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The natural world is full of extraordinary animals
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with amazing life histories.
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Yet certain stories are more intriguing than most.
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The mysteries of a butterfly's life cycle,
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or the strange biology of the emperor penguin.
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Some of these creatures were surrounded by myth
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and misunderstandings for a very long time.
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And some have only recently revealed their secrets.
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These are the animals that stand out from the crowd.
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The curiosities I find most fascinating of all.
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Female Komodo dragons can give birth to live young
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without having contact with a male.
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And female aphids can clone themselves to produce
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hundreds of copies.
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How and why do these very different creatures reproduce by virgin birth?
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And also in this programme, some animals live in conditions so cold
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that they seem to defy the rules of nature.
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The emperor penguin is the only animal able
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to raise its young in the harsh Antarctic winter.
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And the tiny wood frog faces freezing conditions
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that would kill any other amphibian.
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How do they do it?
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Most animals breed by sexual reproduction.
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A male fertilises a female's eggs
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and both parents' genes mix and produce young.
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But in nature a few animals stray from this method
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and breed in a different way.
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In August 2005, here in London zoo,
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a female Komodo dragon called Sungai laid a clutch of eggs
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and several months later four baby dragons hatched.
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That may not seem remarkable, but it was.
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Because Sungai had had no contact with a male Komodo dragon
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for more than two years.
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At first, keepers thought that she had stored sperm from the male
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she'd been kept with previously in France,
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but genetic tests reveal that she had in fact fertilised
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her own eggs and given birth without any male involvement.
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This was an amazing discovery about Komodo dragons,
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that they can breed by a process called parthenogenesis.
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It's a term derived from two Greek words,
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"partheno", meaning virgin, and "genesis", meaning birth.
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Incredibly, the dragon's remarkable reproductive abilities
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went unnoticed until just a few years ago.
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But the species itself had remained unknown well into the 20th century.
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Then stories started to circulate in Indonesia of a strange
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reptilian monster living on a tiny island
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lying far to the east of Bali.
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It was said to be over six metres long
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and strong enough to pull down a buffalo.
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In 1910, two Europeans,
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members of a Dutch pearling fleet, finally confirmed
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the existence of these great dragons on the island of Komodo.
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Excited by this finding, photographs of the skin were sent
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to Major Owens, director of the zoological museum in Java.
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He was equally amazed, and employed an experienced Indonesian collector,
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who captured two live adults and two youngsters for his zoo.
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The land crocodile was identified as a huge
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and new species of monitor lizard.
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He named it Varanus komodoensis.
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The discovery of this living monster caused a flurry of excitement,
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but World War I prevented further visits to the island.
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And then, in 1926, an expedition was launched by an American
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called William Burton to find out more.
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His small team included his wife, Dr Emmett Reid-Dunne,
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a reptile expert, and a newsreel cameraman from Pathe.
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Their film of this giant island creature from a hidden world
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caused great excitement worldwide.
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Then, in 1927, two living Komodo dragons were sent to Europe.
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Although they clearly could be dangerous,
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they proved to be more gentle and intelligent than expected.
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But it would take 80 years before we fully understood
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the way they reproduce.
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We know from other examples that
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the reproduction of reptiles can be more varied than that of mammals.
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In crocodiles, the sex of the eggs is not genetically fixed,
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but is controlled instead by temperature.
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Those incubated at warm temperatures hatch as males
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and those in cooler conditions as females.
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But the sex of an unhatched Komodo dragon
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is determined in a different way.
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The fact that Komodo dragon eggs can develop without fertilisation
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was a surprising and exciting discovery.
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But, interestingly, all the babies that hatched were males.
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Why should that be?
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Well, this is how it works.
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The female Komodo dragon has two different sex chromosomes,
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a "W" and a "Z".
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And the male has two similar chromosomes, a "Z" and a "Z".
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If there are no males, only the female W-Z pair remain.
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In such a case, the female divides her own egg-cell into two halves,
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one of which has a W chromosome and the other a single Z.
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They then duplicate themselves to form a W-W and a Z-Z.
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In the Komodo dragon, the W-W combination is not
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an operative pair, so only the male, Z-Z, will hatch.
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Thus, female Komodo dragons can produce their own males.
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This seems almost unbelievable, but when you come to think about it,
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it's a very useful ability for an animal that lives on a small island.
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Komodo dragons are descended from lizard-like ancestors
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that lived over 40 million years ago in Asia.
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They migrated to Australia
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and later reached the islands of central Indonesia either
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by swimming or by drifting across the ocean on floating vegetation.
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Parthenogenesis would enable a single female
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arriving on an island to start a breeding population all by herself.
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Nobody knew that Komodo dragons could breed asexually
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before lone females hatched fertile eggs in captivity.
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In the wild, it's virtually impossible to know if a female
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has mated with a male, and there are usually males around.
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In most circumstances, sexual reproduction is preferable.
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A mix of male and female genes can enable the repair of DNA
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and prevent unwanted mutations.
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Such genetic variation also helps animals to adapt to changing
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environments, so sexual reproduction seems to make more biological sense
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than parthenogenesis and it should be rare in the wild,
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an extreme last resort.
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Strangely, that's not always so.
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In 2012, odd breeding behaviour was noticed in two species of snake,
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copperheads and cottonmouths.
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Some females were reproducing by parthenogenesis
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even though males were present.
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These females were often small and overlooked by the males,
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so, rather than not breed, they cloned themselves.
