Bob’s feeling may have something to do, in this case as in many others, with the circumstances under which he first got to know his animal. After he paid $1,500 to a dealer in Missouri, Higgins arrived, at about 3 months old, in diapers, with a bottle. Although he had his own cage, in his own room, he often slept in the couple’s bed. Bob changed his diapers several times a day, and often took him to work at his construction equipment business, slipping him under his shirt. On the way back, they would get Higgins an ice cream.

Image BEHIND BARS Bob raised Higgins, a baboon, from infancy. Because Higgins has attacked him, he keeps him caged in a heated building where they often watch TV. Credit... Phil Mansfield for The New York Times

Then, when Higgins turned 3, the problems began. Carlie, who after all runs a preserve that is home to a yak, two emus, alligators and a camel, found Higgins to be loving. But when he was out of the cage, she says, “he was just too destructive.”

“I live in a 200-year-old farmhouse,” Carlie says. “Jumping up and down trying to get out of his cage, he cracked the ceiling and the walls. He took all the filigree off my bedroom furniture. One day I went in to feed him and he grabbed me by the hair and yanked me against the cage. I ended up on the ground in tears, in such agony. They thought I had a detached retina.”

Bob has been bitten several times by Higgins, who now weighs 50 pounds and has large incisors. Once, when Bob was leading him from an outdoor enclosure back to his cage in the house, Higgins exploded and the two got into a battle so ferocious that despite the steel mesh glove Bob was wearing, he screamed for Carlie to get his .22 rifle and put a bullet in Higgins’s head. She got Higgins a slice of raisin bread instead, quickly defusing the fight. But Bob accepts it: a wild animal will never be domesticated, he says. Higgins now lives in a heated building on the property, which includes a 9-by-12-foot cage and a 30-by-12-foot outdoor exercise area with an 8-foot ceiling. One must pass through two locked doors to get inside Higgins’s cage. Even Bob doesn’t get in the cage with Higgins much anymore.

Allen Hirsch, a successful New York City painter, also bonded with his monkey early in its life. Benjamin, a 12-year-old capuchin monkey who came to Mr. Hirsch as a sickly mistreated infant, is like “a primordial human,” he says. “You recognize something very human in his gaze, a certain understanding, a certain awareness.”

From the start, Mr. Hirsch said, it has been a time-consuming, demanding relationship. After Benjamin bit off two of his own diseased toes, Mr. Hirsch stayed with him for four months, rarely leaving his side. Since having a monkey as a pet is illegal in New York City, he now keeps Benjamin in his country house in Catskill, N.Y., where a friend must often look after him. (New York State also banned monkeys as pets four years ago, but Benjamin is grandfathered in.)