0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:08with amazing life histories.
0:00:09 > 0:00:12Yet certain stories are more intriguing than most.
0:00:16 > 0:00:19The mysteries of a butterfly's life cycle,
0:00:19 > 0:00:22or the strange biology of the emperor penguin.
0:00:23 > 0:00:26Some of these creatures were surrounded by myth
0:00:26 > 0:00:30and misunderstandings for a very long time.
0:00:30 > 0:00:33And some have only recently revealed their secrets.
0:00:35 > 0:00:39These are the animals that stand out from the crowd.
0:00:39 > 0:00:43The curiosities I find most fascinating of all.
0:00:52 > 0:00:56Female Komodo dragons can give birth to live young
0:00:56 > 0:00:58without having contact with a male.
0:00:59 > 0:01:03And female aphids can clone themselves to produce
0:01:03 > 0:01:05hundreds of copies.
0:01:05 > 0:01:12How and why do these very different creatures reproduce by virgin birth?
0:01:13 > 0:01:19And also in this programme, some animals live in conditions so cold
0:01:19 > 0:01:22that they seem to defy the rules of nature.
0:01:23 > 0:01:26The emperor penguin is the only animal able
0:01:26 > 0:01:29to raise its young in the harsh Antarctic winter.
0:01:30 > 0:01:33And the tiny wood frog faces freezing conditions
0:01:33 > 0:01:36that would kill any other amphibian.
0:01:36 > 0:01:38How do they do it?
0:01:45 > 0:01:49Most animals breed by sexual reproduction.
0:01:49 > 0:01:51A male fertilises a female's eggs
0:01:51 > 0:01:55and both parents' genes mix and produce young.
0:01:56 > 0:02:00But in nature a few animals stray from this method
0:02:00 > 0:02:01and breed in a different way.
0:02:03 > 0:02:08In August 2005, here in London zoo,
0:02:08 > 0:02:13a female Komodo dragon called Sungai laid a clutch of eggs
0:02:13 > 0:02:16and several months later four baby dragons hatched.
0:02:17 > 0:02:20That may not seem remarkable, but it was.
0:02:20 > 0:02:24Because Sungai had had no contact with a male Komodo dragon
0:02:24 > 0:02:26for more than two years.
0:02:26 > 0:02:30At first, keepers thought that she had stored sperm from the male
0:02:30 > 0:02:33she'd been kept with previously in France,
0:02:33 > 0:02:37but genetic tests reveal that she had in fact fertilised
0:02:37 > 0:02:41her own eggs and given birth without any male involvement.
0:02:43 > 0:02:46This was an amazing discovery about Komodo dragons,
0:02:46 > 0:02:51that they can breed by a process called parthenogenesis.
0:02:51 > 0:02:54It's a term derived from two Greek words,
0:02:54 > 0:02:57"partheno", meaning virgin, and "genesis", meaning birth.
0:02:59 > 0:03:02Incredibly, the dragon's remarkable reproductive abilities
0:03:02 > 0:03:05went unnoticed until just a few years ago.
0:03:06 > 0:03:10But the species itself had remained unknown well into the 20th century.
0:03:11 > 0:03:16Then stories started to circulate in Indonesia of a strange
0:03:16 > 0:03:19reptilian monster living on a tiny island
0:03:19 > 0:03:20lying far to the east of Bali.
0:03:22 > 0:03:24It was said to be over six metres long
0:03:24 > 0:03:26and strong enough to pull down a buffalo.
0:03:30 > 0:03:32In 1910, two Europeans,
0:03:32 > 0:03:35members of a Dutch pearling fleet, finally confirmed
0:03:35 > 0:03:40the existence of these great dragons on the island of Komodo.
0:03:40 > 0:03:43Excited by this finding, photographs of the skin were sent
0:03:43 > 0:03:48to Major Owens, director of the zoological museum in Java.
0:03:48 > 0:03:53He was equally amazed, and employed an experienced Indonesian collector,
0:03:53 > 0:03:57who captured two live adults and two youngsters for his zoo.
0:03:58 > 0:04:02The land crocodile was identified as a huge
0:04:02 > 0:04:05and new species of monitor lizard.
0:04:05 > 0:04:07He named it Varanus komodoensis.
0:04:11 > 0:04:16The discovery of this living monster caused a flurry of excitement,
0:04:16 > 0:04:19but World War I prevented further visits to the island.