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But this kind of breeding is potentially a genetic dead-end.
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If individuals all have the same genes,
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the species can't react to a changing world.
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For whiptail lizards, which live in a harsh but very stable desert,
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being genetically the same is actually an advantage.
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For them, parthenogenesis is better than sexual reproduction,
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as it prevents them from varying from their winning formula.
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Strangely, the females still go through the motions of mating.
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This stimulates their hormones, but these lizards are taking a gamble.
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If their environment changes for the worse,
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they'll be unable to adapt and so they risk extinction.
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Clearly, the best survival technique is to be able to
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reproduce in either way.
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Parthenogenesis has enabled isolated dwellers like the Komodo dragon
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to survive by forming breeding populations from just
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a single female.
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More recently, studies of wild Komodo dragons have revealed
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that two thirds of the population is male,
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suggesting that even when both sexes are present
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asexual breeding is still occurring.
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So Komodo dragons keep their breeding options flexible.
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It's likely that many animals are breeding by parthenogenesis
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or have the potential to do so, but we just don't know about them.
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Parthenogenesis has been occurring unnoticed for millions of years.
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Here is a natural curiosity that's only just revealing its secrets.
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Next, we meet a tiny animal that uses parthenogenesis to be
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one of the fastest breeders in nature.
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Surprisingly, this lives in our own back gardens.
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In summer, this is not an uncommon sight.
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Thousands of aphids massed together on a stem.
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At this time of the year, each of them can produce five to ten
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youngsters in a day, and each is a genetic copy of herself.
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So vast numbers can suddenly appear within a day or so.
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Birds and other insects arrive and prey on them,
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but the aphids usually manage to keep ahead.
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This astonishing ability attracted the attention of early scholars.
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In the mid-18th century,
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a new survey of insects was published in France.
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Its author, Rene Antoine Ferchault de Reaumur,
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expressed surprise that he'd never seen aphids mating.
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Neither had he seen a male.
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He made the revolutionary suggestion that they were reproducing
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without sex and invited his readers to help prove it.
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In the spring of 1740, Charles Bonnet,
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then a young law student from Switzerland, took up that challenge.
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Charles Bonnet took a newborn female aphid from its mother
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immediately after birth and put it in an isolation chamber.
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He placed the aphid on a leaf inside an upturned glass jar
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and, using a magnifying glass, watched it from early morning
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until night for 12 days.
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On the evening of June the 1st, 1740, at 7.30pm,
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the female aphid gave birth to a brand-new baby aphid.
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Then, over the next 21 days, she had 94 more female offspring.
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Bonnet had no clue how this could happen,
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but he knew for sure that the aphid had bred without any male contact.
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He sent his findings to Reaumur in Paris, who published this
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new and important discovery of sexless reproduction.
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But how this parthenogenesis worked
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and why aphids used virgin birth in their life cycles
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was still a mystery
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and entomologists puzzled over it for many years.
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In the 1830s, an entomologist called Francis Walker took a great
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interest in cataloguing various small insects, including aphids.
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He made more than 13,000 slides.
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Walker collected hundreds of aphids, many from Southgate
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and the surrounding areas of London.
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Here we can see some of them.
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He made successive collections of the same species
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of aphid from the same locality across all the seasons.
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As a result, he found several different forms of each aphid
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throughout the breeding cycle.
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They varied in size and some were wingless.
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That suggested that female aphids had a rather extraordinary life cycle.
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It was clear from Walker's study that nearly all individual
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aphids are female,
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but they change in form over the seasons.
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In early spring, when plants are growing, most are without wings.
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With plenty of food on offer, they have no need to fly.
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Later in the season, when overcrowding becomes an issue,
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females are born with wings so that they can travel to find new food.
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Aphids seem to be able to produce females that can exploit
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every situation.
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Although Walker was prolific, he wasn't always entirely accurate.
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He recorded many aspects of the aphids' life cycles,
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but he didn't piece them together to produce the complete picture.
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And then aphid research was taken up by another entomologist,
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called George Buckton.
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He chronicled every detail of the complex aphid life cycle.
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In 1883, George Buckton published a monograph
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of British aphids in four volumes.
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He wanted to share his passion for these tiny insects
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in books that he hoped would not be too dry academically.
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Buckton corresponded with many leading naturalists of his day
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to pull together every possible specimen and record of behaviour.
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He was an accomplished artist and produced beautiful,
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accurate drawings from live specimens
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and they interestingly show a distinct absence of male aphids.
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"The sexual forms of aphides," he wrote,
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"are in many species very rarely met."
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Buckton's drawings confirmed that aphid populations are commonly
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all-female and the males have been almost entirely
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eliminated from the species.
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For most of the breeding season,
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females only give birth to daughters.
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They don't waste time producing males which can't by themselves produce offspring.
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So do aphids need males at all?
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The life cycle of another insect would seem to suggest not.
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This wonderful creature is a Phyllium giganteum,
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a giant leaf insect.
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It's the largest species of its group and it lives wild in Malaysia.
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Nearly all individuals are female.
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In fact, the male of this species wasn't discovered until 1994.
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They're extremely rare.
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The species for the most part reproduces itself by parthenogenesis.
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They lay unfertilised eggs that hatch into more females
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and this method of reproduction has enabled it
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to extend its range dramatically.
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Much like a single female Komodo dragon arriving on an island,
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a lone female stick insect can start a breeding colony
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in a new area even if males never arrive.
