How the stellar mass of early-type galaxies is assembled remains an open question. Are the stars formed in situ, possibly triggered by merger events, or do they form in smaller systems before being added to the host galaxy through mergers? Using the SAURON sample of local early-type galaxies combined with dynamical modelling we searched for correlations between dynamical and stellar population parameters of early-type galaxies in order to address this question. The most striking correlation is that between the local Mgb line strength and the local gravitational potential, expressed here in terms of the local escape velocity. The Mgb-Vesc relation is extremely tight, while most significantly being the same both between different galaxies and within individual galaxies. Such a tight local and global relation can be used to constrain the amount of star formation associated with a merger event in order for a galaxy to remain on the relation. When we transform to single stellar population (SSP) parameters we find that this local and global behaviour is reproduced by the combination: log (Vesc/500 kms-1) = 0.85[Z/H] + 0.43(t/Gyrs). That a combination of age and metallicity is tightly correlated with the local Vesc is somewhat surprising, and may indicate a weakness in the SSP models or a `conspiracy’ in age and metallicity.