A rhesus macaques​ resting on a rock in Cayo Santiago.
A rhesus macaques resting on a rock in Cayo Santiago. Image: Michael James Murray/Motherboard

What Monkeys and ‘Dognition’ Can Teach Us About the Human Brain

Humans clearly have advanced mental abilities compared to other animals on Earth. Laurie Santos wants to know what makes us special.

THE MOST UNKNOWN is Motherboard's love letter to the scientific process. For the next nine weeks, we'll be profiling the people trying to answer science's most difficult questions. Our feature-length documentary is now available on Netflix, and bonus episodes are available on YouTube.

For a species that is uniquely clever, humans sure do act dumb a lot of the time. This puzzling and sometimes calamitous contradiction has been a lifelong fascination for Laurie Santos, a psychologist and cognitive scientist who heads Silliman College at Yale University.


Santos’ work earned international headlines over the past year when her course “Psychology and the Good Life” became the most popular class in Yale’s history. The curriculum is packed with practical tips for optimizing psychological wellbeing, and scientific explanations for why our own minds can sometimes feel like our worst enemy.

Though the course is intended to help students remain psychologically healthy, it also represents the latest iteration of a question that Santos has been asking her whole career: What distinguishes the human mind from other smart creatures on Earth?

“It’s just fascinating to think about what could possibly be so special about the human mind,” Santos told me. “We’re so weird as a species, yet we’re just this biological organism.”

She pondered these kinds of questions while growing up in New Bedford, Massachusetts, in a brainy family. Her father worked as a programmer while her mother served as a guidance counselor at New Bedford High School, the school both Santos and her brother Aaron—who is now a physicist and author—attended.

When she enrolled at Harvard University, she thought she might pursue law, but that plan went out the window once she got hooked on psychology. Inspired by profound questions about brains and behavior, she jumped at the chance in her undergrad to become a research assistant on a trip to Cayo Santiago, a tiny 38-acre island east of Puerto Rico nicknamed the “island of the monkeys” due to its thriving population of rhesus macaques.

rhesus macaque colony

Rhesus macaque monkeys on Cayo Santiago. Image: Lindsey Blatt/Motherboard

There, observing the monkeys interacting with one another in their Caribbean habitat, Santos found her vocation. “You see the monkeys behaving, and they’re struggling with lots of things that humans struggle with,” she recalled. “They want to find friends. They want to figure out how to interact in the world. But they don’t have the tools that we have. They don’t have language and culture or anything like that.”

“Even as a sophomore,” she said, “it was really fascinating and I kind of stuck with it ever since.”

Santos earned her BA in psychology and biology from Harvard, as well as her PhD, which focused on the brain, cognition, and behavior, and won Harvard’s Richard J. Herrnstein Dissertation Prize in 2003. From there, she was quickly snapped up by Yale University, as a professor specializing in psychology and cognitive science.

During her expeditions back to Cayo Santiago over the past two-odd decades, she has only become more enchanted with this unique tropical habitat and its inhabitants. Though she enjoys the other responsibilities of her job—laboratory work, teaching, and publishing research results—she’s always most eager to return to the island for more field work.

“I really love being at Cayo Santiago,” she said. “It’s one of my favorite places in the world, and it’s my favorite spot to do research. That’s in part because of the specific questions we get to ask, and in part because it’s so beautiful.”


Santos is so at home at Cayo Santiago that she recognizes individual monkeys, and knows all about their families and personalities. This makes for fun reunions, but it can also be bittersweet. Rhesus macaques have an average lifespan of 25 years, which is about the same amount of time that Santos has been visiting Cayo Santiago. She’s watched on as a full generational cycle has rolled by on the island, with spritely infants growing up to become parents and grandparents, and eventually settling into old age or passing away.

“It’s kind of sad, because their generation time is a lot shorter than ours,” Santos said. “That can be a little jarring, but it’s really fascinating to see the site evolve over time.”

Her familiarity with the island is obvious in Motherboard’s documentary The Most Unknown, which follows scientists as they shadow researchers in other fields. As she escorts University of Sussex neuroscientist Anil Seth through Cayo Santiago’s forest paths, Santos explains how to interact with the primate population and points out the monkeys’ curiosity about the film crew.

Two scientists on an island with a monkey

Santos and Seth performing an experiment with the monkey. Image: Michael James Murray/Motherboard

The documentary shows some of the experiments that Santos and her colleagues perform with non-human thinkers. The tests are designed to gauge the cognitive abilities of monkeys, such as the extent to which they can understand the perspectives of other individuals. In one setup, for instance, Santos and Seth test whether a monkey will be more likely to sneak up to grab a grape from a platform when a person’s back is turned to it.


As director of Yale’s Comparative Cognition Laboratory, Santos has gained a worldwide reputation for devising these creative ways of exploring the mental capabilities of animals, and pinpointing where they overlap and deviate from the inner workings of the human mind.

Perhaps the most famous example is the lab’s “monkey marketplace” series of experiments, in which capuchin monkeys are given tokens that they can trade for treats from vendors offering various deals. These tests were partly inspired by research into human financial decision-making processes, especially surveys examining rationales for taking gambles (for instance, accepting one prize or gambling for a chance to win more than one prize at the risk of getting nothing).

