I hope you all watched 'The Sperminator', which aired between ten and eleven this evening on Channel Four. It was a documentary about a highly successful US fertility expert who helped hundreds of couples conceive with the aid of sperm donation. What he didn't tell them was that all the sperm was his.

When you've finished considering the mechanics (yes, that does represent a serious amount of masturbation, doesn't it?) you might like to examine your personal feelings about this story. The reaction of the expert's 'victims' was almost universal shock and distress that they'd been deceived by a professional of apparent integrity.

My responses were (in this order): 'ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha' and 'good effort, son'. Though I'm sure the whole experience was terribly traumatic for the couples involved. (Ha ha ha!)

The reason, I think, is that the whole episode is at the zenith of the bell curve of comic schadenfreude. As we all know, ninety percent of comedy is chortling at the misfortunes of others. Rochefoucauld was more right than he knew: not only is there something in the suffering of our friends that does not displease us, more often than not we find the misfortunes of others frankly hilarious.

Imagine, if you will, a graph on which the x axis represents the degree of misfortune suffered by an individual or group and the y axis represents the level of hilarity to be gained from that suffering by objective observers. It soon becomes apparent that comedy itself describes, as I've suggested, a perfect bell curve. Just a little way along the 'misfortune' axis we get people walking into trees, stubbing toes and spilling drinks down their shirts. This may merit a wry smile, or, if you're juvenile enough, a Nelson Muntz-style 'HAR har!'. But there's nothing here that's deeply funny. Move along the axis of suffering and the laughter line climbs steeply as people drop pianos on their feet, accidentally reveal the existence of love children to their wives and drink Extra Strength Andrews Salts when they think they're knocking back vintage Krug. The curve tops off with people like our friends who got more fertility than they bargained for. On the descent we have rather more severe misfortune that is still quite funny: climbers abseiling off the end of ropes, grannies getting run over by ambulances and middle-aged men who sustain permanent rectal damage following the ill-advised misuse of household items. At the right-hand extremity lies Auschwitz, AIDS and misery - the comic preserve of those who are insufficiently funny to get noticed without being tasteless.

How wondrous are the patterns of nature. Tomorrow I shall demonstrate how there can only ever be a prime number of Maltesers in any given packet.

Oh, the munsterlander's just been spayed. She's wearing a lampshade and looking at me accusingly.