Comparison of closely related species is a powerful D. melanogaster. In D. melanogaster, microsatel- approach to understanding the changes that have oc- lites reveal that West African popUlations are more curred since their divergence from a common ancestor. closely related to non-African populations than to The sibling species Drosophila melanogaster and D. East African popUlations. East African populations are simulans are probably the species pair for which the more variable than West African or non-African popu- most genetic data are available. A workshop held at lations, suggesting that East African populations may 1 Gif/Yvette in January 2002 reviewed and discussed more closely reflect African ancestral variability. comparisons between these species, from their ecol- Ecophysiology, popUlation dynamics and popula- tion structure are also important to understanding the ogy and biogeography to their behavior and DNA evolution of the two species. Genetic diversity (8) polymorphism. is higher in D. simulans (S. Mousset and R. Singh).