Rebecca Saxe sat down with her MIT graduate student Alicia Chen to ask a deceptively simple question: if a friend buys you coffee, do you buy the next round? Most of us would say yes. But what if your boss buys the coffee? Or your student? The answer, the researchers have now experimentally demonstrated for the first time, hinges entirely on whether the relationship is between equals.
For decades, anthropologists have observed that reciprocal generosity—the tit-for-tat exchange of favors—works differently depending on power dynamics. Yet behavioral economists, testing generosity in laboratories, consistently found that people default to turn-taking and reciprocity. The disconnect mattered, because it suggested that most experiments missed something crucial about real human life: the relationships we're actually in.
Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences at MIT, and Chen designed a series of experiments to test how social context shapes what we expect. Rather than asking strangers to play economic games, they asked study participants to read everyday stories—a friend buying coffee, a family member preparing a meal, a manager and employee exchanging favors—and predict what would happen next. Some stories involved symmetric relationships between equals; others involved asymmetric ones, where one person held more power or status.
The findings were striking. When the relationship was symmetric—friends, cousins, colleagues of equal rank—people consistently expected reciprocal generosity. But when the relationship was asymmetric, expectations shifted dramatically. If a professor had bought coffee for a student once, participants expected her to keep buying coffee. If a student had helped carry groceries for a resident advisor, participants expected that pattern to continue indefinitely. Generosity could flow up or down the hierarchy, but once the direction was set, it was expected to stay that way.
One possible explanation cuts to something deeper about human nature. Keeping track of "whose turn it is" requires mental work—constantly updating who owes whom what. In equal relationships, we do that work to maintain the illusion of equivalence. But in hierarchical relationships, following precedent is simpler. "If there's no need to keep track of our equal status, then in some ways it's the default to fall back on following precedents," Saxe says.
The study, published in the journal Open Mind, suggests that reciprocity is not the universal default but an exception—something we apply specifically to interactions between equals or strangers. Most of our relationships, by contrast, are asymmetric: parent and child, teacher and student, employer and employee. To keep those relationships stable, we don't bother tracking turns. We simply expect yesterday's pattern to repeat tomorrow.
This has quiet implications for how we navigate the world. It helps explain why certain generosity patterns feel natural in some relationships and jarring in others, and why breaking an established pattern—a boss suddenly expecting a subordinate to treat them to lunch—can feel uncomfortable. Understanding these expectations doesn't just illuminate social psychology. It suggests that fairness in relationships isn't always about equal exchange. Sometimes it's about knowing exactly what to expect, and following through.