Sex and high-status individuals—from celebrities on TV to influencers on Instagram—are advertising staples. Our first question tends to be whether they work, but just as important a question is why. Are they playing on cultural norms and the way each of us has been socialized? Or are they tapping into something more primordial in us, some social trigger deep in our brains, shaped by evolution?

A study published Feb. 20 in the journal Plos One set out to determine the answer. For test subjects, the researchers (from Stanford University’s Graduate School of Business, University of Colorado-Boulder’s Institute of Cognitive Science, Duke University’s Fuqua School of Business, and University of Pennsylvania’s Wharton School) needed a group that hadn’t been exposed to advertising previously. Ideally, it would also share ancient neural circuitry with humans, allowing the researchers to gain some sense of how far back these triggers date.

So they turned to monkeys: Rhesus macaques, to be exact, who along with other monkeys diverged from humans some 25 million years ago, but still have brains that handle social perception and value in much the same way we do. What the researchers found was that they were able to condition the monkeys to prefer one brand over another—and they did so by associating brands with pictures of monkey genitalia and dominant monkeys in the colony. Apparently sex and status sells to monkeys, too.

To test their theory, the researchers had to get creative. They trained male and female monkeys to use a touchscreen device, and then ran different trials using a series of images to see how their small, hairy subjects would respond. In one trial, they created basically a monkey “advertising campaign” that paired the logos of different companies, such as Acura, Pizza Hut, and Adidas, with “social” images. Those included a dominant male monkey, a subordinate male monkey, and finally a female monkey flashing its rear as it gazes backward over its shoulder. They also created control advertisements that paired a brand logo with a scrambled image.

Slide from "Rhesus macaques form preferences for brand logos through sex and social status based advertising"/Plos One Science is amazing.

Then, in another trial, they had the monkeys choose between two brand logos that flashed on the screen. (In each trial, the monkeys received a food reward, but it was just to get them to complete the task. There was no right or wrong answer and the monkey got the same reward no matter which it chose.)

Slide from "Rhesus macaques form preferences for brand logos through sex and social status based advertising"/Plos One

The image pairings, it turned out, did appear to affect which logos the monkeys preferred. The picture of the female monkey’s hindquarters had the strongest influence on both the male and female monkeys. The dominant male monkey was also a persuasive brand ambassador.

Contrary to the researchers’ expectations, the subordinate male, though not a hit with the females, still had an influence on the males. The researchers note however that the monkeys, including those pictured, were all part of one colony, so the result “could reflect a preference for colony-relevant information instead of a preference for an association with subordination.”

Odd as the study sounds, there is precedent for researchers looking at monkeys to glean insights about human psychology, though they have to be read with the understanding that there’s a limit to how much we can generalize the findings to humans. Indeed, not all studies of humans concur that sex is persuasive. A large meta-analysis of advertising studies published last year “found literally zero effect” from sexy advertising on purchasing decisions.

But this study’s authors believe the results indicate sex- and status-based imagery do have influence on monkeys with social brains similar to ours, and advertising is enough on its own to create strong associations, even without a tangible reward involved. They can’t say how that influence might play out in people whose brand preferences and associations are shaped over lifetimes. But it’s some indication that the marketing we’re bombarded with daily, trying to get us to pick one company over another, may be tapping into places deep into our brains.