People mislead themselves all day long. We tell ourselves we’re smarter and better looking than our friends, that our political party can do no wrong, that we’re too busy to help a colleague. In 1976, in the foreword to Richard Dawkins’s The Selfish Gene, the biologist Robert Trivers floated a novel explanation for such self-serving biases: We dupe ourselves in order to deceive others, creating social advantage. Now after four decades Trivers and his colleagues have published the first research supporting his idea.

Psychologists have identified several ways of fooling ourselves: biased information-gathering, biased reasoning and biased recollections. The new work, forthcoming in the Journal of Economic Psychology, focuses on the first—the way we seek information that supports what we want to believe and avoid that which does not.

In one experiment Trivers and his team asked 306 online participants to write a persuasive speech about a fictional man named Mark. They were told they would receive a bonus depending on how effective it was. Some were told to present Mark as likable, others were instructed to depict him as unlikable, the remaining subjects were directed to convey whatever impression they formed. To gather information about Mark, the participants watched a series of short videos, which they could stop observing at any intermission. For some viewers, most of the early videos presented Mark in a good light (recycling, returning a wallet), and they grew gradually darker (catcalling, punching a friend). For others, the videos went from dark to light.

When incentivized to present Mark as likable, people who watched the likable videos first stopped watching sooner than those who saw unlikable videos first. The former did not wait for a complete picture as long as they got the information they needed to convince themselves, and others, of Mark’s goodness. In turn, their own opinions about Mark were more positive, which led their essays about his good nature to be more convincing, as rated by other participants. (A complementary process occurred for those paid to present Mark as bad.) “What’s so interesting is that we seem to intuitively understand that if we can get ourselves to believe something first, we’ll be more effective at getting others to believe it,” says William von Hippel, a psychologist at The University of Queensland, who co-authored the study. “So we process information in a biased fashion, we convince ourselves, and we convince others. The beauty is, those are the steps Trivers outlined—and they all lined up in one study.”

In real life you are not being paid to talk about Mark but you may be selling a used car or debating a tax policy or arguing for a promotion—cases in which you benefit not from gaining and presenting an accurate picture of reality but from convincing someone of a particular point of view.

One of the most common types of self-deception is self-enhancement. Psychologists have traditionally argued we evolved to overestimate our good qualities because it makes us feel good. But feeling good on its own has no bearing on survival or reproduction. Another assertion is self-enhancement boosts motivation, leading to greater accomplishment. But if motivation were the goal, then we would have just evolved to be more motivated, without the costs of reality distortion.

Trivers argues that a glowing self-view makes others see us in the same light, leading to mating and cooperative opportunities. Supporting this argument, Cameron Anderson, a psychologist at the University of California, Berkeley, showed in 2012 that overconfident people are seen as more competent and have higher social status. “I believe there is a good possibility that self-deception evolved for the purpose of other-deception,” Anderson says.

In another study, forthcoming in Social Psychological and Personality Science, von Hippel and collaborators tested all three arguments together, in a longitudinal fashion. Does overconfidence in one’s self increase mental health? Motivation? Popularity?

Tracking almost 1,000 Australian high school boys for two years, the researchers found that over time, overconfidence about one’s athleticism and intelligence predicted neither better mental health nor better athletic or academic performance. Yet athletic overconfidence did predict greater popularity over time, supporting the idea that self-deception begets social advantage. (Intellectual self-enhancement may not have boosted popularity, the authors suggest, because among the teenage boys, smarts may have mattered less than sports.)

Why did it take so long for experimental evidence for Trivers’ idea to emerge? In part, he says, because he is a theorist and did not test it until he met von Hippel. Other experimental psychologists didn’t test it because the theory was not well known in psychology, von Hippel and Anderson say. Further, they suggest, most psychologists saw self-esteem or motivation as reason enough for self-enhancement to evolve.

Hugo Mercier, a researcher at the Institute for Cognitive Sciences in France who was not involved in the new studies, is familiar with the theory but questions it. He believes that in the long run overconfidence may backfire. He and others also debate whether motivated biases can strictly be called self-deception. “The whole concept is misleading,” he says. It’s not as though there is one part of us deliberately fooling another part of us that is the “self.” Trivers, von Hippel and Anderson of course disagree with Mercier on self-deception’s functionality and terminology.

Von Hippel offers two pieces of wisdom regarding self-deception: “My Machiavellian advice is this is a tool that works,” he says. “If you need to convince somebody of something, if your career or social success depends on persuasion, then the first person who needs to be [convinced] is yourself.” On the defensive side, he says, whenever anyone tries to convince you of something, think about what might be motivating that person. Even if he is not lying to you, he may be deceiving both you and himself.