We explore the hypothesis that demographic changes started in the seventeenth and eighteenth centuries are at the root of the acceleration in growth rates at the dawn of the modern age. During this period, life tables for Geneva and Venice show a decline in adult mortality; French marriage registers show an important increase in literacy; historians measure an acceleration of economic growth. We develop an endogenous growth model with a realistic survival law in which rising longevity increases the individual incentive to invest in education and foster growth. We quantitatively estimate that the observed improvements in adult mortality account for 70% of the growth acceleration in the pre-industrial age.