“The more we understand about this particular event in human history, the more it provides a complete picture of our past,” University of Washington evolutionary biologist Joshua Akey told New Scientist recently.

“This particular event in human history” is the early migration of humankind from the so-called Dark Continent to Mesopotamia, the Middle East and beyond, into Europe and, eventually, North America and the equatorial Pacific.

As much as is known about these early migrations — and we know a lot — much remains a mystery. This has been an active and unpredictable period for new discoveries about early humankind, from fossil evidence in regions as far-flung as the Rif mountains of Morocco to the Australian Outback. Incredibly, new cave art is still being discovered in areas of Europe that have been settled for millennia. Carbon dating continues to prove the old adage that the more we learn, the more we learn that we don’t know.

Modern humans emerged out of Africa — that much is reasonably certain — but exactly when, and how, remains the subject of fierce debate.

Two theories have jumped to the fore, emphasis on the word “theory.” One posits that our earliest ancestors left Africa in a single wave, around 40,000 to 60,000 years ago. Many of these groups died out, though, even as a handful passed their DNA to their descendants as they settled the break basket of the Tigris and Euphrates river valleys.

A new theory, which has gained traction of late, is that early humans migrated in several waves, not just one, and that the waves originated thousands of years earlier than was previously believed.

The answer, many scientists now believe, lies buried in our human genome. The authors of no fewer than three recent studies have analyzed the genomes of roughly 800 individuals from 250 populations scattered throughout the globe. In one study, Harvard geneticist David Reich argues that the clear genetic similarities between remote communities far removed from one another suggests that modern humans did indeed emerge in a single wave from Africa, even though DNA evidence shows that our earliest African ancestors were already dividing into separate groups more than 200,000 years ago — a full 120,000 years before that early migration, if the genetic findings are to be believed.

Early human development shows that rapid advances in technology, culture, art, language, religious rites and the use of tools occurred during a relatively short span of time, between 50,000 and 80,000 years ago — in other words, around the same time as those early migrations out of Africa.

In an early sign of how climate change affected human migrations, scientists now believe that fluctuating temperatures and an increasingly unpredictable life cycle of plant growth hastened the urge to move, even as the natural barrier ofmountains and deserts kept groups of people separate, leading to genetic differences in human populations around the world.

Separate genetics studies from Harvard, the University of Washington and the Estonian Biocentre in Tartu, Estonia suggest that while most modern non-Africans are indeed descended from a single, out-of-Africa exodus roughly 80,000 years ago, genome studies in Papua, New Guinea suggest there may have been an earlier exodus, according to Cambridge-educated molecular biologist Luca Pagani, senior researcher with the Estonian Biocentre in Tartu, Estonia.

Another recent study, this one supervised by evolutionary geneticist Eske Willerslev at Denmark’s University of Copenhagen, has found that indigenous groups in Australia are strikingly distinct, genetically speaking, from other groups in Australia, despite sharing the common gene that suggests they were all descended from a single, founding wave of early human migrations from Africa.

©Eske Willerslev/University of Copenhagen

Why do we care? Why do we continue to care?

“People are just inherently interested in their past,” Akey told New Scientist, whether they’re from Seattle or South Yunderup township in Western Australia.

Answers inevitably lead to new questions, even as missing pieces in the puzzle are found. The mystery of early humankind — who we are, where we came from — continues to be one of the most fascinating riddles facing humankind today.

Everybody loves a good story. Even the best stories, though, can change in the telling.
Palaeontologists have argued for years — decades, in fact — that modern humans first emerged in Africa 200,000 years ago and migrated around the world some 50,000 to 100,000 years ago.
Exactly what route they took, though, where they left and where they arrived, is still the subject of much scientific conjecture and debate.
Now a recent study co-authored by the Department of Genetics at Harvard University Medical School in Cambridge, Mass. has brought scientists closer to understanding some of the finer details.

Humankind’s story begins in Africa with a group of hunter-gatherers, no more than a few hundred in all, who set out toward the distant horizon, for reasons known only to them. Today, 100, 000 years later, seven and a half billion of their descendants are spread throughout the Earth, “living in peace or at war,” as National Geographic geneticist Jamie Shreeve put it in a 2006 story for the magazine, “believing in a thousand different deities or none at all . . . faces aglow in the light of campfires and computer screens.”
The unanswered questions, shaped in the silence of prehistory, include: Who were these first modern humans in Africa? What compelled a small band of their descendants to leave the safety and security of the home they knew to set out for the unknown of Eurasia? Did they mix and intermarry other, earlier members of the human family tree along the way? When and how did early humans first reach the Americas?

The Harvard study, reported earlier this year in New Scientist, traced early human migrations by contrasting and comparing previously existing studies of ‘out of Africa’ routes with new DNA techniques that continue to improve the way scientists identify and sequence genomes of our early ancestors. The secret, the scientists say, is to find more efficient ways to analyze and understand the data, and improve our understanding of human migrations.
It’s a work in progress, the paper’s lead author, Dr. Mark Lipson, stressed. There are no easy answers. The secrets of those early human migrations remain just that.
Still, over time, more blanks on the giant, blank canvas of human prehistory are being filled in with each passing day. Incomplete maps are always subject to interpretation. “Here there be dragons,” inscribed on an old map, is always assumed to be true — or possible — until someone proves it isn’t. The slow, painstaking work of scientific discovery is often just as much about proving a negative as it is proving a positive. (Pedants, as typified by The Atlantic’s Robinson Meyer in a 2013 article, will point out that no old map, at least no early-modern European map, actually featured the inscription, Here there be dragons, but why spoil the beauty of a thing with an unprovable? All that means is that if there is a map with the words Here there be dragons or its Latin equivalent, Hic sunt dracones, inscribed on it, it hasn’t been found yet.)

Taking into consideration the possibility — likelihood, even — that early hominids interbred with other hominid species along the way, the Harvard study found that there was a definitive split between eastern and western populations once modern humans left Africa. This split happened as recently as 45,000 years ago, and explains how the early aboriginal inhabitants of Australia and New Guinea diverged genetically from their more northern cousins. Interestingly, unlike the closely studied migration of modern humans into Eurasia, the more southerly branch migration across Australia and the southern Pacific is less well understood.
What’s most relevant today about the study of early human migrations is whether any of these human movements were connected to climate change and, if so, how. Earlier research has suggested that humans spread across the globe in four waves, each one driven by climate change. The new findings suggest the picture may be more complicated than that, though. The Harvard study is a classic example of how, for every question answered, more doors open and more questions are asked.

Evolutionary scientists are naturally excited by the new findings, but Lipson urges caution. The process is slow and painstaking, as it should be. He urges against jumping to quick conclusions until more DNA evidence is found.
“There is some older archaeological evidence from Asia,” Lipson told New Scientist. “And while our results suggest the earliest human inhabitants probably would not have been closely related to Asian and Australian populations today, it would be interesting to see DNA from those sites.”
What we do know, based on DNA connected from 142 populations around the world, is that all non-Africans appear to be descended from a single group that split from the ancestors of African hunter-gatherers while, within Africa itself, humans formed isolated groups and then separated from each other.
The first migration did not end there. The study suggests that, subsequent to that first migration, there was a series of slow-paced migrations spread out over a period of thousands of years. Early Homo sapiens first arrived in southern Europe 80,000 years ago — far earlier than previously believed.
Question remain. Thanks to this new study and studies like it, the plot has thickened.

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“Man is modifying the world so fast and so drastically that most animals cannot adapt to the new conditions. In the Himalaya as elsewhere there is a great dying, one infinitely sadder than the Pleistocene extinctions, for man now has the knowledge and the need to save the remnants of his past.”

— Peter Matthiessen

Most detailed look yet at how early humans left Africa.

Out of Africa: plot thickens in story of early human migrations.

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