Mitochondrial DNA sequences from 74 Swiss individuals were compared to sequences from British and Finish populations. We found that the nucleotide sequence differences between these populations are almost as low as those within the populations. This is in contrast to three African populations, which display substantial differences between each other. The homogeneity of the mitochondrial gene pool in Europe suggests a recent common ancestry for European populations. This may reflect the arrival of anatomically modern humans about 40,000-30,000 years ago or, alternatively, the spread of agriculturalists about 10,000-6,000 years ago. Taking into account the estimated rate of evolution of the mitochondrial control region, the data favor the former explanation.