The Lost Forest
Page 22
Chapter 22
DEBATE ON ORIGINS
In the last decades of the twentieth century, a major debate raged in scientific circles concerning the African origin of Homo sapiens, the chronology of their migration out of Africa, their geographical distribution and the question of their interbreeding with the archaic species that preceded them. This debate attracted a considerable amount of popular attention, not only from the press and general public but also from governments and certain xenophobic politicians.
‘As frequently happens in science,’ Paul Cathary had explained, ‘new technology opens new paths that help us to reply to old questions, and sometimes provides unexpected answers!’
The use of population genetics and molecular biology in the search for human origins had become of great importance in helping science to resolve the long-running debate on where modern humans, that is to say Homo sapiens, first evolved.
On the one hand the ‘Multi-regional’ model explained that an archaic form of man left Africa between one and two million years ago, and from these ancestors modern humans evolved independently and simultaneously in areas of Africa, Europe, and Asia.
On the other hand genetic evidence pointed to the more broadly accepted ‘Out of Africa’ model, which expounded the theory that all modern humans evolved in Africa and then left in several waves of migration, ultimately replacing any earlier species.
‘This shows that Homo sapiens are of recent origin and first appeared in Horn of Africa,’ Paul said. ‘African populations have the most ancient alleles - now this might seem a little complicated at first glance, but it is simply gene pairs coded for specific traits - and the greatest genetic diversity. That means they’re the oldest of Homo sapien populations to have emerged around 160,000 years ago, most likely from a very small population of just a few thousand individuals.
‘Up to the point in time of your discovery John, the Multi-regional model that preaches Homo sapiens had evolved in different regions of the world over a long time scale, was considered by most paleoanthropologists to be as good as dead. Today, no one can now say with certainty, that we are of entirely recent African origin, because we can now see there could have been interbreeding between modern and archaic species.
‘The only general agreement today is that Homo erectus, our precursor, evolved in Africa and gradually expanded to Eurasia about 1.9 million years ago. And 100,000 years ago, several species of hominids coexisted, not necessarily side by side, including Homo sapiens in Africa, Homo erectus in South East Asia and China, and Homo neanderthalis in Europe.
Until Homo borneensis was discovered it was thought that around 30,000 years ago the only surviving hominid species was Homo sapiens.’
‘But when did we, Homo sapiens leave Africa?’
‘Ah! That’s where opinions start to diverge. Evidence based on DNA in the Y-chromosome leads certain of us think that the exodus began between 60,000 and 50,000 years ago, however some of us think that figure is about 100,000.’
‘So how long did it take to get to Borneo?’
‘Well before Mungo man in Australia, who dates back to around 50,000 years ago, meaning that early travellers followed the southern coastline of Asia into Indonesia, over the land bridge that existed at that period, then crossed about 250 kilometres of open sea, and finally colonizing Australia to become the ancestors of our present day Aborigines.’
‘That means the descendants of the first wave of Homo sapien’s migration out of Africa.’
‘Right.’
‘So let me get this right, the first Homo sapiens appeared in Ethiopia about 160,000 years ago and then migrated out of Africa finally reaching Australia around 50,000 years back?’
‘Exactly so, if fact many paleoanthropologists say that the fossil record shows that a first wave of migration occurred around 100,000 years ago.’
‘Is there any fossil evidence?’
‘Yes, if you recall the discoveries made in Israel over the last few decades, we can see fossil evidence that shows modern humans were in at least two places in that region of the Levant 90,000 years ago, they seem to have disappeared about 10,000 years later, but they could have survived further east in Asia.’
‘Could they have survived in Israel, I mean most of it is desert.’
‘Remember that the Levant of 100,000 to 150,000 years ago was very different from that we know today. It was a geographical extension of north-eastern Africa with a savannah like environment; it was probably an extension of the original territory of early Homo sapiens. The evidence in Israel also shows that early Homo sapiens were present over a long period of time, no doubt expanding northwards to Europe.’
‘What does the mean?’
‘Well the problem is that there is 30,000-year gap in the archaeological record of Homo sapiens outside of Africa.’
‘Why?’
‘That’s a little complicated but some of us think that though Homo sapiens may have been anatomically modern around 150,000 years ago, they did not become behaviourally modern until about 100,000 years later, probably due to a genetic mutation related to cognition, the capacity for symbolic thought, all in all making them more intelligent.’
‘So how did these change things?’
‘These mutations enabled them to develop an advanced language ability, thus more sophisticated tools with which they could hunt more efficiently, transform the raw materials they had available, animal skins and bones, making cloths and more elaborate shelters, leading to greater geographical freedom.’
‘Could the same thing have happen to an evolved erectus?’
‘Who knows?’
‘What seems likely is that a second wave of hominids left Africa around 50,000 years ago, possessing this mutation, there numbers grew rapidly and settled in the Middle East with smaller groups migrating further to East and South East Asia and eventually Borneo.’
‘What we should remember,’ he continued, ‘is that until your discovery, the study of DNA has been almost entirely based on modern man, there is very very little DNA from Neanderthals and none at all from erectus. Up until now we have had absolutely no genetic knowledge of Homo erectus. The DNA recovered from Homo borneensis is the equivalent to a force 7 earthquake on the Richter scale, which will have the same effect on our vision of human evolution as the discovery of Eugene Dubois in Java one hundred years ago!’
‘Did erectus evolved in Asia?’
‘Certainly.’
‘Do you think the different races are the result of that?”
“No you’re moving into dangerous territory. If we admit there are different races then things become very complicated in many ways, especially as far as correct political views are concerned.’
‘But you, do you believe there are races?’
‘Well to be precise, we are all Homo sapiens sapiens. But there are of course differences, simply ask a forensic scientist who can identify half a dozen so called varieties of humans.’
‘Is it possible that some of us developed differently in isolation?’
‘Naturally, if you take the Aborigines of Australia or the Bushmen of South Africa who lived in isolation for many many thousands of years they underwent changes even if they are superficial changes.
‘Look at this way, the world is divided between politicians and specialists amongst whom are the scientific professions. The role of politicians is to tell people what they want to hear, at least some of the people – mostly those who vote for them, also to dictate what is politically correct, to avoid civil strife for example. Specialists, at least most who are dedicated to telling the truth and finding logical explanations to things, have other considerations.’
‘So what are you getting at?’
‘Well I am genetician, specialised in human genetics, we believe today that man became Homo sapiens when mutations occurred that enhanced his capacity for symbolic thought.’
‘You told me this occurred about thirty or forty thousand years ago.’
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‘That’s right, something like that, a bit more. Okay. The essential thing is whatever happened had an extraordinary effect; man acquired an evolved language, invented art, new technology and eventually agriculture and civilisation.’
‘Yes.’
‘The point I’m getting at is this mutation occurred in very, very, recent times when you think ancestors that very closely resembled us walked the earth for almost million years.’
‘I get your point, so what?’
‘What I’m saying is that mutations did not suddenly stop! They never have and they never will. This process of mutation transformed Homo erectus into successive forms such as Neanderthal in Europe and evolved versions of erectus in Asia. So why do we assume that similar mutations did not occur in isolated populations?’
‘I don’t know.’
‘Nor do I, the reality is that for the moment we have not found any evidence pointing to this. But our science is young and there are many corners of the world to be explored.’
‘So such mutations continued to occur in isolated erectus populations also?’
‘Yes.’