Hugh Aldersey-Williams previously wrote the highly acclaimed Periodic Table: The Curious Lives of the Elements, and here he proves himself just as fascinating and witty a guide around the geography of the human body. We spend our entire lives inside it yet know so little about it. The author himself confesses, at the start of his journey, ‘I have no idea how my bladder works.’ Some kind of expandable sack, no? ‘Some sort of watertight balloon’ of no particular shape? Actually your bladder is the size and shape of a large avocado.

Modern genetics has only added to, not altered, what we knew before: we have a heart, two eyes, 206 bones and a navel. In fact the bone count is complicated. We have roughly 206 bones, but, as with the Rollright Stones in Oxfordshire, it’s hard to be more precise. We may have more as a baby and later they fuse together. And if you thought your coccyx was just a useless and slightly embarrassing vestigial tail, think again. It actually functions as the third leg of a bony tripod that you use every time you sit down. The other two legs of the tripod are the ischial tuberosities of your pelvis. Without that vestigial tail you might sit down and then find yourself rolling helplessly backwards.

Funny bones are vulnerable because we walk upright. If we walked on all fours, our elbows would be tucked in under our stomachs and rarely get knocked, but now everything has swivelled outwards. The same goes for our overworked knees, another drawback of bipedalism. The lungs of country dwellers have a bluish tinge, but if you’re a city dweller, bad luck, yours are black. As for the clitoris, it ‘seems to have been known, lost, found, lost again and found once more during the course of the last two thousand years’. (Some might say that this can happen during the course of a single night.) The 16th-century anatomist Vesalius dismissed it as a pathological feature found only in ‘women hermaphrodites’, displaying the sort of attitude of fear and disapproval that lies behind the horrible practice of female genital mutilation.

However smooth and unsimian you may proudly fancy yourself, it is humbling to learn that actually we are all just as hairy as any other ape. The only difference is that our hairs are ‘finer, shorter and generally paler than a chimpanzee’s’. The fact remains, you’re covered in them. Again and again, gently but firmly, Aldersey-Williams reminds us that we are animals, closely related to our mammalian cousins in every conceivable way. Wisely, though, he draws no grand metaphysical conclusions from this.

One of the most interesting things here is the material on human beauty. You would have thought this a complex and probably unanswerable mystery, but it seems that Sir Francis Galton, Darwin’s cousin, worked it out quite conclusively in 1908, and his findings have since been confirmed by American psychologists with the latest computer technology. (Galton also found that London had the prettiest women, Aberdeen the ugliest.) His method was brilliantly simple. Take any ordinarily attractive face and merge it photographically with another: the result will always be judged an improvement. Merge it again, at random, and you get the same result. The more you merge, the better. Human facial beauty is always about averages, the absence of any overly small or overly large features – in other words, blandness. It could even be defined as ‘something more sinister’, says Aldersey-Williams, ‘the human face with the individuality washed out of it’. It is a ‘crushingly unromantic’ verdict, but at least the ladies of Aberdeen might find some consolation in it. They’re not ugly, they’re individual-looking.

As well as the hard science there are plentiful broad-ranging cultural allusions and digressions, from Milton to Rubens to Little Women. There’s even some brilliantly astute literary criticism. Aldersey-Williams notes that ‘the worse the novel, it seems, the more important it is to be exact’ in describing the colour of the characters’ eyes. Hardy and Flaubert are both famously vague about the eye colour of Tess and Emma Bovary, but Judith Krantz’s Princess Daisy, he points out, has ‘dark eyes, not quite black, but the colour of the innermost heart of a giant purple pansy’.

Shakespeare mentions the heart 1,047 times but the kidney only once, in The Merry Wives of Windsor, regarding that blubberguts and barrow of butcher’s offal, Falstaff. Today, instead of dieting, Falstaff could opt for an operation that removes the subcutaneous fat from the stomach in narrow furrows so as to leave the impression of a six-pack. Australian installation artist Stelarc and his partner Nina Sellars managed to lose weight and serve the muse simultaneously by having liposuction and then mixing their fat together in a blender, naming the final work Blender. On the whole I think this is less imaginative than the scene in Fight Club where they make soap out of overweight ladies’ fat and sell it back to them at cosmetics counters.

Aldersey-Williams ends on a genially pro-corporeal note. The body has often been denigrated as a nuisance, even a prison of the soul, and there is a thick, unwitting kind of Neo-Platonism in today’s cyber gits and computer geeks – the author can’t help noticing they are all men – who believe they can escape the mortality of the body by downloading their brains onto a disk and so live on forever in ‘some grand ethereal network’, as if you are simply your brain, as if your memory and personality are a fixed set of data, rather than an endlessly changing stream of experiences, stories and personae. No, there is no such escape, says Hugh Aldersey-Williams. We are biological in our very nature, and we should feel happily at home there. ‘It’s quite a place.’