  The properties of Mg II absorption-selected systems show a large variety of
kinematics and higher ionization conditions. A multivariate taxonomic study of
Mg II absorbers has yielded an "extreme" class of "Double" systems. These
Double systems are characterized by kinematic velocity spreads up to 400 km/s,
and by twice the Ly alpha, Mg II, Fe II, and C IV absorption strengths of the
more typical, "Classic", Mg II system. Evolution in the number per unit
redshift of these systems is compared to the redshift evolution in the number
of close pairs of galaxies. It is found to be a plausible scenario that Double
systems arise in small groups of galaxies, implying that they might trace close
pair evolution to high redshifts.
