  Trust and trustworthiness form the basis for continued social and economic
interactions, and they are also fundamental for cooperation, fairness, honesty,
and indeed for many other forms of prosocial and moral behavior. However, trust
entails risks, and building a trustworthy reputation requires effort. So how
did trust and trustworthiness evolve, and under which conditions do they
thrive? To find answers, we operationalize trust and trustworthiness using the
trust game with the trustor's investment and the trustee's return of the
investment as the two key parameters. We study this game on different networks,
including the complete network, random and scale-free networks, and in the
well-mixed limit. We show that in all but one case the network structure has
little effect on the evolution of trust and trustworthiness. Specifically, for
well-mixed populations, lattices, random and scale-free networks, we find that
trust never evolves, while trustworthiness evolves with some probability
depending on the game parameters and the updating dynamics. Only for the
scale-free network with degree non-normalized dynamics, we find parameter
values for which trust evolves but trustworthiness does not, as well as values
for which both trust and trustworthiness evolve. We conclude with a discussion
about mechanisms that could lead to the evolution of trust and outline
directions for future work.
