Africa 60,000 years ago: The Age of Adam

[Michael]

I have been wanting to share my thoughts about something for a long time. Through the past few years scientists have published research which collectively suggests that a series of very important events occurred in modern human prehistory about 80-60,000 years ago. I'm going to call that period The Age of Adam for lack of a better name.

Three very important events took place within the time frame of 100,000 to 60,000 years ago:

• The last warm period between glacial periods in the current ice age came to an end
• Modern humans who were the ancestors of today's peoples migrated out of Africa
• The Toba supervolcano erupted, probably killing most living hominids and bringing on the last glaciation period

When people speak of "ice ages" they are actually thinking about periods of glaciation that have occurred during the present geologic epoch, which is the real ice age. The present ice age is believed to have started about 2-1/2 million years ago and it has so far been divided into four glacial periods and four interglacial periods. Important new hominid groups seem to first appear in at least two of those interglacial periods.

Neanderthals are believed to have appeared about 400,000 to 350,000 years ago -- which is approximate with the second interglacial period, called the Hoxnian. Dates vary for the Hoxnian interglacial period but it probably lasted from about 380,000 BCE to no later than 200,000 BCE.

The Wolstonian glacial period began around 200,000 BCE and ended around 125,000 BCE (some sources suggest 130,000 BCE).

The Eemian interglacial period began around 125,000 BCE and ended somewhere around 70,000 BCE (sources vary on this and some suggest it ended around 110-100,000 BCE).

The Wisconsin glacial period began around 70,000 BCE and ended around 12,000 BCE.

Modern humans are believed to have appeared about 200,000 to 150,000 years ago -- which is approximately in the first half of the Wolstonian glacial period. Some sources suggest that Homo Sapiens (or Homo Sapiens Sapiens) arose as much as 250,000 years ago, which would be within or near the end of the Hoxnian interglacial period.

There is evidence that modern humans began migrating out of Africa about 100,000 years ago and they had reached Asia by about 90,000 years ago. Neanderthals also appear to have gone through periods of migration and expansion (possibly diverging into 3 or 4 major groups, for example).

So, let me add to all that another list of events:

• "Eve", the mother of all modern humans as identified through DNA, lived in Africa about 150,000 years ago
• Sea snail shells found in archaeological sites across Africa, Europe, and Asia 110,000 to 82,000 years ago
• Tool-making improved 80,000 years ago
• Pierced sea snail shells transported inland in Morocco 85-82,000 years ago (see point 2 above)
• South African tool-makers began using pyrotechnics about 72,000 years ago
• Carved ochre stones are left in Blombos Cave (near Cape Town, South Africa) about 70,000 years ago
• Python-shaped rock in Botswana carved by humans about 70,000 years ago
• "Adam", the father of all modern humans as identified through DNA, lived in Africa about 60,000 years ago
• African Pygmies became genetically distinct from other modern humans about 60,000 years ago
• Neanderthals began hunting mammoths in Britain about 60,000 years ago
• Modern human groups migrating out of Africa around 60,000 years ago were mostly male
• Ancestors of Australian aborigines left Africa about 50,000 years ago

An interesting story begins to emerge from these relatively isolated data. It doesn't have to be the right story at this stage as I think it's important that people begin to look at the various pieces of the puzzle with the idea of putting them together. We need to radically reorganize how we think about our ancestors and we'll have to try out some ideas and discard them before we come up with the most plausible explanation.

Still, I think it's fairly clear that from about 200,000 BCE through 70,000 BCE human populations went through periods of migration and diversification. They must have been increasing their numbers both in the north (Neanderthals) and in the warmer regions of Africa and Asia (modern humans) and expanding away from their traditional centers of habitation. And then the Toba event happened. This massive supervolcano erupted and probably threw the planet into a downward spiral of cold temperatures. That may explain why sources disagree on the dating of the last glacial and previous interglacial periods.

Most modern humans probably died. Scientists estimate as few as 10,000 people (comprising about 2,000 mating couples and close relatives) survived to carry on the human race. Now, that does not mean that all 10,000 people had to be located in Africa. Nor does it mean that they all had to be modern humans. And it could be that a larger number of people survived. Still, it seems certain that the most significant human population to survive was probably located in south Africa, perhaps near the coast. They could have spread north as the lands recovered and their numbers increased.

