Everyone seems to have an opinion about middle age.

I’d hoped many people would feel like that – not least when I was bashing out the 80,000 hard-won words of ‘Middle Age: A Natural History‘ – yet I didn’t realise until the book came out how almost everyone seems to want to express their opinion about the topic.

Being a zoologist and, weirdly, you might think, a vet, I started my quest into mid-life’s inner workings from a naïve starting point. I knew two things about middle age – that people are usually nasty about it, and that no other species in the animal kingdom does it. To me, that seemed sufficient evidence that it would make a good topic for a stereotype-puncturing book. I’d tried it before with ‘Teenagers: A Natural History‘, and everyone was very nice to me, although perhaps in the way the are nice to a rather slow child.

Little did I expect the torrent of enthusiasm, disbelief, anecdote and bemusement that has washed over me in the last few days. My central idea that middle age is a distinct, non-negotiable, universal human biological phenomenon did not go down well with my sociological inquisitors on Radio 3, but after that, many people warmed to my relentlessly deterministic, gene-obsessed and upbeat message about the fifth and sixth decades of our lives.

The charming, chatty people on Radio 4’s ‘Start the Week‘ unleashed a wave of self-affirmation and enthusiasm for my ‘it’s a third of your life, so make the bloody most of it’ conjecture, and variations on that theme followed in the Observer, Telegraph, Mail and Sun. People I’d never met found my early-40s sports car purchase far more life-affirming than I seem to remember my wife did.

Someone called me a ‘leading Cambridge academic’, which brought joy to the heart of a this third-rate Cambridge academic. Unfortunately, the Sun did not call me a ‘boffin’ as I had hoped, but my finest hour came when the Mail described me as a ‘portly zoologist and father-of-three.’ It doesn’t get better than that.

The reaction I have enjoyed the most has been the number of middle-aged (and older) people who have felt an inner compulsion to assert just how very young they still feel. I would never claim to be a freedom fighter for the very-slightly-wrinkly and bemortgaged, but I like to think I’ve done my bit, however transiently, to throw open a tiny window of positivity into the world of happy and successful middle age.

Soon I must go back and actually read my book. Once I’ve written one, reading it is usually the last thing I want to do. However, as far as I recall, there was some evolutionary biology, some palaeoanthropology, some physiology and some medicine which came close to a coherent justification for some of the things subsequently attributed to me in the papers.

Middle age, eh? All human life is here – well, all the important bits. Fat, wrinkles, older parenthood, body hair, intelligence, time speeding up, happiness, mid-life crisis, menopause and monogamy. Sex, drugs and vinyl-based rock ‘n’ roll.

Middle age people run all the most important arenas of human activity – government, business, sport, my house. And maybe I’ve nudged them a little further towards self-appreciation. Showing people that evolution has made middle age a blessed gift to us is no Mandela moment, but I suppose it’s a liberation of sorts.

David Bainbridge is a popular science writer, vet and reproductive biologist. At present he is the Clinical Veterinary Anatomist at the University of Cambridge and Admissions Tutor in the Arts and Humanities at St Catharine’s College. After gaining zoology and veterinary degrees from Cambridge he studied at London’s Institute of Zoology and Royal Veterinary College, and Oxford University, as well as working at Cornell and Sydney Universities. His main field of research has been the interactions between fetus and mother in humans and animals. His books include Making Babies – The science of pregnancy, The X in Sex – How the X chromosome controls our lives, Beyond the Zonules of Zinn – A fantastic journey through your brain, and Teenagers: A Natural History. His fifth book, Middle Age: A Natural History was published in March 2012. Although David is 43 and his children are 9, 11, 14, he notes, in his most recent book that the twentieth century was exceptional in human history in that women usually didn’t have babies in their early forties!