Call them the sexy apes. Or the feminist apes. Or the gentle apes.

But for some scientists, they can be downright inconvenient apes - because the little-known bonobo species is hurting old theories that human behavior evolved from war-like, male-dominated chimpanzees.Bonobos are just as related to people as are chimps. But the females are clearly in charge. They're peaceful. More intriguing: They have sex all the time, not to procreate but to settle conflict or get to know each other - and unlike other animals, they have it face-to-face with some French kissing thrown in.

"We may be more bonobo-like than we want to admit," says Frans de Waal, a well-known primatologist at the Yerkes Regional Primate Center whose new book, "Bonobo: The Forgotten Ape," is one of the first major works on the rare species.

Chimps, bonobos and people all evolved from a common ancestor 6 million years ago, though most people have never heard of bonobos. The question is what characteristics that ancestor passed to which species, and why.

Bonobos live in just one remote corner of the world, the deep rain-forests of Congo. Scientists didn't begin seriously studying them until the 1970s. Fewer than 100 are in captivity. There's no word yet on how well they survived last year's bloody civil war in Congo - Japanese experts only recently ventured back into the bush.

Bonobos have smaller heads, slimmer necks and longer legs than chimps, and a more humanlike posture. They're rather stylish, with red lips and distinctive black hair parted neatly down the middle.

Evolutionists had pictured early humans as decidedly chimplike - a violent, hierarchical society led by powerful, competitive males.

The bonobos throw a serious kink into that theory. "That coherent picture we had of our evolution is crumbling," de Waal said.

First, they embody "sisterhood."

Females are only 85 percent as big as males, yet they band together to take charge. Females leave their original group when they're grown, migrating into new bonobo societies where they bond with other females to establish a spot in the hierarchy.