Last week's Orange Prize was a wondrous event, in one particular respect: separate juries of men and women were able to agree on something - which book should win. But if two ordinary book groups, one of men and one of women, had judged the prize, I bet they wouldn't have reached the same conclusion. They probably wouldn't even have been reading the same books.

My wife and I are both members of book groups. Hers is all women, mine is all men. And they have nothing in common. Ours values order. We have a constitution to which we must adhere. We have formal procedures for choosing books: emailed pitches the week before a meeting; verbal pitches at the meeting; a PR voting process that would baffle even Lord Jenkins. We have an order of debate and if anyone breaches it there are howls of outrage. And each of us gives every book a mark out of 10, so we can keep a league table of favoured books.

At Isabel's group, however, they just turn up and talk. Incredible. It sometimes seems, as members of her group admit, that decisions are made by the person who is last to say: "Oh, no, your idea's better than mine." But all the women are happy with that.

Why the difference? I always thought it was, in part, because we enjoyed the preposterousness of our constitution. We celebrate our self-importance with pompous discussions of amendments and standing orders. We are the kind of men who enjoy lists and statistics, and think John Motson's football commentaries add to the sum of human knowledge.

Of course it's not that simple. Men are more competitive than women, some psychologists argue, and so are more concerned with rules. Rules, they think, will help them get their say by ensuring that no single voice can dominate. Women, on the other hand, are more trusting and consensual, more able to have open discussion without any person feeling neglected.

Amanda Holloway, a member of an all-woman book group in London, says her group could benefit from some rules - but not too many. "It might be nice to have a structure, so we could be sure of having time to discuss the book, rather than drifting off into talking about other things," she says. "But it's not because we're consensual. It's not all touchy-feely. We do not just defer to each other."

Another notion is that men are happy to tread on each other's toes in order to reach their goal, whereas women see the group activity as a goal in itself. But what's wrong with being goal-driven? It's healthier - all our resentments and rivalries can be aired because the constitution allows us to vent them. But I have seen my wife and her friends together. They frown on confrontation and without the chance to air their grievances, they must surely get resentful.

Holloway says that need not be the case. "Resentments do get aired. We have all had our say and we've disagreed strongly. It can lead to unpleasant silences and crossed looks."

But that's the point men would make: silences and crossed looks are not signs of a healthy airing of grievances. Maybe we take our openness too far (there was, probably, no need for one member who disagreed with others over Tim Lott's White City Blue to leap to his feet in a restaurant and bellow: "Come on then, I'll take you all on!"), but we know we can say the most outrageous things, secure in the knowledge that the discussion will have moved on within moments.

But members of both groups are adamant that the single-sex make-up is what makes them work. A husband (not me) once attended Isabel's group; the result was a stifling of debate.

Our group, too, would change if women were present. It's hardly a testosterone-fest, but it's not exactly woman-friendly either. We're pedantic in the particularly male way that leads someone to dismiss a book solely because there is an inaccurate reference to halibut fishing on page 136. We shout and swear, loud enough to attract attention in restaurants, though never loud enough to be thrown out or - yet - asked to shut up.

So who is right? Our group or theirs? Or would we all be much healthier if we invited the other lot in for a get-together? Holloway would not want us in her group, she says. "You're anal retentives. You discuss discussing. We discuss books." And women in our group? I'm not sure the constitution would allow it.