Most view academic inbreeding as detrimental to academic careers. We argue that the effects of inbreeding on individual careers depend on the stage of the lifecycle of local research programs at universities. We propose a new ‘genealogical’ view whereby scientists are considered ‘inbred’ if their PhD was supervised by a professor who holds a PhD from the same university and within the same discipline. We can then measure ‘genealogical academic inbreeding’ by reconstructing the number of generations of inbreds preceding an individual scholar at the time of PhD training. We test the effect of inbreeding on seven academic performance indicators for 473 scientists at Dutch universities during the period 1815–1943. We further investigate the main local research programs across disciplines and universities in The Netherlands using historical sources. Our analysis provides evidence that inbreeding generally enhances academic performance, but only in the early lifecycle stages of a new intellectual movement.