Modern human beings evolved in Africa from archaic humans at least 200,000 years ago. Specifically, the roots of all living humans currently date back to a common ancestral population that lived in Africa.
According to calculations, all those ancestral humans added up 14,000 individuals from sub-Saharan Africa, and the population that gave rise to all non-African humans probably counted with less than 3,000 individuals: that fraction of humans dispersed outside the continent 100,000 to 80,000 years ago.
We are all alike
To establish the time and place of origin of our species we use genetic studies in many different people. By comparing genetic variation among humans around the world, geneticists can calculate a family tree of our degrees of kinship. In that sense, we are all amazingly similar.
In fact, we are a genetically very homogeneous species, as explained by the professor of evolutionary biology at Harvard Daniel E. Lieberman in his book The history of the human body:
If we catalog all the genetic variations that exist in the whole of our species, we will find that approximately 86 percent are found in any of the populations. To put this fact in perspective, if we eliminate the population of the whole world less, say, Fiji or Lithuania, we would still retain almost all human genetic variations. This pattern contrasts powerfully with what happens in other apes, such as chimpanzees, in which within any given population there is less than 40 percent of the total genetic variation of the species.