  Cooperative behaviour constitutes a key aspect of both human society and
non-human animal systems, but explaining how cooperation evolves represents a
major scientific challenge. It is now well established that social network
structure plays a central role for the viability of cooperation. However, not
much is known about the importance of the positions of cooperators in the
networks for the evolution of cooperation. Here, we investigate how cooperation
is affected by correlations between cooperativeness and individual social
connectedness. Using simulation models, we find that the effect of correlation
between cooperativeness and connectedness (degree) depends on the social
network structure, with positive effect in standard scale-free networks and no
effect in standard Poisson networks. Furthermore, when degree assortativity is
increased such that individuals cluster with others of similar social
connectedness, we find that bridge areas between social clusters can act as
barriers to the spread of defection, leading to strong enhancement of
cooperation in particular in Poisson networks. But this effect is sensitive to
the presence of Trojan horses (defectors placed within cooperator clusters).
The study provides new knowledge about the conditions under which cooperation
may evolve and persist, and the results are also relevant to consider in regard
to human cooperation experiments.
