It's not easy being interdisciplinary.

It is no surprise that in a world dominated by business models and bottom lines that talk of interdisciplinarity is on the rise in science, as we are increasingly encouraged to be innovative through collaboration that ‘leverages’, ‘exploits’, and ‘optimizes’ resources. If you have not already heard these words around your workplace, you probably soon will. In fact, interdisciplinarity is now being studied as a scientific phenomenon in its own right 1 as scientists and organizations struggle to figure out how to be—well, interdisciplinary. In epidemiology and health research more generally, there is also a growing sense that we need more interdisciplinarity to help produce better answers to questions about causes and cures. It seems to me that, in significant ways, epidemiology is already an interdisciplinary endeavour. This is because, first, epidemiology is practised by people from diverse disciplinary backgrounds, and, second, it is intended to be applied—towards improving individual and population health. Epidemiologists describe distributions of health states in populations, make inferences about the causes, and intervene to change those causes to improve population health. Interdisciplinarity— whether residing in an individual whose knowledge spans disciplines or multiple individuals on a team who collectively span disciplines—is neither necessary nor sufficient to produce useful epidemiology. But like it or not, we are being induced to be even more interdisciplinary. Nowhere is this more evident than in striving to understand gene–environment interaction and to figure out how such knowledge can be applied to improve individual and population health. 2 The general tendency seems to be that the need for interdisciplinarity increases as we move from description, to causal inference, to applications in interventions and policy change. The IJE is a prime example of a journal oriented toward interdisciplinary research in epidemiology. I am reliably informed that one of the editors has been accused of being a social scientist masquerading as a geneticist and as a geneticist masquerading as a social scientist—that seems like testament to interdisciplinarity. It is not surprising then that the editorial board of the IJE also spans many disciplines. And so it is common and welcome to see the influences of anthropology, medicine, sociology, economics, history, politics, genetics, mathematics, biology, and other disciplines in papers, editorials, and commentaries in the IJE. And that is what helps make the IJE such an interesting and compelling read. What makes the contributions in the IJE interdisciplinary? Is it because of the range of exposures that are included? Is it because of the use of ideas from other disciplines to broaden conceptual models, and better explain and contextualize results? Is it because of the academic qualifications of the first author or the array of disciplines represented on the author list? Is it the application of methods developed in adjacent disciplines? Is it because of the background processes by which the idea for the research was generated? I really do not know nor do I think it matters. These may all be useful hints to help us recognize interdisciplinary research when we see it. There are several examples of interdisciplinary research informing epidemiology in this issue of the IJE. For instance, Vineis and Berwick 3 apply ideas from another discipline when they bring evolutionary biology to bear on proposing a ‘Darwinian’ model of carcinogenesis. Catalano, who is an economist by training, and Bruckner use time series analysis to show that early life environmental insults reduce subsequent lifespan—an example of ‘diminished entelechy’. 4 Hoosseinpoor et al. 5