It’s an old truism of magazine publishing that if you want to sell a magazine to women, put a pretty woman on the front. And if you want to sell a magazine to men – put a pretty woman on the front. Desmond Morris’s new study of the male body has a pretty man on the front. Who exactly is it for?

Morris is an animal behaviourist, fascinated by insights that evolutionary biology might offer into the way we live, work and mate. There is little physiology here and little under-the-bonnet stuff. It’s all about why we do what we do, why the male body looks the way it does from the outside. Some dismiss evolutionary biology on the grounds that mere nature cannot explain human behaviour in the way it can animal, because, for better or worse, we stepped out of nature and its narrow determinism long ago. Morris’s position, though, is that a million years or more of prehistoric human existence underpin even our most modern habits without our knowing it, and on a number of counts he’s persuasive, and often fascinating.

His broadbrush characterisations of male and female nature allow for little overlap, or ideas of “social constructs”. Women are designed to be essentially “cautious” and “caring”, while men are, as he bluntly puts it, “expendable”. It only needs one man to fertilise 50 women. The rest can all go and kill each other in some stone-age border war, and the next generation will still be just fine. But 50 men and one woman: the tribe is doomed. Men are more playful (or juvenile), women more sensible (or mediocre). Aware at some primeval level that they are expendable, men tend to be more risk-taking and aggressive. In the modern world, a man is both more likely to get a first-class degree and to kill someone while driving drunk.

The chapter on beards is especially entertaining, although again you might wonder about the reliability of Morris’s facts. While he acknowledges that the miraculous beard of St Wilgefortis, virgin and martyr, was probably legendary, he tells us that a beard, or lack of it, also contributed to the outbreak of the Hundred Years’ war. When Louis VII of France shaved off his beard, his spirited wife, Eleanor of Aquitaine, was so horrified at the weedy features thereby revealed that she left him for Henry II of England, along with her vast French possessions: the root cause of war two centuries later.

“There has never been a bearded Pope,” declares Morris. Since the great schism of 1054, eastern orthodoxy has been bearded but Catholicism clean-shaven. Yet surely an art-lover such as Morris could have recalled Raphael’s portrait of Pope Julius II, or Titian's of Pope Paul III, both splendidly bearded pontiffs, to name but two?

Fortunately, Morris is more guarded when recounting the unlikely story that any new Pope must have his balls checked by the College of Cardinals, being raised aloft on a kind of lavatory seat and carried over the craning heads of the assembled dignitaries, while one of their number actually thrusts his hand up the papal skirts and does a manual check. “ Testiculos habet et bene pendentes!” he then supposedly cries, to which the Cardinals all murmur, “ Deo Gratias”. (A good thing this isn’t done to our Anglican bishops nowadays; some of them might enjoy it a bit too much.)

In the spirit of upsetting religious sensitivities, Morris also tells us that Muslim men shave their armpits and their pubic hair. This was quite a revelation. Do they shave or wax? Do the Taliban check on “down below” as well as on beards? Is there an official punishment for the man who neglects to keep his furbelow in trim? In the UAE, as Morris points out, you can get a public flogging just for ignoring traffic regulations. And what about the ladies? Morris says the Prophet himself taught such practices, presumably in a hadith rather than the Koran itself (he cites no sources). Does this mean that Mohammed himself was also . . .? But perhaps we should disembark from this rather dangerous train of thought.

As for Prince Albert actually having a, y’know, a Prince Albert, as Morris says, this is the most hackneyed of urban apocrypha, pub-quiz stuff, and unworthy to be repeated in a serious book of science. It is no more true than Catherine the Great dying in flagrante with a horse, or that stuff about the Pope’s testicles. All the evidence is that the penis-piercing named after our upright, high-minded and humourless Prince Consort first popped up on the Californian gay scene in the 1970s. Those who opt for such a decoration often end up having to sit down to pee.

In the conclusion to his rambling, diverting, if sometimes unreliable study, Morris suggests that for secular modern man, at least, his “soul”, his only chance of immortality, resides not in his brain, or his heart, or his pineal gland, as our more credulous ancestors and nonwestern contemporaries believe, but only in his genetic material. So there you have it. Not only is there no God, not only are we close relatives of the chimpanzee and orang-utan, not only do we face the certainty of personal extinction in a cosmos of chilly and infinite indifference, but as a final indignity, it turns out that the modern man carries his soul in his underpants.

Display case

Cultural attitudes to the male penis, Morris points out, vary greatly around the world. In the West the general approach has been to keep it hidden, and pretend that it hardly exists. The great exception to this rule was the male codpiece, which began life in the 14th century as a modest covering for the genitals, but which by the 16th century had grown into an outsize symbol of male virility. Not everyone used this often extravagant piece of clothing as an advertisement for sexual wares. Larger examples were also useful for wastrel members of the nobility who were suffering from syphilis, and who could employ their codpieces as a protective covering for their medication and special bandaging.

The Naked Man: A Study of the Male Body

by Desmond Morris (Cape £18.99 pp280)

Available at the Sunday Times Books First price of £17.09 (inc p&p) on 0870 165 8585

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy