  Weber examines how the investigation of several particular Drosophila genes changed as the science of genetics developed. His study shows that the methods of molecular genetics provided new ways to identify genes that were first identified by classical techniques. The reference of the term changed, not simply as a result of theoretical developments, but also as a result of the implementation of new methods to identify genes. He concludes that unlike concepts of physical science that have been analyzed by philosophers, the gene concept has a “nonessentialistic character that allows biologists to lay down different natural classifications, depending on the investigative methods available as well as on theoretical interests” (Weber 2005, p. 228). Weber calls this feature “floating references”.