  This paper compares the population of BBH mergers detected by LIGO/Virgo with
selected long GRB world models convolved with a delay function (LGRBs are used
as a tracer of stellar mass BH formation). The comparison involves the redshift
distribution and the fraction of LGRBs required to produce the local rate of
BBH mergers.
  We find that BBH mergers and LGRBs cannot have the same formation history,
unless BBHs mergers have a long coalescence time of several Gyr. This would
imply that BHs born during the peak of long GRB formation at redshift z~2-3
merge within the horizon of current GW interferometers. We also show that LGRBs
are more numerous than BBH mergers, so that most of them do not end their lives
in BBH mergers.
  We interpret these results as an indication that BBH mergers and LGRBs
constitute two distinct populations of stellar mass BHs, with LGRBs being more
frequent than BBH mergers. We speculate that the descendants of LGRBs may
resemble galactic High-Mass X-Ray Binaries more than BBH mergers. We finally
discuss the possible existence of a sub-population of fast-spinning LGRBs
descendants among BBH mergers, showing that this population, if it exists, is
expected to become dominant beyond redshift z ~ 1, leading to a change in the
observed properties of BBH mergers.
