Scientists in Scotland have discovered that female chimpanzees can be just as violent as their male counterparts.
Female chimps were previously thought to be less aggressive
The St Andrews University psychologists found examples of female chimps killing the offspring of incoming mothers, previously regarded as a male trait.
The Fife team has been studying chimps in the Budongo Forest, Uganda.
The researchers said only three previous instances of lethal aggression in wild female chimps had been documented in the past 50 years.
The belief was that male and females differed greatly in nature but the psychologists found that if the chimps' resources come under threat, the females could become just as aggressive as males.
While observing chimps in the Sonso community, the researchers came across three examples of female apes killing the offspring of incoming mothers.
One attack was so violent that a baby chimp's head was bitten off.
Simon Townsend, who led the study, said: "It's true that males are much more often seen to engage in extreme physical violence than females, and this has led to the notion of violent and demonic males in contrast to quite peaceful females.
"However, our research shows that, under the right socio-ecological circumstances, these chimp gender stereotypes collapse completely.
"If their resources are under threat, females can become just as violently aggressive as males."
Similar behaviour was described by a leading primatologist in the 1970s, but her findings were later disregarded as inconsistent.
Mr Townsend said female aggression only occurred under specific circumstances.
He added that an increase of immigrant females entering the Sonso community had put pressure on food and mate resources, which had caused the violence.
"It is impossible to predict when another instance may occur," Mr Townsend said.
"However, we are very interested in keeping a close eye on levels of female aggression in the Sonso community, especially in the instances when new females attempt to immigrate."