Recently, it has been suggested that the metallicity aversion of long-duration gamma-ray
bursts (LGRBs) is not intrinsic to their formation, but rather a consequence of the
anti-correlation between star-formation and metallicity seen in the general galaxy
population. To investigate this proposal, we compare the metallicity of the hosts of
LGRBs, broad-lined Type Ic (Ic-bl) supernovae (SNe), and Type II SNe to each other and to
the metallicity distribution of star-forming galaxies using the SDSS to represent galaxies
in the local universe and the TKRS for galaxies at intermediate redshifts. The differing
metallicity distributions of the LGRB hosts and the star-formation in local galaxies
forces us to conclude that the low-metallicity preference of LGRBs is not primarily driven
by the anti-correlation between star-formation and metallicity, but rather must be
overwhelmingly due to the astrophysics of the LGRBs themselves. Three quarters of our LGRB
sample are found at metallicities below 12+log(O/H) < 8.6, while
less than a tenth of local star-formation is at similarly low metallicities. However, our
SN samples are statistically consistent with the metallicity distribution of the general
galaxy population. Using the TKRS population of galaxies, we are able to exclude the
possibility that the LGRB host metallicity aversion is caused by the decrease in galaxy
metallicity with redshift. The presence of the strong metallicity difference between LGRBs
and Ic-bl SNe largely eliminates the possibility that the observed LGRB metallicity bias
is a byproduct of a difference in the initial mass functions of the galaxy populations.
Rather, metallicity below half-solar must be a fundamental component of the evolutionary
process that separates LGRBs from the vast majority of Ic-bl SNe and from the bulk of
local star-formation.