It is thought chimpanzees are capable of deception
Schoolchildren have been given a lesson in deception by psychologists at Abertay University.
Pupils attended a lecture at the Dundee university which examined why humans lie - and how to detect when people are telling fibs.
Abertay's head of psychology Dr Derek Carson said they were not advocating lying, but wanted to show why it was an important human behaviour.
"Some lies help us get on with each other," Dr Carson said.
"It helps maintain social relationships. When asked by your spouse: 'Does my bum look big in this?' we may not be entirely honest in our response.
"Lying helps maintain the social fabric."
More than Freud
The talk was given by Dr Carson and three other psychology lecturers at the university: Dr Clare Cunningham, Dr Vera Kempe and Dr Ken Scott-Brown.
More than 50 students from Kilgraston School in Perth and Kinross and Fife's Beath High School attended the lecture.
Dr Carson said he hoped it would introduce the pupils to what topics psychologists were interested in.
"Many members of the public think psychology is all about Freud and psycho-analysis and of course it's about a whole lot more than that," he said.
The pupils were shown examples from the animal world which appear to indicate that not just humans are capable of lying.
The head of psychology said: "If a chimp spots some food in his immediate environment and then a more dominant chimp comes on scene, the first chimp is likely to look away from the food."
"Tentative" evidence that some large-brained primates could be deceptive indicated that humans could have "evolved to use deception", Dr Carson told the BBC.
Pupils were also given some tips on how to catch liars out.
"People tend to over-estimate the importance of non-verbal cues, like fidgeting and maintaining eye contact," Dr Carson said.
"What you actually find is that when someone is lying they tend to control the amount of fidgeting they do and make eye contact - because they're aware that's what people think.
"If you do want to get better at detecting liars, you need to pay more attention to what people are saying instead."
Research has shown that people's answers tend to be shorter when they are lying and they make fewer references to themselves.
People who are telling the truth will put more details in, he added.
And Dr Carson had a message for all parents who were upset their young child had started to lie.
"It's quite an important indication of a developmental change in the way a child thinks," he said.
"The parent should actually be quite pleased as it shows normal development."