'Bystander effect' seen in chimps too

Chimps, like humans, can detect what is right and wrong but will only react if someone is trying to harm a member of their own group, finds a significant study.

They will remain bystanders if an unfamiliar chimp is being killed in an another group.

The study adds to the growing body of evidence that identifies the building blocks of human morality in our closest living relatives.

"The results suggest that chimpanzees detect norm violations both within their group as well as in a group of unfamiliar individuals but they will only respond emotionally to such norm violations which is within their own group," said lead researcher Rudolf von Rohr from University of Zurich in Switzerland.

For the study, the researchers filmed two social groups of chimpanzees living in two Swiss zoological gardens while the animals repeatedly viewed film clips that portrayed the actions of other chimps unknown to them.

The experimental clips included aggressive scenes, such as an infant chimpanzee being killed by its own kind, a small colobus monkey being hunted and killed by chimps and socially aggressive behaviour between chimpanzee adults.

The chimps did not merely respond to the infant screams they heard, they paid preferential attention to these scenes as a whole.

This shows that chimpanzees can distinguish severe aggression against infants from other forms of aggression and harmful behaviour.

Interestingly, although the chimps viewed the infanticide scenes much longer, the team found only limited evidence that what they saw caused the viewing chimps to be more aroused or to react to them.

According to Rohr, future research might provide important insights into the evolution of specific social norms in humans and why some of them are widely accepted and others are more difficult to establish.

The paper appeared in Springer's journal Human Nature.