Our lab has struggled to answer this question in a variety of ways. Ben Basile (2003) tested whether committing a socially synchronous act would peak sharing behavior in tamarins. Julia Greenberg (2009) trained tamarins to pull ropes to acquire reward boxes, and then tested whether they could spontaneously pull together when it was necessary for 2 monkeys to move the box together. Chris Leppink-Shands (2019) tried this more recently with a box with 3 buttons that varied the payoff — if a monkey pushed a button when a human did, they doubled their reward payoff. Lydia Henderson (2016) developed a game involving taking turns and examined whether tamarins, like human partners who were also tested, would alter their choices to match the benevolence or selfishness of their partner. And Cathy Chen (2017) tested whether tamarins would choose to be deceptive in their choices as a tactic to maximize rewards. In every case, there was evidence that the tamarins could manipulate their own behavior in consistent ways that reflect considering another’s behavior and motives.