Polynesia, and Africa which saw cultural exchange with places as far away as Madagascar and South America, are likely to reflect innovation and technological exchange after people left Africa 125,000 years ago.

Australian raft, made of two overlapping layers of mangrove trunks, with fish spear and paddle (Australian National Maritime Museum).

        The Aborigines make a wide variety of rafts. These didn’t just drift, but like a paddleboard, whitewater river raft, or Zodiac raft, could be maneuvered and propelled. These rafts could be poled along in shallow water, or in deep water, paddled using one’s hands, or a bark paddle. They were made in different ways depending on how they were used and the available materials. Some were made by bundling then lashing reeds together. Others were made by pinning mangrove trunks together to form a platform, still others by layering bark.

        The Aborigines also made more sophisticated bark canoes which can properly be called boats. They’re long and narrow, with a streamlined shape that lets them cut through the water, and use a hollow hull. The vessel is literally a vessel- a hollow, watertight container that displaces water to create a buoyant force. A boat hull has several advantages over a raft. For a given amount of material, a hollow hull can carry more people and cargo than a simple raft. Because people and cargo sit below the waterline, it provides better stability in rough conditions. The shape is more hydrodynamic, requiring less energy to transport its cargo, and this also lets it reach higher speeds. All this makes displacement hulls the best, if not only option for long sea journeys.

Australian bark canoe (Australian Maritime Museum). Bark was heated and shaped into a hollow hull, with ends tied together to amke a sharp prow and square stern (towards the viewer).

        These bark canoes were made by cutting pieces of bark from trees, then shaping it into boats, often using heat or steam to bend the wood. Dugout canoes were used in historic times, but appear to be a later invention, imported from Asia, and therefore seem unlikely to have been used by the Out-of-Africa people. More sophisticated designs- long-range, seagoing outrigger canoes of the sort used in Polynesia, Indonesia, Madagascar, and Africa, or sails- aren’t known.

        Given that perhaps 70,000 years have passed since the Aborigines colonized Australia, and that came long after people left Africa, these designs probably aren’t the ones the Out-of-Africa people used. Still, they’re some of the simplest known watercraft, and so give an idea of the kind of craft hunter-gatherer cultures could have built with simple techniques and tools 125,000 years ago. Their diversity is also striking- consistent with the idea that the Aborigines have been using watercraft for a very long time.

        The small, simple vessels used in Australia in historic times seem unsuitable for long-range travel, but it’s likely that once Australia’s shores were settled, people had little reason to travel and stopped building vessels capable of long journeys. We see this pattern in New Zealand- the Maori’s Polynesian ancestors sailed to colonize New Zealand on sophisticated ocean-going double-canoes. Once they settled, they abandoned this complex, long-range boat technology for simple paddled canoes, because they had no unsettled lands left to colonize. So while in some ways Australia might give insight into early maritime technology, the culture is probably not a time capsule either- it’s probably evolved, in some ways becoming more complex, but in others, perhaps becoming more simple. To make the long crossings from Asia into Australia, which would have taken several days it’s likely that the first people into Australia may have had more sophisticated seafaring capabilities than the indigenous Australians encountered in historic times.

        The simplest way to improve upon the simple designs used in Australia would simply be to make the canoe longer. Every boat has a hull speed, the top speed it can reach without planing. Hull speed is hit when the bow wave is as long as the boat, so the longer the hull, the higher your hull speed. In short, to go faster, make a longer boat. That’s why a sea kayak, designed for long trips, is long and narrow compared to a river kayak, and why counterintuitively, a 1000-foot aircraft carrier can cruise at 30 knots. Longer boats can also have more power, in the form of oarsmen.

        The major constraint on longer journeys would have been the fact that people can only go a few days without water. Water-carriers, made of skins or coconut shells, could have made longer voyages possible. By the time they reached Australia, humans clearly had the ability to make relatively long sea voyages; Australia would have been over 50 miles away from by sea, even with lower sea levels. Yet the first crossing could easily have been accomplished with even simple technology- they could simply have ferried people across on rafts, perhaps even using just a few small rafts, if they made a lot of trips.

        This raises a question- if humans did cross the sea, why? Why not take the seemingly straightforward route up the Nile and out the Sinai? It may be that this route was blocked. Archaic humans may have still inhabited North Africa. Even if modern humans did successfully displace them, warlike Neanderthals occupied the Levant. The Nile valley and the narrow entrance to the Sinai may have acted as defensive chokepoints, rather than accessible highways. The long western shoreline of the Arabian Peninsula may have been harder to defend against invasion, since some stretches may have had few people, or none at all. A people with watercraft could have chosen the time and place to make their Out-of-Africa beachhead, like when the Allies invaded Europe at Normandy rather than better-defended Calais.

