The results of the field experiment do not
inform us as to which theoretical approach is
the most appropriate for explaining conditional
cooperation. Results from previous experiments
that attempt to discriminate among the
various explanations are ambiguous. Some experimental
studies indicate that conformity
can explain conditional cooperation better
than reciprocal considerations (Iris Bohnet and
Richard Zeckhauser, 2004), while others come
to the opposite conclusion (Falk et al., 2003;
Robert Kurzban et al., 2001). Yet other laboratory
experiments find evidence supporting
the third mechanism, that cooperative
behavior of others is used as an indication of the
quality of the public good (Jan Potters et al.,
2001). Future research should concentrate on
testing in the field under which conditions the
motives that lead to conditional cooperation
prevail.