Category: Science

The parental dilemma

There is a fascinating aspect of avian parenting. Birds perhaps more than any other group of animals show how the environment plays a key role in driving the separate interests of males and females.

Jacanas inhabit tropical pools and lakes and can pick their way across floating vegetation, spreading their weight on their very long toes—hence the alternative name of ‘lily-trotters’. Bearing a vermilion shield of their foreheads, American jacanas have reddish-brown plumage with brilliant golden-green pinions which are conspicuous in flight. But it is their breeding arrangements that make these birds especially interesting: the females practice a particularly extreme form of polyandry, with the males undertaking all the duties normally performed by their partners.

A female jacana enjoys the services of several males, which do all the work of building the floating nests, incubating the eggs for nearly a month until they hatch and then caring for the chicks for a further two months. They make devoted fathers and when danger threatens any of the brood, the chicks either shelter beneath his wings or, on a call from him, sink under the water with only the tip of their bill showing so that they can breath.

The females are 75 per cent larger than their mates, do all the courting and scrap among themselves for territories. The most successful fighters are the heaviest with the biggest, reddest wattles. The shields display a record of their owner’s fighting history, as the scars of old injuries are yellow. Such fierce females may manage to defend a territory with as many as six males. Within her area, each male has his own nest located in his own patch of vegetation, but as he is relatively puny, he is unable to drive off the trespassing females. When there is a female intruder, he screams for his own mate to defend his share of her freehold. In the event of a new hen taking over, the males make a feeble attempt to expel her, but within a few hours they have accepted the inevitable and mate with her. Such takeovers are bad news for the vanquished females, because the victor will set about destroying the eggs and methodically hunting down the chicks of her predecessor so that she can immediately employ the males to look after her own eggs.

In effect, a female jacana acts like a fierce egg factory with no constraint on her production line, completing a clutch of four every ten days or so. By contrast, the reproductive potential of each of her partners is severely limited because, once he has received a clutch of eggs, the male is tied up with parental responsibilities for the best part of three months. The female’s sexual potential is limited only by the number of males she can exploit and retain in the face of serious competition from other hens.

Apart from laying eggs, hen jacanas behave just like the strutting cocks of other species—they are big, aggressive, passionate and less choosy than most females about their sexual partners. On the other hand, their mates act like traditional hens—the caring, gentler sex. This is such a reversal of the normal situation that it raises the question, what are the special circumstances which favour the evolution of polyandry on such a scale?

The answer may be found in the rich environment which jacanas inhabit. With no shortage of moisture and heated by the tropical sun, the swamps are among the most productive places on the planet. Such is their immense fertility that it has been estimated that the calorific value of the food available on 1 square metre (10 square feet) of ground is equivalent to two dozen chocolate bars. In fact, for the jacanas, these places are like open bird tables groaning with goodies. So easy are the pickings that, unlike most female birds, hen jacanas have evolved into ‘battery hens’, churning out egg after egg with little physiological stress. They have therefore seized the reproductive initiative, pursuing a strategy of continuous egg production while coercing a coterie of males into incubating the eggs and guarding the chicks…

Jacanas are not the only birds to indulge in polyandry. Several kinds of shore birds practice it on the Arctic or sub-Arctic breeding grounds.
 
Single mothers

Examples of polyandry are few and far between for the simple reason that the environment rarely gives females such an easy ride as it does the jacanas and Arctic wading birds. For most birds, finding enough extra food to manufacture eggs packed with nutrients is an arduous business. World wide, hen birds are constrained in the number of eggs they can lay in a season and so they, as the limited resources, are fought over as the males—which are free to copulate with as many partners as they can secure. In most wading birds, wildfowl and members of the pheasant and goose family, all parental duties are sifted firmly on the females. Their mates play no part in incubation or protecting their vulnerable chicks after they have emerged from the eggs.

In all of these cases, the young are hatched in a relatively advanced state and can run around and forage for themselves. The parent which defects—whether it is the cock or the hen in the polygamous species—is therefore not needed as provider of food, which makes his or her desertion that much easier.