0:04:20 > 0:04:24And then, in 1926, an expedition was launched by an American
0:04:24 > 0:04:27called William Burton to find out more.
0:04:29 > 0:04:33His small team included his wife, Dr Emmett Reid-Dunne,
0:04:33 > 0:04:37a reptile expert, and a newsreel cameraman from Pathe.
0:04:39 > 0:04:43Their film of this giant island creature from a hidden world
0:04:43 > 0:04:46caused great excitement worldwide.
0:04:49 > 0:04:55Then, in 1927, two living Komodo dragons were sent to Europe.
0:04:57 > 0:04:59Although they clearly could be dangerous,
0:04:59 > 0:05:02they proved to be more gentle and intelligent than expected.
0:05:05 > 0:05:08But it would take 80 years before we fully understood
0:05:08 > 0:05:10the way they reproduce.
0:05:14 > 0:05:16We know from other examples that
0:05:16 > 0:05:20the reproduction of reptiles can be more varied than that of mammals.
0:05:23 > 0:05:27In crocodiles, the sex of the eggs is not genetically fixed,
0:05:27 > 0:05:30but is controlled instead by temperature.
0:05:32 > 0:05:36Those incubated at warm temperatures hatch as males
0:05:36 > 0:05:39and those in cooler conditions as females.
0:05:44 > 0:05:48But the sex of an unhatched Komodo dragon
0:05:48 > 0:05:50is determined in a different way.
0:05:52 > 0:05:56The fact that Komodo dragon eggs can develop without fertilisation
0:05:56 > 0:05:59was a surprising and exciting discovery.
0:05:59 > 0:06:03But, interestingly, all the babies that hatched were males.
0:06:03 > 0:06:05Why should that be?
0:06:05 > 0:06:07Well, this is how it works.
0:06:07 > 0:06:12The female Komodo dragon has two different sex chromosomes,
0:06:12 > 0:06:14a "W" and a "Z".
0:06:16 > 0:06:20And the male has two similar chromosomes, a "Z" and a "Z".
0:06:23 > 0:06:28If there are no males, only the female W-Z pair remain.
0:06:28 > 0:06:34In such a case, the female divides her own egg-cell into two halves,
0:06:34 > 0:06:39one of which has a W chromosome and the other a single Z.
0:06:39 > 0:06:45They then duplicate themselves to form a W-W and a Z-Z.
0:06:47 > 0:06:51In the Komodo dragon, the W-W combination is not
0:06:51 > 0:06:55an operative pair, so only the male, Z-Z, will hatch.
0:06:57 > 0:07:01Thus, female Komodo dragons can produce their own males.
0:07:03 > 0:07:08This seems almost unbelievable, but when you come to think about it,
0:07:08 > 0:07:13it's a very useful ability for an animal that lives on a small island.
0:07:13 > 0:07:16Komodo dragons are descended from lizard-like ancestors
0:07:16 > 0:07:19that lived over 40 million years ago in Asia.
0:07:19 > 0:07:21They migrated to Australia
0:07:21 > 0:07:25and later reached the islands of central Indonesia either
0:07:25 > 0:07:29by swimming or by drifting across the ocean on floating vegetation.
0:07:29 > 0:07:32Parthenogenesis would enable a single female
0:07:32 > 0:07:37arriving on an island to start a breeding population all by herself.
0:07:40 > 0:07:43Nobody knew that Komodo dragons could breed asexually
0:07:43 > 0:07:47before lone females hatched fertile eggs in captivity.
0:07:47 > 0:07:51In the wild, it's virtually impossible to know if a female
0:07:51 > 0:07:55has mated with a male, and there are usually males around.
0:07:55 > 0:07:58In most circumstances, sexual reproduction is preferable.
0:07:58 > 0:08:03A mix of male and female genes can enable the repair of DNA
0:08:03 > 0:08:06and prevent unwanted mutations.
0:08:06 > 0:08:10Such genetic variation also helps animals to adapt to changing
0:08:10 > 0:08:15environments, so sexual reproduction seems to make more biological sense
0:08:15 > 0:08:19than parthenogenesis and it should be rare in the wild,
0:08:19 > 0:08:21an extreme last resort.
0:08:21 > 0:08:23Strangely, that's not always so.
0:08:25 > 0:08:31In 2012, odd breeding behaviour was noticed in two species of snake,
0:08:31 > 0:08:34copperheads and cottonmouths.