“There are tons of survey-type methods asking people about gambles,” Santos said. “We just asked: ‘Could we turn those gambles into the kinds of things that monkeys could do?’ That was how we came up with our trading method. We can use this kind of currency to ask the monkeys what they know.”

Over her years of conducting versions of monkey business scenarios, Santos has discovered that many primates share a lot of basic financial impulses with humans. They suss out which vendors offer better deals, and recognize bargain situations. They prefer to gamble on a potential profit rather than a potential loss. They are sensitive to fairness.

These economic concepts—especially loss aversion and reference dependence—closely align with human reactions to similar propositions, providing an intriguing window into the evolutionary roots of our own financial behavior (and misbehavior).


“For many of the cognitive things that we study, we see pretty remarkable similarity across monkey species and across the primate order generally,” Santos said.

These primate studies are a fruitful way to study the “nature” side of the “nature versus nurture” debate about human cognition. As our closest relatives, primates can shed light on the evolutionary wiring that drives our daily lives, and human civilization en masse.

For the “nurture” side of the coin, however, Santos and her colleagues turn to dogs for insights. “Even though [dogs] are not a close evolutionary relative of humans, they are one of the few animal species that grows up in the same context as humans,” Santos explained. “Dogs are growing up in the same homes as human children, yet they don’t develop language or teaching. They don’t go off to college.”

“It raises this real question about what it is that makes humans special,” she continued. “We get the same input as dogs but dogs do something different” which makes them a “great model to test this question of nature and nurture.”

Santos explores these mysteries of “dognition” at Yale’s Canine Cognition Center, which she heads. One of the lab’s most intriguing experiments explored the concept of “overimitation,” a behavior that has been widely observed in human babies and toddlers. If an adult demonstrates a multi-step process of solving a puzzle to a human infant, the child will usually try to replicate the exact sequence of steps as it was shown to them, whether or not those steps are actually necessary for solving the puzzle.


Non-human primates, in contrast, tend to only proceed through relevant steps to solve puzzles, suggesting that there is a special mechanism in the human mind that results in overimitation. Since dogs are raised to be extremely sensitive to human cues Santos wondered if they would also be prone to copying an exact pattern of steps. To find out, they adapted these tests for dingoes and domestic dogs.

For instance, in one study, dogs watched as researchers shifted a lever on a box before opening the lid, which was an action that was not necessary to open the box. The dogs ignored this lever and just opened the lid to get the treat.

“What we found, as we expected, is that dingos don’t fall prey to [overimitation]; they just learn to solve the puzzle on their own,” she said. “What we didn’t expect, though, is that dogs also don’t fall prey to overimitation. When they see a human doing something silly in terms of how to open a box, unlike humans, they don’t fall for it.”

“This is cool because it suggests that dogs learn from us in, maybe, an even more efficient way than humans do,” she added. “They are using different mechanisms than human children are when learning from other agents in the world.”

These fresh insights about human cognition, gleaned from non-human sources, are helping Santos and her colleagues capture some of the basic mental strategies that differentiate our species from other animals. Of course, it can be a bit trippy to ponder such profound biases in the human brain with—what else?—a biased human brain. To that point, despite her expertise, Santos emphasizes that it’s impossible to outsmart those underlying psychological processes.


“It feels like when you know about your mind, you should be able to get your mind to do the right things, but that’s just not the case,” she told me. “One finds it humbling that you can be a complete guru in this stuff, but not be any better at it. You can’t just will your mind to work in a certain way. It works the way that it does.”

That said, the overwhelming success of Santos’ new Yale course “Psychology and the Good Life,” which began in January, suggests that people are eager to prioritize their own psychological wellbeing—a more achievable goal than overcoming one’s mental biases completely.

A quarter of Yale’s undergraduate population enrolled in the class, which outlines positive psychology concepts and recommends science-backed methods for reducing stress and living a more balanced and fulfilling life.

Santos was inspired to offer the course party due to her position as head of Yale’s residential Silliman College, which she has occupied since 2016. These residential institutions are somewhat like the houses at Hogwarts, Santos told me, in that they are tight-knit and have different cultures. Because the faculty heads actually live with the student population in their housing complexes, Santos has experienced a close-up view of undergraduate life and its modern pressures.

“In that capacity, I saw that college students today are just a lot more overwhelmed and less happy than folks often think,” she said, adding that this is not only a problem at Yale, but at academic institutions across the US. “College isn’t supposed to be a time where students are so stressed out. It would be fantastic if they learned the right skill-sets to be a little bit more happy. Being a psychologist, I know that there’s a lot of evidence-based strategies for students to use to do that.”

Examples of those strategies include expressing gratitude, prioritizing social connections, and focusing on “time affluence,” which means setting aside substantive time to pursue passions and leisure activities. Santos expected her course to attract interest, but was floored when it rapidly became Yale’s most popular class ever.

“The response that we’ve gotten so far has been completely surreal,” she said. “I didn’t expect so many students to want to be part of it. I didn’t expect it to be an international conversation.”

But now that the course has made such a splash, Santos is looking forward to exploring new ways to adapt her expertise about cognition, in humans and in animals, to help people lead healthier and happier lives.

“It really builds on the kind of work I was doing before,” she told me. “The main reason that people need this stuff is because of these biases of our mind. It’s because we have this dumb monkey mind that’s built to seek out these dumb things that we don’t actually want and we really need some help from science to teach us what we can do to be better.”