One of the most surprising, and perhaps confounding, facts of charity in America is that the people who can least afford to give are the ones who donate the greatest percentage of their income. In 2011, the wealthiest Americans—those with earnings in the top 20 percent—contributed on average 1.3 percent of their income to charity. By comparison, Americans at the base of the income pyramid—those in the bottom 20 percent—donated 3.2 percent of their income. The relative generosity of lower-income Americans is accentuated by the fact that, unlike middle-class and wealthy donors, most of them cannot take advantage of the charitable tax deduction, because they do not itemize deductions on their income-tax returns.

But why? Lower-income Americans are presumably no more intrinsically generous (or “prosocial,” as the sociologists say) than anyone else. However, some experts have speculated that the wealthy may be less generous—that the personal drive to accumulate wealth may be inconsistent with the idea of communal support. Last year, Paul Piff, a psychologist at UC Berkeley, published research that correlated wealth with an increase in unethical behavior: “While having money doesn’t necessarily make anybody anything,” Piff later told New York magazine, “the rich are way more likely to prioritize their own self-interests above the interests of other people.” They are, he continued, “more likely to exhibit characteristics that we would stereotypically associate with, say, assholes.” Colorful statements aside, Piff’s research on the giving habits of different social classes—while not directly refuting the asshole theory—suggests that other, more complex factors are at work. In a series of controlled experiments, lower-income people and people who identified themselves as being on a relatively low social rung were consistently more generous with limited goods than upper-class participants were. Notably, though, when both groups were exposed to a sympathy-eliciting video on child poverty, the compassion of the wealthier group began to rise, and the groups’ willingness to help others became almost identical.