  Large parts of professional human communication proceed in a request-reply
fashion, whereby requests contain specifics of the information desired while
replies can deliver the required information. However, time limitations often
force individuals to prioritize some while neglecting others. This dilemma will
inevitably force individuals into defecting against some communication partners
to give attention to others. Furthermore, communication entirely breaks down
when individuals act purely egoistically as replies would never be issued and
quest for desired information would always be prioritized. Here we present an
experiment, termed "The expert game", where a number of individuals communicate
with one-another through an electronic messaging system. By imposing a strict
limit on the number of sent messages, individuals were required to decide
between requesting information that is beneficial for themselves or helping
others by replying to their requests. In the experiment, individuals were
assigned the task to find the expert on a specific topic and receive a reply
from that expert. Tasks and expertise of each player were periodically
re-assigned to randomize the required interactions. Resisting this
randomization, a non-random network of cooperative communication between
individuals formed. We use a simple Bayesian inference algorithm to model each
player's trust in the cooperativity of others with good experimental agreement.
Our results suggest that human communication in groups of individuals is
strategic and favors cooperation with trusted parties at the cost of defection
against others. To establish and maintain trusted links a significant fraction
of time-resources is allocated, even in situations where the information
transmitted is negligible.
