  Detecting defection and alarming partners about the possible danger could be
essential to avoid being exploited. This act, however, may require a huge
individual effort from those who take this job, hence such a strategy seems to
be unfavorable. But structured populations can provide an opportunity where a
largely unselfish excluder strategy can form an effective alliance with other
cooperative strategies, hence they can sweep out defection. Interestingly, this
alliance is functioning even at the extremely high cost of exclusion where the
sole application of an exclusion strategy would be harmful otherwise. These
results may explain why the emergence of extreme selfless behavior is not
necessarily against individual selection but could be the result of an
evolutionary process.
