  Game theory research on the snowdrift game has showed that gradual evolution
of the continuously varying level of cooperation in joint enterprises can
demonstrate evolutionary merging as well as evolutionary branching. However,
little is known about the consequences of changes in diversity at the
cooperation level. In the present study I consider effects of costly rewards on
the continuous snowdrift game. I show that not evolutionary merging but
evolutionary branching can promote the emergence of pool reward, which can then
enhance social welfare.
