It was the end of my sabbatical in Canada, and I was strolling around Stanley Park, one of the many jewels of Vancouver British Columbia. I was just finishing a four month trip in Australia and Canada studying educational methods used to teach general practitioners. OK I'll come clean—I was having an “extended holiday with a purpose”. On this beautiful autumnal Sunday, the air was crisp and, as the sun sparkled on Burrard Inlet, the colours of the spruce, maple, and arbutus painted the lower slopes of the snow clad peaks across the bay. “No wonder this is one of the most popular places to live in our world” I thought.

Despite this idyll most of the people I saw that day looked ill at ease, in pain even. Why? I hear you ask. The answer is obvious: they were jogging! Why is an activity that is so blatantly uncomfortable so universally popular? At least it is good for them I thought.

Weeks later I was idly sharing these observations with a friend. He asked casually for another example of a bodily system that functions …