  LIGO's detection of gravitational waves from binary black hole mergers was an
unexpected surprise that immediately raised the question - what is the origin
of these black hole binaries? The "simplest" scenario is evolution of field
massive stellar binaries. However, other possibilities involving capture have
been proposed. We explore here one of the more interesting clues on this
puzzle: the relatively modest spins of the resulting black holes that imply
that the progenitor black holes were not spinning rapidly. More specifically we
consider the implication of observed distribution of, $\chi_{\rm eff}$, the
mass weighted projected (along the orbital axis) spins on the field evolution
scenario. In all cases $\chi_{\rm eff}$ is small and in two of the cases the
best fit value is negative. Only in one event the spin is positive at 90\%
credible. These observations are puzzling within the field binary scenario in
which positive higher spins ($\chi_{\rm eff} \ge 0.5$) are expected. At first
sight one may expect that this rules out the field evolutionary scenario.
Indeed we show that with typical parameters a significant fraction ($\ge 25\%$)
of the mergers should have high effective spin values. However, uncertainties
in the outcome of the common envelope phase (the typical separation and whether
the stars are rotating or not) and in the late stages of massive star evolution
(the strength of the winds) make it impossible to rule out, at present, these
scenarios. While observations of mergers with high effective spin will support
this scenario, future observations of negative spin mergers would rule it out.
