  The Calar Alto Legacy Integral Field Area (CALIFA) is an ongoing 3D
spectroscopic survey of 600 nearby galaxies of all kinds. This pioneer survey
is providing valuable clues on how galaxies form and evolve. Processed through
spectral synthesis techniques, CALIFA datacubes allow us to, for the first
time, spatially resolve the star formation history of galaxies spread across
the color-magnitude diagram. The richness of this approach is already evident
from the results obtained for the first 107 galaxies. Here we show how the
different galactic spatial sub-components ("bulge" and "disk") grow their
stellar mass over time. We explore the results stacking galaxies in mass bins,
finding that, except at the lowest masses, galaxies grow inside-out, and that
the growth rate depends on a galaxy's mass. The growth rate of inner and outer
regions differ maximally at intermediate masses. We also find a good
correlation between the age radial gradient and the stellar mass density,
suggesting that the local density is a main driver of galaxy evolution.
