Quasars appear to all reside in host galaxies and so may represent an early phase of galaxy evolution.
Quasars appear to be due to material from a large star in a binary system falling onto the surface of a neutron-star companion within the same system.
All quasars appear to have been ejected from parent galaxies by catastrophic phenomena that destroyed their host galaxies.
Most quasars show evidence of being due to interacting pairs of black holes.
Quasars appear to all reside in galaxies fairly close to the Local Group and so must represent a recent phase of galaxy evolution.