ere's a question for you. You're sitting on a park bench, reading a newspaper. A stranger is sitting next to you, feeding the birds. An economist walks up, and makes the pair of you an offer. "I have $100 to give you, but I don't know how much each of you should receive," the economist says. He looks directly at you and says: "I'm going to let him" ? the stranger ? "decide how to split the $100. Then, I'm going to let you decide whether to approve or reject his decision."

If you approve the stranger's decision, the economist says, the money will be divided up that way. If you reject it, neither of you will get anything at all.

What would you decide? Put the newspaper down, or push it away, and think about your answer.

That conundrum was posed in an article in 's September 18 issue. Since we can't hear from you, I'll tell you what my response was.

My immediate, answer was: "No way". The stranger would decide to take it all, and why should he have $100 if I were going to get nothing?

A little after 12 seconds later, I changed my mind. If I rejected whatever the stranger might decide, I'd get nothing. If I approved his decision, the worst I could get was nothing, and maybe I'd get something. Since, financially speaking, the chance of a profit is better than the certainty of nothing, I decided that my final answer would be to approve whatever the stranger decided.

I had nothing at the start of the exercise, and the worst case was that I'd have nothing at the end. But since accepting the offer might mean I'd make a gain, my second answer was, in my opinion, the better one.

Now that, my friends, is a slap in the face for all those who think I'm a weirdo, because that response ? or more precisely those two responses ? are the perfect example of how the human brain is wired. My initial reaction (and probably yours) was visceral, the classic "gut reaction". Why should I let some stranger decide how much we each should have? And wasn't it likely that he'd decide to take it all? Screw that, I thought. If I'm getting nothing, he should get nothing. That would serve him right for being a greedy so-and-so in the first place. My inner caveman is apparently alive and well.

Given enough time, however, that unsophisticated version of me was supplanted by a rather smarter one, the one that worked out that it might actually be in my best interests to accept the economist's offer. I recall thinking: "I don't know the stranger. What do I care if he walks off with the $100? Good luck to him. I'd be no worse off than I was before, and I might even be a little better off."

I said that it took more than 12 seconds for the smarter me to work things out. The reason I chose that amount of time is that 12 seconds is all the time that people taking this test under clinical conditions are allowed in which to give their answer. And what the tests show is that, within 12 seconds, most of us refuse to accept the stranger's decision.

The article, written by John Cassidy, is a fascinating read. In the clinical tests, volunteers were shown an image of the stranger, and a series of proposed splits of the $100 was presented to them. "Low offers were usually vetoed," Cassidy writes.

Our response to unfairness, especially where it concerns ourselves, may have something to do with a basic instinct for fairness. When injustice is meted out, we might react so violently that we punish the nearest person ? in this case, the stranger ? even if we ourselves suffer in the long run. That notion would certainly go a long way to explaining the behaviour of some of the cavemen I have run into the past few years.

The article suggests that certain behavioural patterns innate in human beings since our caveman days are in conflict with certain other responses that we have learned since. The brain can sometimes be a battlefield. Yet the research says that those who remain more in touch with their caveman side after 12 seconds, i.e. the more aggressive among us, may do better as investors.

In a broader sense, that's why markets don't work as well as they should. Most economists agree that people usually act in their best interests, and in theory the market aggregates all that behaviour and produces results that are best for the common good. But not all decisions that people make are in their own best interest. Some are motivated by anger, jealousy, thoughts of revenge and other less positive responses. When markets aggregate mixed feelings, they produce mixed results.

My inner caveman, of course, wishes these were still the caveman days. If we were, I'd have a wife, because I'd have clubbed some unfortunate cavewoman on the noggin and dragged her off to my cave. I've tried that, but it doesn't work very well. Thank goodness I don't let my inner caveman make my financial decisions.