Abstract

This article examines how a molecular "solution" to an important biological problem-how is antibody diversity generated? was obtained in the 1970s. After the primarily biological clonal selection theory (CST) was accepted by 1967, immunologists developed several different contrasting theories to complete the SCST. To choose among these theories, immunology had to turn to the new molecular biology, first to nucleic acid hybridization and then to recombinant DNA technology. The research programs of Tonegawa and Leder that led to the "solution" are discussed, and some of their strategies and heuristics are broadly characterized: (1) to what extent does the new recombinant DNA technology provide what the scientists claim is "direct evidence," what does that term mean, and what are the implications of that claim for biological "realism," and (2) is this episode one of reduction, partial reduction, or explanatory extension, and what do these terms mean in the context of a successful molecular "solution" to a biological problem.