Could Homo erectus have left Africa 1.5 million years ago to populate the world?

Homo sapiens: Out of Africa



Since the time the most advanced species of man, H.sapiens, appeared and evolved, about 150 000 years ago, plus or minus several tens of thousands of years, possibly in Africa, there is evidence of rapid population growth around the globe. So how did H.sapiens spread?

It is generally accepted that Homo erectus, the forerunner to H.sapiens, left Africa about 1.5 million years ago to populate other parts of the world, there are two main theories about the spread of Homo sapiens.

The first theory, known as the 'Out of Africa' model, or mono-genesis theory, is that H.sapiens developed first in Africa and then spread around the world between 100 and 200 000 years ago, displacing and superseding all other hominid species. The implication of this is that all modern people would be of African descent.

The other theory, known as the 'Multi-regional' Model, is that H.sapiens evolved simultaneously in different parts of the world as descendants from original H.erectus and H.habilis. This means that people in China descended from the H.erectus population there (the fossil known today is the Peking man), while Australians may have descended from the H.erectus population in South East Asia.

Both theories have their staunch defenders who cite DNA evidence - analysis of the genetic blueprint passed down from generation to generation - to advance their case. Out of Africa theorists, for example, say that most genetic variation in human populations is found in Africa, suggesting that humans evolved from there for the longest period.

To further the case, I may say the mono-genesis theory does not readily explain racial differences, however minor, for example between asiatic (yellow), black and white populations. One has to imagine some genetic variation within the population of H.sapiens that appeared in Africa and from then onwards, due to the process of "one assembles with who resembles you", white, blacks and yellows developed in numbers separately and in different parts of the planet.

Conversely, the 'Multi-regional' theory does not readily explain why H.sapiens is the only modern descendant of previous species of homidids (eg. H.erectus, H.habilis, H.neanderthalis), with basically the same genetic pool, such as to allow yellows, blacks and whites to mix and produce fertile off-spring. Neither does it explain why all members of H.sapiens today share the same physiological characters, brain, language etc. If the 'Multi-regional' theory was true, it is natural selection would have to have produced the same variation in every part of the world where different species of hominids were living, separated by geography and environment of which climate.

The debate is far from concluded, but it is probably fair to say that most scientists today, support the 'Out of Africa' theory and believe that all humans share a common origin. But the two theories cannot both be true. As in all domains of human knowledge, the two theories are just representations of the human brain; paradigmes, or ways by which we explain what we see of the world we live in, in particular fossils of ancient primates and hominoids dated back in time by techniques that our brain has developed.... and also what we know of our body, with its brain and our ability to communicate by interchangeable languages, characters which are common to all men, be them yellow, black or white...

As with all paradigmes, these will change; some day in the future, a new paradigme, probably combining the two, will be developed, thanks to new knowledge and evidence being found...