        Once they became established in Arabia, Homo sapiens appears to have rapidly spread down the coast into lands inhabited by Neanderthals and Denisovans. Watercraft and associated technology may have given humans an edge in territorial conflicts. If humans had boats, then they may have been able to launch surprise raids from the sea, like Vikings in medieval times, turning the sea from a defensive moat to a vulnerable route of attack. Alternatively, boats may have let H. sapiens skirt well-defended territories to establish themselves on more poorly defended beachheads, or uninhabited islets and beaches, like the island-hopping strategy used in the Pacific in World War II. The primitive nature of early watercraft likely limited their effectiveness, but if the peoples that Homo sapiens faced didn’t have them, they would have still provided a massive tactical and strategic advantage.

Aboriginal fishermen, New South Wales, c. 1817. Men in the foreground use fish spears, while men in the background dive for shellfish. A bark canoe lies on the sand. By Joseph Lycett.

        Along with boats, the ability to exploit the sea might have given coastal people a huge competitive advantage against people without such technology. Technology like fish spears, fish traps, nets and so on could have let people exploit fish, spiny lobster, shrimp, sea turtles, dugongs, dolphins, and soforth. In other words, the first people out of Africa may have been fishermen. If so, the sea would have been a rich source of protein, allowing populations to grow faster and to sustain larger numbers, giving them an edge in territorial conflicts with other species. The fact that some of the earliest traces of modern Homo sapiens tools are from the East Coast of Africa fits with the idea that early humans exploited coastal habitats.

        To be fair, evidence now shows that Neanderthals figured out how to use marine resources as well- mussels, crabs, fish, seabirds, seals, sharks and dolphins. At least some Neanderthals inhabited islands, suggesting they had some kind of watercraft. So fishing isn’t unique to modern humans, and maybe watercraft weren’t either. Still, if the Out-of-Africa people had better fishing gear or boats than the people they encountered this would have given them an advantage.

        Again, Australia’s indigenous peoples may provide some insight into what an early fishing cultures looked like. The Aborigines are often thought of as a desert people, hunting kangaroos in the Outback, but historically they were densely settled along coasts and waterways, exploiting fish and shellfish, and they’ve done so for tens of thousands of years.

Aboriginal fish traps, Darling River, Victoria (State Library of Victoria).

        Aboriginal fishing technology includes hand-thrown fish spears, simple dip-nets, stone fish weirs, which funnel fish or trap them as the tide recedes, and woven fish traps made of cane or other material, similar to modern crab pots and lobster traps. Fishhooks made from shell are found in Australia too, but fishhooks appear to be a relatively late invention and a recent import to Australia. Again, we see hunter-gatherers were ingenious in exploiting the sea. Even if early hunter-gatherers lacked more sophisticated fishing techniques like hooks and seine nets, this may not have been a problem. Without modern fisheries and fishermen exploiting them fish would have abundant.

        Evidence to test these ideas is unfortunately, scarce. One problem is that the seas were so much lower at the time. If humans did cross the Red Sea then spread along the coasts to Australia, many of the traces of these early settlers will lie 300 feet of water, buried under corals, sand, and mud.

barbs of an Aboriginal fishing spear (Australian Museum)

The other problem is that almost nothing of their technology will preserve. While we call the Pleistocene the “Stone Age”, most of the tools “stone age” hunter-gatherer people like Khoi-San, Amerindians, Aleuts and Aborigines use are largely or entirely made of non-stone materials- wood, bark, roots, leaves, grass, animal skins- which rot. The same would be true of early fishing gear and boats. Early out-of-Africa migrants might have used wood rafts, bark paddles, and fishing spears. Of this technology, only the small stone or bone tip of a fishing spear might preserve, and archaeologists might struggle to understand its purpose.

        Still, while there’s limited evidence, a southern, coastal route out of Africa explains a range of evidence no other hypothesis does- an otherwise perplexing pattern of stone tools, fossils, and DNA. That implies it’s right.

Modern fishing boats result from a 100,000 year history of seafaring and fishing

        It’s remarkable how long we’ve been seafarers, and its hard to overstate the effect of sea voyages on our history. As humans crisscrossed the Mediterranean, diverse peoples- Egyptians, Greeks, Phoenicians, Berbers, Jews, Romans- exchanged philosophy, religion, science, technology and genes, creating the Western Civilization. Polynesian outrigger canoes sailed from Taiwan to Melanesia, Fiji, Rarotonga, New Zealand, Tahiti, Hawaii, Easter Island- and in the process discovered South America (only to discover the Amerindians got there first). America was ‘discovered’ again by seafaring Aleuts, Vikings, Basques, and last, Columbus. Eventually, European voyages of exploration linked the peoples scattered by the Out-of-Africa diaspora, leading to the exchange of technology, culture, and genes. Sea trade become central to the global economy, with trade by sail and later by container ships and oil tankers linking economies. Sea power is also military power, with the destruction of the Spanish Armada, or battles like Trafalgar and the Coral Sea altering the global balance of power and seeing the rise and fall of empires.

Captain Cook’s ships Resolution and Discovery in Tahiti. Two great seafaring peoples- the Polynesians and the British- encounter one another.

What’s astonishing to think is that all these odysseys began with a single, short voyage. This voyage started with someone standing on the sands of Africa, looking out over the water, wondering what lay on the far side. And all the other explorers are the result of that first dream, the first odyssey.