The fascinating relationship between human and chimp and the inspiration to save what is an intrinsic part of all of us.

In a remote patch of jungle along the Gambia River in West Africa, there lives a most unusual member of the primate species. Known by local villagers simply as “the chimp-woman,” Janis Carter – a tall, fair-skinned, Oklahoma native – has spent the past 33 years living among and working to save some of the world’s last remaining wild chimpanzees. There are roughly 100,000 chimps left in Africa, down from more than two million at the turn of the last century; some primatologists now estimate that our nearest biological kin may be totally extinct in another ten years. Carter, 60, has long been in the very thick of things, a lone pioneer on the increasingly fraught frontier between the chimp’s shrinking habitat and our ever-expanding one. She shuttles between the Gambia and the jungles of neighboring Senegal and Guinea, working with everyone from local villager hunters to government officials to the representatives of Chinese mining companies in order to save what little remains of our own primal ancestry.

Her career path was unlikely, not to say remarkable. Prior to her departure for Africa in 1977, Carter had never stepped foot outside of her home state. At the time, she was a graduate student in psychology at the University of Oklahoma. She was also employed on the side by her psychology professor Maurice Temerlin to be a babysitter and caretaker for one of his children. It was an ordinary sounding arrangement, except that the child in question happened to be a full-grown chimpanzee named Lucy.

In 1966, Temerlin and his wife had taken Lucy at one-day-old from her mother in a Florida roadside zoo and flown her back to Oklahoma to raise her as their own “daughter.” Considered at the time to be a bold, cutting-edge scientific experiment, Lucy would soon become a worldwide sensation, featured in Life Magazine, Psychology Today, and Science Digest. She lived entirely as a human being, having no contact with another chimpanzee. She slept on a king-sized Simmons Beautyrest mattress, ate meals at the family dinner table, raised a pet cat, and mixed her own gin and tonics, habitually sipping them while flipping through magazines on the living room sofa. Carter quickly became Lucy’s closest companion. She helped teach Lucy more than 150 words in sign language. She led her through her daily play and exercise sessions. She also regularly cleaned up the caged wing of the house that the Temerlins had built in order to minimize the mayhem that the increasingly powerful and precocious Lucy was causing to their civil environs. But it would be in the wild that the real drama between Lucy and Janis would unfold.

By 1977, the Termerlins felt they could no longer manage their 11-year-old chimp daughter; they opted to send her to a jungle reserve for former captive chimpanzees outside the city of Banjul in the Gambia, Africa. Carter was handed the enormous responsibility of helping Lucy make the transition to a wild existence she’d never known. She initially arranged for a three-week leave of absence from her university studies. Immediately on arriving at the Gambia reserve, however, Lucy became deeply depressed and contracted several illnesses. Carter felt she couldn’t leave her in that condition; three weeks became three months, then a year. When Carter decided to follow Lucy and eight other former captive chimps to a new island refuge on the Gambia River some 200 miles inland, one of the strangest interludes in the history of human-animal relations ensued.

Although Lucy was the largest of the chimps on the island and the only one who knew sign language, she quickly showed herself to be the least capable of surviving on her own. Carter would go off with Lucy and the others into the jungle and play their surrogate chimp mother, climbing up and building herself a nest in the trees, eating ants, grubs, and leaves in hopes that the chimps would emulate her. The other chimps were soon up in the trees with Carter foraging for food, but Lucy steadfastly refused to climb. She’d position herself at the base of the trees and wait for edible crumbs to fall. She also insisted on drinking water as Carter did, from a bottle and not from the river.

“I tried to show her a quick way up a tree one day,” Carter recalled in a recent phone conversation from The Gambia. “But when I came back down, Lucy took me by the hand, put my hand against the tree trunk, and then signed ‘More food. Janis go.’”

Knowing that drastic measures were needed, Carter had a group of British Commandoes who were conducting military exercises on the island build her a huge steel enclosure. She then retreated with all her belongings and provisions inside the enclosure and locked Lucy out. For part of the day she’d emerge, going off with Lucy and the others in an ongoing attempt to get Lucy to interact with fellow chimps. Then Carter would return to her self-imposed captivity in hopes of finally forcing Lucy to look after herself.

“From the beginning, I wanted Lucy to accept that I alone lived in a cage,” Carter said. “But she’d just position herself outside and ask me in sign language to come out and help her. She was growing more and more emaciated. She’d whine and pluck her hair out and occasionally sign: ‘Food… drink. Janis, come out. Lucy hurt.’”

The surreal standoff went on for months. And then one day, exhausted from their struggle, the two of them fell asleep alongside each other on opposite sides of the cage. When Carter awoke, she found Lucy sitting up, offering Carter through the bars a leaf from a branch Lucy had clearly climbed a nearby tree to secure. Carter ate some and gave the rest to Lucy.

“From that point on,” Carter recalled, “she began to fend for herself and gradually started to regain her strength and health again.”

Yet, unbelievably, it would take another six years before Carter left Lucy to her own devices. During that time, Lucy adopted an orphaned infant male chimpanzee and raised him as her own child until the age of three, when he died of a stomach parasite. Lucy herself suffered a near fatal bout of hookworm but recovered. Then one day in 1985, a young male chimp on the island named Dash attacked Carter, dragging her until she got caught in a thorn bush. She managed to slip away into the river and swim back to her cage. But Carter knew then that she’d been supplanted as the dominant “chimp” on the island and decided it was time to make a break.

She moved back down river and took up residence in the jungle hut outside of Banjul that she still calls home. Six months later, she took a boat back to the island, overcome with curiosity about how Lucy was faring. Even before Carter’s boat reached the shore, Lucy rushed out of the jungle to greet her.

“She was clutching me so intently,” Carter recalled. “The two of us rocking back and forth on the beach. She didn’t want to let go.”

Another year passed before Carter returned to the island. On this second visit, however, Lucy wasn’t there to meet her.

“I sensed right away that something was wrong,” Carter said. “Lucy was always the first one to greet any human visitor to the island.”

A short time later, Carter found Lucy’s skeleton on the grounds of her old camp, lying beside the spot where Carter’s old cage used to be. It isn’t clear how she died, but the fact that she had no hands or feet—commonly coveted trophies among hunters and poachers—makes Carter suspect that one or the other shot Lucy, a readily available target given her unnatural affinity for members of our species.

“Knowing Lucy,” Carter said, “she may have directly approached some visitors, and they shot her in what they thought was self-defense. We’ll never know.”

Carter doesn’t question or regret the Temerlin’s decision to let Lucy try to find her true self. What she never expected is that Lucy would eventually help Carter find her own. What began as a sense of responsibility to her friend Lucy has since evolved into a lifelong commitment to help save what is left of an intrinsic part of all of us.

“I often wonder,” Carter said, “not just about what kind of hybrid species we made of Lucy by taking her away from her natural environment, but about what sort of species I was by the time I left that island. After all those years there with Lucy in the jungle, it was difficult for me to go back to who I was.”

Charles Siebert is a contributing writer for The New York Times Magazine and is the author most recently of “The Wauchula Woods Accord: Toward a New Understanding of Animals.”