The origin of humans: Africa, Asia or both?

What is the classic theory?
Roebroeks: 'The classic theory is that some 1.8 million years ago, there were in East Africa people who, apart from their skulls, were physically very similar to modern humans. They were perfectly adapted to the savannah, had relatively large brains and had a relatively rich diet which included a good amount of meat. This means that they were near the top of the food chain. Carnivores need a large area to be able to satisfy their requirement for meat, and these early humans did as well. This species is supposed to have spread slowly from East Africa to the rest of the ancient world. Nobody knows precisely which species this was. It is often given the name Homo ergaster/erectus.'

What do you believe actually happened?
Roebroeks: 'Recent years have seen the discovery of so many new things in Asia that make the classic story too simple, in our opinion. Recent finds in Asia show that probably much earlier than 1.8 million years ago, early hominins left Africa. These hominins must have developed further in Asia, and may then have returned to Africa. We are not disputing that the earliest origin of man probably was in Africa, some six to seven million years ago. But we do have our doubts whether these African people with their large brain capacity started to slowly appear in Asia 1.8 million years ago. In any event, there are very good alternatives to this theory, which ought to be tested. It is quite possible that there was more two-directional traffic between Africa and Asia than the classic theory indicates. What is most important here are the 1.75 million year old finds from Dmanisi in Georgia. These are the remains of small hominins with surprisingly small brains. In an article which will shortly appear in the Journal of Human Evolution, the palaeontologist Rightmire poses the theory that these Dmanisi people represent a very primitive form of Homo erectus, and that they could well be the ancestors of the erectus of both Java and East Africa. Unfortunately, we have not been able to include his article; it is too recent, but it fully supports our doubts.'

How does modern man fit into this situation?
Roebroeks: 'This is not part of our discussion. In our article we mention the theory, the Out of Africa 2 theory*, only as a framework text.'

Is Out of Africa 1 - the classic theory - older than the 1.75 million years of the Dmanisi man?
Roebroeks: 'At the moment, 1.75 million years is the lower limit for the Dmanisi finds. Finds from Java are estimated at 1.8 million, but could be more recent. Ten years ago, we still thought that outside Africa there was nothing dating from more than one and a half million years ago. We have so far found two locations in Asia for primitive man: Dmanisi and Java. In the whole area of some 6000 km between the two, no human fossils have been found dating from the same period. It is quite probable that as yet not enough archaeological fieldwork has been conducted.
If you want to make it clear what is the centre and what is the periphery in the evolution of mankind, you need to have comparative information. This is not available. East Africa in particular, where the various members of the Leakey family made spectacular finds at the end of the 1950s, is extremely well known. Other areas, including in Asia, have hardly been investigated. In the 1980s, Robin Dennell found stone implements in northern Pakistan which are probably more than two million years old. These never fitted in with the Out of Africa 1 theory. Asia should be as well researched as Africa. As long as this is not the case, we will have to treat this theory much more carefully. You shouldn't sell Out of Africa 1 as a truth which is written in stone, while we still know so little about the Asia of 3 to 1.5 million years ago.
In Nature of 15th December, there was a publication by English archaeologists who had found implements on the east coast of England which are probably 700 thousand years old.   That is 200 thousand years older than we had imagined. What is shocking is that these implements were discovered in deposits which had been studied for more than two centuries by hundreds of English palaeontologists, archaeologists, bone specialists and fossil hunters. England is one of the best researched parts of the world. If this kind of surprise can happen there, what more can we expect in Asia?'

How does Flores man, recently found in Indonesia and thought to have died out ten thousand years ago, fit into the hypothesis put forward by you and Dennell?
Roebroeks: 'In the first place, the findings show what potential there is for surprises in Asia.  Also, the discoverers of Flores man in the first instance wanted to present him as an Australopithecus, that is as a late descendant of one of the earliest hominins. This species would then have developed independently in the east of Asia over a period of two to three million years into the dwarf species which eventually died out more than ten thousand years ago. There are few palaeontologists who would support such a scenario. Flores in any event indicates that there is still a great deal yet to be discovered.'

What sort of reaction do you expect to get from your colleagues?
Roebroeks: 'Undoubtedly very mixed. Robin Dennell and I are archaeologists who dare to touch upon the field of human palaeontology and then even go as far as to question Out of Africa 1, one of the last great stories of our discipline. That's asking for trouble. Science should primarily study what can be observed, not what is possible. But in Out of Africa 1 both concepts have for years been mixed: observed means that we have many very old fossils from Africa, and it is therefore possible that Africa was the core area for the evolution of mankind. But this popular scenario is no longer valid. As long as the information from both continents is not comparable in terms of research intensity, we have to be careful with our conclusions. One of the referees of our article put it very succinctly. He advised to publish our article as a much needed reflection on the state of affairs in this specialist field: "() since whether it is 'right' or not, is a less important issue than whether it is raising the right questions".'  

Resource: Wood, B. A., and M. C. Collard. 1999. The human genus. Science 284:65-71.

* With the Out of Africa 2 theory, it is a question of the origin of modern man.  According to this theory, all modern species of man originate from one ancestor who lived in East Africa 200 thousand years ago.

(21 December 2005)