Complex sentence: Early in his career he was an Adjunct Professor of Pharmacology at the Universidad Mayor de San Marcos (1958-1960), and a Ricker Research Fellow, at the University of Pennsylvania, Philadelphia (1960-1961).
Split into simpler sentences: Early in his career he was an Adjunct Professor of Pharmacology at the National University of San Marcos (1958-1960). He was a Ricker Research Fellow, at the University of Pennsylvania, Philadelphia (1960-1961).