But there can be intense rivalry between single mothers and lone fathers. Barrow’s golden eye, for example, is a tough little diving duck and one population breeds on Lake Myvatn in Iceland. The females nest alongside fast flowing rivers leading out of the lake, and when the ducklings hatch the mother leads them on a perilous journey upstream to the best feeding areas. The journey is dangerous because they literally risk their lives getting there.

If they pass a male whose female is late hatching and still sitting on eggs, he mercilessly beats them to death, because he doesn’t want any ducklings competing with his own offspring. If they survive the hurdle and reach the feeding area, other females already there will also attack and kill newcomers to protect the best sources of food for their own broods. In July each year, the upper reaches of Lake Myvatn can be a scene of carnage, with hundreds of dead ducklings—the result of mothers furiously fighting for the interests of their own broods at the expense of others.
 
Mammals: natural-born mothers

In just over 90 per cent of birds, monogamy prevails. This reflects the near impossibility of females producing an unlimited supply of eggs in most habitats, and the fact that male birds are able to make a significant contribution to the survival of the chicks. But there is one major group of creatures in which this is not so—the mammals. Among these equally hot-blooded, very active animals, monogamy is confined to a mere 5 per cent; in the rest the males have completely opted out of parenting…

Dwarf antelopes—such as the klipspringers and dik-diks of southern and eastern Africa—are unusual among hoofed animals in that they go around in pairs. They frequent clustered bush and thickly vegetated forest where nourishing herbage of the kind that they like is widely scattered. It therefore pays these animals to be territorial so that they can acquire an intimate knowledge of the places where their food occurs.

The buck, which is often slightly smaller than his mate, ensures success in the paternity stakes by commandeering an area of desirable bush and then behaving as a constant consort to his female, never moving more than a few paces from her aside for fear of losing sight of her in the dense vegetation—and possibly losing his sexual monopoly of her as well. It has been recorded that a pair of klipspringers spend their entire adult lives literally within 5 metres (16 feet) of each other. When the fawns arrive, the female cares for them, though the father is always nearby, preoccupied with guarding the mother. Such long bonds lessen the competition between males and so preclude the need for large, aggressive bucks of the kind found in deer and some larger antelopes.

A similar situation prevails in gibbons. These singing apes from South-East Asia appear to live like happily married couples together with their immature children. However, on close inspection, it can be seen that a male gibbon is not so much a caring father as the guardian of the adult female with whom he has chosen to breed. He is also a valiant defender of the swathe of jungle through which she and their joint offspring need to forage for tender leaves and ripe fruit. For a male gibbon, monogamy pays reproductive dividends; by keeping a close track of his ‘wife’ in the complex, cluttered canopy of the rain-forest, he can be sure of fathering her offspring. Unlikely among apes, male gibbons are virtually indistinguishable from their mates—a characteristic that reflects the low level of competition for females.

Only the male siamang—the largest of the gibbons, from the Malay Peninsula of Sumatra—shows a high level of paternal interest, taking over the daily care of his infant when it is about a year old and continuing to look after it closely for the next two years.

The sexual connection

This chapter is about some of the obvious and some of the surprising ways in which females force sperms to prove their worth before reaching their goal, and how males bypass—or cheat their way past—any obstacles put in the way of their gametes.

The quest for conception, which is fundamentally what the battle of the sexes is all about, has driven the evolution of bodily design, the greatest natural technology race on earth. As both sexes ‘strive’ to take control of the process of fertilization, the females develop hurdles for sperm to overcome, and the sperm’s delivery systems—the males—counter with cunning copulatory devices and practices which raise the odds on ensuing their success. This aspect of sexual strife is universal, even among lowly creatures such as millipedes, whose intricate love life belies their simple nature…

Bedbugs once inhabited bat caves and the dens of large European mammals. Now they are better known as denizens of dirty doss houses and squalid accommodation, and emerge at night to crawl stealthily between the bedclothes to suck blood, leaving only an irritating blotch on the skin as a memento of their visit.

The males avoid the natural genital route of inseminating their mates in favour of a rapid but uniquely barbarous method. They drive their penis like a hypothermic syringe through the body wall of the female and inject sperm directly into the cavity occupied by the circulating blood (the haemocoel). The process is known, appropriately, as ‘traumatic insemination’!
 
Penis power

Land vertebrates are not quite so enterprising as insects in the way they make the sexual connection. Their generations have a much slower turnover, and the relatively smaller populations mean that the engine of evolution works more slowly because innovations are thrown up less often. And yet the same considerations prevail.

