This paper is an attempt to reconstruct the history of genetic and evolutionary theories of same-sex sexual behavior using Imre Lakatos’ methodology of scientific research programs . Although distinct, those two programs are complementary. Whereas the genetic program maintains that homosexuality is genetically inherited, the evolutionary program attempts to explain how such a gene, which apparently reduces the reproductive fitness of its homozygous carrier, is maintained in the population. This appraisal reveals that the two research programs have not been empirically (...) progressive in the Lakatosian sense. I argue that this situation has arisen precisely because of inappropriate over-commitment to the respective hard cores of the two research programs. As adherence to such cores is essential for success in research programs, according to Lakatos, I argue that Lakatos’ account of science may be descriptively adequate but is normatively inadequate. I provide grounds for generalizing this case as follows: the MSRP may successfully capture the logic of axiomised sciences, such as physics, but applies poorly to most sciences, including biological and social sciences, which do not lend themselves to axiomatic organization. (shrink)