How has a DNA test changed my view of humanity? Well, it occasionally shakes my brain out of the humdrum routine of modern living – commuting, supermarket shopping, etc. When you begin to consider our origins as the subspecies of human known as homo sapiens sapiens (i.e. anatomically modern humans), our physical traits, behaviour, language, culture etc., then mundane concerns about things like work and what to make for dinner can be put into a different perspective.
Archaeology tells us that anatomically modern humans evolved from our immediate ancestors – archaic homo sapiens – in Africa just over 200,000 years ago. We emerged generally as a slimmer, taller breed: ‘gracile’ in scientific parlance, rather than ‘robust’ like our relatives the archaic heavy-boned Neanderthals. 200,000 years is an immense amount of time to get your head around. My simple brain copes with it better by condensing it into a 1 year timeline. To put our development into this context, after we rang in New Year on 1 January, we didn’t actually start farming until 14 December; the first recorded civilisation began 22 December; and we landed on the moon around 10 pm on 31 December. Yet, as ‘anatomically modern’, we looked like we do today. A shave, a haircut and a suit and we wouldn’t really notice the 200,000 year difference.
They looked like us, but did these people behave like us? And in our one year timeline [which I’ll keep referring to] what the hell were they doing all year?
There were two theories on when modern human behaviour began.
The first was known as the Great Leap Forward theory: For the first 150,000 years [up to end of September] modern humans were primitive in behaviour and no more advanced than other older hominids like the Neanderthals. They lived in apparent cultural stagnation. This was based on an explosion of complex artifacts, such as fine toolwork and artwork, that suddenly appear in the fossil record after 50,000 years ago. This was also when modern humans began to explore and colonise new environments outside of Africa. It also marked the beginning of the decline of the Neanderthals – perhaps brought on by our new competitive edge. Precisely what caused the Great Leap Forward was unknown, possibly a major genetic mutation that perhaps led to the emergence of modern human language. If there is any truth to the Great Leap Forward theory, it would make you wonder if another could occur again; or if anthropologists of the far future would conclude it has already happened given our advances in the 20th century; or even if we had broken out of our evolutionary programming by being able to manipulate the environments we live in.
However, the Continuity theory – now gaining acceptance as the more likely scenario – is that there was no single genetic or biological Great Leap Forward. Modern human behaviour has resulted from the gradual accumulation of knowledge, skills and culture occurring over hundreds of thousands of years of human evolution. Archaeologists have found increasing amounts of evidence which can be interpreted as showing modern behaviour at sites in Africa and immediately adjacent such as the Levant, including a ritual human burial with grave goods dating back 90,000 years [mid July]. The major breakthrough for the Continuity theory came in 2007 when it was reported that anthropologist Curtis Marean had found evidence of early modern humans living on the coast in South Africa, harvesting food from the sea, using complex bladelet tools and symbolic red ochre 164,000 years ago [early March]. These coastal dwelling early humans expanded their diet to include shellfish and other seafood for survival in the face of harsh environmental conditions. The world was in the grip of an ice age 130,000 to 200,000 years ago and swathes of Africa had become mostly desert, making food difficult to find. The sudden change in temperature wiped out many species elsewhere. There were probably only five or six places in all of Africa where humans could have survived these harsh conditions and this is what led Marean to consider Pinnacle Point at the Cape of South Africa as a prime candidate for a human enclave. It also explains why evidence of modern human behaviour earlier than 100,000 years ago is so rare. Their populations were very small and concentrated in coastal areas that have long since disappeared beneath the sea. Marean explained how coastal areas were of little use to more primitive hominid species as they didn’t know how to use the sea as a food source, so for millions of years they only ate land plants and animals. Shellfish was one of the last additions to the human diet before domesticated plants and animals were introduced.
So it seems a move to coastal areas was one of the keys to our development. Marean explained how coastlines made good migration routes for these early modern humans who could now exploit the sea for food and use coastlines to move long distances. Marean believes that as well as finding evidence for the earliest modern human behaviour he could well have discovered the founding, or progenitor, population for all modern humans. Anthropologist Chris Stringer said he agreed with Marean’s views on the early evolution of intelligence, but was not convinced by the argument that there was a single small population of humans in one region of Africa from whom we are all uniquely descended. He said that there was also evidence of early modern humans in Ethiopia 160,000 years ago and others in Morocco, whose populations may also have contributed to our ancestry.
Genetic testing shows how all humans alive today still carry the DNA of one of the earliest modern humans. Mitochondrial DNA (mtDNA) is passed from mother to offspring and all mtDNA in every living person is directly descended from a woman who as been termed Mitochondrial Eve. Despite the biblical tag, she was not the only living female of her times, it’s just that all of her female contemporaries failed to produce a direct unbroken lines to the present day. Mitochondrial Eve lived in East Africa around 200,000 years ago, making her one of the earliest of our subspecies (though not the first, by scientific convention – she still has her own lineage through her mother).
Mitochondrial Eve’s male counterpart is termed Y-chromosomal Adam. By analysing the Y-chromosome DNA from sample populations of males in various parts of the world, geneticists have concluded that all humans alive today are descended through their father’s direct male line from this one man. Like Mitochondrial Eve he also lived in East Africa – most likely in the Rift Valley region due to its abundance of resources. Unlike the biblical Adam and Eve, they did not live together as the mother and father of humanity – they were separated in time by at least 100,000 years. Y-chromosomal Adam lived around 75,000 years ago, give or take 10,000 years.
