Manhood: The Rise and Fall of the Penis (3 page)

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t h e t e s t i c l e s a n d t h e s c ro t u m Van Leeuwenhoek lived to be ninety and continued with microscopic research until his death in August 1723, fifty years after his introduction to the Royal Society by Reinier de Graaf (1641–1673).

His daughter sent his collection of microscopes and specimens to London, where it eventually disappeared, so that only a few of his better micro scopes survive in museums, where visitors are usually more interested in the silver slides and the adjustment knob than in the most important component: the tiny glass globule that served as a lens.

With his microscopes Van Leeuwenhoek had found the answer to the problem Harvey and Reinier de Graaf had wrestled with: semen played a direct physical role in reproduction, the reason being that sperma -

tozoa could find their way to the womb. He had dismissed the views deriving from, for instance, the work of Redi, Jan Swammerdam (1637–1680) and De Graaf, in which the ovum played a central role in reproduction. Van Leeuwenhoek had focused on the male aspect, while the others had had looked mainly at the female side.

The argument on the question as to what was more important: the ovum or the spermatozoon, between ovists and animaculists (also called
spermists
) was not finally decided until the second half of the nineteenth century, in 1875 to be exact. In that year the German anatomist Wilhelm Hertwig (1849–1922) showed in an animal experiment that fertilization comes about through the merging of the nuclei of the ovum and the spermatozoon. The exact process was revealed only in 1944, when John Rock of Harvard University put a human ovum in a dish and added a drop of living human sperm. After placing this mixture in human blood serum, Rock was the first person to observe the division of the fertilized ovum into two, the beginning of a strange process that some nine months later results in the birth of a new human being.

Today we know that the female ovum contains more than half the information necessary for the future human being. It provides not only 23 nuclear chromosomes to complement the 23 from the spermatozoon, but also the cytoplasmatic dna located in the mitochondria, the genes of which derive exclusively from the mother. The mitochondria are simply tiny power stations in the cell. This fact torpedoes the arrogant notion that the father is most important in reproduction. More of that anon!

Hanging left

As regards appearance there is great diversity in the protuberances we have given the prosaic name of scrotum. Scrotums may be large or small, long or short, smooth or wrinkled, heavily or lightly pigmented, nicely rounded or extremely asymmetrical. In fourteenth-century Europe high-ranking nobles were allowed to walk around with naked 17

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genitals under their short tunics. Their tight-fitting short breeches were not closed at the crotch. If their private parts were not sufficiently large to dangle about alluringly, they wore a
braquette
, a set of simulated genitalia in leather. Later, in the fifteenth and sixteenth centuries, another ornament came into fashion, the so-called codpiece (
cod
means scrotum), which was sometimes embroidered or encrusted with jewels.

It was a final relic of the age of chivalry, and today’s double-stitched fly may be the last of the codpiece.

The left testicle usually hangs slightly lower than the right. This has nothing to do with being left- or right-handed. The anomaly is probably due to the fact that in most men the left testicle is slightly larger and heavier than the right. As a result the penis also usually

‘hangs left’, as the saying goes.

Until quite recently tailors making a bespoke suit asked their customer whether he ‘dressed left or right’, so that extra material could be sewn in to camouflage as far as possible the effect of dribbling after urination. The modern clothing industry certainly also takes this into account: the better makes of menswear cut the front of the left leg of a pair of trousers three-quarters of a centimetre wider as standard!

Apart from that, opinions differ on whether the scrotum couldn’t have been made slightly more appealing in appearance and on whether the positioning of the scrotum couldn’t have been a little more convenient, certainly in an age when cycle sports are exceptionally popular. After all, in many animals the semen-producing organs are tucked neatly into the abdominal cavity. In rodents and prosimians, for example, the testicles descend only in the mating season and subsequently return to the abdomen. This is not the case in man or in his oldest domesticated animals. Recent research has shown that the positioning of the testicles is mainly connected with the lifestyle of the species. This actually undermines the ‘balls-as-coolbox’ theory (of which more below). Animals that move fluidly have their sperm -

factories enclosed in their bodies, while those that run, jump, jolt and bump, were better off with testicles located externally.

Long before birth the testicles and epididymides are formed in a place at the back of and high above the abdominal cavity, in the vicinity of the kidneys. From there the testicles descend down a kind of slide formed by the back of the bulging abdominal membrane, towards the inguinal canal at the bottom of the abdomen. If everything goes to plan in the last three months of pregnancy the testicles and accompanying seminal ducts and blood vessels descend through that inguinal canal into the scrotum. The above explanation is not totally accurate, since in fact the testicles gradually move lower and lower as the body grows lengthways. Be that as it may, in approximately 95 per cent of ‘full-18

t h e t e s t i c l e s a n d t h e s c ro t u m term’ males the testicles are in the appointed place around the time of birth. It may happen that the testicles remain within the abdomen.

When this occurs in a male pig the animal is known as a ‘cryptorchid boar’ or sometimes, more colloquially, a ‘rig pig’.

A true cryptorchid boar takes at least ten minutes to complete ejaculation of his sperm – two coffee mugs full, containing as it does over 80 billion spermatozoa. In mating a zebra stallion may ejaculate as much as 300 millilitres of sperm, that is, over a quarter of a litre.