It could be that in the years following the super volcano's eruption human groups that were near to each other worked together to improve their chances of surviving. These human groups could have taken the first steps toward forming social organizations that eventually became clans, tribes, and nations (in the modern era). Until that time, lacking agriculture and the means to grow food in large quantities, human groups would have had to remain small.

Research into the psychology of human relationships led Dr. Robin Dunbar to propose a practical limit to the number of relationships the modern human brain can manage: 148. Rounded up, this number has been called Dunbar's Number or the Monkeysphere. Dunbar's research suggests that -- depending on brain size -- animals can work together groups that have practical limits. Of course, social insects like ants and bees would seem to defy this principle but they are extremely alien to mammalian physiology. Among primates, the principle holds up well under close scrutiny.

In hunter-gatherer groups, for example, the maximum size is reached around 30-50 individuals (the same as among chimpanzees). If you add the ability for the group to obtain more food than hunter-gatherers normally can, the maximum group size increases to about 150. Sociologists point to Hutterite communities, which sub-divide after their populations exceed 150 because (the Hutterites say) their ability to control behavior through public shunning diminishes as the group grows beyond 150. The next larger division, requiring moderate social organization, achieves a range of between 500 and 2500 individuals. Dunbar calls these three groups bands, cultural lineage groups, and tribes.

I find it doubtful that actual tribes developed among ancient humans after the Topa Event but their clans (cultural lineage groups) may have been able to sustain themselves in coastal environments if the waters remained warm enough to support large numbers of fish and shellfish. In fact, new research suggests that Neanderthal diets were extensively dependent upon large game animals while early modern human diets included smaller animals, fish, and seafood. In a rich coastal environment, large numbers of early modern humans could have lived closer together and shared food resources when need arose.

This is a significant factor in social development, obviously, because as people live close together in larger numbers the potential for conflict and competition for resources arises. As the population of the coastal peoples increased they may have split off colony groups that emigrated northward, and yet those splinter groups may have stayed in contact with their parent groups for both social and economic reasons.

Archaeology has already established that sea snail shells were being transported overland as late as 70,000 BCE in northern Africa and that human groups were capable of expression abstract thought through art. Hence, it's completely plausible that as modern humans re-colonized Africa their groups maintained some contact with each other -- at least for a while. In other words, modern humans had reached a point where they could look beyond their own groups and acknowledge some sort of kinship with other groups. And perhaps in that time frame a struggle arose which led to two consequences: the retreat of the ancestors of the pygmies into a region of central Africa where they had no interaction with other humans for thousands of years; and the migration out of Africa of new human groups whose members were mostly men.

Since those ancient peoples lacked the social integration to create kingdoms and empires it's highly unlikely that companies of warriors were seeking adventure outside of Africa, but perhaps there were conflicts between loosely allied groups that led to an imbalance in the populations. The losers of such conflicts would have to retreat, and if they had few women among them then perhaps they would have been motivated to seek out other groups of humans (missing the ancestral Pygmies) from which to attract mates.

There is no archaeological evidence pointing to any sort of war or conflict, but the DNA studies which revealed that one man was the ancestor of the modern human race offer a parallel to a historical trend that has been well documented both in literature and through DNA analysis: the expansion across the globe of Genghis Khan's descendants. Genghis Khan is known to be the ancestor of about 8% of Asia's men, and he only lived 800 years ago (1162-1227). It has now also been shown that Genghis Khan has non-Asian descendants in Europe and probably the Americas.

Genghis Khan, of course, controlled vast armies and conquered an empire that was the largest of to its time (and his heirs grew that empire into the world's largest empire to date). Still, his victories in war gave him access to many women, and his sons and grandsons also took many concubines and wives. It therefore follows that if ancient modern humans had drawn together in the wake of the Topa Event near the coast of southern Africa -- and if those groups subsequently went through a period of competition and conflict -- our forefather "Adam" might have been a warrior who imposed himself on many women.

"Adam" need not have built up a tribal state at all -- he only need have set into motion a pattern followed by his sons of taking the most desirable women from neighboring groups and using them to establish his influence on his neighbors. His sons would have lacked the means to build a strong support network so they could have expanded outward from Adam's homeland, gradually breaking off contact with older groups.