In the paranoid quest for as many partners as possible, males attempt to scatter their seed in all directions, and females, in the search for the perfect male, ideally like to keep their options open by encouraging rivalry between sperm from different males. Whether aphid or elephant, ensuing paternity is an issue that exercises males, and females still seek the best fathers for their offspring…

The mammalian penis has a dual function, not only serving to pipe semen into the vagina, but also doubling up as a spout for directing urine away from the body. Fully grown African elephants have a mechanical difficulty during their rare bouts of pachydermous passion. Weighting up nearly 10 tones, they are rigidly constructed and incapable of gyrating their pelvis to dock their penis. The cows have evolved an unusual genital lay-out to assist intercourse—their vaginal opening has relocated from the usual position beneath the anus to a site under their baggy bellies where you would expect to find a navel. This saves the bull from having to attempt the impossible task of bringing his groin close up against his mate’s thighs in order to copulate.

Although the cow elephant’s low-slung vulva is much easier to reach, the bull still has to mount her, putting great stress not only on her legs, but also on his own hind quarters. Young cows occasionally break a leg as a result of being chased and mounted by heavyweight males.

Once in position, much of the action is performed by the bull’s ‘motorized’ penis. It is a monster, weighting 25 kilograms (55 pounds) and extending nearly 2 metres (6 foot 6 inches) under the influence of a pounding heart. The jumbo penis is also a veritable power-pack, containing not only erectile tissue but its own engine muscles, enabling it to trash around, searching for the vaginal opening. Shaped rather like a hook, it is well adapted for reaching a long way beneath the female’s belly and probing upwards, penetrating deeply into her low-slung receptacle to make contact with the cervix. After performing a few piston-like thrusts, the bull ejaculates. Once mating is complete, competition from other males forces the bull to protect his paternity by guarding the cow for a while, preventing her from taking another partner whose sperm might usurp his own.
 
Chastity belts

By means of packages of various kinds of extendible organs, males deposit their all-important sperms as close to the eggs as possible. And yet females can be promiscuous in the search for quality males and there are always rivals ready to seize an opportunity to mate. To counteract the danger, the males of some species go to extreme lengths to guarantee their paternity.

Male murcuri monkeys, which live in the Amazonian rain-forest, pump copious amounts of semen into the females and this coagulates into a conspicuous gelatinous plug. However, the females remain eager for sex and other males learn to winkle the plugs out before copulating. In the case of foxes and eastern grey squirrels in the USA, the females foil the males’ attempts to enforce further chastity by removing the rubbery copulatory plugs themselves within thirty seconds of mating, clearly indicating that there is a conflict between their own sexual agenda and that of the males…

The evolution of the sphragis has been one of escalating moves and counter-moves between males and females, males each attempting to gain the advantage over the other. Following insemination, males of many butterflies secrete a viscous plug that hardens and more or less seals their partner’s orifice. However, as the art of lock-picking flourished in medieval times when padlocks guarded the pudenda of love-lorn maidens, so the males of some butterflies are equipped with a pair of abdominal tweezers for extracting genital bungs, allowing them to supplant sperm from a previous partner.

The females of some species have also resisted the males’ attempts to enforce celibacy because they derive nutrients from the semen, and so for them promiscuity pays dividends in the form of bigger clutches of eggs. These females have responded to the males’ plugs by developing ‘externalized’ genitalia, surrounded by very smooth and glossy plates with the properties of teflon. During copulation, the males could not make their sexual stoppers stick and so the stage was set for the evolution of the ultimate chastity belt—the full sphragis. That of an Australian swallowtail or an apollo is virtually moulded on to and completely girdles the rear of the female’s abdomen, and can be removed only with the greatest of difficulty. Furthermore, they often bear long projections that trail beneath the body and act as a deterrent to other sexy males.
 
Bondage

‘Sperm wars’ favour the males which indulge in protracted copulations, because these give their own gametes more time to reach the eggs. Some male crustaceans, such as crabs, keep their mates to themselves by the simple expedient of carrying them around…

Mating moths and butterflies stay tied together for a day, while male locusts often stay mounted for two. This pales into insignificance when compared with male weevils belonging to the species Rhytirrhinus surcoufi; they have been recorded as staying on the backs of their mates for a month without losing contact, thus imposing a kind of monogamy on the females.
 
