be sufficiently potent to influence helpers’ efforts on behalf of the
larger groups to which beneficiaries belong. This evidence dovetails
with research demonstrating spillover effects of grateful feelings,
which encourage individuals to engage in upstream reciprocity
by “paying forward” help to other beneficiaries (Bartlett &
DeSteno, 2006). Our findings complement this line of research by
demonstrating that expressions of gratitude, not only experiences
of gratitude, have spillover effects on prosocial behavior. As such,
our research suggests that gratitude expressions may have important
theoretical and practical implications for encouraging prosocial
behaviors that promote cooperation (see also Nowak & Roch,
2007)