Following Dreyfus' advice, in 1938 he enrolled in a course of natural history at the University of São Paulo, continuing to work in biological research under his mentor.
In 1942, Pavan became involved in a pioneering research project on the genetics, taxonomy and ecology of Drosophila fruit flies, financed by the Rockefeller Foundation under the direction of the noted Russian-American biologist Theodosius Dobzhansky.