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A couple of years ago while I was at Latitude festival I went to a really interesting talk by a chap who had written a book about middle age (David Bainbridge – Middle Age – A Natural History). He had been inspired to write it by reaching middle age, noticing the changes which were happening to his body and wondering why they were happening. Apparently humans and whales are the only creatures which experience the menopause; no other mammal does. Other mammals grow up, they start breeding, and then they die. There is no post-breeding period for any other animal.

So why us? What evolutionary purpose might the changes which accompany the menopause, and middle age in both sexes, achieve? Well, we become infertile, for a start, or at least women do, and it now seems that as men get into middle age their useful fertility may decline. We become long-sighted as opposed to short sighted. And we put on weight, as our metabolism slows down from the age of about forty. Why?

The theory which David Bainbridge came up with was ingenious. We experience middle age, he said, because middle aged people are an essential support for the tribe. Human young require a huge investment of time and energy to raise, and even when raised to maturity, it takes an awfully long time for them to become good at the highly complicated and difficult means we employ to get food. It takes a long time to become a competent hunter-gatherer, and during that time, the young and their mothers have to be fed and protected.

Modern studies done on hunter-gatherer tribes have shown that, surprisingly, it’s not the fit young men who bring in extra food which can be eaten by those who are net consumers. The fit young men bring in a lot of food, true, but they also eat a lot. The net providers, the ones bringing in the extra food for others to eat, are the middle aged.

In this context, it makes sense to stop breeding, so you can go out hunting. It makes sense to be long-sighted, so you can spot potential prey and foodstuffs from a distance. It makes sense to have more fat and less muscle, because fat burns far fewer calories than muscle, and keeps you warm into the bargain, so you need to eat less. You won’t be much good as a fighter, but that’s OK, the fit young men can fight, that’s what they’re for. You more than pull your weight by being an awesome hunter-gatherer, because while you’re not as strong or fast as you once were, you make up for it with skills you have honed over a lifetime. You become, in short, a wily old bird.

More tomorrow.