We must never forget the danger that lies beneath the surface of the human heart

Our thoughts continue to be with the families of the victims of the shootings in Cumbria that left 12 dead, 25 injured, and families and communities torn apart. And in the aftermath people have been asking, how could it have happened?

The killer, Derrick Bird, was described by those who knew him as quiet, unassuming and friendly. He had just become a grandfather. He looked after his elderly mother, enjoyed his hobbies and had just come back from a holiday. A close friend said: “He was a really nice guy. Something must have clicked in his head. He must have just snapped.”

People do just snap, and there have been other similar tragedies in recent times, in Dunblane in Scotland, and in America in Columbine and Virginia Tech. Usually the killers are younger but it can happen in the most unpredictable way, leaving behind a trail of grief and bewilderment.

One of the great errors of modern thought was to believe that we are rational creatures who make decisions on the basis of deliberation and calculation. Reason, said the heroes of the enlightenment, can cure of us the passions and prejudices of the past. We now know that the human mind doesn’t work that way.

Neuroscientists have shown how decision making is inseparable from emotion. There are two systems at work in the human brain: the amygdala which generates highly charged emotional reactions, and the prefrontal cortex, more rational and deliberative, capable of thinking beyond the immediacy of the situation. The second system is significantly slower, so it’s always at risk of being overridden under stress or fear or anger. That’s how we often act irrationally and how, in extreme cases, ordinary people can commit terrible crimes.

Christianity called this original sin. Jews called it the evil inclination. “The heart,” said Jeremiah, “is deceitful above all things, and beyond cure. Who can understand it?” The Bible traces this back to the first two human children, when Cain in a fit of anger killed his brother Abel -- then said, in sudden realisation of his guilt, “My sin is more than I can bear.” That’s why perpetrators of violence like Derrick Bird often end by turning it against themselves.

So for all our everyday calm, we must never forget the danger that lies, like an unexploded mine, just beneath the surface of the human heart. Meanwhile to the injured and the bereaved, we send our shared grief and our prayers.