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And that's what happened in southern England in 1903,
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when a different species of stick insect arrived on vegetation
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imported from New Zealand.
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Now, all female populations survive thousands of miles
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away from their native home.
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These populations have no males and don't appear to need them.
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The females produce fertile eggs that survive the cold winters
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and new females hatch out in the spring.
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But, without males, the population could become dangerously inbred.
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00:17:52,520 --> 00:17:56,640
Aphid populations face the same problems, but most species
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00:17:56,640 --> 00:18:00,600
have a twist in their life cycle that freshens up their gene pool.
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00:18:01,640 --> 00:18:05,240
In the autumn, the aphid production line switches from producing
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just asexual females to producing sexual males and sexual females.
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00:18:11,400 --> 00:18:14,000
At the end of the season, as the food supply wanes
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00:18:14,000 --> 00:18:16,080
and the temperature drops,
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00:18:16,080 --> 00:18:20,280
there's a phase of sexual reproduction that produces eggs.
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00:18:20,280 --> 00:18:25,840
These eggs will overwinter to produce next spring's new aphid generation.
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00:18:30,440 --> 00:18:33,640
Aphids don't produce their eggs until the autumn.
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00:18:34,880 --> 00:18:39,000
However, most populations survive until then, because in many cases
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they form a relationship with another insect, ants.
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00:18:44,400 --> 00:18:48,360
An aphid feeds by piercing the stems of plants
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and drinking the sugary sap.
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00:18:51,360 --> 00:18:55,200
But sap contains far more sugar than the aphids can use,
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so they excrete the excess as honeydew.
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00:18:58,720 --> 00:19:01,520
This is perfect food for the ants
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00:19:01,520 --> 00:19:05,240
and they keenly farm the aphids to harvest the rich liquid.
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00:19:06,360 --> 00:19:09,160
And in return the ants protect the aphids
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from insects that try to prey on them.
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00:19:13,040 --> 00:19:16,640
So, with ants guarding them, the aphids have a good chance
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of surviving until the end of the year, when they produce their eggs.
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00:19:28,120 --> 00:19:32,720
In the spring, new females will emerge from the eggs and start
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once more to produce new versions of themselves over and over again.
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00:19:50,080 --> 00:19:55,160
And aphids have a final, almost unbelievable twist in their life cycles
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that greatly speeds up their breeding.
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They do something truly astounding.
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00:20:05,160 --> 00:20:07,920
Even before they're born, they have embryos
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00:20:07,920 --> 00:20:10,320
developing inside their bodies.
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00:20:10,320 --> 00:20:14,440
Parthenogenesis, combined with this telescoping of generations,
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00:20:14,440 --> 00:20:18,600
give aphids an extremely rapid turnover of generations.
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00:20:18,600 --> 00:20:20,400
Like tiny Russian dolls,
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00:20:20,400 --> 00:20:23,680
they just keep popping out smaller copies of themselves.
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00:20:25,240 --> 00:20:29,000
A newly born summer aphid has inside her body
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00:20:29,000 --> 00:20:32,840
her own developing daughters, who in turn contain her
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00:20:32,840 --> 00:20:35,720
fully formed unborn granddaughters.
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00:20:35,720 --> 00:20:40,240
So several generations of aphid overlap in time and space
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00:20:40,240 --> 00:20:43,440
and in one season a single female can produce
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00:20:43,440 --> 00:20:46,680
thousand upon thousand of cloned females.
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00:20:48,600 --> 00:20:53,920
Aphids' lives are varied, often complicated and truly amazing.
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00:20:53,920 --> 00:20:57,400
They can change plant host, change their form
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00:20:57,400 --> 00:21:00,040
and alter their method of reproduction.
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00:21:00,040 --> 00:21:02,960
In the spring, females hatch from eggs and
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produce several generations of wingless females.
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00:21:06,440 --> 00:21:10,080
Their numbers grow, and they produce winged females that can fly to
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00:21:10,080 --> 00:21:14,560
new food and rapidly produce even more females.
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00:21:14,560 --> 00:21:19,200
In the autumn, the sexual forms of both males and female appear,
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00:21:19,200 --> 00:21:23,280
which mate and lay eggs, which then can survive the winter.
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00:21:28,400 --> 00:21:31,400
The ability to breed by parthenogenesis seems almost
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00:21:31,400 --> 00:21:36,600
magical to us. But in nature virgin birth is not uncommon.
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00:21:36,600 --> 00:21:40,240
Having the ability to produce daughter clones or more males
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00:21:40,240 --> 00:21:42,560
can save a species or create a new one.
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00:21:43,880 --> 00:21:47,000
Flexible ways of breeding have allowed creatures
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00:21:47,000 --> 00:21:48,400
to colonise new areas
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00:21:48,400 --> 00:21:52,600
and survive in small communities, like those on islands.
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00:21:52,600 --> 00:21:56,440
The Komodo dragon has certainly survived for many centuries.
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00:21:56,440 --> 00:22:00,680
And aphids have been around for more than 200 million years.
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00:22:00,680 --> 00:22:06,120
So parthenogenesis is a breeding strategy that is a real life-saver.
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00:22:24,600 --> 00:22:27,160
These eggs were collected more than 100 years ago
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00:22:27,160 --> 00:22:31,080
during an expedition to the Antarctic.
311
00:22:31,080 --> 00:22:34,160
The conditions were so cold that the man that collected them
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00:22:34,160 --> 00:22:36,920
never made it back to England alive.
