  According to Thomas Hobbes' Leviathan [1651; 2008 (Touchstone, New York),
English Ed], "the life of man [is] solitary, poor, nasty, brutish, and short,"
and it would need powerful social institutions to establish social order. In
reality, however, social cooperation can also arise spontaneously, based on
local interactions rather than centralized control. The self-organization of
cooperative behavior is particularly puzzling for social dilemmas related to
sharing natural resources or creating common goods. Such situations are often
described by the prisoner's dilemma. Here, we report the sudden outbreak of
predominant cooperation in a noisy world dominated by selfishness and
defection, when individuals imitate superior strategies and show success-driven
migration. In our model, individuals are unrelated, and do not inherit
behavioral traits. They defect or cooperate selfishly when the opportunity
arises, and they do not know how often they will interact or have interacted
with someone else. Moreover, our individuals have no reputation mechanism to
form friendship networks, nor do they have the option of voluntary interaction
or costly punishment. Therefore, the outbreak of prevailing cooperation, when
directed motion is integrated in a game-theoretical model, is remarkable,
particularly when random strategy mutations and random relocations challenge
the formation and survival of cooperative clusters. Our results suggest that
mobility is significant for the evolution of social order, and essential for
its stabilization and maintenance.