Dirty tactics

Aedes aegypti is one of the most notorious mosquitoes in the world, because egg-bound females carry the malignant virus responsible for yellow fever throughout tropical Africa and America. Deadly though they may be, one aspect f their sex life is fascinating. Once the female Aedes has been impregnated, her drive to mate vanishes.

The males are responsible for the sudden mood swing because their semen contains an hormone which is rapidly absorbed through the vaginal walls into the female’s nervous circuitry and switches off her urge to mate. As a sexual sedative, the substance is exceptionally potent; a sample taken from one male is sufficient to make over sixty females utterly frigid.
 
Lolitas

Such are the reproductive rewards for males of being the first to impregnate females that those of a few species are genetically primed to have sex with barely mature partners…

As with the Heliconids, sex is taken into the pupal case in Orygia splendida, a moth related to the gypsy moth. The male is normal looking with a pair of pretty wings, but the female is dowdy. In fact she never really grows up, because she becomes fertile as a grub, when still imprisoned in her cocoon. Without ever emerging into the light of day, she attracts a male to her by her irresistible smell. When a male alights, his exciting body odour stimulates her to claw a hole in her cocoon, which allows him to mate. Afterwards, he flies off to find another moth Lolita, while she lays her eggs and dies without setting foot outside.

Sex takes place in the nursery even in stoats. During the summer, males are combing the countryside not only for prey, but also for nests containing young virgin stoats. On finding one, the male forcibly insinuates her, even though she protests vigorously and may well be so young that her eyes are closed.

Bizarre though such behaviour appears, it is but one of the outcomes of the fierce pressures that males are under to mate in a hurry to ensure their genes live on. The females themselves may benefit because their sons will indulge in the same behaviour and successfully propagate their genes.
 
Poisonous semen

Fruit-flies provide the ultimate expression of warfare between sexes—the males, in attempting to control their mates chemically, poison them while the females search frantically for antidotes. The discovery came to light when it was noticed that highly promiscuous female flies were short-lived. This was due not to the undoubted strain of egg production, but to a surfeit of sex. Further investigation revealed that the seminal fluid was the culprit leading the females to an early grave. Semen is not just a medium for transporting sperm; it is a cocktail of secretions, some of which affect the female’s behaviour, usually to the male’s benefit…

Sex has become murder. Now, to enhance his chances of fathering offspring by advancing ovulation, the male fruit-fly produces seminal fluid so ‘strong’ that is toxic and prematurely poisons the female, but not before she has laid her eggs.
 
Suicidal sex

For the males of species in which the females are born killers, mating is a dangerous proposition. Having delivered their sperm, some males appear to make the supreme sacrifice—and end up as meals. And yet, such suicidal tactics make sense in the context of sperm wars, especially if the males are unlikely to have more than one stab at breeding. There is little point in a male escaping with his life if his paternity is not assured. If, by committing suicide during sex, he keeps his savage partner occupied while his, and not someone else’s, gametes seek hers, the sacrifice pays off.

One in the best-known dangerous liaisons is forged by male praying mantises… The male’s body is the ultimate nuptial gift, because by consuming her partner the female is able to produce significantly more eggs. She therefore benefits from her macabre habits, but so does he—he literally gives his all and, as a consequence, fathers offspring. Male spiders always face the risk of being devoured when they consummate their courtship, but male red-backs appear to be the only ones which positively commit suicide during sex…

Other remarkable strategies have evolved which illustrate the extremes to which males will go to give their own sperm the best chance of reaching the eggs first.

In Australia, male red-tailed phascogales—small, squirrel-like carnivores—burn themselves out in an all-or-nothing quest for fatherhood. These endearing little marsupials have a short but exhausting mating season during the southern spring, which leaves the males wrecked. They are intensely territorial and supremely competitive, chasing up and down trees and racing in and out of hollows searching for females. The female phascogales are extremely shy and make the males court them energetically before submitting to prolonged and vigorous sex.