Eventually the competition for women would have driven less capable men into exile -- some of whom might have fled with their wives and children. Think of it as a sort of ripple of bad behavior spreading through the small pool of human groups living in southern Africa. Within only a few hundred years, maybe 1,000 years at most Adam's male line could have displaced all other male lines through primitive aggression with no significant organization.

The fact that "DNA Eve" predates "DNA Adam" by as much as 90,000 years suggests to me that there must have been other modern human groups surviving outside of Adam's region, whose male lines were eventually replaced by Adam's male descendants. We certainly know that Neanderthals had survived the Topa Event, and by their survival we can infer that other human groups could have survived as well.

Adam's Genghis Khan-like legacy simply leads me to wonder exactly how he became the most genetically successful human male in our timeline.

[Michael]

So this is hardly an original idea -- it has been proposed before by other people. In the essay to which I link, the author writes:

Now comes a fascinating new paper in press at Molecular Biology and Evolution. Scientists at the University of Arizona suspected that some of the confusion over Adam and Eve might be the result of comparing the results of separate studies on the Y chromosome and mitochondrial DNA. One study might look at one set of men from one set of ethnic backgrounds. Another study might look at a different set of women from a different set of backgrounds. Comparing the studies might be like comparing apples and oranges. It would be better, the Arizona team decided, to study Y chromosomes and mitochondrial DNA all taken from the same people. Obviously, those people had to be men. The researchers collected DNA from men belonging to three populations--25 Khosians from Southern Africa, 24 Khalks from Mongolia, and 24 highland Papuan New Guineans. Their ancestors branched off from one another tens of thousands of years ago.

The results they found were surprisingly consistent: the woman who bequeathed each set of men their mitochondrial DNA was twice as old as the man whose Y chromosome they shared. But the ages of Adam and Eve were different depending on which group of men the scientists studied. The Khosian Adam lived 74,000 years ago, and Khosian Eve lived 176,500 years ago. But the Mongolian and New Guinean ancestors were both much younger--Adam averaged 48,000 years old and Eve 93,000 years.

You wouldn't expect these different ages if a single Y chromosome had been favored by natural selection, the Arizona team argues. Instead, they are struck by the fact that Khosians represent one of the oldest lineages of living humans, while Mongolians and New Guineans descend from younger populations of immigrants who left Africa around 50,000 years ago. The older people have an older Adam and Eve, and the younger people have a younger one. The researchers argue that some process has been steadily skewing the age of Adam relative to Eve in every human population.

Now here's where things may get a little sticky for the "one-man-one-woman-is-traditional-and-natural" camp. The explanation the Arizona scientists favor for their results is polygyny--two or more women having children with a single man. To understand why, imagine an island with 1,000 women and 1,000 men, all married in monogamous pairs, just as their parents did, and their grandparents, and so on back to the days of the first settlers on the island. Let's say that if you trace back the Y chromosomes in the men, you'd find a common ancestor 2,000 years ago. Now imagine that the 1,000 women are all bearing children again, but this time only 100 men are the fathers. You'd expect that the ancestor of this smaller group of men lived much more recently than the common ancestor of all 1,000 men.

Of course, this proposal doesn't offer as many details or justifications as I do. And the author notes that other research has found discrepancies in the mitochondrial trees of various isolated populations (although I'm not sure the researchers ruled out connections to the 160,000-year-old Mitochondrial Eve).

[badlands]

Can you cite all the info please? It is interesting where did you get all evidence from?

[Michael]

I linked to as many sources as possible. If I had had time to do this right, I would have cited the relevant passages as end-notes or something.

Sorry.

[august]

Originally Posted by badlands

Can you cite all the info please? It is interesting where did you get all evidence from?

He's got at least 20 links in there already!

[Michael]

Really having nothing to do with this, but introducing an interesting parallel, is the newly announced Ardipithecus ramidus hominid species, which is believed to have lived 4.4 million years ago. Scientists now suspect that Chimpanzees and Gorillas (our closest primate cousins) may have evolved extensively since the large primate group diverged into hominids and apes.

[Michael]

Just to add to the timeline I provided above, this article suggests that human populations in sub-Saharan African began expanding, perhaps growing to ten times their previous size, around 40,000 years ago.

