  Low-ionization broad absorption line (BAL) QSOs present properties that
cannot generally be explained by simple orientation effects. We have conducted
a deep spectroscopic and imaging study of the host galaxies of the only four
BAL QSOs that are currently known at z < 0.4, and found that all four objects
reside in dusty, starburst or post-starburst, merging systems. The starburst
ages derived from modeling the stellar populations are in every case a few
hundred million years or younger. There is strong evidence that the ongoing
mergers triggered both the starbursts and the nuclear activity, thus indicating
that the QSOs have been recently triggered or rejuvenated. The low-ionization
BAL phenomenon then appears to be directly related to young systems, and it may
represent a short-lived stage in the early life of a large fraction of QSOs.
