  We investigate the environmental dependence of stellar population properties
of galaxies in the local universe. Physical quantities related to the stellar
content of galaxies are derived from a spectral synthesis method applied to a
volume-limited sample containing more than 60 thousand galaxies extracted from
the DR4 of the SDSS. Mean stellar ages, mean stellar metallicities and stellar
masses are obtained from this method and used to characterise the stellar
populations of galaxies. The environment is defined by the projected local
galaxy density estimated from a nearest neighbour approach. We recover the star
formation--density relation in terms of the mean light-weighted stellar age,
which is strongly correlated with star formation parameters derived from \Ha.
We find that the age--density relation is distinct when we divide galaxies
according to luminosity or stellar mass. The relation is remarkable for
galaxies in all bins of luminosity. On the other hand, only for an intermediate
stellar mass interval (associated to a transition in galaxy properties) the
relation shows a change in galaxy properties with environment. Such distinct
behaviours are associated to the large stellar masses of galaxies with the same
luminosity in high-density environments. In addition, the well known star
formation--density relation results from the prevalence of massive systems in
high-density environments, independently of galaxy luminosity, with the
additional observed downsizing in galaxy formation, in which the star formation
is shifted from massive galaxies at early times to low-mass galaxies as the
universe evolves. Our results support that a natural path for galaxy evolution
proceeds via a nurture way, in the sense that galaxy evolution is accelerated
in denser environments, that took place mainly at high-redshifts.