So intent are the males on finding as many targets as possible for their precious sperm that they have no time to feed during their week of frenzied sexual activity. While the freshly impregnated females retire to their nests, the knackered males rapidly succumb to a combination of infections, failed livers, gut ulcers, extensive haemorrhages and extreme weight loss. These symptoms accompany the level of their blood cortico-steroids and a catastrophic suppression of their immunological system—characteristics of severe stress.

Not one adult male survives. But 50 per cent of the females’ babies will be males and by the following spring they will be mature enough to enter the lethal sexual arena.
 
One battle over, another looms

The egg is now fertilized—in a split second, a new life has been initiated. This has been achieved against astronomical odds. Both the sperm and its slave, the male body which produced it [Editor’s italics] and propelled it into the female’s tract, have had to be supreme players in the most rigorous and demanding contest on earth: survival. The male has relied on countless brawling ancestors, themselves winners endowed with the skills needed to overcome both physical dangers and cut-throat competition from rivals. His sperm has passed the female’s demanding tests for quality control. Of the billions that started the race, many were deformed, most simply got lost or died of exhaustion. Of the few the lashed their way to the egg, one was victorious.

On arriving at its destination, it began a complex sequence of chemical code-breaking whereby enzymes—special proteins—in the tip of its head unlocked the egg’s surface and allowed the sperm to enter its protoplasm. In a fraction of a second, a miraculous transformation took place in the composition of the cell, enabling the egg to shut out other sperms which subsequently attempted to pierce it. Once safely inside, the sperm cast off its tail, leaving only the head, packed with the male’s genes, his sole contribution to the new offspring.

The sheer complexity of what follows defies imagination. If there be miracles, then the defining moment of one was when the hereditary instructions of both male and female were collected in the fusion egg and sperm nuclei and a new life was conceived in a flurry of membranes and rapidly dividing cells. Although it takes place on a microscopic scale, this is the key event over which the sexes have been striving to exert control.

However, the share each parent has in this new individual is already unequal—the sperm donates only its genes to the relatively massive egg. For the time being, it seems, the male has got away with the smaller down payment. But now a fresh conflict looms—over the question of parental care. The mother would prefer to go on and produce more eggs, and the father to spread his sperm around more females. Nevertheless, conception does not end the ‘costs’ of reproduction for all creatures. For many, a great deal of effort will have to be explained on caring for their offspring. And who does that is very much decided by yet another dispute between the sexes.

Choosy females

Although females behave less dramatically than males, they have a very crucial hand to play in the mating game. They are not, as usually portrayed, passive recipients of male lust, but are naturally cautious and highly discriminating when deciding with which to copulate. From their point of view, all males are different and, as every female wants only the very best possible specimen to father her offspring, she plays for time while assessing the quality of what is on offer.

Females therefore go shopping for sex and males must market themselves like animated billboards to attract a customer. Lavish ornamentation often means quality, because mediocre males cannot afford the luxury of ‘expensive’ displays. By weighing up the choice of mates and choosing only the chirpiest or flashiest partners, females act as wildly imaginative artists, capable of ‘creating’, through sexual selection, males which are as breathtakingly gorgeous as they are bizarre…

Among the amphibians, male frogs woo by trilling or croaking. Male anolid lizards erect brightly coloured dewlaps, while fish tend to flourish decorative fins. Most mammals have keen noses and accordingly use seductive odours to meet up with the opposite sex. Some insects stridulate—make a chirping or scraping sound, like grasshoppers—for sex, whereas others deploy potent scent to lure mates. Emperor moths can home in from 3 kilometres (2 miles) away by following a plume of perfume which acts as both an irresistible attractant and an aphrodisiac to members of the opposite sex; in web-building spiders, the males strum a tattoo on the silken threads which their partners perceive through their feet. Fireflies emit flashes of light, certain diurnal butterflies reflect patterns of ultra-violet and electric fish communicate with each other in the murky waters where they live by discharging pulses of electrical energy. In some species, the males advertise for sex in such extravagant manner as to defy imagination—and all because they must catch the eye of a discerning female.