0:08:34 > 0:08:37Some females were reproducing by parthenogenesis
0:08:37 > 0:08:40even though males were present.
0:08:40 > 0:08:44These females were often small and overlooked by the males,
0:08:44 > 0:08:49so, rather than not breed, they cloned themselves.
0:08:49 > 0:08:53But this kind of breeding is potentially a genetic dead-end.
0:08:53 > 0:08:56If individuals all have the same genes,
0:08:56 > 0:08:59the species can't react to a changing world.
0:09:01 > 0:09:05For whiptail lizards, which live in a harsh but very stable desert,
0:09:05 > 0:09:09being genetically the same is actually an advantage.
0:09:10 > 0:09:14For them, parthenogenesis is better than sexual reproduction,
0:09:14 > 0:09:18as it prevents them from varying from their winning formula.
0:09:21 > 0:09:25Strangely, the females still go through the motions of mating.
0:09:28 > 0:09:32This stimulates their hormones, but these lizards are taking a gamble.
0:09:34 > 0:09:37If their environment changes for the worse,
0:09:37 > 0:09:40they'll be unable to adapt and so they risk extinction.
0:09:43 > 0:09:46Clearly, the best survival technique is to be able to
0:09:46 > 0:09:48reproduce in either way.
0:09:50 > 0:09:54Parthenogenesis has enabled isolated dwellers like the Komodo dragon
0:09:54 > 0:09:58to survive by forming breeding populations from just
0:09:58 > 0:09:59a single female.
0:10:00 > 0:10:04More recently, studies of wild Komodo dragons have revealed
0:10:04 > 0:10:07that two thirds of the population is male,
0:10:07 > 0:10:10suggesting that even when both sexes are present
0:10:10 > 0:10:13asexual breeding is still occurring.
0:10:13 > 0:10:18So Komodo dragons keep their breeding options flexible.
0:10:18 > 0:10:21It's likely that many animals are breeding by parthenogenesis
0:10:21 > 0:10:26or have the potential to do so, but we just don't know about them.
0:10:26 > 0:10:30Parthenogenesis has been occurring unnoticed for millions of years.
0:10:30 > 0:10:34Here is a natural curiosity that's only just revealing its secrets.
0:10:39 > 0:10:43Next, we meet a tiny animal that uses parthenogenesis to be
0:10:43 > 0:10:46one of the fastest breeders in nature.
0:10:48 > 0:10:55Surprisingly, this lives in our own back gardens.
0:10:55 > 0:10:59In summer, this is not an uncommon sight.
0:10:59 > 0:11:03Thousands of aphids massed together on a stem.
0:11:03 > 0:11:07At this time of the year, each of them can produce five to ten
0:11:07 > 0:11:12youngsters in a day, and each is a genetic copy of herself.
0:11:16 > 0:11:20So vast numbers can suddenly appear within a day or so.
0:11:22 > 0:11:25Birds and other insects arrive and prey on them,
0:11:25 > 0:11:27but the aphids usually manage to keep ahead.
0:11:29 > 0:11:34This astonishing ability attracted the attention of early scholars.
0:11:34 > 0:11:35In the mid-18th century,
0:11:35 > 0:11:38a new survey of insects was published in France.
0:11:38 > 0:11:42Its author, Rene Antoine Ferchault de Reaumur,
0:11:42 > 0:11:46expressed surprise that he'd never seen aphids mating.
0:11:46 > 0:11:48Neither had he seen a male.
0:11:48 > 0:11:52He made the revolutionary suggestion that they were reproducing
0:11:52 > 0:11:56without sex and invited his readers to help prove it.
0:11:59 > 0:12:02In the spring of 1740, Charles Bonnet,
0:12:02 > 0:12:06then a young law student from Switzerland, took up that challenge.
0:12:10 > 0:12:14Charles Bonnet took a newborn female aphid from its mother
0:12:14 > 0:12:18immediately after birth and put it in an isolation chamber.
0:12:18 > 0:12:23He placed the aphid on a leaf inside an upturned glass jar
0:12:23 > 0:12:28and, using a magnifying glass, watched it from early morning
0:12:28 > 0:12:31until night for 12 days.
0:12:31 > 0:12:36On the evening of June the 1st, 1740, at 7.30pm,
0:12:36 > 0:12:41the female aphid gave birth to a brand-new baby aphid.
