It is generally accepted that there are six major groups of living primates: (1) lemurs (including all the primates of Madagascar), (2) lorises (including galago and potto), (3) tarsiers, (4) New World monkeys, (5) Old World monkeys and (6) apes (including man). Tree shrews, once considered to be primates, are now generally recognized as not significantly more closely related to the six groups than other mammals. The first surviving primate lines to diverge from the common primate ancestor are believed to have given rise to one or more of the first three groups. However, the fossil record is insufficient to determine their relative branching order. Furthermore, neither morphological considerations nor studies of protein evolution produce unanimity as to whether tarsiers are more closely related to the prosimians (the lemurs plus lorises) or the simians (the monkeys and apes). In an attempt to resolve these discrepancies, we have measured the DNA sequence difference between several primates. We report here that the evolution of DNA of primates from Madagascar is significantly less than that of all other groups of living primates. This is not expected in the simplest form of the theory of neutral selection and may be important for our understanding of evolution at the molecular level.