Lost wallets which contain a snapshot of a baby are more likely to be returned to their owners, scientists have discovered.
Researchers left 240 wallets on the streets of Edinburgh last year to see how many were returned to their owners. Some of the wallets contained one of four photographs – the baby, a cute puppy, a family and a portrait of an elderly couple.
Other wallets contained a card suggesting the owner had recently made a charity donation, while a control batch contained no additional items.
Professor Richard Wiseman, a psychologist who supervised the experiment, said 42 per cent of the wallets were posted back in total.
Those containing the picture of the infant were most likely to trigger an honest reaction from the finder, with 88 per cent being returned, followed by those containing pictures of the puppy at 53 per cent.
Of those featuring the family snapshot, 48 per cent were sent to the return address and only 28 per cent of those with the picture of the elderly couple.
Wallets containing the charity cards and the control sample were least likely to be returned, with rates of 20 and 15 per cent respectively.
Prof Wiseman, of the University of Hertfordshire, said: "The baby kicked off a caring feeling in people, which is not surprising from an evolutionary perspective.
"We were amazed by the high percentage of wallets that came back."
The wallets were planted at random about a quarter of a mile apart. Snapshots were inserted into a clear plastic window inside the wallets, none of which contained money.