The effects of population growth on long-term economic development are obviously important. This paper introduces new predictions from a general Malthus-Boserup model of population growth and ideas-based technological change. It also tests these predictions using numerous data sources, empirical specifications, and sample periods. Time series tests reveal that the empirical associations that hold true in the modern era are completely reversed in pre-modern samples. Inferences drawn from the pre-modern population growth of geographically isolated populations are also reversed when relevant controls are taken into account. While there is a clear break with Malthusian theory, in general, and especially outside of the modern era, there is no unequivocal evidence supporting Boserupian views. An alternative model consistent with transitional demographic patterns is briefly discussed.