Imagine a place where all the females give birth at the same time, where grandmothers nurse their daughters' children and baby-sit for them, and where all children are raised in a protective nursery. Where females join together in defending the community against dangerous strangers and those of the same age eat together without squabbling. Sounds rather progressive, almost idyllic, doesn't it?

But these mothers don't wear Birkenstocks. They will fight to the death to protect their territory, and their children, when their teeth are grown, eat freshly killed meat, raw, the blood still warm. This is a place where rogue males may show up and indiscriminately slaughter all the youngsters in the group.

Things like this happen in Tanzania, among lion social groups. Female African lions have a unique system of "plural breeding," whereby pride members consistently produce similar numbers of offspring. Craig Packer and colleagues, of the Department of Ecology, Evolution and Behavior at the University of Minnesota, analyzed data gathered over three decades from several generations of Tanzanian lions and found that, unlike other animal societies in which a dominant female controls the reproduction of her subordinates, lion society is egalitarian.