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  The parasite responsible for infecting the stingless wasp is the Wolbachia bacterium. Wolbachia live in the eggs of the host wasp, through them passing from mother to young. But these tiny wasps are not their only targets: Wolbachia are among the most abundant and remarkably widespread of all parasitic bacteria, and the number of species known to be infected by the bacteria is increasing rapidly. Just how far afield Wolbachia are distributed is uncertain, but so far, they have been found in over seventy-five percent of arthropods, which include eighty insect species, seventeen isopods (a category of crustaceans that includes the woodlouse), many spiders, and one type of mite. It is also likely that there is probably an equivalent proportion of infections among nematode worms. And there is a good chance that it will spread.

  If this doesn’t seem like much to be concerned about, bear in mind that between them, arthropods and nematode worms comprise something in the order of 99.99 percent of animal species in the world. From cockroaches to termites, dragonflies to ladybirds, woodlice to worms, Wolbachia wreaks havoc with ovaries, testes, eggs, and sperm in many ways – not all of which are entirely clear. What is clear is that Wolbachia need eggs; they live in them. This means that the bacteria must be assured of a good supply of eggs – and in this respect, males are dispensable. So Wolbachia has found a way to make the eggs of stingless wasps develop without any sperm involved.

  When the wasps reproduce through parthenogenesis, they produce only daughters, of course. But in 1990, scientists found that they could make females and males start having sex again, and that they could induce mothers once again to have sons. All it took was a dose of antibiotics.

  Wolbachia may be the most prevalent bête noire of male insects, but it is by no means the only parasite to play this game. There is a parasitic fungus, Ichthyophonus hoferi, that causes parthenogenesis epidemics in fish worldwide. Among its targets is the green swordtail (Xiphophorus helleri), a species in which the female fish is able to turn into a sperm-producing, fully functional male, indistinguishable from a true male. In the fish, the fungus causes haemorrhages, destroys muscle, and rots fins and skin – so there is reason to worry about its effects. One of the toxins it produces also seems to make eggs develop without sperm. In addition, there is a large and diverse array of micro-organisms that alter the ratio of males to females in their host populations, usually by killing or feminizing the males. These include protozoa, which affect mosquitoes and amphipods, an order of tiny crustacean, most usually less than ten millimetres in size; spiroplasms, which affect fruit flies; enterobacteria in wasps; and rickettsiae in ladybird beetles. For most of the planet’s species, the sexes and reproduction are not always what they seem.

  Then, there are those few animals that normally would have sex to reproduce, but don’t strictly have to do so. In recent years, the list of these animals has been steadily getting longer. It’s not that virgin birth as a phenomenon is necessarily increasing in the natural world; rather, that scientists have simply started to realize that some very large animals – not just insects – are able to reproduce without mates, should they need to.

  On 14 December 2001, the list was extended in an exciting new way. Before then, virgin births had been documented in all of the jawed vertebrates – that is, animals with backbones and jaws. The exceptions, therefore, were the mammals and cartilaginous fishes, the latter of which include sharks and rays but also the aptly named chimaeras – peculiar-looking deep-sea rat-fishes and egg-laying ghost sharks that have glowing eyes and snouts like an elephant. But that December, an adult bonnethead shark gave birth to a normal, live female pup at the Henry Doorly Zoo in Nebraska.

  The adult shark had been captured from the Florida Keys when she was not yet a year old. For the bonnethead shark (Sphyrna tiburo), that meant it was two years away from hitting puberty. Once captured, it had been raised in a tank at the zoo, in the company of only two other sharks – both female. Now, sharks of the hammerhead family, of which the bonnethead is a member, normally can store up sperm from a previous mating for as long as five months. But that would not have been possible for this female, as it was so young when it was caught. The other possibility that the zookeepers considered was that it may have both male and female genitals, as some humans do. But there again, it didn’t have any claspers, a kind of penis that a shark that is biologically both male and female could use to fertilize itself. There was only one other way a pup could have ended up in a tank full of adult female bonnethead sharks. And genetic tests later confirmed that the pup was in fact a virgin-born animal, the first of its type to be identified.

  For obvious reasons, it is extremely difficult to spot a virgin birth in a wild animal population. Unless you are very lucky, and stumble on a female-only group that cannot possibly be accessed by males – the shark in a tank – reproduction by parthenogenesis in an animal that usually has sex is easy to miss. So it’s not surprising that the next reported virgin shark mother was once again found in captivity, seven years later, at the Virginia Aquarium, in Virginia Beach. This time the mother was an eight-year-old blacktip shark (Carcharhinus limbatus) named Tidbit; unfortunately, her parthenogenetic offspring was only discovered during Tidbit’s necropsy. Like the bonnethead shark mother, Tidbit had been caught in the wild when very young, less than a year old, and had reached sexual maturity in a tank at the aquarium. The shark had died during a routine physical examination – nothing had seemed amiss. When the body was cut open, it was found to be carrying a pup that was thirty centimetres (one foot) long and nearly full term. Like the bonnethead baby, DNA analysis revealed that the female blacktip foetus did not have a shred of genetic material from a father. There couldn’t have been, as there were no male blacktip sharks in the tank for the entire eight years that Tidbit had lived there.

