The researchers recorded GHC behaviour in four social groups of semi-wild chimpanzees living in the Chimfunshi Wildlife Orphanage Trust (CWOT) in the north west of Zambia.

BBC: Chimpanzee grooming is a 'postcode lottery'

Of the four groups studied, two engaged in GHC behaviour - one had a preference for wrist-to-wrist GHC whilst the other preferred palm-to-palm.

BBC: Chimpanzee grooming is a 'postcode lottery'

To survive and attract more help from the outside, the rebel groups need not only to rein in such behaviour but also to hone their military and political skills, says Emile Hokayem, a Bahrain-based analyst with the International Institute for Strategic Studies.

ECONOMIST: Rebel forces

There were also no significant differences between the groups in relation to their speech, language, behaviour or neurological development.

BBC: Pregnant woman undergoing an ultrasound

She said extra policing sponsored by Butlins was being brought into the town because residents were intimidated and put off visiting the centre due to the high level of groups in the pubs and bars, and incidents of alcohol-related anti-social behaviour.

BBC: Minehead Butlins