The eccentric professor aiming to make maths sexy


Assuming that all human behaviour produces patterns, it’s possible to view our sex life through a mathematical prism. Jean Paul Van Bendegem brings the torch of reason into the vault of human desire

The science of love

Anyone who’s been taught by Jean Paul Van Bendegem, a professor in mathematics, philosophy and logic at the Free University of Brussels (VUB), will always remember this slightly eccentric figure. Best described as a hybrid of Rasputin (his looks), a vicar (his clothing) and some obscure ancient Greek philosopher (his thinking), Van Bendegem is surely one of the most colourful scientists in Flanders.

Two years ago his book De vrolijke atheist (The Merry Atheist), in which he describes his life without a god, was a bestseller. Now the latest product of his pen, Elke drie seconden (Every Three Seconds), might just do the same. It’s about sex.

But beware if you detest numbers and formulas: If you open the book at a random page, the chances of finding a naked woman are equal to running up against a complex equation.

Strategic courtship

Van Bendegem (pictured) takes you back and forth between maths and sex – and you can almost hear him sniggering while you read. But apart from its little facts about sex, the book also has a message: There’s a strategy – a mathematically proven one – to finding the best partner. So, should you dump someone for the sake of maths?

“Statistically speaking, the optimal strategy to find the best partner goes as follows,” he explains. “First of all you set an upper limit for the total number of partners you want to have – for example, 10. Then, if you choose all your

Nothing prevents us from looking for patterns, structures and regularities in the human sex life

- Jean Paul Van Bendegem

partners arbitrarily, you have a 10% chance of meeting the ‘best one’.

“But maths tells us that it’s possible to raise that chance to 37%. The only thing you have to do is to drop the first four – no matter how good they are. Then you take the first one who is as good as or even better than the best of the four you’ve dumped. Now you have a 37% chance that this one is the best.

“Of course, I’m not telling you to follow this strategy. I only want to show you that a mathematically proven method exists to find a better partner.”

I suggest that he is using sex as an “in”, a way of confronting the general public with higher mathematics. To me, few things belong together less than sex and maths.

“That’s exactly the reason I wrote this book. For years people have told me that maths has nothing to do with love, sex, emotions, etc. Of course, when I’m having sex I’m not thinking about numbers and formulas. But nothing prevents us from looking for patterns, structures and regularities in the human sex life. Mathematics is one of the most convenient ways to uncover these.

The bean jar theory

“In my book I use very complex equations,” he continues. “Like in the part where I explain the ‘bean jar theory of married sex’. It says that if you put a bean in a jar every time you have sex during the first year of your marriage or relationship and from the second year you take one out every time you have sex, the jar will never become empty.”

Van Bendegem believes the moral of this story is that the first year is filled with passion, but afterwards “it’s merely trouble and affliction”. And for him, the bean jar theory is the perfect opportunity to unleash a mathematical formula.

You could say that a condom used by a cautious man counts for two

- Jean Paul Van Bendegem

“So I’ve calculated the problem for different scenarios. Take a couple that has a lot of sex during the first year, and later – for the rest of their lives – they maintain a fixed pattern. In this scenario, it’s very easy to empty the jar.

“Two other scenarios, in which frequency diminishes over the years, have different endings. When the frequency is below a certain value, the jar never becomes empty, and when it’s above, the jar is empty after eight years. And then I show that the theory makes no sense, because this threshold is really low.”

Apparently, I say, having more sex is the best way to fight STDs. “It’s not originally my idea, but I included it in my book because I love the way of reasoning: It’s scientifically well-proven, but also counterintuitive,” Van Bendegem says.

“If we assume that the ‘sex market’ – the idea comes from an economist – is dominated by the so-called reckless people, then it’s clear that this results in an unsafe situation. But if we urge the more cautious ones to participate more in sexual activities, then the market expands. The part occupied by the reckless ones becomes smaller. Furthermore, the cautious will persuade the reckless ones to have more safe sex. You could say that a condom used by a cautious man counts for two.”                                                                                                          

I’m still curious about the title of the book, I tell him. Do men really think about sex every three seconds?

“Not at all,” he says. “I would say it’s every 51 for men and every 96 for women – minutes, that is. But when you read my book, the frequency might be much higher.”

Elke drie seconden is published by Houtekiet

Photo by Bernadette Mergaerts

The maths behind sex: Professor Jean Paul Van Bendegem brings the torch of reason into the vault of human desire

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