  Sharks are not the only new animals joining the parthenogenetic ranks. Two years before Tidbit’s examination, two virgin births in Komodo dragons at zoos in the United Kingdom were announced; since then, a third has occurred in Kansas. Komodo dragons (Varanus komodoensis) are the largest of all lizards; the adults can grow to a length of three metres (ten feet) and can weigh more than ninety kilograms (two hundred pounds). Yet, as wild Komodo populations have become smaller and more fragmented, these legendary creatures have come under threat of extinction. Today, there are fewer than four thousand Komodo dragons remaining in the wild, of which fewer than a thousand are believed to be mature females.

  Because of these worrisome figures around the species’ future, at least fifty zoos had begun participating in an international breeding programme by the time the virgin births were discovered; it could be said that quite a few people were paying quite a bit of attention to Komodo sex life. In all of Europe, there were only two sexually mature female lizards: Flora at Chester Zoo and Sungai at London Zoo. Both had been bred in captivity, and were therefore crucial to the success of the European breeding programme. But what the zoo staff involved had not realized is that female Komodos can reproduce without a male.

  It’s not that Komodos need males to lay eggs – much like chickens, it has long been known that some of the eggs Komodos lay will be unfertilized. But in 2006, the then zoo-keeper in Chester, Kevin Buley, took a clutch of twenty-five eggs that Flora had laid and incubated them ‘on a zoo-keeper’s whim’. It was a serendipitous moment for science, and, indeed, for Komodo conservation. Flora had never been with a male dragon. Yet of the twenty-five eggs that Buley fostered, eleven looked just like normally fertilized eggs would. And in January 2007, eight hatched into healthy male Komodo babies. The three eggs that didn’t make it had collapsed early during the incubation, but they proved useful in providing embryonic material for genetic fingerprinting. Through such analyses, Flora was proven to be both mother and father to the surviving eight sons. Similarly, Sungai in London Zoo laid twenty-two eggs – two and a half years after her last contact with a male. Nearly eight months later, four of these eggs hatched, producing healthy sons. Sungai subsequently successfully mated with R
aja, a male also housed at the zoo. Two months later, Sungai laid a second clutch of six eggs, only one of which hatched. Sungai has since died, but at Chester Zoo, Flora has been set up with Norman, a two-metre (seven-foot) male in whom the female has so far showed no interest whatsoever.

  Komodo dragons and sharks aren’t like whiptail lizards; they aren’t all females, and they don’t behave – as has been said of whiptails – ‘like lesbians’. Flora the dragon and Tidbit the shark only experienced virgin births because they had no males to mate with. Theirs was an artificial situation, because they were living in zoos, but sometimes the situation in the wild isn’t altogether different. Poaching and human encroachment have decimated the population of Komodo dragons in the wild. Sharks are also increasingly overexploited: in the north-west Atlantic, there have been rapid declines in large coastal and oceanic shark populations – over a seventy-five percent decline, in fact, in the past twenty years or so.

  Usually, hammerhead sharks in the wild have litters of around fifteen pups, and blacktips have four to six. Of the two sharks that were found to have had virgin births in captivity, both only had one pup. Having babies without a mate means that the offspring won’t enjoy as much genetic diversity as they would if they had a father’s genes too. And low genetic diversity is almost always a bad thing – something to be avoided in a population struggling for its existence; if every member of a family line has the same DNA, and that DNA is not well suited to the existing environment, it could spell disaster. Then again, a Komodo mother creating a male with which it can breed doesn’t appear to be such a bad option, when faced with extinction. And it’s not such a bad option to have just one shark daughter, instead of six, if the alternative is not reproducing at all.

  Whether in situations where males are sparse, or simply as a matter of course, it is perfectly possible to create life from eggs alone – it’s a strategy that females of many species have long exploited. And indeed, parthenogenesis in animals has even been exploited, in a more domestic context, by us humans.

  After the war, the US Department of Agriculture and British animal research units sponsored some interesting experiments with the ostensible aim of improving the efficiency and sustainability of animal husbandry. Then, in 1952, scientists at the Beltsville Agricultural Research Center in Maryland discovered parthenogenesis in turkey eggs. Immediately, selective breeding programmes were launched in an attempt to intensify the trait in certain lines of turkeys and chickens – it was the hunt for the ultimate breeder.

  Those turkeys that showed the greatest predisposition for reproducing without sex were crossed, and were a runaway success – the Beltsville Small White breed. The percentage of virgin births in the turkeys increased from nearly seventeen percent to around forty-five percent in the space of a mere decade – a mote of evolutionary time.

