A recent piece of mine, Another Reason Races Don't Exist, has generated considerable interest, so I thought I'd continue on the same topic. As before, I'll begin by pointing out the difference between what might be called social race--that is, using the term race to classify people by what they look like, or by their ancestry, or according to some other sociocultural criteria--and biological race. Obviously, if unfortunately, social races exist--though racial systems of classification differ from one culture to another--and form the basis for unequal treatment of differently categorized groups
There are many reasons that there has been, for about a half-century, a consensus among specialists--biological anthropologists and evolutionary biologists--that biological races do not exist in the human species. The scientific consensus stems from overwhelming and convergent evidence from genetics and archaeology documenting the actual history of the human species.
Anatomically modern humans originated in East Africa about 200,000 years ago, having diverged from earlier forms. Their initially small numbers grew over time, but were reduced to near extinction about 70,000 years ago, perhaps as the result of a global climatic catastrophe following the eruption of the Toba supervolcano in Indonesia. At that relatively recent date in human evolution, the great bulk of whatever genetic variability had developed by then was wiped out.
While new research is constantly revising the dates for the first human migrations out of Africa, it does appear that it was not until after that catastrophe that the first humans left for Eurasia, taking with them much less genetic variability than the reduced amount then extant in Africa. Thus, African populations contain 200,000 years of human genetic variability, while Eurasians, with less variability to start with, have had less than a third of that time for it to increase.
About 15,000 years ago during an ice age, much of the Earth's water was in the form of ice, leaving ocean levels substantially lower. As a result, there was a land bridge where the Bering Strait now separates Alaska from Siberia. A small number of humans crossed it into the New World. They brought with them a small proportion of the limited genetic variability that then existed in Eurasia.
Thus, instead of the supposed existence of different races on different continents, we see that there are actually three regions of differing genetic variability. The great majority of human genetic variability is in Africa, where we have been evolving for 200,000 years. There is some genetic variability in Eurasia, where we have been evolving for less than 70,000 years. And there is relatively little genetic variability in indigenous populations of the New World, where we have been evolving for about 15,000 years.
If the human species did have biological races, they would all be in Africa. It is easy to see biological variability in Africa--for example, the Mbuti pygmies are very short and the Masai are very tall. Despite these obvious differences, Americans classify them both as belonging to the same "race" because they have dark skins. This is an illustration of the way "race" is cultural classification masquerading as a biological one.
However, as the above discussion indicates, there just isn't enough variability among humans to produce biological races. And that is the main reason races don't exist.
A schematic showing the spreading of humans in history (2009)
Check out my most recent book, The Myth of Race, which debunks common misconceptions, as well as my other books at http://amazon.com/Jefferson-M.-Fish/e/B001H6NFUI
Visit my website: www.jeffersonfish.com