A discussion about human races has broken out in the comments to The Problem of Race .... Again. One of quesitions on that thread has come up many times in the past so I'm devoting a separate posting to the answer.
Hopefully, this will stimulate discussion and debate about the scientific data and evidence for genetically distinct humans populations. I want to get away from the other aspects of the debate about races since they always seem to devolve into accusations of racism and/or political correctness. (mea culpa)
i always feel in these discussions people are talking past each other, especially when they have differing definitions of words like 'race'. so to clarify matters for me, i would like Dr. Moran to give the likely number of races that currently exist, say something on the stability of such groupings,give examples (if possible) of these racial groupings along with their differing genetic markers e.g. race 1 - geographically located in region A & B, with unique (almost Unique) gene combination 1,3,4,5 occuring at frequencies A,B,C,E.Are you serious? Please tell me this is a joke.
Are you one of those people who want to deny the existence of races just because your question can't be answered precisely in the manner you phrase it? That sounds very much like the kind of thinking I encounter when dealing with creationists.
Biology is messy. There are no nice and tidy boundaries around terms like race, species, or even higher taxonomic levels. You may not like it but you have to deal with it. If you understand evolution then it all makes sense and you know why things are so messy.
Our species is subdivided into many different genetically isolated(1) populations ranging from very small ones, such as the residents of Tristan da Cunha, to very large ones, such as Africans and Asians.
The term "race" usually refers to the largest populations within a species. In the case of humans, the group who migrated out of Africa founded a genetically isolated population that subsequently split into several different populations. The main ones are Asian, European, Australian, and American.
These are reasonable examples of races. Each of them can be subdivided into numerous examples of demes and populations. Their genetic distinctiveness is so obvious that most of us would have no difficulty identifying their members if we encounter them on the streets of a major cosmopolitan city.(2)
The African group from which the migrants split is "polyphyletic" and deciding how to divide it into races is problematic. However, it's clearly a group that's genetically distinct from the other races so it's not unreasonable to refer to the Africans as a race, as long as you keep in mind that there are subdivisions and that this group is much more genetically divers than the others.
The genetic distinctiveness of Africans is pretty obvious to me. I'm constantly surprised by those who pretend it doesn't exist. People of African ancestry certainly don't have any trouble recognizing that I'm Caucasian and that some of my other neighbors are Asian.
There are dozens of phylogenetic trees on the web showing these major splits and subdivisions. Probably the most famous is the mitochondrial tree but others show roughly the same tree. It would be hard to imagine anyone denying the existence of human races unless they completely reject that kind of analysis.
There are several commercial, for-profit, companies that are more than willing to take your money (and your DNA) and provide you with an analysis that identifies where your ancestors came from. They are able to do this because certain haplotypes evolved in certain parts of the world. The mitochondrial haplotypes are shown on the map above and the Y-chromosome haplotypes are shown on the map on the left.
Given all the publicity about tracing your genealogy by haplotyes and all the scientific papers on the genetic differences between races, it surprises me that in 2009 there are still people who question whether these genetic differences even exist.
1. "Genetically isolated" does not mean that there's no genes flow between populations. It means restricted gene flow. If gene flow was zero they the populations wouldn't be populations. They would be species.
2. This does not mean that there won't be examples where the identification is difficult and it doesn't deny the existence of interbreeding between races. If you're looking for that kind of example then you won't find it in humans or in any other species where the biological term race is commonly used.
[Photo Credit: Downtown Toronto]