The blue peafowl is the largest and most spectacular of the true pheasants. In full courtship mode the male is, without a doubt, one of the wonders of nature and an eloquent testament to the creative force of sexual selection. He is nothing less than an ostentatious sexual advertisement, proclaiming with strident voice and ornate plumage that he is the best source of sperm…

But sex is not the end of this affair. Peahens are remarkably possessive of the peacock with which they have mated and, although they need to be inseminated only once to have their eggs fertilized, each female tries to monopolize his attentions by being aggressive to other hens or by actively soliciting further copulations from the male if he starts to court another. By exhausting the male’s supply of sperm, the peahen attempts to prevent him passing on his desirable characteristics to the offspring of other peahens, which will inevitable compete with her own.
 
Bridal bowers

Some of the most extraordinary birds to be seen in Australia and New Guinea are the dozen or so bowerbirds which rate as the landscape artists of the avian world. The fact that most native mammalian predators in Australasia are nocturnal makes it possible for the males to spend the days displaying on courts close to or on the ground, which they meticulously prepare for the purpose of sex and seduction. As they eschew parental duties and the forest provides plenty of easily obtained food, the males are able to dedicate much of their year to building and decorating their bowers.

The hens behave like connoisseurs of art, awarding their sexual favours to the owners whose works impress the most. Depending upon the species, the male bowerbirds build structures ranging from the simple avenues of twigs—like the dazzling yellow and black regent bowerbird’s—to more elaborate ones which the owners embellish with all manner of bright objects; the cock satin bowerbird even daubs the walls of his bower with ‘paint’ derived from strongly coloured berries crushed in his break.

But there are as nothing compared to the achievements of three gardener bowerbirds—Macgregor’s, the striped and the Vogelkop—which practise their art deep in the forests of New Guinea. These mostly brown birds, the size of a starling, are master builders, constructing out of interlocking twigs maypole-like towers up to 3 metres (10 feet) in height, and huts resembling tepees supported by internal columns with passageways connecting inner chambers. Furthermore, The birds landscape their buildings with carefully tended forecourts on which all kinds of eye-catching treasures are displayed. In the case of Macgregor’s bowerbirds, and possibly the others, decorative fruit is brought into the bower and the cache doubles up as a snack bar, allowing the cock bird to spend more time on site advertising for hens.

Although they all construct amazing bowers, Vogelkop bowerbirds—from the mountains of the western tip of Irian Jaya—produce the most extravagant exhibitions of landscape art. The male’s arena is 5-6 metres (16-20 feet) across, with his astonishing bower in the centre. This is constructed around a sapling and is completely covered in by a thatched roof which is supported internally by several pillars.

In front of the entrance is the garden, on which is meticulously arranged a variety of pretty or conspicuous objects gathered from the surrounding forest—a number of faded yellow leaves laid out in a pattern, a heap of brightly coloured berries, the iridescent wing-cases of a certain kind of beetle and fresh flowers which are changed daily before they wilt. The industry involved in maintaining such an arena must be phenomenal and yet the investment will be well worth while if the hens are impressed and allow the male to father their next broods.
 
Dazzling duets

Scientists working in the sweltering forests of Costa Rica claim to have discovered that female long-tailed manakins may be the fussiest females in the animal kingdom. Cock long-tailed manakins are forced to be really high-pressure salesmen; they will be chosen to mate on the basis of how well they sing in tune, shine on the dance floor and excel themselves in an extraordinary test of stamina.

These sparrow-sized birds belong to a family of forty or so exotic species which are confined mostly to South America. Second only to the incomparable humming-birds, male manakins are dazzling feathered jewels, their plumage sparkling with sky blues, brilliant reds and yellows set against the deepest velvet black. Some of their wing and tail feathers are modified for producing a variety of instrumental sounds which supplement the curious vocalizations the male utters to draw the attention of the hens.

The courtship displays are nothing short of virtuoso performances, choreographed into series of pivoting movements, mincing steps, jumps, somersaults and butterfly flights. Although the details vary from species to species, the acrobatic displays of the manakins rival those of any bird of paradise and are equally difficult to observe because they take place either in the forest canopy pr in deep cover near ground level…

Once she has made her choice, the top male signals his junior partner to make himself scarce. He then performs a solo dance in front of his admirer and then, in a flash, mounts and inseminates her. The reward for the junior male may come later—he may inherit the stage when the more experienced bird dies or vanishes, but he may have a long time to wait, because long-tailed manakins live for about fifteen years.

