Imagine that you're walking along a quiet street and you see a wallet lying on the pavement. Would you take it? Now imagine a slightly different situation - the wallet has a red circle drawn around it. While many people would be tempted in the first scenario, almost no one would touch the wallet in the second. The key difference is that the lone wallet was most likely dropped accidentally by a passer-by buy the encircled wallet was clearly placed and marked by someone, who may well still be watching. And there is nothing that keeps people more honest than the presence of a watchman.

Social experiments like these are of great interest to biologists because they tell us more about the nature of selfishness and altruism. In recent years, selfishness has become something of a biological buzzword and many influential writers have cast living things as self-serving vessels acting for the benefit of their genes. In this harsh light, individuals co-operate with each other only if their genes reap a reward.

But some acts of altruism, particularly human ones, are harder to explain. We are often kind and generous to others, even if they are unrelated (and so share no genes) or are unlikely to ever repay the good deed. Is this true selflessness, or is there something else going on? One theory is that such selfless acts do provide benefits - they raise the reputation of the do-gooder in the eyes of their peers. Even selfish people can act selflessly when their reputation is on the line.

Lab experiments have shown that people co-operate more strongly if they know they are being watched. But Melissa Bateson and colleagues at the University of Newcastle have shown just how honest people become when they feel that Big Brother is watching them, using a cunning experiment in a more natural environment. Rather than artificial confines of a lab, they chose to run a simple test on the unwitting members of their university's Division of Psychology in their own coffee room.

The walls have eyes

For years, Bateson had put up a friendly notice reminding staff members to pay for their tea, milk and coffee by putting money into an honesty box. To run her experiment, she made one small change - she added an image banner to the top of the notice which alternated on different weeks between some flowers and a pair of eyes. Each time, different eyes were used of varying gender and expression but in all cases, they were staring straight at the reader.

When she compared the amount of money collected from week to week, with the amount of drink that people bought, the results were striking. On average, people paid almost three times more for their drinks when the pair of eyes watched over them. When the image changed from flowers to eyes, the payments always went up and when they were changed back, they always went down. The mere appearance of Big Brother prompted people towards greater heights of honesty.

It's very unlikely that the eyes made the staff members consciously believe that they were actually being watched. After all, the room's layout ensured that cheats who didn't pay up could not be spotted and would never be caught by their colleagues.

Instead, Bateson believes that the eye images probably set off unconscious and automatic reactions in people who viewed them, a sort of mental reflex. Her theory is that our brains are very keenly attuned to cues that indicate that our behaviour could affect our reputation. The presence of onlookers could be one such cue, and indeed, human brains have special neurons that are primed to respond to eyes and faces. The effect of such cues must be very strong indeed, since the relatively weak stimulus of an image of eyes produced such strong changes in behaviour.

But what does this say about us? Are we truly all self-serving hypocrites, helping each other solely to further our status? Clearly not. For a start, even the images of flowers prompted staff members to contribute small amounts of money to the honesty box. If we were all the wholly selfish creatures, then even these paltry payments might be unexpected.

More importantly, the responses to the eye images were sub-conscious, rather than active decisions. A selfless act consciously designed to further one's status might be robbed of its valour. But a selfless act based on an instinctive reaction is a selfless act nonetheless. If this experiment tells us anything, it is that safeguarding our reputation, for whatever reason, is very much part of being human.

Reference: Bateson, M., Nettle, D., Roberts, G. (2006). Cues of being watched enhance cooperation in a real-world setting. Biology Letters, 2(3), 412-414. DOI: 10.1098/rsbl.2006.0509