Every great cause has its galvanic moment, when the world finally takes notice. Then comes the hard part—sustaining the commitment long enough to make a real difference. The campaign on behalf of the great apes enjoyed this kind of collective epiphany in the early 1970s after researchers discovered, among other things, that chimpanzees fashion crude tools, demolishing a supposedly essential difference between ourselves and our closest genetic kin. Around then, a wave of researchers, many of them women, set off in search of primates to study. Most have long since returned home. Among the exceptions is Janis Carter, who arrived in West Africa in 1977 for what she expected to be a three-week stay. She has been there ever since.

When I reached her by telephone in Banjul, Gambia, she seemed perplexed to be reminded that she has been working with chimpanzees in Africa for nearly 30 years. "I'm 54," she said as if passing on an unlikely news flash. "I still consider myself young even though I don't climb trees anymore, and I'm trying to be more careful."

Carter was on her way to visit the sanctuary for orphaned and captive-born chimpanzees that she helped establish on three islands in the Gambia River. Then she planned a return to the forests of Guinea, where she has been working with hunters, villagers and government officials to protect habitat for endangered wild chimpanzees. "I do have an odd sort of lifestyle," she conceded.

Blame it on serendipity. Carter was a graduate student in psychology at the University of Oklahoma when she accompanied two chimpanzees being released in the wild in Gambia, a coastal West African country. One was Lucy, a captive-born chimpanzee famous for being able to communicate in sign language. Carter was supposed to stick around just long enough to smooth the chimps' transition, but the venture proved far more difficult than she'd expected. After all, Lucy had been raised in a human home and perhaps thought of herself as a human child. In some senses, Lucy and other chimpanzees arriving on the island had to be instructed in how to become more fully themselves.

Carter demonstrated which foods were safe, led foraging expeditions, and communicated through chimp vocalizations. In one of two stories she wrote about her experiences for Smithsonian in the 1980s, she stated: "I knew that if the chimps' return to the wild was to be successful, I too would have to limit my contact with humans." The chimps were let loose on the island. She slept in a cage.

In 1985, Dash, a young male chimpanzee, attacked Carter, dragging her a considerable distance. Her body got caught in a thorn bush, and she escaped by rolling into the water for a swim back to her cage. As she nursed her wounds, it dawned on Carter that she'd just been knocked off her perch as the dominant leader on the island and would have to move.

Shortly after Carter left the island, Lucy died, possibly killed by a poacher. Devastated, Carter considered leaving Africa. But while puzzling over Lucy's death, Carter realized, with a start, how little she knew about the people who occupy dozens of villages along the Gambia River near the refuge. She saw that their support was essential to ensure the chimps' safety. "What Lucy's death did was push me toward human beings and away from the island."

When she reached out to the villagers, she discovered how little they understood her. One told her about a dragon-like creature that villagers believe lives on the island and about villagers’ suspicions that she was in cahoots with it.

Carter began surveying the attitudes of villagers toward chimpanzees and monitoring chimpanzee populations in neighboring Senegal and Guinea. In the Nialama Classified Forest in Guinea, she tapped local hunters' knowledge about where chimps find water and food, marked the corridors that link their feeding areas and mapped their migration patterns. This knowledge helps government officials and community leaders direct farming and logging where they won’t interfere with chimp survival.

Toward the end of our conversation, she mentioned Dash. She'd taught him how to recognize crocodiles and gather food before he drove her from the island. Thirty years old, he remains the swaggering, dominant male in his group, one of four groups in a population of more than 60 chimpanzees. Now, though, he's down to his last tooth. Like the mother of an aging son, Carter seemed startled to have discovered that Dash has grown pudgy. "It just seems unnatural that I’m going to outlive him," she said. "Unnatural somehow."