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00:22:36,920 --> 00:22:40,960
He perished alongside Captain Scott during the ill-fated journey
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00:22:40,960 --> 00:22:43,400
to reach the South Pole.
315
00:22:43,400 --> 00:22:46,640
The eggs were laid by an emperor penguin, a bird whose life history
316
00:22:46,640 --> 00:22:50,960
would surprise and confound those early polar explorers.
317
00:22:52,760 --> 00:22:56,400
At the end of the 19th century, the Antarctic was an unfamiliar
318
00:22:56,400 --> 00:22:58,320
and mysterious place.
319
00:22:58,320 --> 00:23:01,280
Only a handful of explorers had ventured this far south
320
00:23:01,280 --> 00:23:04,040
and there was still a huge blank in the world map.
321
00:23:05,320 --> 00:23:07,200
But then, in 1901,
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00:23:07,200 --> 00:23:11,960
a British expedition set off on a purpose-built ship, the Discovery,
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00:23:11,960 --> 00:23:14,560
to explore this most southerly land.
324
00:23:14,560 --> 00:23:18,000
In charge was Commander Robert Falcon Scott.
325
00:23:20,320 --> 00:23:24,880
Scott took on board with him a young man named Edward Wilson,
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00:23:24,880 --> 00:23:27,920
who would serve as the ship's doctor and naturalist.
327
00:23:28,960 --> 00:23:31,600
Wilson had only just qualified as a surgeon
328
00:23:31,600 --> 00:23:34,880
and had no formal training in scientific research.
329
00:23:34,880 --> 00:23:38,240
But the young man's passion for natural history and art
330
00:23:38,240 --> 00:23:41,600
would prove to be an invaluable asset to the expedition.
331
00:23:41,600 --> 00:23:44,120
Wilson's job was to draw and record
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00:23:44,120 --> 00:23:46,520
any plants and animals that they encountered.
333
00:23:46,520 --> 00:23:49,440
But from the start there was one creature that fascinated him
334
00:23:49,440 --> 00:23:52,240
more than any other - the emperor penguin.
335
00:23:54,080 --> 00:23:56,160
This largest of all penguins
336
00:23:56,160 --> 00:23:59,280
had only been discovered 60 years earlier.
337
00:23:59,280 --> 00:24:03,720
But, as yet, nothing was known about its habits or where it breeds.
338
00:24:03,720 --> 00:24:06,760
The expedition was an opportunity to find out more.
339
00:24:08,880 --> 00:24:11,640
When the Discovery reached the southern continent,
340
00:24:11,640 --> 00:24:15,840
they put up a hut in which they would spend the long, dark winter.
341
00:24:15,840 --> 00:24:19,360
Then, as the sun started to appear again in spring,
342
00:24:19,360 --> 00:24:21,920
the sledge teams started to explore,
343
00:24:21,920 --> 00:24:25,680
and one returned with some tantalising news.
344
00:24:25,680 --> 00:24:29,320
They had discovered a breeding colony of emperor penguins
345
00:24:29,320 --> 00:24:31,960
in a place called Cape Crozier.
346
00:24:31,960 --> 00:24:35,240
It was the first colony any human being had ever seen
347
00:24:35,240 --> 00:24:40,400
and, much to their surprise, the birds were breeding on sea ice.
348
00:24:41,600 --> 00:24:44,240
It was a truly astonishing discovery.
349
00:24:44,240 --> 00:24:46,560
No other bird breeds on ice,
350
00:24:46,560 --> 00:24:50,520
and Wilson was keen to find out more about this remarkable creature.
351
00:24:52,720 --> 00:24:57,360
Very little was known about emperor penguins but there was another bird
352
00:24:57,360 --> 00:25:01,880
which could give Wilson some insights into their lives - the king penguin.
353
00:25:04,280 --> 00:25:09,200
Adult king penguins look very much the same as adult emperors.
354
00:25:09,200 --> 00:25:11,760
The main difference is in size.
355
00:25:11,760 --> 00:25:15,840
These kings are only about half as big as an emperor,
356
00:25:15,840 --> 00:25:18,920
and they live in the northern part of Antarctica.
357
00:25:20,280 --> 00:25:23,200
They breed in the middle of the Antarctic summer -
358
00:25:23,200 --> 00:25:28,040
November, December - and incubation takes about seven weeks.
359
00:25:28,040 --> 00:25:31,680
Wilson thought that emperors would do very much the same.
360
00:25:33,520 --> 00:25:36,520
But he was about to discover otherwise.
361
00:25:36,520 --> 00:25:40,000
The following spring, with the hope of collecting some penguin eggs,
362
00:25:40,000 --> 00:25:43,800
Wilson left for Cape Crozier as early as he dared.
363
00:25:46,400 --> 00:25:49,440
When he got there, however, much to his surprise,
364
00:25:49,440 --> 00:25:52,040
he found only well-grown chicks.
365
00:25:53,440 --> 00:25:57,760
After repeated calculations, he finally concluded that these
366
00:25:57,760 --> 00:26:02,520
penguins must lay their eggs in the middle of the Antarctic winter.
367
00:26:05,640 --> 00:26:08,880
That emperors should start breeding at the coldest
368
00:26:08,880 --> 00:26:12,120
and bleakest time of the year was an astonishing discovery.
369
00:26:12,120 --> 00:26:15,520
It seemed to defy all the rules of nature,
370
00:26:15,520 --> 00:26:18,040
and Wilson was indeed amazed.
