Impact of inbreeding on scientific productivity: A case study of a Japanese university department

Recent science policies emphasize academic mobility and denounce inbreeding as an impediment to scientific productivity. This study aims to investigate the impact of inbreeding on productivity, distinguishing various forms of inbreeding, and to explore the mechanism behind which inbreeding is translated into productivity, drawing on in-depth longitudinal data of academics' careers in a university department in Japan. The results suggest that the effect of inbreeding on productivity differs with the organizational levels (university, department, and laboratory) with which inbreeding is defined, as well as with past affiliation to other institutions (purely inbred vs. silver-corded). A negative effect on productivity is indicated for inbreeding that occurs at the department level, which seems to be partly explained by non-merit-based employment criteria. The results also suggest that laboratories consisting of higher rates of their own graduates yield lower productivity. Finally, inbred academics tend to change research subjects less frequently over their career, implying that inbreeding may cause risk-averseness and deter creativity.