I couldn’t believe what I was seeing: somebody was standing on our garden wall and lopping off the branches from our hazel tree that overhung the wall slightly. And the tree-lopper hadn’t even bothered to knock on our door to talk to me about it first! I hesitated for a second or two – I rarely lose my temper – and then hurtled outside to ask them what they thought they were doing. A few heated words were exchanged and I spent the rest of the day smouldering with rage, until an apology and a bottle of wine helped set matters right.

Even at the time, I was taken aback by the strength of my anger and how it flared up seemingly out of nowhere. The overwhelming sense of affront and indignation – of how very dare they! And now, when I see our 11-week-old terrier puppy starting to yap at the passing strangers he glimpses through the gate, I’m struck again by how deeply rooted this territorial instinct of ours goes.

The theory proposed by neuroscientist Paul D MacLean in the 1960s argues that primitive drives such as this are processed by the reptilian brain, which comprises the basal ganglia and brain stem, and which also governs vital functions such as breathing and blood pressure as well as procedural memory. According to this model, like the fight-or-flight impulse, the territorial instinct is hardwired into us as human beings.

Which is quite a sobering thought.

At least, I guess, I didn’t rush outside and try to bite the offending tree-hacker (though if I’d had the teeth for it, I might have been tempted). If the territorial instinct comes as naturally to us as breathing, then perhaps it’s a question of how to adapt these kinds of instincts to the times we live in – and trying to make conscious decisions about when to suppress and, likewise, when to give in to our animal drives?

The new pup: butter wouldn’t melt…