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The job of a Secret Service agent is to assess threats; hundreds, perhaps thousands in a given day, sizing up a perfect stranger in a split second. It's something we all do as humans. We're wired for it. Well, researchers at UCLA have found that wielding a gun doesn't just make someone feel bigger and stronger. It makes the people around him believe it.

In a new study, survey participants were asked to look at pictures of hands holding various items: a power drill, caulking gun, large saw and a .45-caliber handgun. When asked to guess the size of the men behind the pictures, people thought the gun-wielding hand models were consistently larger than the rest.

Joining us is the author of the study, Dan Fessler, anthropologist and head of the UCLA Center for Behavior, Evolution and Culture.

Welcome, Dan.

DAN FESSLER: Thank you. Nice to speak with you, Audie.

CORNISH: So, the participants thought the hands with the guns belonged to larger men. How much larger and what do you think is going on there?

FESSLER: Well, there are different ways of measuring how much larger. We asked people for an estimation of height in feet and inches. And we also asked them to select an image from a set different silhouettes, or six different male bodies differing in muscularity. When we look at their choices on the sets of silhouettes or the sets of male bodies, we that it's about a one-point difference on that six-point scale. So, in other words, about 17 percent larger and more muscular.

CORNISH: So what's surprising about this? I mean, it seems pretty obvious, like someone with a gun looks bigger and scarier than they really are.

FESSLER: The important thing to remember here is that we are trying to explore not people's perceptions, so not how they view the world through their eyes, but instead their representations. That is, how they store and manage information in their heads. So we think that people form a mental image, a little picture in their heads of others in situations of potential violent conflict. And that summarizes all the different features of the other individual that contribute to how dangerous they might be to the observer.

So, every time you have a piece of information that tells you this person might be dangerous, each of those pieces of information makes that little picture seem larger and more muscular in your mind. And then when it comes time to make a decision, you don't need to pay attention to all the information that contributed to the shape and size of the image, you just pay attention to the image.

If the image is small and non-muscular, then you might attack. And if the image is large and very muscular, then you retreat. And if the image is somewhere in between, then you negotiate or appease.

CORNISH: So, Dan, this study was funded in part with some support from a grant from the U.S. Air Force. And put this in context, how could this information be helpful to the Armed Services or law enforcement, or any other group where they've got lots of gun-wielding employees?

FESSLER: We can envision a way of understanding how people make decisions in situations of potential violent conflict that could be useful for all of those individuals. So, if you have a better understanding of what contributes to people's decision to aggress or not to aggress, to attack or to retreat, then you can more strategic decisions as an actor in those situations.

And importantly, also, in many conflicts - ranging from fights in the street to military clashes on a global scale - third parties play an important role. So, there are observers on the sidelines watching the conflict unfold. And importantly, they're frequently trying to decide which side to choose. And one of the factors in their decision is who they think is going to win.

Well, if we have a way of better tapping into how they're thinking about who's going to win, then we have a way of forecasting which side those third parties are likely to take. And frequently it's the case that the decisions of those third parties are crucial in determining the outcome of the conflict.

CORNISH: Dan, thank you so much for explaining your research.

FESSLER: It's been my pleasure to speak with you, Audie.

CORNISH: Dan Fessler, anthropologist and head of the UCLA Center for Behavior, Evolution and Culture.

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