We’ve all heard the adage: monkey see, monkey do. But it is literally true—if a monkey sees you looking at something, it will look, too. Now, a study shows that this tendency for a monkey to track what another is looking at is age-dependent. And in a very similar way to the same behavior in people.

The ability to what’s called “gaze-follow” is a fundamental skill that underlies our social lives. When we turn to see what other people see, we recognize their interest and join in their curiosity—or concern. Stand on a busy street corner and look up. It won’t be long before you have a crowd of people trying to see what it is you’re looking at. And other primates do it, too.

Researchers studied a large population of free-ranging macaques on an island off Puerto Rico. One scientist would approach a macaque that was sitting by itself and would attempt to get its attention by clapping or snapping or by saying, “Monkey, monkey.” That’s lead investigator Alexandra Rosati of Harvard. When the macaque made eye contact, Rosati would look straight up in the air. A second researcher would film the interaction to see whether the monkey also looked up.

The humans pulled the same stunt on nearly 500 monkeys of all different ages, from infants just two weeks old to elders of 28 years. And they found that, for macaques, gaze following kicks in a few months after birth, peaks in juveniles, and declines in old age—a pattern that matches what happens in humans. To see the results for yourself, take a look at the write-up in the Proceedings of the Royal Society B. [Alexandra G. Rosati et al., Rhesus monkeys show humanlike changes in gaze following across the life span]

The researchers also found that juvenile and adult macaques quickly figured out that Rosati was faking: when she looked up, there wasn’t actually anything in particular worth seeing. At which point the clever primates disengaged from the activity. Which suggests that, yes, you can make a macaque look. But you can’t make it a monkey’s uncle.

—Karen Hopkin

[The above text is a transcript of this podcast.]