  We explore the effect of AGN activity on the star formation history of
galaxies by analysing the stellar population properties of ten pairs of nearby
twin galaxies -- selected as being visually similar except for the presence of
an AGN. The selection of such twin samples represents a method to study AGN
feedback, as recently proposed by del Moral Castro et al. We use integral field
unit (IFU) data from CALIFA, stacked within three fixed apertures. AGN galaxies
in a twin pair suggest more evolved stellar populations than their non-AGN
counterpart 90% of the time, regardless of aperture size. A comparison with a
large sample from SDSS confirms that most twins are representative of the
general population, but in each twin the differences between twin members is
significant. A set of targeted line strengths reveal the AGN member of a twin
pair is older and more metal rich than the non-AGN galaxy, suggesting AGN
galaxies in our sample may either have an earlier formation time or follow a
different star formation and chemical enrichment history. These results are
discussed within two simple, contrasting hypotheses for the role played by AGN
in galaxy evolution, which can be tested in the future at a greater detail with
the use of larger data sets.
