Chimpanzees have distinct personalities that can be quantified in the same way as human personalities, according to research by Lindsay Murray of University College Chester.

"Some people think that personality is the last bastion of human uniqueness, but my work shows that we can quantify and scientifically prove that chimpanzees have personalities," said Dr Murray. She presented her findings yesterday to the British Psychological Society's meeting in Belfast.

Dr Murray spent 1,000 hours watching 59 chimps at Chester, London and Twycross zoos. She rated each chimp on a scale of one to seven for each of 28 different characteristics, including playfulness, aggression, sociability and intelligence. She also asked the zoo keepers to complete the same assessment.

Each chimp was found to have a statistically unique personality. Dr Murray also demonstrated that personalities varied between the sexes and age groups of the chimps.

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She identified five distinct types of personality. The "excitably confident" type was found only in adults, while the "sociably confident" type was found among both adults and immature chimps; and the "sociably placid" type was found only in immature chimps. The "excitably timid" type was found only in female chimps. "Whenever an argument broke out in a group, males made a display but females tended to run to each other, to embrace and reassure each other or to fight," said Dr Murray. "The males generally didn't seem to get in a flap as much as the females did." The fifth personality type was "sociably timid".

The conditions in which chimps were kept also influenced their personality, Dr Murray discovered. The 22 chimps at Chester Zoo and 11 chimps at London Zoo were kept in large groups, and were more sociable, intelligent, curious and irritable than the seven chimps at Twycross Zoo, which were hand-reared and kept in pairs and a trio.

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"Although the chimpanzees are in captivity and cannot escape, in a large group they can keep a distance from another individual. Keeping chimpanzees in pairs does not allow for preferences or personality clashes."

Dr Murray believes that her findings will strengthen the case for chimpanzees to be granted rights. "You cannot help but be affected by these animals and you do tend to campaign for them," she said. "Chimpanzees should be granted the right not to be killed or kept in atrocious conditions. You wouldn't treat humans that badly so you shouldn't treat something so human-like that badly."