This site says that humans began using bone artifacts for weapons and tools about 40,000 years ago.

Britannica notes that small stone tools called microliths first appeared around this time. Evidence of "plant foods" also appears in this time frame.

It does sound like more efficient tool/weapon-making and the adoption of plant-foods into the human diet would have helped the populations expand. There must have been cultural changes as well. Since long distance trade also occurred in this period, it seems to me that the first true tribal groups may have appeared around this time. Different clan-groups may have acknowledged kinship and worked together or at least cooperated in protecting hunting ranges and food sources.

One other data point: This article says some DNA studies suggest that early modern human populations "reunited" after a 100,000 year-long separation to form a true pan-African population around 40,000 years ago. That implies significant exchange between population groups.

[Michael]

Some interesting new research has offered a tentative correlation between the greening of the Sahara desert and the exodus of humans from Africa on three occasions: 120,000 BCE, 50,000 BCE, and 9,000 BCE.

In this article:

A team of scientists from the NIOZ Royal Netherlands Institute for Sea Research and the University of Bremen (Germany) has determined that a major change in the climate of the Sahara and Sahel region of North Africa facilitated early human migrations from the African continent. The team's findings will be published online in the Nov. 9th installment of Early Edition of the Proceedings of the National Academy of Sciences USA. Among the key findings are that the Sahara desert and the Sahel were considerably wetter around 9,000, 50,000 and 120,000 years ago than at present, allowing for the growth of trees instead of grasses.

There is more in the article, which explains the nature of their research.

These estimates do not all line up exactly with the year data I provided in the original post but the numbers are very close ("close enough for science", I suppose, as the joke goes). This research may be very significant. It could help explain a number of questions that have arisen about how modern humans came to be distributed in the ways they currently are.

[Michael]

So Discovery Archaeology News has an interesting article reporting that hominid remains have been found on Crete dating to about 130,000 BCE (which approximately marks the end of the Wolstonian glacial period).

You can read the full article here. Here is an excerpt:

Several hundred double-edged cutting implements discovered at nine sites in southwestern Crete date to at least 130,000 years ago and probably much earlier, Strasser reported January 7 at the annual meeting of the American Institute of Archaeology. Many of these finds closely resemble hand axes fashioned in Africa about 800,000 years ago by H. erectus, he says. It was around that time that H. erectus spread from Africa to parts of Asia and Europe.

The article also mentions earlier claims from other finds of sea-faring Neanderthals and Homo Erectus which have until now been disputed. The idea that pre-modern humans might have been building rafts implies many possibilities for cultural and technological traits that have hitherto not been associated with those peoples.

In other words, it's starting to look like hominid cultures from around 100,000 years ago were much more sophisticated than our museums make them out to be.

[Michael]

Archaeologists digging in India have unearthed tools and other remains from just prior to and after the Toba event that suggest modern humans were in that area much sooner than previously believed. No hominid remains have yet been found but the tools match those of modern human cultures from Africa.

'Pompeii-Like' Excavations Tell Us More About Toba Super-Eruption
ScienceDaily (Mar. 3, 2010) — Newly discovered archaeological sites in southern and northern India have revealed how people lived before and after the colossal Toba volcanic eruption 74,000 years ago.

The international, multidisciplinary research team, led by Oxford University in collaboration with Indian institutions, unveiled to a conference in Oxford what it calls 'Pompeii-like excavations' beneath the Toba ash.

The seven-year project examines the environment that humans lived in, their stone tools, as well as the plants and animal bones of the time. The team has concluded that many forms of life survived the super-eruption, contrary to other research which has suggested significant animal extinctions and genetic bottlenecks.

Read the full article here.

Although this find does not directly challenge the "Out of Africa" theory it certainly calls into question the proposed timeline for modern human migrations out of Africa.

DNA studies may have overlooked pockets of ancient DNA pools, or it may be that older populations were absorbed by waves of younger populations emerging from Africa after the Toba event.

[EDSEL_PK]

Once upon a time, Humans were not at the top of the food chain. Saber-toothed cats, giant hyenas and baboons....our ancestors lived in bad neighborhoods for a loooooong time.

I wish somenody would make a more authentic film about early humans, more like 'Quest for Fire', but with Cro-Magnon.