  Interestingly, parthenogenesis in the eggs of both chickens and turkeys was notable for the seeming lack of cell organization within the early embryos. A chaotic, multi-layered mess of cells would develop, whether it was grown in a hen’s oviduct or in an incubator. This made the scientists at Beltsville wonder whether an infection could have triggered the birds’ new mode of reproduction – an avian version of Wolbachia.

  As a culprit, the researchers suspected a particular group of viruses, Rous sarcoma retrovirus, fowlpox virus, and Newcastle disease. Each of the viruses was found to enhance parthenogenesis; in other words, they appeared to stimulate the egg to develop into an embryo, an effect that, as with Wolbachia, persisted in the eggs of the daughters and granddaughters produced through virgin birth. Unlike with Wolbachia, however, virgin birth in the turkeys was not ‘curable’. If an already vaccinated turkey was infected with the fowlpox virus, the incidence of parthenogenesis in the eggs of that same hen increased markedly over the level recorded for her eggs before she was vaccinated – the opposite to what the scientists had expected.

  Still, the data indicated that parthenogenesis could be boosted by selective breeding. The team could identify the ‘high-incidence’ turkeys, those recorded to have the highest predisposition for virgin birth, and keep the line going, without introducing sperm. The finding was backed by studies of fruit flies, among which it was observed that both males and females could transmit the parthenogenetic trait to their offspring. Through cross-breeding these flies, scientists increased the rate of parthenogenesis by around thirty-four times, compared to unselected fruit flies, in just twelve generations.

  That, of course, leaves the question: if the birds and the bees can do it, why couldn’t we?

  4

  THE CONCERT IN THE EGG

  The history of man for the nine months preceding his birth would probably be far more interesting, and contain events of greater moment, than all the three score and ten years that follow it.

  Samuel T. Coleridge, annotation to Religio Medici, 1802

  It was March 1984. In a small town in Lesotho, a fifteen-year-old girl walked to a local bar to start work for the day. At some point during her shift, her new boyfriend showed up. Unfortunately, so did a jealous ex-lover – just in time to catch her with her boyfriend’s penis in her mouth: to the ex’s eye, in flagrante delicto. The details of the fight that ensued are unclear, but it seems the girl tried to protect her boyfriend (and herself) from attack, because she ended up with lacerations on her hand; she also sustained two stab wounds to her stomach.

  Just over nine months after the doctors at Mafeteng District Hospital stitched up her wounds, the girl returned. This time she was much larger in girth and complained of acute, but unexplained, pains in her lower abdomen. The possibility that she was pregnant had never occurred to her – not because she was naïve, but because she was well aware, as her doctors were soon to discover, that she did not have a vagina.

  In one sense, having sex and getting pregnant is as straightforward an event as any. You need a male and a female, they have sexual intercourse, sperm meets egg, and, some time later, a baby is produced. All of this we take for granted, though not in a glib sense; as we have seen, much can go wrong along the way, and sometimes babies are born with debilitating diseases and sometimes they are miscarried or emerge stillborn. Yet, in all these cases, we assume that at one point a sperm met an egg, thereby beginning a pregnancy. But step back from that assumption and consider the circumstance within which sperm meets egg, and even whether or not sperm meets egg at all.

  The Lesotho teenager was treated by Douwe Verkuyl, who reported on her predicament in the British Journal of Obstetric Gynaecology. Dr Verkuyl suggested that the pregnancy may have been the first recorded case of ‘oral conception’: the knife wound to the stomach may have allowed the sperm the girl had swallowed to find its way from her gut to her womb. As unlikely as it may seem, this is a strategy that has seen precedents in nature. There are animals in which fertilization can be achieved artificially by injecting sperm into the abdominal cavity, from where they swim down a Fallopian tube to the egg. In fact, for some, like the blood-sucking African bat bug, impregnation via the abdomen is the standard mode of operation. Even though the females of the species have not one but two vaginas – one real, one fake – the males use neither. Instead, a male will stab a female’s abdomen and inseminate the female’s blood. Of course, just because a relative of the bed bug can do it doesn’t imply it can happen in humans too. But Verkuyl noted two conditions that she thought made the scenario more likely: when her young patient arrived at hospital after the fracas, her stomach was devoid of food (and the gastrointestinal juices that are produced to digest it) and saliva itself tends to be alkaline (it has a high pH). These things, she thought, helped the sperm survive what would have otherwise been the hostile, acidic environment in the stomach.

  Shortly after the child’s birth by Caesarean section, the families of the girl and her boyfriend exchanged cattle to seal their union. But the girl’s son, conceived from that gruesome and bizarre violent encounter was to be her only child. Around the time her son reached the age of
two and a half, the girl began to suffer crippling pains, because her menstrual blood, which had no outlet, was collecting in the cavity of her uterus. Unable to stop her periods through drug treatments, doctors ordered a hysterectomy, the removal of the uterus. ‘By that time,’ Verkuyl wrote, ‘the son looked very much like the legal father,’ a fact that ‘excludes an even more miraculous conception’. By which, one assumes, the doctor was alluding to the conception of a child without the involvement of sperm at all.