Howard Jacobson: What do you do if you've got too much time on your hands? Start a fight

The boredom of existence explains our going astray in nine cases out of 1

He's called Santino, he lives in Sweden, he's 31, he's an alpha male, he stockpiles rocks, and there's speculation that he might just be a genius. Oh, and have I mentioned he's a chimpanzee?

I have to say that building up an arsenal of stones to throw at visitors doesn't suggest genius to me. I could cite you hundreds of similarly well-planned acts of aggression drawn from every corner of the planet. But for some reason we are still amazed, Darwin notwithstanding, whenever chimpanzees do what we do. Jane Goodall, who know chimps better than anyone, is not surprised. She tells of chimps who work computers, never mind hoard pieces of masonry – chimpanzees who recognise themselves in mirrors, who mourn the loss of friends and partners, and sometimes die from grief. What does it say about us, then, that the presence of refined emotion in primates impresses us less than their ability to prepare for war?

Rather than marvel at his capacity to arm himself, oughtn't we to ask what struggle Santino is arming himself for? He isn't specifically the victim of Western imperialism. He doesn't have recourse to holy books telling him to murder unbelievers. That I know of, no banker has run off with his life savings. So whence the pent-up rage? What has the world done to Santino that Santino must attack the world?

Silly question. Only imagine living in Furuvik Zoo for most of your adult life and you have your answer. Not that I have any particular charges to make against Furuvik Zoo. Being confined in any zoo cannot be fun. But a zoo that's cold and dark for half the year must be the least fun of all. Similarly having people pointing and laughing at you every time you peel a banana. It's immensely intriguing for us to see our backward reflection in a chimp's behaviour, but there's no reason to suppose the chimp will be entertained by the prospect of where evolution's taking him. By God we must look ugly to Santino's eye, and if he is half the genius experts make him out to be, he won't be much impressed by what he reads of our intelligence as we grimace and gibber at him through the bars in the hope that he will grimace and gibber back.

But while intense dislike of our appearance and demeanour explains Santino's throwing whatever he can lay his hands on at us at the time, it doesn't quite get to the bottom of his forward planning. Such an orchestrated campaign suggests either a more simmering resentment – an ideology of hatred, fed night after after night by memories of grievance aggravated by calculations of revenge – or it suggests boredom. Myself, I go for boredom. Where there is nothing to occupy the mind, where the daily routine is a hell of unchanging repetition, collecting stones has plenty going for it. As in the politics of the street, so in a zoo. You build your little arsenal because there's eff all else to do.

The boredom of existence explains our going astray in nine cases out of 10, whether we fall into bad personal habits, keep unsuitable company, wield knives, shoot guns, or join a terrorist organisation that enables us to do all these things simultaneously. The devil finds work for idle hands – never was there a truer saying. Because of its specificity as to the manual nature of sin, I have always assumed this expression originated as a warning against masturbation – the first thing idle hands find to do – and proceeded from there to include acts of wider devastation. Masturbation, anyway, remains the model of human wastefulness. It is true that at a certain age boys must masturbate or implode, but later on it is boredom as much as lust that drives men to self-abuse. The long day wanes, the slow moon climbs, friends are away, there is no book to read and nothing on television – what could be simpler than to reach for the only other available distraction, which enjoys the added advantage of being free?

I know that our society has decided there is nothing devilish in treating one's own body as a toy, but in this as in other matters our society is wrong. I once had a cat that climbed on to the couch and masturbated as soon as he had finished with a mouse. Leave him with nothing to do for more than five minutes and he was at it. And what showed in his eyes when he had done with himself was a depth of weariness and self-disgust that would have put Saint Augustine to shame. Whatever we think, the cat knew the devil had gone to work on him.

Even sex proper – sex with a person who is not yourself – is finally as much tedium-driven as it is prompted by ungovernable desire. It is idleness, half the time, that turns a man's wastrel thoughts to adultery or the safer option of prostitutes and pole dancers. The spare hour, the spare night, and then, if you're not careful, the spare life.

Ditto most acts of teenage violence and what sentimentalists call freedom fighting. Scratch a terrorist and you find a man with too much time on his hands. Sympathy with terrorism is also born of tedium, hence its doing such brisk business on university campuses; for idle minds, too, the devil finds business. This is not to say that consciousness of oppression doesn't sometimes rouse the onanist from his slumbers – it's a small step from self-abuse to abuse of others – but time weighing heavy usually counts for more than grievance (indeed time weighing heavy often is the grievance) and missing violent excitement for its own sake explains why terrorists return to their weapons, as they are doing now in Northern Ireland, when all justification for using them has long passed.

Hard to be a moth of peace when you have been an engine of war. Which is why it's a good idea to parley with terrorists and give them jobs in local government. With little fiefdoms to control they can sustain the illusion of purpose in the face of life's unbearable monotony. But leave them to the streets and we cannot complain when they start stockpiling stones again. Large-scale unemployment beckons. With unemployment comes idleness, and with idleness bored hearts turn to hatred. We should have provided the fail-safe of education – just think, a year out of work means you can finally finish Middlemarch – but we didn't. We just threw in bananas. So we shouldn't be surprised when the bored neglected Santinos of our society start throwing back.