Almost all the hen manakins end up mating with but a handful of males. In one area with about eighty cocks, just five of them accounted for over 90 per cent of the matings over a course of ten years. So it pays to be a senior male manakins in a top performing team because such a bird is likely to be chosen by as many as fifty or sixty hens a year.

However, the cost of that achievement is considerable. It has been estimated that during his apprenticeship as a junior partner, a male will utter about 3 million ‘to-le-do’ calls and spend about 1000 hours perfecting his cartwheel routine before standing a chance of graduating to the status of a senior male.

John Sparks studied animal behavior with Desmond Morris at the Zoological Society of London. I will be adding excerpts of each chapter of Sparks’ Battle of the sexes (1999). But the introduction of his book I’ll quote complete:
 

Every living creature has an overwhelming urge to breed. This is not simply a trivial expression of bestial lust, but a fundamental characteristic of life, the fulfilment of which determines whether an animal is a success or a failure. ‘Succeeding’, in evolutionary terms, means nothing more nor less than leaving offspring who will survive long enough to carry on the parents’ line. Anything less means the extinction of their own genetic heritage. Each individual therefore strives to populate the planet with its own descendants at the expense of those of its rivals. And in order to do so, each and every one of them attempts to attain reproductive supremacy by means of the sexual process.

The nature of sex is widely misunderstood, a matter of which this book will attempt to rectify. The human ideal of sex is that it is the romantic outcome of love and leads the participants into a long-term alliance, enabling them to produce and rear children—an arrangement that is all too often shattered in the divorce courts. And yet a wealth of observation on how animals conduct their private lives shows that, in the wild, sexual skulduggery and infidelity are much more the norm than the exception. Sex does not and never did encourage sharing and caring.

On the contrary, as the story which unfolds in the next six chapters reveals, it compels the participants to engage in civil war at all stages of their lives. Although mates consent to donate eggs and sperm towards the creation of new life, on almost every other issue—the choice and number of partners, the size of the families and who is going to look after them—males and females are far from agreement. Even when the sexes appear to co-operate, powerful forces of self-interest are at work. The relationship between the genders is constantly rife with tension and mistrust. Why should this be so?

Ideally, every individual, whether male or female, would like to mix and match its genes with the best of its kind to create the healthiest and sturdiest offspring—a recipe for their survival. This aspiration involves females in a quest to find the perfect sexual partner—perhaps the most elegant dancer, the most accomplished hunter or simply the biggest and most belligerent male. Once she has found him, she may resort to various forms of subterfuge in order to keep him—and his genes—to herself. Males, on the other hand, generally try to give themselves the best chance in the reproductive stakes by mating with as many females as possible.

In addition to this basic conflict of interest, the problem is that someone else always seems to have the best mate. Of course, there is no such thing as a faultless female or an impeccable male; however, when animals are set on breeding, they frequently appear to behave as though they have settled for second-best while continuing to keep their options open—in other words they divorce, swap partners and have affairs. Throughout the animal kingdom, males have inherently roving eyes, are ever ready to cheat on their partners and are accordingly paranoid about being cuckolded themselves. Females are also open to offers from males more desirable than the ones with whom they have paired up, and they use infidelity as a weapon in the battle of the sexes. All this sexual skulduggery leads to discord, as animals of every kind strive to ensure the survival of as many of their genes as possible.

The very concept of sex also calls for explanations. Intercourse is mechanically cumbersome and does not necessarily result in a net increase in numbers. Budding or cloning would seem, at first glance, to be much more effective ways of propagation. Without a doubt, sex in its various manifestations involves the expenditure of huge amounts of energy. For some animals, it shortens life expectancy; it is sometimes even lethal, usually for males but occasionally for females as well. So why do it? We shall look at some of the possible answers to these questions in Chapter 6.

Sex and foraging are two fundamental characteristics of animal life, and are often the only ones which draw creatures out into the open. Sex especially demands very public behaviour among many species. Males and females need to find each other, repel rivals, court, make the sexual connection and provide for their young. However, in talking such a high profile, they face the danger of being haunted or sexually cheated.

Individual species have inevitably evolved their own strategies for dealing with these risks, and these strategies have fashioned the dazzling array of individual species who share our planet. For all of them, sex is a continuing battle.