371
00:26:20,240 --> 00:26:24,760
But it seems that this strange lifestyle does, in fact, make sense.
372
00:26:24,760 --> 00:26:28,080
Emperor penguins are big birds and the chicks take more than
373
00:26:28,080 --> 00:26:31,000
a year to grow large enough to be independent.
374
00:26:31,000 --> 00:26:33,960
By laying the eggs earlier in winter,
375
00:26:33,960 --> 00:26:36,320
emperors give their chicks a head start
376
00:26:36,320 --> 00:26:38,960
so that they first go to sea in the summer months
377
00:26:38,960 --> 00:26:40,360
when food is plentiful.
378
00:26:42,600 --> 00:26:44,880
But how do emperor penguins protect their eggs
379
00:26:44,880 --> 00:26:46,760
and chicks from the bitter cold?
380
00:26:50,320 --> 00:26:53,080
Neither kings nor emperors make a nest
381
00:26:53,080 --> 00:26:55,360
or lay their eggs on the ground.
382
00:26:55,360 --> 00:26:58,400
If they did, the eggs would freeze within minutes.
383
00:26:58,400 --> 00:27:01,480
Instead, they keep their eggs on the top of their feet
384
00:27:01,480 --> 00:27:05,280
and cover them with a feathered fold of skin from the abdomen,
385
00:27:05,280 --> 00:27:06,520
and inside that pouch
386
00:27:06,520 --> 00:27:10,040
the temperature is about 70 degrees warmer than it is outside.
387
00:27:14,320 --> 00:27:17,160
With temperatures of minus-60 degrees Celsius,
388
00:27:17,160 --> 00:27:22,840
and winds gusting at 200km/h, the birds huddle together for warmth.
389
00:27:28,240 --> 00:27:31,320
Even under these extremely difficult conditions,
390
00:27:31,320 --> 00:27:33,880
Wilson recorded everything he saw.
391
00:27:33,880 --> 00:27:35,520
WIND ROARS
392
00:27:35,520 --> 00:27:38,520
Able to work for only a few minutes at a time,
393
00:27:38,520 --> 00:27:42,760
he still managed to produce detailed notes and drawings that give us
394
00:27:42,760 --> 00:27:45,480
a first insight into the southern continent.
395
00:27:50,360 --> 00:27:53,840
This is the expedition's scientific report.
396
00:27:53,840 --> 00:27:58,360
And it contains most of Wilson's observations on the Antarctic.
397
00:27:58,360 --> 00:28:01,000
At a time when illustrations of animals were often
398
00:28:01,000 --> 00:28:03,160
drawn from dead specimens,
399
00:28:03,160 --> 00:28:07,320
Wilson drew his subjects live in the field wherever possible,
400
00:28:07,320 --> 00:28:10,080
to capture the true nature of the animal.
401
00:28:10,080 --> 00:28:13,000
Despite the extreme conditions under which he had to work,
402
00:28:13,000 --> 00:28:16,800
he made over 900 detailed drawings in the Antarctic.
403
00:28:23,640 --> 00:28:28,280
Wilson was an exceptional artist and a meticulous scientist
404
00:28:28,280 --> 00:28:31,880
and most of his observations have stood the test of time.
405
00:28:31,880 --> 00:28:35,440
But some things puzzled him more than others.
406
00:28:35,440 --> 00:28:39,680
He noted, for example, that the brooding of the chick was not
407
00:28:39,680 --> 00:28:43,360
just carried out by one bird or even by a single pair.
408
00:28:43,360 --> 00:28:48,240
It appeared as if numerous birds were taking turns in looking after
409
00:28:48,240 --> 00:28:53,800
the chick. Today, of course, we know that this is not quite correct.
410
00:28:53,800 --> 00:28:57,920
It's only the parents who care for both the egg and then the chick.
411
00:28:57,920 --> 00:29:00,160
RAPID STACCATO CAWING
412
00:29:00,160 --> 00:29:02,880
We now have a much better understanding of how
413
00:29:02,880 --> 00:29:06,440
emperor penguins breed, but Wilson's confusion as to
414
00:29:06,440 --> 00:29:09,800
who cares for the chicks is in fact quite understandable.
415
00:29:09,800 --> 00:29:11,400
He observed numerous occasions
416
00:29:11,400 --> 00:29:15,080
when a youngster was accidentally dropped by its parent.
417
00:29:15,080 --> 00:29:17,160
In his report, he writes,
418
00:29:17,160 --> 00:29:22,360
"what we actually saw again and again was the wild dash made by adults,
419
00:29:22,360 --> 00:29:25,640
"each weighing anything up to 90 pounds, to take possession
420
00:29:25,640 --> 00:29:30,480
"of any chick that happened to find itself deserted on the ice.
421
00:29:30,480 --> 00:29:34,040
"It can be compared to nothing better than a football scrimmage."
422
00:29:36,400 --> 00:29:38,320
The birds Wilson had observed
423
00:29:38,320 --> 00:29:41,760
were in fact females who had lost their own egg or chick
424
00:29:41,760 --> 00:29:45,800
and were trying to adopt or kidnap any unattended youngsters.
425
00:29:47,800 --> 00:29:52,680
What he couldn't know was that these adoptions are never successful.
426
00:29:52,680 --> 00:29:56,240
A new parent rarely feeds its foster chick
427
00:29:56,240 --> 00:29:58,480
and simply broods it for a few days.
428
00:29:58,480 --> 00:30:01,640
After that, the youngster is abandoned again
429
00:30:01,640 --> 00:30:03,240
or dies of starvation.