0:12:41 > 0:12:48Then, over the next 21 days, she had 94 more female offspring.
0:12:48 > 0:12:51Bonnet had no clue how this could happen,
0:12:51 > 0:12:57but he knew for sure that the aphid had bred without any male contact.
0:13:00 > 0:13:04He sent his findings to Reaumur in Paris, who published this
0:13:04 > 0:13:07new and important discovery of sexless reproduction.
0:13:09 > 0:13:12But how this parthenogenesis worked
0:13:12 > 0:13:15and why aphids used virgin birth in their life cycles
0:13:15 > 0:13:18was still a mystery
0:13:18 > 0:13:21and entomologists puzzled over it for many years.
0:13:25 > 0:13:30In the 1830s, an entomologist called Francis Walker took a great
0:13:30 > 0:13:35interest in cataloguing various small insects, including aphids.
0:13:35 > 0:13:38He made more than 13,000 slides.
0:13:38 > 0:13:41Walker collected hundreds of aphids, many from Southgate
0:13:41 > 0:13:43and the surrounding areas of London.
0:13:43 > 0:13:45Here we can see some of them.
0:13:45 > 0:13:48He made successive collections of the same species
0:13:48 > 0:13:52of aphid from the same locality across all the seasons.
0:13:52 > 0:13:56As a result, he found several different forms of each aphid
0:13:56 > 0:13:58throughout the breeding cycle.
0:13:58 > 0:14:02They varied in size and some were wingless.
0:14:02 > 0:14:07That suggested that female aphids had a rather extraordinary life cycle.
0:14:10 > 0:14:14It was clear from Walker's study that nearly all individual
0:14:14 > 0:14:16aphids are female,
0:14:16 > 0:14:19but they change in form over the seasons.
0:14:19 > 0:14:23In early spring, when plants are growing, most are without wings.
0:14:23 > 0:14:27With plenty of food on offer, they have no need to fly.
0:14:28 > 0:14:32Later in the season, when overcrowding becomes an issue,
0:14:32 > 0:14:38females are born with wings so that they can travel to find new food.
0:14:38 > 0:14:41Aphids seem to be able to produce females that can exploit
0:14:41 > 0:14:43every situation.
0:14:45 > 0:14:50Although Walker was prolific, he wasn't always entirely accurate.
0:14:50 > 0:14:53He recorded many aspects of the aphids' life cycles,
0:14:53 > 0:14:57but he didn't piece them together to produce the complete picture.
0:14:57 > 0:15:01And then aphid research was taken up by another entomologist,
0:15:01 > 0:15:04called George Buckton.
0:15:04 > 0:15:09He chronicled every detail of the complex aphid life cycle.
0:15:09 > 0:15:13In 1883, George Buckton published a monograph
0:15:13 > 0:15:17of British aphids in four volumes.
0:15:17 > 0:15:20He wanted to share his passion for these tiny insects
0:15:20 > 0:15:24in books that he hoped would not be too dry academically.
0:15:24 > 0:15:28Buckton corresponded with many leading naturalists of his day
0:15:28 > 0:15:32to pull together every possible specimen and record of behaviour.
0:15:32 > 0:15:35He was an accomplished artist and produced beautiful,
0:15:35 > 0:15:38accurate drawings from live specimens
0:15:38 > 0:15:43and they interestingly show a distinct absence of male aphids.
0:15:43 > 0:15:46"The sexual forms of aphides," he wrote,
0:15:46 > 0:15:49"are in many species very rarely met."
0:15:51 > 0:15:55Buckton's drawings confirmed that aphid populations are commonly
0:15:55 > 0:15:59all-female and the males have been almost entirely
0:15:59 > 0:16:01eliminated from the species.
0:16:02 > 0:16:04For most of the breeding season,
0:16:04 > 0:16:06females only give birth to daughters.
0:16:06 > 0:16:11They don't waste time producing males which can't by themselves produce offspring.
0:16:13 > 0:16:16So do aphids need males at all?
0:16:17 > 0:16:21The life cycle of another insect would seem to suggest not.
0:16:22 > 0:16:28This wonderful creature is a Phyllium giganteum,
0:16:28 > 0:16:30a giant leaf insect.
0:16:30 > 0:16:35It's the largest species of its group and it lives wild in Malaysia.
