Science in Mind

Do leaves exist to provide shade? Even scientists susceptible to human bias to find purpose in nature

Scientists pride themselves on being rational. They seek to describe the world as it is, and stay up late looking for new insights. Most scientists carefully avoid the idea that nature has a purpose, at least in their professional lives. But human beings are also natural storytellers, and stories often have reasons. It can be irresistible to think that if something in nature does something—the Earth has an ozone layer that protects it from ultraviolet light, for example—that its function might be the reason it exists.

A team of psychologists at Boston University decided to examine just how deep-seated the impulse to find meaning in nature is, by recruiting professional scientists—chemists, geoscientists, and physicists at BU, Brown, Columbia, Harvard, MIT, and Yale—to participate in an experiment.

What the researchers found, in a study published in the Journal of Experimental Psychology, is that scientists were less likely than comparison groups (including college undergraduates) to rate sentences that assigned meaning to nature as true, such as “The sun radiates heat because warmth nurtures life.” But under time pressure to answer quickly, scientists became more likely to rate such statements true than when they were not racing the clock. To the BU team, that suggests that even the most reasonable among us may have a default tendency to look for reasons—albeit one that is easily overridden by conscious thought. Deborah Kelemen, an associate professor of psychology at BU who led the study, reflected on the findings and their implications.

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Q: You’re a scientist. Did your own experiences motivate this research at all?

A: The work with professional scientists was actually motivated by child research from our lab, which shows that from around preschool, children start to display very broad tendencies to think natural phenomena occur for a purpose. So, for little kids, it makes perfect sense to say that rivers exist so crocodiles have a place to live, that rocks are pointy so that animals won’t sit on them and smash them or, my personal favorite, that mountains came to exist so the earth wouldn’t fly away from not being weighted down enough. ... It seemed possible that purpose-based explanations remain as the default way of thinking about nature even among professional physical scientists despite all of their countervailing scientific biases and knowledge.

Q: Under time pressure, scientists became more likely to say statements like “trees produce oxygen so that animals can breathe” are true. Why?

A: Because under time pressure, people give their gut reactions. Human beings naturally find purpose-based explanations very attractive and satisfying. When they aren’t under time pressure, scientists can use the conscious, reflective parts of their minds and can reject purpose-based ideas as scientifically inaccurate. However, when they are thinking quickly, under time pressure, they do not have that luxury: They don’t have time to censor their thinking, so they end up revealing their underlying human bias to think natural phenomena can be explained by some purpose.

Q: How do you know that really suggests there’s a cognitive default to find purpose in nature—couldn’t it just be that under time pressure people are more likely to choose wrong?

A: We carefully control for that possibility. Obviously, it would not be interesting if we were just revealing people’s inability to think and evaluate ideas at speed. In our research, participants also judge a great many accurate and inaccurate statements about physical phenomena—explanations that do not involve ideas about purpose. What we find is that, under time pressure, people slip up on the purpose-based explanations but not other kinds of equally technical explanations.

Q: Does this suggest the type of thinking that underlies religious beliefs are innate?

A: The details of this research don’t provide support for the idea that purpose-based beliefs (or religious beliefs) are innate or hard-wired. However, they do suggest that we are strongly predisposed to construct purpose-based ideas about nature, which robustly persist from early development. Those purpose beliefs seem likely to bias human minds to entertain certain kinds of religious ideas (e.g. creationism, ideas about supernatural beings). They also set the stage for making many scientific ideas (e.g. evolution, natural selection) extremely hard to acquire and truly understand.

Q: What are the implications? How do you incorporate this into your own life, as a scientist and a teacher?

A: Scientists have to realize that they need to think twice. However much we would love to believe the practice of science is entirely objective, it is not. Unexpected, unconscious mental biases have influence over our machinations. Furthermore, as teachers, we need to be very careful about the language that we unconsciously use when talking about and explaining natural phenomena to our students: inadvertent purpose- and design-talk is really a big problem in the context of science education. Careless language just helps to reinforce all kinds of purpose-based scientific misconceptions about natural processes and mechanisms. (The other day, I was watching a nature show with my 7-year-old and I almost wanted to tear my hair out when they were explaining .... natural selection).