430
00:30:11,680 --> 00:30:14,960
It's likely that the female eventually recognises that
431
00:30:14,960 --> 00:30:16,960
the adopted chick is not her own.
432
00:30:27,520 --> 00:30:32,120
Although Wilson had been the first man to find an emperor penguin colony,
433
00:30:32,120 --> 00:30:36,560
he had not been able to obtain any freshly laid eggs.
434
00:30:36,560 --> 00:30:40,440
These were particularly sought-after by scientists of the day.
435
00:30:41,960 --> 00:30:45,080
It was thought at that time that the emperor penguin was
436
00:30:45,080 --> 00:30:46,800
one of the most primitive birds
437
00:30:46,800 --> 00:30:50,160
and possibly a missing evolutionary link with dinosaurs.
438
00:30:51,800 --> 00:30:55,760
If embryos could be obtained at an early enough stage then maybe
439
00:30:55,760 --> 00:30:59,760
one would see reptilian scales or some other dinosaur features.
440
00:31:01,200 --> 00:31:05,680
So the emperor penguin egg was regarded as a great scientific prize.
441
00:31:11,120 --> 00:31:13,480
A few years later, Scott and Wilson
442
00:31:13,480 --> 00:31:16,720
planned a second expedition to the Antarctic.
443
00:31:16,720 --> 00:31:19,680
The main objective was to reach the South Pole,
444
00:31:19,680 --> 00:31:22,160
but Wilson was determined to bring back
445
00:31:22,160 --> 00:31:24,400
newly laid emperor penguin eggs.
446
00:31:25,640 --> 00:31:29,920
This time, he made plans to travel to Cape Crozier even earlier,
447
00:31:29,920 --> 00:31:32,360
so as not to miss the birds on eggs.
448
00:31:32,360 --> 00:31:34,120
BIRD CAWS
449
00:31:34,120 --> 00:31:38,680
He picked two men to accompany him, Bowers and Cherry-Garrard,
450
00:31:38,680 --> 00:31:42,000
and they set off in the pitch black of the winter.
451
00:31:43,480 --> 00:31:49,360
It was a journey of over 70 miles and they had to cover it on foot.
452
00:31:49,360 --> 00:31:51,080
For six painful weeks,
453
00:31:51,080 --> 00:31:54,040
the three men pulled their heavy sledges in complete darkness
454
00:31:54,040 --> 00:31:59,560
and howling gales at temperatures of minus-40 degrees centigrade.
455
00:31:59,560 --> 00:32:02,640
Never before had anyone travelled in such bitter cold
456
00:32:02,640 --> 00:32:04,840
or in such difficult conditions.
457
00:32:04,840 --> 00:32:07,880
They sometimes barely covered a mile a day.
458
00:32:07,880 --> 00:32:10,720
It was what Cherry-Garrard would later call
459
00:32:10,720 --> 00:32:12,800
"the worst journey in the world".
460
00:32:14,800 --> 00:32:17,560
Their clothes were iced up and their breath
461
00:32:17,560 --> 00:32:19,520
and sweat froze on their bodies.
462
00:32:22,000 --> 00:32:26,560
Each night, it took them an hour to chip into their sleeping bags,
463
00:32:26,560 --> 00:32:28,000
which were frozen solid.
464
00:32:31,880 --> 00:32:35,840
When they finally reached the penguin colony, they collected five eggs,
465
00:32:35,840 --> 00:32:40,840
with great difficulty, and put them inside their mittens for safety.
466
00:32:40,840 --> 00:32:44,160
The men staggered back to base camp close to death
467
00:32:44,160 --> 00:32:46,880
and only three eggs survived the journey.
468
00:32:46,880 --> 00:32:48,680
These are two of them.
469
00:32:51,640 --> 00:32:54,880
It was an extraordinary feat of determination
470
00:32:54,880 --> 00:32:56,960
by Wilson and his companions.
471
00:32:56,960 --> 00:33:01,000
The precious eggs were supposed to reveal the evolutionary links
472
00:33:01,000 --> 00:33:02,760
between reptiles and birds,
473
00:33:02,760 --> 00:33:05,960
but getting them had nearly killed the collectors.
474
00:33:08,280 --> 00:33:09,800
A few months later,
475
00:33:09,800 --> 00:33:14,840
Scott led his party on the final push to reach the South Pole.
476
00:33:14,840 --> 00:33:18,080
His team consisted of just five men,
477
00:33:18,080 --> 00:33:20,080
and Wilson was amongst them.
478
00:33:21,880 --> 00:33:27,040
On their return journey, all five men perished, succumbing to the cold
479
00:33:27,040 --> 00:33:31,600
and starvation just a few kilometres from their nearest food depot.
480
00:33:33,880 --> 00:33:36,480
In the end, Wilson's eggs didn't contribute as much
481
00:33:36,480 --> 00:33:39,280
to our understanding of the development of the penguin chick
482
00:33:39,280 --> 00:33:42,760
as he had hoped, but his beautiful drawings
483
00:33:42,760 --> 00:33:47,360
and meticulous observations are quite a different matter.
484
00:33:47,360 --> 00:33:51,400
They helped to unravel the biology of a bird that is able
485
00:33:51,400 --> 00:33:54,680
to rear its young in the depths of the polar winter.
486
00:33:59,200 --> 00:34:01,040
The emperor penguin amazes us
487
00:34:01,040 --> 00:34:05,520
by raising its chicks in the most inhospitable place on earth.
