1. Max Planck Research Group on Comparative Population Linguistics; MPI for Evolutionary Anthropology; Leipzig 04103 Germany.
2. Department of African Studies; Humboldt University; Berlin 10099 Germany
3. Department of Linguistics; MPI for Evolutionary Anthropology; Leipzig 04103 Germany
4. Institute of Global Studies; Tokyo University of Foreign Studies; Tokyo 183-8534 Japan
5. Department of Biological Sciences; University of Botswana; Gaborone Botswana
6. Department of Evolutionary Genetics; MPI for Evolutionary Anthropology; Leipzig 04103 Germany