Abstract
Summary
Evolutionary theory provides the biological sciences, with a fundamental and
powerful model to explain the emergence of cooperative behavior. A detailed
explanation for the existence of cooperation between related individuals is provided
by the theory of kin selection. When kin cooperate the helper gives the receiver an
advantage and thereby increases the relative probability that copies of his own
genes are present in the next generations. However, one cannot explain examples of
apparent altruism through kin selection, because in these cases unrelated individuals
interact. The answer for many of these examples is provided by the theory of
reciprocal altruism, where individuals behave reciprocal by returning help to a
previous donor. By applying these two theories it is possible to explain many, but by
far not all cooperative situations. There have to be other mechanisms that lead to
cooperation and sustain already established cooperation.
In my dissertation I have tested empirically new models and predictions of
how cooperation between unrelated humans can be established. This research is
especially important because we interact in a close net of relationships, where
cooperation between unrelated individuals plays one of the main roles. Modern
human societies are impossible to imagine without cooperation between unrelated
individuals. By identifying the circumstances under which cooperation is stable
between unrelated individuals, it will be possible to understand the deciding factors in
politics, economy and in our private lives. As a consequence we would be provided
with intellectual tools to positively influence the deciding factors by alternating the
circumstances accordingly.
We are often not aware of the importance of cooperation between unrelated
partners in our daily lives. Regularly people find unconsciously cooperative solutions,
for instance when they try simultaneously to walk through a narrow door. Some
professions depend very strongly on cooperative behavior between unrelated
colleagues. To act uncooperatively in such a profession can endanger the health or
even the lives of the colleagues (e.g. firemen and firewoman). Cooperative strategies
for these kinds of situations have to have evolved and need to be evolutionary
stable, otherwise we would hardly ever find cooperative behavior in the present and
then only between related individuals. According to the evolutionary theory the
cooperative strategies found today, also have to provide an advantage to the bearer.
For a long time economists and biologists have been interested in the
emergence and sustainability of cooperative behavior. Nevertheless, only with the
introduction of game theory, a mathematical basis was established to incorporate
this behavior into biological evolutionary models. From then on it was possible to
make predictions with the help of theoretical models, about the circumstances under
which certain behavioral patterns emerge and what underlying mechanisms possibly
sustain these patterns.
In my dissertation I have empirically tested predictions of circumstances that
promote cooperative behavior between unrelated humans. The main results of my
work are the following: (i) Humans often donate money to charity. On first sight this
seems to be a disadvantageous behavioral trait. Donations to charity include costs
that reduce the direct fitness of the individual. However, it has to be beneficial to the
bearer, otherwise it would be eliminated from the population through evolutionary
processes. The study showed that there is indeed an advantage. By donating money
to charity (here to UNICEF) one builds up a good personal reputation in the own
social group. Participants that donated to UNICEF received with higher probability
help from other participants and were as well more likely to be voted the group
representative. (ii) Reputation is known to be an important currency in indirect
reciprocity games. Humans therefore should also try to establish a good reputation in
other social games, when this reputation is known in future indirect reciprocity
games. Humans are in general unable to sustain a public resource that everybody is
free to overuse anonymously. Is it possible that humans sustain a public resource if
the use of the resource is linked to the personal reputation? The experiment showed,
that the risk of loosing a good reputation by overusing the public resource actually
lead to sustaining it. Furthermore the public resource was not only sustained, but
also turned out to be surprisingly profitable to all group members. (iii) A theoretical
model supplied a new possibility to sustain a public resource and hereby make
humans act cooperatively. The strikingly simple idea was to introduce the possibility
not to participate in the public goods group and instead use a personal resource with
a low but sure payoff. The prediction was an always recurring rise to dominance, of
three strategies ((a) not to participate in the public goods group, (b) participate in the
public goods group and to cooperate within the group or (c) participate and to defect
within the group) within the population. This dynamic was expected because
whenever most members of the population choose the same strategy, one of the
other two strategies had a higher payoff. The same type as the predicted dynamic
has also been found in models of the famous children game of “rock-paper-scissors”.
The model predicted that the public resource is sustained by the ongoing dynamic,
which is liked with a recurring rise of cooperative behavior. Is it enough to supply
humans with the possibility not to participate in the public goods game to produce
such recurring rise of cooperation? The dynamic was established as predicted,
whereby the changing dominance of the three strategies with repeated cooperative
phases could be observed and the resource was on average sustained. (iv) When
humans make decisions about using a public resource, which at some times are
reputation relevant and at other times are not reputation relevant, do they use this
information strategically? In this study it was shown that, humans are aware when
their decisions are not reputation relevant and immediately reduce their cooperation
to maximize their personal profit. Once more, as soon as the decisions about using
the public resource were linked to the reputation, cooperation was much higher and
the resource was sustained. (v) In some potentially cooperative situations humans’
meet partners from outside the own social group. These “strangers” have a
reputation that they have built in another social group. Do humans put a different
value on a strangers’ reputation in comparison to the reputation of members of the
own social group? It was shown that it is not relevant if the reputation was built within
the own or in a foreign social group.
In summary we found the following: Humans behave uncooperatively, when it
is to the personal advantage. However, certain circumstances lead to cooperative
behavior in humans. Reputation building is one of the most important mechanisms in
this context, which enables us to cooperate even with not related strangers. However
humans consciously make strategic use of situations where they do not harm their
reputation by behaving uncooperatively. Nevertheless, even in completely
anonymous situations it is possible to create circumstances, like introducing optional
participation in the public goods situations, which promote cooperative behavior in
humans.