488
00:34:05,520 --> 00:34:08,960
But a small frog has a way of coping with the cold
489
00:34:08,960 --> 00:34:11,360
that seems to be beyond belief.
490
00:34:13,080 --> 00:34:15,880
This is a North American wood frog,
491
00:34:15,880 --> 00:34:18,960
and it lives as far north as the Arctic Circle,
492
00:34:18,960 --> 00:34:21,320
but, like all cold-blooded creatures,
493
00:34:21,320 --> 00:34:24,920
it can't generate its own heat and its body temperature rises
494
00:34:24,920 --> 00:34:26,760
and falls with the surroundings.
495
00:34:26,760 --> 00:34:31,560
So when conditions drop below zero the frog risks freezing.
496
00:34:31,560 --> 00:34:35,040
How does a creature like this survive the harsh winters?
497
00:34:38,160 --> 00:34:42,920
The skin of amphibians is thin and moist and this makes them
498
00:34:42,920 --> 00:34:45,920
particularly vulnerable to the cold.
499
00:34:45,920 --> 00:34:50,320
Any contact with ice can instantly trigger freezing within
500
00:34:50,320 --> 00:34:55,000
their bodies and, for most animals, this means almost certain death.
501
00:34:56,600 --> 00:34:58,840
When water freezes, it expands,
502
00:34:58,840 --> 00:35:02,440
and the sharp ice crystals can puncture blood vessels
503
00:35:02,440 --> 00:35:06,040
and break cell walls, causing irreparable damage.
504
00:35:06,040 --> 00:35:09,800
The animal's internal organs may never function properly again.
505
00:35:12,200 --> 00:35:15,080
So, how do frogs avoid freezing?
506
00:35:16,440 --> 00:35:20,920
Many sit out the winter by hibernating at the bottom of a pond.
507
00:35:20,920 --> 00:35:23,560
The surface may freeze but underneath the ice
508
00:35:23,560 --> 00:35:26,760
the temperature remains just above freezing.
509
00:35:27,760 --> 00:35:31,280
And most land-living amphibians seek out a sheltered spot
510
00:35:31,280 --> 00:35:34,240
on the ground to avoid the deadly frost.
511
00:35:38,840 --> 00:35:43,160
But, in the 18th century, Arctic travellers came back with tales
512
00:35:43,160 --> 00:35:46,560
so extraordinary they were scarcely believable.
513
00:35:48,000 --> 00:35:52,640
A British explorer called Samuel Hearne reported seeing
514
00:35:52,640 --> 00:35:55,600
frozen frogs among the piles of leaves in Arctic Canada.
515
00:35:58,560 --> 00:36:01,680
He went on to make an extraordinary claim.
516
00:36:01,680 --> 00:36:05,720
"Frogs of various colours are numerous in these parts.
517
00:36:05,720 --> 00:36:09,000
"I have frequently seen them dug up with moss,
518
00:36:09,000 --> 00:36:11,240
"frozen as hard as ice,
519
00:36:11,240 --> 00:36:15,760
"in which state the legs are as easily broken off as a pipe stem,
520
00:36:15,760 --> 00:36:19,920
"without giving the least sensation to the animals.
521
00:36:21,200 --> 00:36:25,040
"But, by wrapping them up in warm skins and exposing them
522
00:36:25,040 --> 00:36:28,760
"to a slow fire, they soon recover life
523
00:36:28,760 --> 00:36:32,400
"and the mutilated animal gains its usual activity."
524
00:36:35,800 --> 00:36:40,320
Frozen frogs that, if gently warmed by a fire, would come back to life.
525
00:36:40,320 --> 00:36:42,960
What truth could there be in this account?
526
00:36:42,960 --> 00:36:44,120
Well...
527
00:36:45,240 --> 00:36:47,480
..this is a marsh frog
528
00:36:47,480 --> 00:36:50,360
and it's found in ponds and marshes throughout
529
00:36:50,360 --> 00:36:52,240
central and northern Europe.
530
00:36:52,240 --> 00:36:56,720
It's lying completely immobile on my hand because it's frozen solid.
531
00:36:58,720 --> 00:37:01,480
From the outside, it feels much like a rock.
532
00:37:01,480 --> 00:37:05,080
And you might be forgiven for thinking it was dead.
533
00:37:05,080 --> 00:37:09,360
Well, watch what happens when I put it into a bowl of warm water.
534
00:37:17,040 --> 00:37:21,000
Although it appears dead and has in fact stopped breathing,
535
00:37:21,000 --> 00:37:23,480
the frog's heart is still beating.
536
00:37:23,480 --> 00:37:25,360
Only the outer layer has frozen.
537
00:37:25,360 --> 00:37:27,960
The vital organs inside are still undamaged.
538
00:37:31,640 --> 00:37:35,840
Lab experiments have shown that, in this state, the marsh frog
539
00:37:35,840 --> 00:37:40,520
can survive temperatures of two degrees below freezing.
540
00:37:43,000 --> 00:37:45,880
Yes! It's lifted itself up, it's moving.
541
00:37:45,880 --> 00:37:47,360
Look at this.
542
00:37:48,480 --> 00:37:51,680
There, it's moving its right leg.
543
00:37:51,680 --> 00:37:56,480
Within a few minutes the frog has awakened to life once again.
544
00:37:58,680 --> 00:38:02,240
This is surely one of the most extraordinary miracles of nature.
