As of March 2015, Instagram’s some 200 million monthly active users had uploaded 30 billion photos. Although many of these photos are gratuitous selfies, shots of lackluster meals, and holiday pictures meant to make followers jealous, there are scores of others that are a bit more risque.

Celebrities show off skin all the time. You only need to glance at a supermarket’s magazine rack to see that, but recently, male celebrities have been posting some surprisingly cheeky photos.

Following the Fourth of July weekend, pop superstar Justin Bieber posted a picture of himself in the full-monty. In the shot, Bieber stands on a boat in his birthday suit, facing away from the camera, pointing towards a majestic island a good distance across cerulean water, his bare butt there for the world to see.

In less than 24 hours, Bieber’s butt had racked up as many likes as there are people in Manhattan.

He wasn’t alone. Soon after Bieber bared his butt to behold, Chrissy Teigen posted a picture of her husband, singer songwriter John Legend, displaying his derriere.

What’s particularly interesting about this little trend isn’t the boldness these celebs seem to have, but rather the effect it has. As the New York Post reports, evolutionary scientists claim that rears are particularly attractive because they represent “real estate that is in some ways the most intimate part of us, and in other ways is terra incognita.” Basically, butts are both mysterious and sexy.

The strategy of using one’s posterior for social media fame isn’t new, either. Instagram celebrity Jen Selter has racked up a whopping 1.3 million followers simply by posting photos and videos of her exercising her yoga-panted- and tights-clad gluteus maximus.

In other words, if you want to get more famous on Instagram, you may want to hang a moon.