It’s feeding time at the Myakka City Lemur Reserve, a leafy 90 acres about 25 miles east of Sarasota, Florida. On this steamy morning in early March, baskets containing pellets of monkey chow, fruit, and other treats drop from the trees onto a clearing. Three ferretlike brown lemurs, the pint-size alpha dogs of the preserve, make a beeline for the food. They elbow aside their less aggressive—and slightly affronted—brethren: the red-ruffed lemurs, sporting stiff Elizabethan collars of fur, and the hypervigilant ring-tailed lemurs, whose facial markings and luxurious striped tails give the impression of svelte raccoons.
Yale University psychologist Laurie Santos squats on the ground surrounded by half a dozen of these curious primates. They regard her quizzically while she takes pictures of them with a digital camera. The photos aren’t keepsakes of her field trip but will be used to help her comprehend the social structure of lemurs, specifically whether they have an affinity for forming social cliques.
Lemurs, from the island of Madagascar off the coast of Africa, evolved in isolation for some 30 million years. Despite this long separation from the rest of the primates, they now have something in common with a group of rhesus macaques in Puerto Rico and capuchin monkeys living at Yale: They all contribute to Santos’s wide-ranging study of our primate relatives, offering an unparalleled glimpse into our evolutionary past. Monkeys, it turns out, have many of the same survival skills that we do, from a predilection for forming groups to a knack for taking risks and deceiving adversaries.
Santos’s studies show that monkeys also possess many of the quirks and foibles once considered uniquely human. Like us, they intuit what others are thinking by reading social cues, a skill that may be millions of years old, hardwired into the primate brain. They make the same errors in economic reasoning that we do, suggesting our sometimes irrational attitude toward money might once have conferred an evolutionary edge. Through a series of groundbreaking experiments, Santos has seen in her primates a humanlike propensity for hoarding, larceny, and competitiveness. By exploring the inner lives of primates, she has offered persuasive evidence that monkeys are capable of sophisticated insight, complex reasoning, and calculated action.
Although the 33-year-old New Bedford, Massachusetts, native grew up surrounded by cats and dogs—her mother is a pet rescuer —Santos originally aimed for a career in law. The switch to studying animal behavior was, she says, “utterly serendipitous.” Shut out of a prelaw seminar in her freshman year at Harvard, she took a psychology class that ultimately led her to the study of nonhuman primates. She was captivated. Now an associate professor at Yale and head of the university’s Comparative Cognition Laboratory, Santos explains to DISCOVER how she learned to think like a monkey—and, in the process, came to understand more about how humans think too.
You first observed monkeys with your mentor at Harvard, the evolutionary psychologist Marc Hauser. What intrigued you?
Initially it was just the opportunity to go to his field site on this island near Puerto Rico. But when I saw the monkeys, I got hooked. Watching them, you can’t help but see that they have the same kinds of issues that we do. They play. You can see their social striving. You can see their battles, their caring. They want to make friends and mate and be on top. They care about their kids, and they want their friends to do well.
One day I was alone on the beach and I picked out a nice spot to eat. A monkey came and sat beside me, and he had his monkey chow and was eating. We sat there together and I wondered what this monkey was thinking. Did he think the spot was beautiful? And how would I know that he did? That got me thinking about how they’re a lot like us, but on the other hand so different. They’re navigating these complicated motor situations, jumping from tree to tree, dealing with the stresses of new environments, and foraging. They do all of this minus language, minus the kind of social and cultural learning we humans have, yet they live, they mate, and they do some extremely complicated things, particularly in the social domain. How they achieve these same ends minus computers, BlackBerrys, or tape recorders is fascinating.
Your research with rhesus macaques in Puerto Rico suggests that they are capable of discerning human intentions. How did you realize that they were studying you even as you were studying them?
The monkeys were good at deception. Nowadays when out in the field we eat lunch inside a cage that we bring along, in part because the monkeys have gotten very good at stealing our lunch. And it’s not just the food we eat but the fruit we use as stimuli in our testing sessions. Many days we went home early because the monkeys ate all the fruit. We would be doing number experiments where one plus one is supposed to equal two. But with only one lemon left, they can’t add one plus one and we can’t test their addition skills. In order for the monkeys to have taken the lemons when we didn’t notice, they must have paid attention to what we could see and what we couldn’t see. They’d have to wait for the moment we were no longer looking, and step in and take the lemons away.
So they were watching you intently?
Not just watching us but specifically paying attention to the cues that were related to whether or not we could see, whether our eyes were pointed toward the lemons. You’d turn to write in your notebook and you’d look up and there was a monkey running up the hill.
That led us to develop a series of experiments where we directly asked whether or not the monkeys were good at using cues, such as where eyes are pointed. The real question is this: Are the monkeys just good at reading our behavior? “Oh, she’s turned away now.” Or are they thinking about our perceptions, mainly “She can’t see now.” And this is still a question of much controversy in the field.
Do you think that, in a very rudimentary way, these monkeys were able to read your mind?
To the extent that they’re reading behavioral cues that are correlated with mental states—things they can’t see—yes, they are mind readers. But do they know that you have a mind in the first place? Do they understand that we have thoughts?
One of the most basic mental states that we think about in others involves perceptions—what you can see or hear—and that builds up to what you know or don’t know. The ability to discern these states in others was probably enormously powerful back in the evolutionary day, when we grew up as social primates who lived and died on the basis of how well we were able to predict others’ social actions: Are you going to be a friend to me? Are you going to back me up later?