  Evolutionary synthesis models (ESM) have been extensively used to obtain the
star formation history in galaxies by means of SED fitting. Implicit in this
use of ESM is that (a) for given evolutionary parameters, the shape of the SED
is fixed whatever the size of the observed cluster (b) all regions of the
observed SED have the same weight in the fit. However, Nature does not follow
these two assumptions, as is implied by the existence of Surface Brightness
Fluctuations in galaxies and as can be shown by simple logical arguments.
