発表者：佐藤尚（橋本研D1）
タイトル：Evolution of indirect reciprocity by image scoring

アブストラクト：

Nature に掲載された Martin A. NowakとKarl Sigmund の論文を
紹介いたします。
論文のアブストラクトは以下の通りです。

Darwinian evolution has to provide an explanation for
cooperative behaviour. Theories of cooperation are
based on kin selection(dependent on genetic relatedness),
group selection and reciprocal altruism. The idea of 
reciprocal altruism usually involves direct reciprocity:
repeated encounters between the same individuals allow
for the return of an altruistic act by the recipient. Here
we present a new theoretical framework, which is based on
indirect reciprocity and does not require the same two
individuals ever to meet again. Individual selection can
nevertheless favour cooperative strategies directed 
towards recipients that have helped others in the past.
Cooperation pays because it confers the image of a valuable
community member to the cooperating individual. We
present computer simulations and analytic models that 
specify the conditions required for evolutionary stability
of indirect reciprocity. We show that the probability of 
knowing the 'image' of the recipient must exceed the 
cost-to benefit ratio of the altruistic act. We propose that
the emergence of indirect reciprocity was a decisive step
for the evolution of human societies.