In early 1959, the geneticist Arno Motulsky collected blood from people in several regions of the Belgian Congo for a study of inherited blood traits, and the samples were flown to Seattle and stored. One of them came from an adult Bantu man living in Léopoldville, now Kinshasa. Nothing more is recorded about him, and decades later researchers still could not say whether he had ever been ill.

The serum bank was tested for HIV once a test existed. In 1986, André Nahmias of Emory University in Atlanta reported in The Lancet that one plasma sample from the Léopoldville group, labeled L70, carried antibodies to HIV. The claim was met with skepticism, in part because the sample was not made available for further study.

In February 1998, Tuofu Zhu and David Ho of the Aaron Diamond AIDS Research Center in New York, working with Nahmias and others, published An African HIV-1 Sequence from 1959 and Implications for the Origin of the Epidemic in Nature,…