In the blood: the myth and reality of genetic markers of identity

The differences between copies of the human genome are very small, but tend to cluster in different populations. So, despite the fact that low inter-population differentiation does not support a biological definition of races statistical methods are nonetheless claimed to be able to predict successfully the population of origin of a DNA sample. Such methods are employed in commercial genetic ancestry tests, and particular genetic signatures, often in the male-specific Y-chromosome or maternally-inherited mitochondrial DNA, have become widely identified with particular ancestral or existing groups, such as Vikings, Jews, or Zulus. Here, we provide a primer on genetics, and describe how genetic markers have become associated with particular groups. We describe the conflict between population genetics and individual-based genetics and the pitfalls of over-simplistic genetic interpretations, arguing that although the tests themselves are reliable, the interpretations are unreliable and strongly influenced by cultural and other social forces