  We present a spectroscopic study of the incidence of AGN nuclear activity in
two samples of isolated galaxies (Karachentseva, V.E. & Varela, J.). Our
results show that the incidence of non-thermal nuclear activity is about 43%
and 31% for galaxies with emission lines and for the total sample 40% and 27%
respectively. For the first time we have a large number of bona-fide isolated
galaxies (513 objects), with statistically significant number of all types. We
find a clear relation between bulge mass and the incidence of nuclear activity
in the sample with emission lines. This relation becomes flatter when we take
into account the complete sample with no emission line galaxies. A large
fraction (~70%) of elliptical galaxies or early type spirals have an active
galactic nucleus and ~70% of them are LINERs. Only 3% of the AGN show the
presence of broad lines (a not a single one can be classified as type 1 AGN).
This is a remarkable result which is completely at odds with the unified model
even if we consider warped or clumpy tori. Finally, we interpret the large
fraction of AGN in isolated galaxies as the result of secular evolution of
their supermasive black holes.
