  It has been an old unsolved puzzle to evolutionary theorists on which
mechanisms would increase large-scale cooperation in human societies. Thus, how
such mechanisms operate in a biological network is still not very understood.
This study addresses these questions with empirical evidence from agent-based
models designed to understand these network interactions. Repeated Prisoner's
Dilemma games were designed to study how costly punishment, diversity, and
density of connectivity interact to influence cooperation in a biological
network. There are 1000 rounds in each game made up of 18 players engaged in
pairwise relationship with their neighbors. This study shows three important
interactions. (1) Introducing diversity to costly punishment favors both
cooperation and defection, but not vice versa. Introducing costly punishment to
diversity disfavors defection but favors cooperation. (2) Costly Punishment,
alone, disfavors defection but decreases average payoff. Decreasing the density
of connectivity, Dc, when there is no costly punishment applied, increases
average payoff. (3) A synergy of diversity and decreasing density of
connectivity favors cooperation in a biological network. Furthermore, this
study also suggests a likelihood from empirical findings that spatial
structures may not be favoring cooperation, as is the widely-accepted notion,
but rather disfavoring defection in the global scale.
