The AIDS virus made its nest in humans long before it was identified in the West in the early 1980s. The latest advances in research conducted by African and Western teams have just dated the origin of the deadliest epidemic of modern times to the beginning of the 20th century. Brought to light by exemplary cooperation between doctors, virologists, anthropologists, historians and geographers brought together by the Research Institute for Development, it was located in the extreme south-east of Cameroon. A single exchange of blood between a chimpanzee and a man opened the doors to an unprecedented health tragedy.