Chimps' personalities are like people's, study says
Chimpanzees and orangutans really do have personalities "like people", researchers say.
For years experts have debated whether great apes truly display human-like personalities - or if such behaviour is simply the anthropomorphic projections of human observers.
The research team used a statistical technique to "remove" any biases apparent in human observers of the apes' behaviour, and they say their findings suggest man and ape really do share "personality dimensions".
- Common chimpanzees (Pan troglodytes) share 98% of human genes and are mankind's closest living relative. They are thought to be the most intelligent non-human animal
- Chimpanzees are known to modify sticks, rocks and leaves into "tools" to help the gather food such as ants, nuts and honey
- Orangutans are divided into two species: Bornean orangutans (Pongo pygmaeus) and Sumatran orangutans (Pongo abelii)
- The word orangutan translates as "people of the forest"
- They are also capable of learning to use "tools" such as sticks to gather termites. This knowledge is then passed down through the generations
"[Chimpanzees] have the same social problems that we do, they want to make friends and find mates and sort of gain position within their society," says team member Mark Adams, a researcher who conducted the research while studying for his PhD at the University of Edinburgh, UK.
Dr Alexander Weiss, senior lecturer at the University of Edinburgh, who also worked on the study, agrees that chimpanzee personality is "highly similar" to that of humans.
Researchers categorise human personality into five "dimensions", sometimes known as "the big five", he explains.
"Those dimensions are neuroticism, extroversion, openness to experience, agreeableness and conscientiousness."
Previous studies into non-human primates suggest that chimpanzees (Pan troglodytes) share these five dimensions with people, whilst orangutans (Pongo pygmaeus and Pongo abelii) display three of the five: extraversion, neuroticism and agreeableness.
These shared personality dimensions are best explained by our genetic similarities, says Dr Weiss.
"Humans and chimps share a common ancestor about 4 to 6 million years ago."
The common ancestor for humans and orangutans is thought to have existed fifteen million years ago, which explains why chimpanzees and humans are more similar in personality than orangutans and humans, says Dr Weiss.Ape vs man
There is continuing debate amongst experts as to whether scientists should use anthropomorphic projections when studying how animals behave.
Dr Clive Wynne, professor of psychology at the University of Florida, Gainesville, US describes anthropomorphism as "a mistake" when "trying to understand animal behaviour."
"Human beings have a very natural tendency to project human agency into almost anything that moves," he tells BBC Nature.
"It's very deeply ingrained into our ways of trying to understand the world around us."
But despite our inevitable "human perspective" in the way we see the animal kingdom, he says, "since these animals are not us, although it is difficult, we should nonetheless struggle to get our own perspective out of the way and to try and see them for themselves."
The research team carrying out the study, which features in the journal Animal Behaviour, wanted to test the extent to which human observers of chimpanzee and orangutan behaviour might be biased in their reports.
"There's sort of a fear that human observers and 'raters' are projecting their own ideas about personality on to these animals," says Mr Adams.
But until now, this theory "hasn't actually really been tested in great apes."
Members of the research team - who also came from from Kyoto University in Japan and the University of Arizona, Tucson, US - issued questionnaires to around 230 people observing chimpanzees and orangutans in zoos and research centres in the US, Canada, Australia and Japan.
The survey described about 40 to 50 personality "items", which when grouped together make personality dimensions.
What is "animal personality"?
- Individual animals display different personalities across a range of species, including mammals, fish, birds, insects and molluscs
- These personality traits control whether individual animals are leaders or followers, bold or shy, aggressive or passive, for example. As with people, some animal's personalities change as they age
- Great tits look for partners that are as outgoing as themselves, while zebra finches with similar personalities make better parents
- Some fallow deer are braver than others, spending less time looking out for predators and being more likely to try new foods
- A fish's personality may determine how likely it is to be captured - with bold fish more likely to be hooked
The human observers - called "raters" - were instructed to rate the apes' behaviour on a one-to-seven point scale for each personality item.
From the questionnaire results, the team determined the type of biases present in the raters' observations of the animals.
"We used a statistical technique to remove these observer differences before extracting personality traits from the data," explains Mr Adams.
"What we found is that controlling for these differences among observers made no difference, which suggests that the observers are not projecting their own ideas about personality onto the animals."
Dr Weiss says that the research "vindicates both the view that chimpanzees have personalities and perhaps the more controversial statement that their personalities are quite similar to those of humans."