Two major hypotheses on the evolution of modern humans

This hypotheses states that modern Homo sapiens evolved simultaneously from Homo erectus and archaic Homo sapiens in different regions around the world. In Europe, they evolved from Neanderthals. And in Asia, from archaic Homo sapiens who were the descendants of Peking Man and Java Man.

The scenario that is the complete opposite to this theory is the "Out of Africa" hypotheses that states Modern Homo sapiens had evolved in Africa and then spread throughout the world and totally replaced Homo erectus and archaic Homo sapiens. And this hypothesis would successfully explain the fact that modern Homo sapiens had lived for millenia in the area near Levanto situated on the northern part of "Africa where the evolution towards modern Homo sapiens first took place."

Furthermore, recent research on mitochondrial DNA shows that the origin for all modern humans lies in Africa. This theory, called Mitochondrial theory became the key evidence for "Out of Africa" hypotheses.

Recently, DNA analysis of ancient people is becoming a trend, but the DNA used in general is not the nuclear DNA that relates to human heredity but mitochondrial DNA. Inside each cell of animals is the energy-producing organelles called mitochondria. It is thought that these mitochondria was originally an independent life form that became an energy-producing organelle by way of symbiosis after being taken in by the animal's cell. Therefore, mitochondria hold their own DNA.

The difference between this mitochondrial DNA and nuclear DNA is that while nuclear DNA inherits its genetic information from parents and randomly changes on every reproduction, mitochondrial DNA is maternally inherited and therefore no change would occur. The only time changes occur in mitochondria DNA is mutation.

So while nuclear DNA experiences changes every time parents unite and also through mutation, mitochondrial DNA experience it only through mutation. Since mutations are thought to occur at a constant rate, it works as a molecular clock if we follow through its changes for a span of long time.

Moreover, since the rate of mutation is much higher in mitochondrial DNA than in nuclear DNA, we can calculate the time each groupings separated by measuring the changes in mitochondrial DNA of each groupings.

Based on this method, comparisons of each modern population were made. And it indicated that modern humans could be traced back some 150,000 to 200,000 years ago to a particular group in Africa.

And what made "Out of Africa" hypotheses decisively strong is the success in extracting the mitochondrial DNA of the Neanderthals. Several DNA researches indicated that modern humans, Europeans in particular, have no genetic linkage with the Neanderthals.

Does this mean that all modern humans are of African origin? So now, let's return to the Aborigines.

Translated by Rie Ishida