Why did Mitochondrial Eve and Y-chromosomal Adam live so far apart in time? Clearly something put pressure on the Y chromosome. There could be a genetic explanation for this. It might be natural selection working on the male of the species. More males than females end up producing no offspring, so male gene lines die out faster than female ones – therefore any remaining will only converge in the more recent past. It could be down to specific catastrophic events which, by chance, Eve’s genes survived through to today, but her contemporary male’s genes didn’t; the human population ‘bottlenecked’ when it was nearly wiped out and it was Adam that picked up the male line from there.
Some scientists believe that this event was the largest known volcanic eruption on Earth around 75,000 years ago (again give or take a few thousand years). The catastrophe theory is that the supereruption of the Toba volcano in Indonesia plunged the planet into a 6 to 10 year volcanic winter, which resulted in the world’s human population being reduced to as low as 1,000 breeding pairs. It’s not certain where human populations were living at the time of the eruption, but it’s most likely that the survivors were living in Africa and their descendants went on to populate the world. Genetic evidence does suggest that all humans alive today, despite our apparent variety, are descended from a very small population.
The migration out of Africa occurred around 60,000 years ago [mid September on our timeline]. It has been estimated that from a population of 2,000 to 5,000 individuals in Africa, only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea into the Middle East and beyond. What made them finally ‘go global’ after almost 150,000 years? It’s been suggested that protein from our enhanced seafood diet somehow changed our brains, or a genetic mutation triggered something that made us want to explore the world. It was probably a combination of factors, but environment usually plays the biggest part in the migration patterns of any species. Perhaps the Toba catastrophe and subsequent climate change affected food supply, or prolonged cold spells lowered sea levels and opened new land bridges – as was probably the case with the Red Sea crossing. The Great Migration out of Africa is portrayed in epic terms: The Journey of Mankind, Exodus from Africa, The Peopling of the World, etc, which of course, for our destiny it was. I think it’s important though not to necessarily see them as some intrepid band of Stone Age Marco Polos, deciding one day to backpack their way into Europe, Asia and Australia. They may not have all gone at the same time for a start, but in successive small waves. And their journeys didn’t take a few months, but thousands of years, over hundreds of generations. The oldest modern human remains in Europe were found in a cave in the Carpathian Mountains in southwestern Romania and have been dated to around 40,000 years ago. If you assume a 20 year gap between generations and a 3,000 mile overland route hugging the coastline between Ethiopia and Romania, then in the 20,000 years between leaving Africa and dying in a Romanian cave, every one of the 1,000 generations would only need to cover an average of 3 miles each within their own lifetime.
But that’s not to downplay their achievement. Life was harsh for our early ancestors. Their every waking moment was spent surviving – looking for food, fending off wild animals and keeping warm. Pregnancy, toothache, or a broken ankle could easily spell an agonising death. They were at the mercy of their environment. If they weren’t dealing with short term catastrophes like the Toba supervolcano, they were dealing with the long term effects of climate change. In our 200,000 year history, we have spent 170,000 years living through 2 Ice Ages [on our timeline, this ‘winter’ period lasted from January to early April, then from mid-May up to 9 December]. If we weren’t dealing with the ice itself, then we were dealing with the effects of having vast volumes of the Earth’s fresh water placed out of bounds. This is probably what sent the pioneers of Pinnacle Point into retreat to the southernmost tip of the African continent, and finding that crab meat actually tasted quite nice.
image souce – Arizona State University
We have teetered on the edge of extinction on a number of occasions, our entire species possibly going down to its last couple of thousand individuals – yet, somehow remaining viable. As the few remaining humans looked out to sea from their cave at Pinnacle Point 164,000 years ago, they couldn’t have known whether there were any other isolated communities of their kind left. They couldn’t have comprehended the idea that their descendants would mushroom to nearly 7 billion in number, and that 60% of them would follow their lead and live along the world’s estuaries and coasts. We were on a knife-edge and could so easily have gone the way of the Neanderthals. Almost 120,000 years later, the last of the Neanderthals similarly looked out to sea from their cave in Gibraltar, not knowing that they were doomed.
Or were they? The final twist in the story of early ancestors has only recently come to light through genetic study. As well as Y-DNA and mtDNA testing, a test of autosomal DNA is also available to geneticists. This determines the genetic percentages of a person’s overall ancestral makeup from particular continents/regions around the world. Recent studies have revealed that up to 4% of the autosomal DNA of people of European and Asian descent comes from the extinct Neanderthals. The DNA of people of African descent show no traces of Neanderthal DNA. The Neanderthal Genome Project, which has recovered and sequenced 40,000 year old Neanderthal DNA samples, is being coordinated by the Max Planck Institute for Evolutionary Anthropology in Germany and 454 Life Sciences in the US. Their initial results, reported in Science magazine in May 2010, points to interbreeding between modern humans and Neanderthals. Neanderthal/human hybrid children were the product of brief liaisons, perhaps during trade between human and Neanderthal tribes, or maybe through more violent meetings. The first opportunity for interbreeding probably occurred between 50,000 and 60,000 years ago in the Middle Eastern, soon after humans left Africa, but before they split into groups that moved on to colonise Europe, Asia and New Guinea. Archaeological evidence shows that the two groups overlapped here for a time.
So the Neanderthals didn’t die out after all. They live on, and I see it every time I shave in the morning.
image source – bbc.co.uk – © 2005 BBC
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