545
00:38:04,840 --> 00:38:09,880
Nonetheless, the marsh frog can only survive a few hours of freezing.
546
00:38:09,880 --> 00:38:12,640
Anything more would mean certain death.
547
00:38:14,280 --> 00:38:17,680
Where it lives, it rarely faces extreme winters
548
00:38:17,680 --> 00:38:21,320
and is protected from the worst by the insulating water.
549
00:38:23,560 --> 00:38:26,080
So what about Samuel Hearne's story?
550
00:38:26,080 --> 00:38:30,000
Could some frogs survive longer periods of freezing?
551
00:38:30,000 --> 00:38:33,800
Another account from North America would seem to suggest so.
552
00:38:35,160 --> 00:38:39,480
In the 19th century, a naturalist called John Burroughs
553
00:38:39,480 --> 00:38:42,280
found a wood frog underneath the leaf litter
554
00:38:42,280 --> 00:38:44,320
at the beginning of the winter.
555
00:38:44,320 --> 00:38:46,120
Burroughs was surprised,
556
00:38:46,120 --> 00:38:49,880
but reasoned that the frog must know that a mild winter was on the way
557
00:38:49,880 --> 00:38:53,000
and had therefore not bothered to bury itself deeper.
558
00:38:55,040 --> 00:38:57,720
In fact, a very severe winter followed.
559
00:39:00,520 --> 00:39:03,680
Wondering about his frog, Burroughs went back to the same spot
560
00:39:03,680 --> 00:39:07,760
in spring and found the animal seemingly unharmed.
561
00:39:09,280 --> 00:39:12,520
The wood frog must have spent the entire winter above ground
562
00:39:12,520 --> 00:39:15,720
and survived temperatures that should have killed it.
563
00:39:16,880 --> 00:39:19,080
How did the tiny frog do it?
564
00:39:21,640 --> 00:39:26,160
The wood frog is not strong and large enough to dig itself into the ground,
565
00:39:26,160 --> 00:39:30,120
so it has to sit out the winter beneath the leaf litter.
566
00:39:30,120 --> 00:39:33,960
But this doesn't provide sufficient protection against the cold.
567
00:39:33,960 --> 00:39:36,840
So, how does this small frog survive?
568
00:39:37,840 --> 00:39:39,520
Today, we know the truth,
569
00:39:39,520 --> 00:39:43,360
and if Burroughs had done so he would have been astounded.
570
00:39:45,960 --> 00:39:49,120
It's only recently that we've discovered just how the wood frog
571
00:39:49,120 --> 00:39:53,000
avoids the usually fatal consequences of freezing.
572
00:39:54,720 --> 00:39:59,800
As winter sets in, the frog prepares for an extraordinary change.
573
00:40:07,600 --> 00:40:11,200
First, it draws water out of its cells into spaces where it
574
00:40:11,200 --> 00:40:13,120
will do less damage if it freezes.
575
00:40:14,200 --> 00:40:18,280
At the same time, its liver produces large amounts of sugar
576
00:40:18,280 --> 00:40:20,560
that act as antifreeze.
577
00:40:20,560 --> 00:40:24,520
This is pumped through the body to slow down the freezing.
578
00:40:30,080 --> 00:40:35,680
Now the entire frog slowly freezes from the outside inwards.
579
00:40:47,400 --> 00:40:50,480
And finally, the heart stops.
580
00:40:50,480 --> 00:40:52,360
The frog isn't dead,
581
00:40:52,360 --> 00:40:55,040
but it's probably about as close as you can get.
582
00:40:56,240 --> 00:40:59,040
70% of its body is frozen.
583
00:40:59,040 --> 00:41:02,800
And it can remain like this for several weeks on end.
584
00:41:11,360 --> 00:41:13,960
Then, as the air warms up again,
585
00:41:13,960 --> 00:41:16,440
a miraculous transformation takes place.
586
00:41:18,160 --> 00:41:23,440
The ice melts and the frog's body thaws and suddenly
587
00:41:23,440 --> 00:41:25,960
the heart sprouts back to life.
588
00:41:30,400 --> 00:41:34,200
Unlike the marsh frog, the deeply frozen wood frog needs
589
00:41:34,200 --> 00:41:37,800
several hours before it can resume normal activity.
590
00:41:42,960 --> 00:41:46,120
The wood frog's ability to survive in a frozen state
591
00:41:46,120 --> 00:41:48,840
has fascinated scientists.
592
00:41:48,840 --> 00:41:52,800
Could this one day help enhance our own medical understanding?
593
00:41:54,760 --> 00:41:58,440
We still don't understand completely how the wood frogs survive
594
00:41:58,440 --> 00:42:01,440
something that would kill most animals.
595
00:42:01,440 --> 00:42:04,760
What we do know is that, when freezing occurs slowly
596
00:42:04,760 --> 00:42:09,000
and in the right places, it appears to do less damage.
597
00:42:09,000 --> 00:42:12,080
This little frog seems to have mastered the problem
598
00:42:12,080 --> 00:42:15,440
by controlling how and where ice forms in its body.
599
00:42:17,960 --> 00:42:21,400
The emperor penguin's ability to breed during the Antarctic winter
600
00:42:21,400 --> 00:42:24,520
is a remarkable feat of endurance,
601
00:42:24,520 --> 00:42:28,720
but for a small frog to freeze solid and come back to life
602
00:42:28,720 --> 00:42:33,480
must surely be one of the most astonishing curiosities of nature.
53494
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