The Human Evolution Blog

(A longer discussion of animal communication can be found in my book.)

Mandrills are, literally, one of the most colorful creatures on earth and certainly the most colorful primates. Their striking faces are matched only by the bright coloring of their hindquarters. (Their genitals are colorful, too, if you must know!) The coloring is part of their sexual displays, and the males are much more colorful than the females. The unique coloring made mandrills popular with children even before Rafiki stole the show in The Lion King.

Mandrills are also the subject of a curious new discovery. Professor Mark Laidre, now of Dartmouth University, has observed more than 30 separate communities of mandrills while studying their social activities and structures. In one such community – a zoo in Colchester England, it appears that a gesture has been invented.

The gesture in question is simply covering the face with one hand, like a face-palm, and holding it for several minutes, sometimes up to a quarter of an hour. The mandrills do this in the shade as much as the direct sun and independent of wind conditions. After studying the monkeys as they made the gesture, Laidre hypothesized that it was a “do not disturb” signal that the mandrills use when they want to be left alone.

“I had been studying mandrill gestures for a while, both in captivity and in the wild in West Africa… and I haven’t seen this eye-covering gesture in any of the hundreds of other mandrills.”

To test this, he carefully documented the behavior of nearby mandrills and found that, during the time that a mandrill was making the gesture, there was significantly reduced social advances by other mandrills. Fewer mandrills approached the gesturing mandrill, and fewer touched him or her, compared to mandrills in similar postures but not making the gesture. The gesture really does seem to mean “leave me alone.”

This is the first documented example of an intentional unambiguous gesture in any non-ape primate species. However, that is not even the most interesting part. This gesture was “invented” in one particular community of mandrills in an English zoo and has since spread through that community. It has never been seen in any other community of mandrills, despite Laidre and many others looking.

The first mandrill to be seen making the gesture is a female named Milly. “She’s not very dominant. She sticks to her own area and is not as socially involved as others.” says Laidre. It makes sense, then, that Milly would be the originator of the “leave me alone” gesture, since she prefers to be left alone. However, that the other mandrills have picked up the gesture and used it themselves is quite remarkable.

The transmission of knowledge and practices is the hallmark of culture. Accordingly, Professor Laidre aggressively titled his paper, “Meaningful Gesture in Monkeys? Investigating whether Mandrills Create Social Culture.” Laidre is correct that this example of gestural communication meets all the usual criteria for social cultural transmission: the behavior is learned, not instinctual, it is unique to a specific community, and it has remained stable despite demographic changes in the community (births, deaths, etc.).

Another remarkable aspect of this story is that it appears that we actually know how the gesture began. Milly, the first to be observed making the gesture, was the only one using it for years before it caught on. Milly’s social position gives clues to its genesis: she is shy, withdrawn, and low-ranking. It’s no surprise that she’d rather be left alone since she ends up on the short end of most social transactions.

The mechanism of the gesture also makes sense. By covering the face, eye-contact is prevented. Since eye-contact is usually the way that social interactions are initiated in primates, including humans, by subverting eye-contact, social contact is halted before it can even begin. As Laidre says,

“In this case, simply covering the eyes could be mechanistically an act that might block others from ever starting the beginnings of a social interaction.”

Perhaps Milly figured out that if she can preclude others from locking eyes with her, she can avoid them altogether and go about her business.

As the other mandrills were rebuffed in their attempts to engage Milly over the years, they eventually learned that the gesture could be useful for when they wanted to be left alone. And so a new cultural meme was born.

“Obviously primates are smart animals and they can very quickly learn this correlation,” says Laidre.

It remains to be seen if the receivers of the gesture actually understand its meaning or if their obeyance of the “do not disturb” request is merely a consequence of their having been denied eye contact. Either way, the “leave me alone” face-palm has been self-sustaining in this community of mandrills for nearly a decade and a half. “Yep, they’re still doing it!” says Laidre.

The experiment that would clinch this would be to exchange mandrills from other zoos to see if the gesture can spread into different communities. If so, that would provide another window into the evolution of language.

-NHL