Genomics and human diversity

Abstract

The sequencing of the human genome (2003) has been followed by a number of technical developments that allow detailed characterization (including complete sequencing) of the DNA of thousands of individuals. This has provided an estimate of human genetic diversity: approx. 3 million base substitutions within our genome that includes 3,000 million bases. Although the divergence between any two individuals is small, it is responsible for much of the phenotypic diversity observed within the human population, and current techniques make it possible to measure genetic distances between any two individuals whose genome has been analysed. When results from a large sample of persons are analysed by sophisticated multi-dimensional representation, fairly distinct clusters appear in the population, indicating groups of individuals that are more similar to each other than to persons from other groups. Although these groups are defined by genome analysis, without any a priori information on their origin, it turns out that they largely correspond to so-called “ethnic” categories that reflect genetic ancestry (e.g. Europeans, Africans and Asians). Every group is internally quite diverse, but analysis of thousands of genetic markers does indeed differentiate between them. “Race”, as commonly defined, is a very imperfect proxy for these ancestry groups, as it suggests high homogeneity within each group, implies assumptions about behaviour and “character” that have no scientific basis, and is heavily tainted by past uses in support of oppression and even genocide. Thus “ancestry” or “ancestry group” is a highly preferable term, especially now that more and more people are of mixed ancestry. These methods have been widely applied to current populations and to “ancient DNA” from historical samples, and have made possible great strides in understanding the history of our species.