Philadelphia - Baboons live in a complex soap opera that mirrors the social world of humans, American scientists reporting from Botswana have revealed.

A study showed that, just like people, the monkeys are able to combine their knowledge of kinship and group rank.

The ability to classify others by membership of a social group requires a lot of brainpower.

Scientists believe such social complexity may have contributed to the evolution of human mental abilities and language.

To investigate baboons' social thinking, scientists studied 80 animals at the Okavango Delta in Botswana.

Baboon groups are organised around a rank hierarchy of matrilineal families.

At the top of the pecking order is the matriarch of the highest-ranking family, followed in descending rank order by her offspring.

Next in line comes the highest-ranking female in the next family down, followed by her offspring, and so on.

A team led by Dorothy Cheney, from Pennsylvania University in Philadelphia, played to wild female baboons sequences of recorded calls mimicking fights between two other females.

Not only could the listening females tell which individuals were fighting, but they knew what families they belonged to - whether dominant or subordinate.

The calls were manipulated to produce "dominance rank reversals" both within and between families.

Rank reversal between families caused the most upheaval.

Writing in the journal Science, the researchers said: "Our results suggest that baboons organise their companions into a hierarchical, rule-governed structure based simultaneously on kinship and rank.

"The selective pressures imposed by life in complex social groups may therefore have favoured cognitive skills that constitute an evolutionary precursor to at least some components of human behaviour."

Another study, also from the University of Pennsylvania, showed that friendly baboon mothers raised their infants more successfully than unfriendly mothers. - Sapa-DPA