Unlike most books which combine philosophy and genetics in their titles, this is not a discussion of the ethical, legal, and social implications of science. It is a contribution to the philosophy of science, the branch of epistemology (theory of knowledge) which sets out to understand how science works. The word ‘genetics’ is construed broadly to include a wide range of molecular biosciences, and the exposition of these sciences is a backdrop to our discussion of the philosophical issues of reductionism and reductive explanation, the status of theoretical entities, and the relationship between scientific representations – models – and the targets of those representations. Genetics and molecular biology have been a powerful source of philosophical insights into these issues. Recent scientific developments in this rapidly changing area hold new lessons for philosophy of biological science.

Since Aristotle philosophers and scientists have reflected on the nature of living systems and the distinctive nature of the sciences that study them. However, the emergence of the philosophy of science as a distinct academic field in the early twentieth century was marked by an almost exclusive focus on the physical sciences. When philosophers of science turned their attention to biology in the 1960s, one of the first issues to be raised was whether the new molecular biology constituted a successful reduction of earlier biological theories, and particularly earlier theories of genetics (Schaffner 1967; Schaffner 1969; Ruse 1971; Hull 1972; Hull 1974). As well as addressing general issues like reduction, philosophers of science are tasked with analysing key scientific concepts, and the concept of the gene has proved both attractive and elusive. In part this is because it is a moving target. The concept of the gene had evolved considerably in the years between the introduction of the concept at the turn of the twentieth century and the papers just cited, and it has continued to evolve during the past forty years of intense philosophical attention.