0:16:36 > 0:16:39Nearly all individuals are female.
0:16:39 > 0:16:42In fact, the male of this species wasn't discovered until 1994.
0:16:42 > 0:16:44They're extremely rare.
0:16:44 > 0:16:50The species for the most part reproduces itself by parthenogenesis.
0:16:50 > 0:16:55They lay unfertilised eggs that hatch into more females
0:16:55 > 0:16:58and this method of reproduction has enabled it
0:16:58 > 0:17:00to extend its range dramatically.
0:17:02 > 0:17:06Much like a single female Komodo dragon arriving on an island,
0:17:06 > 0:17:10a lone female stick insect can start a breeding colony
0:17:10 > 0:17:14in a new area even if males never arrive.
0:17:14 > 0:17:18And that's what happened in southern England in 1903,
0:17:18 > 0:17:22when a different species of stick insect arrived on vegetation
0:17:22 > 0:17:24imported from New Zealand.
0:17:24 > 0:17:28Now, all female populations survive thousands of miles
0:17:28 > 0:17:31away from their native home.
0:17:31 > 0:17:35These populations have no males and don't appear to need them.
0:17:37 > 0:17:41The females produce fertile eggs that survive the cold winters
0:17:41 > 0:17:43and new females hatch out in the spring.
0:17:45 > 0:17:50But, without males, the population could become dangerously inbred.
0:17:52 > 0:17:56Aphid populations face the same problems, but most species
0:17:56 > 0:18:00have a twist in their life cycle that freshens up their gene pool.
0:18:01 > 0:18:05In the autumn, the aphid production line switches from producing
0:18:05 > 0:18:11just asexual females to producing sexual males and sexual females.
0:18:11 > 0:18:14At the end of the season, as the food supply wanes
0:18:14 > 0:18:16and the temperature drops,
0:18:16 > 0:18:20there's a phase of sexual reproduction that produces eggs.
0:18:20 > 0:18:25These eggs will overwinter to produce next spring's new aphid generation.
0:18:30 > 0:18:33Aphids don't produce their eggs until the autumn.
0:18:34 > 0:18:39However, most populations survive until then, because in many cases
0:18:39 > 0:18:43they form a relationship with another insect, ants.
0:18:44 > 0:18:48An aphid feeds by piercing the stems of plants
0:18:48 > 0:18:50and drinking the sugary sap.
0:18:51 > 0:18:55But sap contains far more sugar than the aphids can use,
0:18:55 > 0:18:58so they excrete the excess as honeydew.
0:18:58 > 0:19:01This is perfect food for the ants
0:19:01 > 0:19:05and they keenly farm the aphids to harvest the rich liquid.
0:19:06 > 0:19:09And in return the ants protect the aphids
0:19:09 > 0:19:11from insects that try to prey on them.
0:19:13 > 0:19:16So, with ants guarding them, the aphids have a good chance
0:19:16 > 0:19:20of surviving until the end of the year, when they produce their eggs.
0:19:28 > 0:19:32In the spring, new females will emerge from the eggs and start
0:19:32 > 0:19:37once more to produce new versions of themselves over and over again.
0:19:50 > 0:19:55And aphids have a final, almost unbelievable twist in their life cycles
0:19:55 > 0:19:58that greatly speeds up their breeding.
0:19:58 > 0:20:01They do something truly astounding.
0:20:05 > 0:20:07Even before they're born, they have embryos
0:20:07 > 0:20:10developing inside their bodies.
0:20:10 > 0:20:14Parthenogenesis, combined with this telescoping of generations,
0:20:14 > 0:20:18give aphids an extremely rapid turnover of generations.
0:20:18 > 0:20:20Like tiny Russian dolls,
0:20:20 > 0:20:23they just keep popping out smaller copies of themselves.
0:20:25 > 0:20:29A newly born summer aphid has inside her body
0:20:29 > 0:20:32her own developing daughters, who in turn contain her
0:20:32 > 0:20:35fully formed unborn granddaughters.
0:20:35 > 0:20:40So several generations of aphid overlap in time and space
0:20:40 > 0:20:43and in one season a single female can produce
0:20:43 > 0:20:46thousand upon thousand of cloned females.
0:20:48 > 0:20:53Aphids' lives are varied, often complicated and truly amazing.
0:20:53 > 0:20:57They can change plant host, change their form
0:20:57 > 0:21:00and alter their method of reproduction.
