There's a fairly feeble joke about a lone cowboy who falls off his horse in the middle of nowhere, breaking a leg. As he lies in the dust, facing certain death under the blazing sun, his trusty steed trots over and drags him into the shade of a tree, before galloping off to get help.
Later, the cowboy is telling the story to a friend, who is very impressed. "Don't be," he says. "Dumb critter came back with a vet."
David Bainbridge, the author of Middle Age: A Natural History, is a vet. Not just any vet, mind - he is the clinical veterinary anatomist at Cambridge University's department of physiology, development and neuroscience, and responsible for organising the preclinical veterinary course at the university. But a vet, nonetheless.
Now, it may not be fashionable to go corralling people into little talent pens but, rather like the cowboy disappointed by his mount's choice of medical professional, if I'm going to read a book about human biology I'd rather it was written by a doctor than a vet.
Bainbridge, however, is a vet with a yearning to be something else - a writer of popular science books.
Of course, these days the key word is "accessible", and Bainbridge is certainly that ("I was 40 years old when I started to write this book and My! How the months have flown by!"), unless, of course, you happen to find all that sort of chummy gook annoyingly patronising.
His crossover moment came in 2001 with the book A Visitor Within - The Science of Pregnancy, in which he nailed his colours firmly to the populist mast. For the American market, for which that book was reissued in 2003, some additional downward-dumbing was deemed necessary, and the demandingly oblique Visitor Within was ousted in favour of the more direct Making Babies.
But it was with Teenagers: A Natural History, that the vet embarked on what was - or, at least, now is - undoubtedly intended to be a three-part franchise.
Having been Bainbridged, the teenager emerged not as the sulky, rude, spotty, noisy and annoying little ingrate we all thought we knew, but as "an awe-inspiring natural phenomenon that evokes reverence and wonder".
And so to middle age.
Here, Bainbridge is on firmer ground, having an additional claim to being an authority on the matter: at the time of writing, he was 42 (he turns 44 next month) and - guess what?
That's right: he was having a Mid-Life Cliché. Sorry, Crisis.
"It was," he writes in his introduction, in the chatty style that pervades the book, "not supposed to be like this. I was supposed to buck the trend."
Bainbridge, we learn, felt young at 38 "and I still felt young on my 40th birthday - not for me the clichés of middle age, surely?"
Yet now, "I am 42, and suddenly time is screaming past, contemporary popular music means nothing to me, and I have a belly, miscellaneous aches and a sports car. What on earth is happening?" In this book, says Bainbridge, he sets out "to find out what middle age is and what it is for". The real question might be, what or who are books like this for?
Cue lots of the usual genetics tosh ("Only humans have the necessary information to make middle-aged people") and spurious analogies with the animal kingdom ("If an amoeba's DNA is damaged … it is essential that the malfunction is repaired quickly before it does any more damage. If similar problems develop in one of the cells in your body, then it is likely that you'll make only half-hearted attempts to do anything about it").
Perhaps not unnaturally for a vet, Bainbridge cannot resist constant surprised comparisons between the human family and other animals, occasionally with disquieting results. So while men and women load on body fat in predictable ways and places, "There are, for example, no curvy, Jayne Mansfield-esque chimpanzees or gorillas, and perhaps it would be disturbing if there were".
Statistics, of course, exist solely for books like this, and this one finds frankly pointless work for loads of them ("Estimates published by the United Nations indicate that 89 per cent of all humans have married by the age of 49", "One study suggests that over the fifth and sixth decades of life, percentage body fat increases from 23.6 to 29.3 per cent in men", etc).
Obsessing over the minutiae of the universal experience of life overlooks the central truth of being human, best summed up by a doctor who, weary of the chiefly western and fundamentally political obsession with keeping people alive as long as possible, once reminded me that "After all, the mortality rate for the human condition is 100 per cent".
What happens en route to the inevitable grave, however - how we handle the journey - is largely up to us.
We are conditioned to see life as a dome-shaped curve and middle age as a zenith after which it is all downhill, but this is to waste the bulk of our time on Earth, gripped with fear as though a passenger on a stricken, powerless aircraft shallow-gliding to a fiery, wheels-up end.
There are, of course, biological realities, without which a book like this would have no content. But does anyone really need to revel in the mechanics of their own decline? What of the non-biological psychological truths, that can lift individuals above the herd? Bainbridge, too late, as though suddenly realising he has gone too far, addresses this most important factor.
Sure, he has joyfully deconstructed all the bad news - the failing eyesight, waning sex drive, sagging skin, mental deterioration, greying of the hair; all the usual birthday-card jokes, in other words - and admitted that he ascribes "a great deal of influence to our genes, our biology and our evolutionary history".
Nevertheless, on the last page he offers the unconvincing hope that, by the end of his curiously soulless book, "you do not feel powerless, directed in your every thought and action by the bullying hand of evolution".
Well, if we do, it is thanks to what must rank as one of the feeblest rallying calls ever uttered: "Fight against your evolutionary inheritance if you want to," he shrugs, grudgingly. "It will not make it go away, but it will not do you too much harm either."
We can, like Bainbridge, surrender to the clichés and grow fat, moan about our aches and pains and buy a sports car.
Or we can live our lives to the full - at any age.
Like Greg Searle, who this summer rowed to a bronze medal in the British Olympic rowing eight at the age of 40.
Or Hiroshi Hoketsu, the equestrian who competed for Japan in London at the age of 71.
Or American Carol Masheter, who greeted a series of life calamities at the age of 50 by turning to mountaineering and, in March this year, completed her ambition to climb the highest peaks on all seven continents, at the age of 65.
And so on. It seems unlikely that any of these fighters against evolutionary inheritance will have had the time, or inclination, to read any of Bainbridge's oddly pointless books. For them, life really is too short.
Jonathan Gornall is a former senior features writer for The National.