People seek wealthy partners for upward mobility, while the wealthy benefit from the cooperation of those around them, reinforcing resource advantages. This research examines how exchange networks and cooperation co-evolve, focusing on when network partners influence cooperation and whether people choose partners based on wealth or cooperation homophily.

We collected data from 1,080 participants via Prolific, assigning them to 40 randomly generated networks of ~28 players. Participants engaged in repeated interactions where they decided how much to cooperate with network alters. Networks varied by (1) whether players started with equal endowments and (2) whether cooperation from wealthier partners had a productive effect. A stochastic actor-based model estimated both network formation and changes in cooperation levels.

Cooperation increases faster in networks with resource inequality and wealth productivity, suggesting inequality promotes cooperation. Regarding network formation, we find a wealth heterophily tendency—poorer players prefer ties with wealthier players over other poorer individuals, regardless of endowment equality. Further, in unequal endowment conditions, players move in the opposite direction of their alters’ cooperation levels. They are less likely to cooperate when many alters have high cooperation rates, suggesting resistance against defection.

Networks amplify inequality, as individual disadvantages and network effects accumulate. While cooperation is generally valued, this study highlights its potential downsides in stratified resource environments, where prosocial behaviors benefit actors unequally.