Seeking the roots of primate personality
By Michael Knezovich, courtesy of the University of Chicago Magazine
Photo by Dan Dry
The question for me is always the same. How does environment get under your skin? How does it affect your brain?”
So you step into an elevator with another rider. You smile, move away from each other, stand still, and stare—at the floor, the ceiling, the doors—anything but each other.
It’s as automatic as it is peculiar, but Dario Maestripieri, Professor of Comparative Human Development, Evolutionary Biology, Neurobiology, and Psychiatry, has an explanation: It’s our inner monkey.
Maestripieri has studied the behavior of primates for decades. Riding up and down every day to his 20th-floor Chicago apartment, he saw that elevator riders act a lot like monkeys do when in tight quarters. For monkeys, he says, it’s a genetically programmed behavior to avoid conflict. In the monkey world, for example, direct eye contact signals threat. “If you stare at a rhesus macaque, they’ll freak out,” Maestripieri says. “They’ll think you’re going to attack.” But baring the teeth briefly signals friendliness. For humans, the discomfort in the elevator may be a leftover piece of the genetic heritage we share with other primates.
An anthropologist might have a different explanation—perhaps it’s a need for personal space. But to Maestripieri, that only raises a more fundamental question: Why do we need that space? His work examines the interplay between the biological and environmental roots of behavior, both in people and in animals. Sometimes biology is the main influence, sometimes environment, but they always work in tandem. “The question for me is always the same,” Maestripieri says. “How does environment get under your skin? How does it affect your brain?”
In his 2007 book, Macachiavellian Intelligence: How Rhesus Macaques and Humans Have Conquered the World, Maestripieri drew on 20 years of research to detail how rhesus macaques display human-like behavior, especially in creating societal order. Now Maestripieri is co-editing a book, Animal Personalities, due in 2011, which collects research into genetic and environmental influences on personality.
“Why does it make sense to have some individuals in the same species that are bold and aggressive,” Maestripieri asks, “and others that are shy and peaceful?”
One place Maestripieri goes for answers is Cayo Santiago, also called Monkey Island, a primate research center off the coast of Puerto Rico. In 1938, a researcher brought rhesus macaques to the island from India, and now it’s home to more than 1,000 of the animals.
Maestripieri has studied the Cayo Santiago monkeys for eight years. One project attempts to unravel why some monkeys age well (the typical lifespan is 20 to 25 years), while others deteriorate. “Are you born with different genes?” Maestripieri wonders. “Or is it all, say, quality of life?” He points out that for humans—who share approximately 93 percent of their DNA with rhesus macaques—environmental factors play a significant role in aging.
So far Maestripieri has found that higher-status rhesus macaques age gracefully, remaining healthy and active. His results also suggest that quality of life is critical and can change the biological makeup. Analyzing monkeys’ blood and spinal fluid year after year, he and his researchers track their levels of cortisol, a hormone released in response to stress. Low-status monkeys have continually high levels of cortisol, as if living in a constant state of emergency. In humans, prolonged periods of high cortisol can damage the brain, Maestripieri says, “especially when you’re older.”
He’s also exploring a possible genetic component to the monkeys’ aging. The human gene controlling serotonin, a neurotransmitter associated with mood, can vary in size, one form slightly longer than the other. “Having either version of the gene is OK,” Maestripieri says, but those with the shorter gene have less serotonin in their brains and may be more at risk for depression and anxiety if they’re in a stressful environment. Rhesus macaques have the same genetic variation, and Maestripieri is analyzing its correlation with how well the monkeys age.
Maestripieri, who earned his bachelor’s and master’s in biology and his PhD in psychobiology all from the University of Rome, expanded his primate studies to include humans in 1999 when he came to Chicago.
A 2009 study (PDF) published in the Proceedings of the National Academy of Sciences looked at risk aversion. By and large, men are more apt than women to take risks—financial and otherwise. “Some would argue that societal cues account for this difference in behavior,” Maestripieri says. “Why is it that there are some women who are very competitive, aggressive, and career-oriented, and end up being CEOs of big companies?”
Maestripieri and two colleagues—Luigi Zingales, the Robert C. McCormack Professor of Entrepreneurship and Finance at the University of Chicago Booth School of Business, and Paola Sapienza, Professor of Finance from Northwestern University—studied behavior in 550 Chicago MBA students. They found that it wasn’t gender, per se, that predicted risk taking. It was how much testosterone the students had. Women and men with equal testosterone levels took the same levels of risk. Testosterone predicted eventual careers: higher testosterone correlated with riskier careers, such as finance.
Maestripieri’s work suggests that the links between biochemistry and personality apply equally to humans and animals. Psychologists increasingly understand that personality is not uniquely human, even as animal researchers have begun to study psychology. “In the last 10 or 20 years,” Maestripieri says, “there’s been a lot of work done on personalities in fishes, insects, birds, cats and dogs, elephants—you name it.”