Sorry about the picture of Michael Portillo (above). Who’d have thunk I’ve have his fatty features squished onto my pages?

But he was on BBC 2 last night, presenting an ep of Horizon which has found its way onto my radar this series in a way it never has before. Maybe it’s the sleb presenters (David Baddiel et al), maybe it’s just that the BBC has made the subjects of each documentary more relevant and accessible than before. But this is the second or third Horizon film I’ve knowingly sought out and watched.

Last night’s film was all about violence and what makes humans behave so violently. Is it something we learn or something that’s innate, that we’re born with?

Portillo suggested he was normally a peacable type of bloke, although in psychiatric testing he revealed he’d smacked at least two computers and a fax machine in his time. “Scientists” say this sort of behaviour indicates the “core” personality of someone, which that person tries to control in everyday life. Certainly, most people try to control their violent tendencies after the age of three, when, we were told, the front part of the brain begins to develop strong links with the emotional centre of the brain, telling us that violence is wrong and it’s better to share than simply stab your neighbour to death.

But even Portillo’s supposedly equable personality changed after enduring 60 hours of sleep deprivation and the unrelenting, shrill demands of simulated three-month-old twin babies. “The noise goes through you like a knife,” said the presumably child-free Portillo on videocam. Tell me about it, Mike. I’ve got the bloody T-shirt for enduring night-time crying.

Apparently sleep deprivation, like alcoholism or a car accident, can damage the front part of the brain that controls violent instincts, leading to increased hostility and aggression. (At last! The explanation I’ve needed to put to my partner for years of barely concealed anger and resentment!) If Portillo was still in politics, perhaps he’d factor this sort of thinking into dealing with the perpetrators of terrible crimes like the abuse of Baby Peter. I’m not condoning that violence. I’m just saying the perpetrators need help too.

But there are other causes of violence involving more subtle changes to a personality. The sort of pre-meditated violence that led to the Holocaust in Nazi Germany or the massacres in Rwanda and Bosnia comes, it seems, from a human ability to swap morality for submission to authority. Portillo observed a terrifying experiment in which 9 out of 12 ordinary people subjected someone to a 450-volt electric shock because they believed it was being done in the name of science and because they took a professor’s word for it that no lasting damage was being done to the person receiving the shocks.

The sequence showed us everything we need to know about ideolody, totalitarianism, gang violence and how individuals can succumb to something bigger than themselves which overrides their own sense of what’s morally right.