THOMAS ap Rhys Pryce’s death at the hands of two teenagers generated many headlines this week. However, one in particular seemed to amplify the senselessness of his death: “Muggers commit crime for kicks”.

Then there was the news that two public school boys had embarked on a burglary spree just for the buzz. While research published by the Economic and Social Research Council this week suggested that many street robberies are not undertaken for financial gain but simply for the thrills.

So what’s the science behind the thrill-seeking of adolescence? Risk-taking in teenage boys is traditionally blamed on excessive levels of the male hormone testosterone. And it’s true that 20 times more testosterone courses round their bodies after puberty than before. It is also true that accidental deaths — whether the result of violence, speed or foolhardiness —- soar at puberty, reaching their peak in males aged 16 to 25.

But this neat hormonal explanation for violence has always been troublesome. While extreme levels of testosterone are associated with criminality, levels at the high end of normal are as likely to be found in young men who are popular leaders with bright futures as they are among troubled joy-riding teens. And testosterone doesn’t explain the behaviour of the packs of teenage girls who roam city centres on a Friday night.

Greater understanding has come only in the past decade. MRI scanning has revealed the teenage brain to be under construction or, rather, reconstruction.

Far from the brain being fixed by the age of 3, as previously thought, it goes through an extensive period of remodelling after puberty. This principally affects the pre-frontal cortex, an area of the brain involved in executive action, such as planning, control, impulse-inhibition and so on. Testosterone might light the fire but it is the brain that has responsibility for spotting a danger and turning on the extinguisher, and in some still evolving brains the lever may still be a bit sticky.

But all teenagers’ brains are experiencing the same rebuilding process, so why do a minority behave as they do? Another hormone altogether might be in the frame.

Children who are abused or who suffer periods of deprivation have high levels of stress hormones, particularly cortisol but also adrenalin. It’s an adaptation that helps them to cope better with challenging circumstances and confers high levels of “startle” and alertness that might be life-saving.

It has always seemed to me that the higher your level of adrenalin, the more extreme the risk needs to be to generate a rush. Add this to a brain not able to control impulse as effectively and you have a recipe for the kind of pointless tragedy we’ve been reading about this week.

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