After being mounted the mare appears to urinate, but in fact this is part of the seminal fluid flowing out of her body. A man discharges between 2 and 4 millilitres at each ejaculation. To put things in perspective, the volumes of a number of other animal species are as follows: bats 0.05, foxes 1.5, dogs 6, domesticated donkeys 50, domesticated horses 70, domesticated billy-goats 1 and turkeys 0.3 millilitres.

The male actually owes the scrotum to his female origin. It is only at the moment when it is decided that the embryo is to continue its development as a male that the embryonic labia grow together to form the scrotum. One has only to look closely: right down the centre of the scrotum runs a line of raised skin, the scrotal seam.

According to some experts, there is a good reason for the positioning of the testicles outside the abdominal cavity (though dissenting voices will also be heard in this book). The first group see the normal body temperature of between 36.5˚c and 37˚c as too high for the Testicular descent

in a male foetus.

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efficient production, maturation and storage of healthy human sperm cells. That is the principal reason why nature has opted for a location in the cool-box that we call the scrotum, where the prevailing temperature is between 33 and 34 degrees. One way in which this cool-box operates is through vascular temperature regulation: the artery supply -

ing warm blood from the abdominal cavity is quite convoluted just above the testicles and is surrounded by a complex network of vessels called the
plexus pampiniformis
. This network transports cool arterial blood from the testes back towards the heart. That colder blood washes around the main artery and ensures that the arterial blood flowing to the testicles is cooled so that it cannot harm the young sperm cells. The fact that testicles need protection from both excessively high and excessively low temperatures is evident from a feature that in our modern society benefits only inveterate naturists: the strong pigmenta-tion of the skin of the scrotum. This dates from when primitive man wandered around the African savannahs without protective clothing. A dark skin after all offers more protection against sunlight than a light one. But too low a temperature is not good either! Every man who walks into the sea from a warm beach knows this: the cremaster muscles instantly lift the testes back towards the warmer groin.

The location of the testicles outside the body was therefore pro bably designed to protect the reproductive cells from extremes of temperature. However, one further safety measure was put in place, namely the so-called blood-testicle barrier. Sperm cells are very unusual, in more than one respect. They are haploid, that is, they contain only one copy of our genetic material. All other cells are diploid, containing a copy in dupli cate of hereditary characteristics. Such diploid cells are regarded as malignant intruders in the testicles. By its own logic the immune system has an irresistible tendency to attack anything with the characteristics of a sperm cell. This is why the blood-testicle barrier, with the aid of a membrane and special Sertoli cells, seals off the sperm-producing tubes from diploid body cells. If this line of defence is breached the man will start producing antibodies against his own spermatozoa.

Animals

The testicles of the blue whale are over 70 cm long and weigh about 50 kg.

Testicle dimensions in whales vary greatly, as they do in man. Yet the sperm cells of this whale are no larger than human sperm cells. Human testicles have a combined weight of approximately 40 g, corresponding to roughly 0.06 per cent of total body weight. The testicles of a stallion weigh almost 350 g, or 0.27 per cent of its total body weight.

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t h e t e s t i c l e s a n d t h e s c ro t u m Chimpanzees have the heaviest testicles of all anthropoid apes, with a combined weight of 119 g (0.27% of body weight), while a gorilla’s testicles are much smaller, in both relative and absolute terms (29.6 g, 0.02%). The human male is therefore somewhere in the middle.

Species

Weight of testicles

Percentage

in grams

of body weight

man

40

0.06

chimpanzee

118.8

0.27

gorilla

29.6

0.02

orang-utan

35.3

0.05

rhesus monkey

46.2

0.50

mantle baboon

27.1

0.13

rabbit

5.5

0.13

golden hamster

0.3

0.30

water vole

3.8

0.68

wild boar

720

0.41

ram (sheep)

500

0.63

stallion (horse)

340

0.71

There is very special sub-group among fighting cocks: they have especially large testicles, and are both ‘transvestites’ and ‘homosexual’. This type of male was discovered some years ago by a Frisian potato farmer and bird expert, Joop Jukema. The unusual creature turned out to be hard to distinguish from a female with the naked eye and displayed homosexual behaviour. The discovery was a bombshell for the biological community. The farmer christened his discovery
faar
, which in Frisian means patriarch. Only 1 per cent of the breed are patriarchs. It had been discovered fifty years previously that there are different types of fighting cock males: ‘basemen’, which defend a small territory against others like themselves, and ‘satellites’. The latter forage about and are tolerated by the basemen. At the time this discovery caused a sensation, but finding a third type half a century later was extraordinary.

According to the potato farmer the faar was discovered so late because its appearance meant that it was mistaken for a female.

Females are brown, while males have strikingly coloured neck feathers to impress females, and in addition the male is considerably larger than the female. The discoverer began to doubt the received wisdom when he occasionally spotted a bird that departed from the norm: a fighting cock without spectacular neck feathers, but with the dimensions of a male. As regards colour it was a female, but the wings were over 17 cm long, which was very unusual for a female. Internal examination 21

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showed it to be a male, with particularly large testicles. Of course the farmer called in back-up, from scientists at Groningen University. There was great curiosity about the faar’s reproductive behaviour: it was found to have a preference for mating with its own sex.

The researchers assumed that the faars ‘leave their sperm behind’

in basemen, which then transfer it to a female. Thanks to their large testicles they can easily swamp sperm from other males with their abundant production. Normally they have little chance of mating with a female, because females are closely guarded by other males. These homosexual ‘transvestites’ are not inclined to compete openly, and yet have found a way of reproducing!