Many important activities, such as charitable
giving, voting, and paying taxes, are difficult to
explain by the narrow self-interest hypothesis.
In a large number of laboratory experiments, the
self-interest hypothesis was rejected with respect
to contributions to public goods (e.g.,
John O. Ledyard, 1995). Recent theories on
pro-social behavior focus on “conditional cooperation”:
people are assumed to be more willing
to contribute when others contribute. This behavior
may be due to various motivational reasons,
such as conformity, social norms, or
reciprocity. According to the theory of conditional
cooperation, higher contribution rates are
observed when information is provided that
many others contribute. This prediction is not
trivial: if people behave according to pure altruism
theories (e.g., Charles Clotfelter, 1997),
they reduce their own contribution when informed
that others are already contributing.