  We present deep wide-field K-band observations of six Hyperluminous Infrared
Galaxies (HLIRGs) spanning a redshift range 0.44<z<1.55. The sample resides in
a wide variety of environments, from the field to Abell 2 clusters, with a mean
galaxy-HLIRG clustering amplitude of B_gh=190+/-45. The range in environments,
and the mean clustering level, are both greater than those seen in local
IR-luminous galaxies, from which we infer that the range of galaxy evolution
processes driving IR-luminous galaxy evolution at z>0.5 is greater than
locally, and includes mergers between gas-rich spiral galaxies in the field,
but also includes encounters in clusters and hierarchical buildup. The
similarity in the range of environments and mean clustering amplitude between
our sample and QSOs over a similar redshift range is consistent with the
interpretation where evolutionary connections between IR-luminous galaxies and
QSOs are stronger at z>0.5 than locally, and that, at these redshifts, the
processes that drive QSO evolution are similar to those that drive IR-luminous
galaxy evolution. From comparison of the HLIRG and QSO host galaxies we further
postulate that a larger fraction of IR-luminous galaxies pass through an
optical QSO stage at z>0.5 than locally.
