One reason, according to Singer, that people are so hesitant to give is they think their kindness will not matter. This tendency to think that one can’t do very much, or to dismiss all forms of aid as useless, is what researchers call “futility thinking:” What difference can one person even make? Research indicates that money makes people more individualistic and less altruistic. In other words, as societies become wealthier, their citizens become more individualistic and depend less upon one another. Self-interest becomes the norm.

But one antidote against futility thinking is to carefully research charities and organizations—something that Singer’s $100 donation experiment allowed students to do. They were presented with four organizations, asked to research and discuss their merits, and vote on where the $100 should go. They applied the lessons they’d learned in the course: that not all donations are equal, and that some donations have a measurably more positive impact than the same amount donated elsewhere (consider, for instance, the difference between donating $2000 to an organization ranked highly by the charity evaluator GiveWell, such as the Against Malaria Foundation, which provides mosquito nets to help protect children from contracting malaria, versus the same amount of money donated to an arts museum in the United States). They learn that their money will always go much further overseas: that a very small amount of money for an American can be life-saving to someone who is desperately poor. In other words, they learn about the tenets of effective altruism: how to evaluate organizations for transparency and benefits, and figure out which forms of aid are the most cost-effective. This is information that tends to inspire more giving.

What would ultimately help people overcome their tendency to not give? “We don’t really have a good answer to that question,” Singer admitted. He did mention research that indicates that people are more influenced by emotions than by reasoning, which is why that picture of a small girl in a distant land would promote more spontaneous giving than information about African girls in general. A photograph is specific and concrete. In his book, Singer argues that global tragedies that have been filmed have attracted more contributions than those that have not, regardless of the actual amount of casualties and damage. Altruism is often, at a gut level, emotionally prompted. But when combined with an understanding of human nature and the right sort of rational information, emotions and reasoning can combine to cultivate a formidable culture of giving.

“I’ve always been inclined to give to charity,” Adam Tcharni, a junior at Princeton who took the course his freshman year, told me. But the class made him think about giving differently. He now believes that geographical borders don’t matter, that there is no difference between his obligation to the hypothetical drowning child in front of him and the dying child half a world away. As Singer calls his students’ attention to the tremendous inequality in how the world’s resources are allocated, he suggests that it’s hardly ethical to live in luxury when so many do not and that it’s unethical to fail to save a single life when so little money would be needed to do so.