Primal Fear: Can Monkeys Help Unlock the Secrets of Trauma?

On Valentine’s Day, 2018, five months after Hurricane Maria made landfall, Daniel Phillips stood at the edge of a denuded forest on the eastern half of a 38-acre island known as Cayo Santiago, a clipboard in his hand, his eyes on the monkeys. The island sits about a half-mile off the southeast coast of Puerto Rico, near a village called Punta Santiago. Phillips and his co-workers left the mainland shortly after dawn, and the monkeys had already begun to gather by the time they arrived, their screams and oddly birdlike chirps louder than the low rumble of the motorboat that ferried the humans.

The monkeys were everywhere. Some were drinking from a large pool of stagnant rainwater; some were grooming each other, nit-picking; some were still gnawing on the plum-size pellets of chow that Phillips hurled into the crowd a half-hour before. Two sat on the naked branch of a tree, sporadically mating. They were all rhesus macaques, a species that grows to a maximum height of about two and a half feet and a weight of about 30 pounds. They have long, flexible tails; dark, expressive eyes; and fur ranging from blond to dark brown.

Phillips’s notebook was full of empty tables. There were places for the monkeys’ ID numbers, which were tattooed on their chests and inner thighs, places for a description of their behavior, places for the time of day. There was a place for his own name, too, and he wrote it at the top of each page. Daniel Phillips is not a Puerto Rican name, whatever that means, but he was born here, in a big hospital in Fajardo. He arrived more than a month early and spent his first weeks in an incubator, but grew up to be a high school and college wrestler; as a biology major, he became interested in monkeys, and was invited by a primatologist from Duke University to take a job as a research assistant here on Cayo Santiago.

Like humans, rhesus macaques possess advanced problem-solving skills and opposable thumbs and have been known to use tools. They have complex emotional and social lives. Although chimpanzees and a few other ape species are closer cousins to humans — we share approximately 93 percent of our DNA with macaques and 98 percent with chimps — macaques are easier to manage and less protected by regulations, which is partly why they account for 65 percent of research on nonhuman primate subjects funded by the National Institutes of Health.

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