To export ivory and rubber from what is now Cameroon, traders created routes that enabled the first cases of HIV to reach large population centers. This photograph is from a collection by Alice Seeley Harris and her husband, John Harris, who were missionaries in the Belgian Congo at the turn of the century. They documented the horrific abuses of the indigenous people of the Congo by Belgian King Leopold II's regime. Anti-Slavery International/PANOS
We are unlikely to ever know all the details of the birth of the AIDS epidemic. But a series of recent genetic discoveries have shed new light on it, starting with the moment when a connection from chimp to human changed the course of history.