0:21:00 > 0:21:02In the spring, females hatch from eggs and
0:21:02 > 0:21:06produce several generations of wingless females.
0:21:06 > 0:21:10Their numbers grow, and they produce winged females that can fly to
0:21:10 > 0:21:14new food and rapidly produce even more females.
0:21:14 > 0:21:19In the autumn, the sexual forms of both males and female appear,
0:21:19 > 0:21:23which mate and lay eggs, which then can survive the winter.
0:21:28 > 0:21:31The ability to breed by parthenogenesis seems almost
0:21:31 > 0:21:36magical to us. But in nature virgin birth is not uncommon.
0:21:36 > 0:21:40Having the ability to produce daughter clones or more males
0:21:40 > 0:21:42can save a species or create a new one.
0:21:43 > 0:21:47Flexible ways of breeding have allowed creatures
0:21:47 > 0:21:48to colonise new areas
0:21:48 > 0:21:52and survive in small communities, like those on islands.
0:21:52 > 0:21:56The Komodo dragon has certainly survived for many centuries.
0:21:56 > 0:22:00And aphids have been around for more than 200 million years.
0:22:00 > 0:22:06So parthenogenesis is a breeding strategy that is a real life-saver.
0:22:24 > 0:22:27These eggs were collected more than 100 years ago
0:22:27 > 0:22:31during an expedition to the Antarctic.
0:22:31 > 0:22:34The conditions were so cold that the man that collected them
0:22:34 > 0:22:36never made it back to England alive.
0:22:36 > 0:22:40He perished alongside Captain Scott during the ill-fated journey
0:22:40 > 0:22:43to reach the South Pole.
0:22:43 > 0:22:46The eggs were laid by an emperor penguin, a bird whose life history
0:22:46 > 0:22:50would surprise and confound those early polar explorers.
0:22:52 > 0:22:56At the end of the 19th century, the Antarctic was an unfamiliar
0:22:56 > 0:22:58and mysterious place.
0:22:58 > 0:23:01Only a handful of explorers had ventured this far south
0:23:01 > 0:23:04and there was still a huge blank in the world map.
0:23:05 > 0:23:07But then, in 1901,
0:23:07 > 0:23:11a British expedition set off on a purpose-built ship, the Discovery,
0:23:11 > 0:23:14to explore this most southerly land.
0:23:14 > 0:23:18In charge was Commander Robert Falcon Scott.
0:23:20 > 0:23:24Scott took on board with him a young man named Edward Wilson,
0:23:24 > 0:23:27who would serve as the ship's doctor and naturalist.
0:23:28 > 0:23:31Wilson had only just qualified as a surgeon
0:23:31 > 0:23:34and had no formal training in scientific research.
0:23:34 > 0:23:38But the young man's passion for natural history and art
0:23:38 > 0:23:41would prove to be an invaluable asset to the expedition.
0:23:41 > 0:23:44Wilson's job was to draw and record
0:23:44 > 0:23:46any plants and animals that they encountered.
0:23:46 > 0:23:49But from the start there was one creature that fascinated him
0:23:49 > 0:23:52more than any other - the emperor penguin.
0:23:54 > 0:23:56This largest of all penguins
0:23:56 > 0:23:59had only been discovered 60 years earlier.
0:23:59 > 0:24:03But, as yet, nothing was known about its habits or where it breeds.
0:24:03 > 0:24:06The expedition was an opportunity to find out more.
0:24:08 > 0:24:11When the Discovery reached the southern continent,
0:24:11 > 0:24:15they put up a hut in which they would spend the long, dark winter.
0:24:15 > 0:24:19Then, as the sun started to appear again in spring,
0:24:19 > 0:24:21the sledge teams started to explore,
0:24:21 > 0:24:25and one returned with some tantalising news.
0:24:25 > 0:24:29They had discovered a breeding colony of emperor penguins
0:24:29 > 0:24:31in a place called Cape Crozier.
0:24:31 > 0:24:35It was the first colony any human being had ever seen
0:24:35 > 0:24:40and, much to their surprise, the birds were breeding on sea ice.
0:24:41 > 0:24:44It was a truly astonishing discovery.
0:24:44 > 0:24:46No other bird breeds on ice,
0:24:46 > 0:24:50and Wilson was keen to find out more about this remarkable creature.
0:24:52 > 0:24:57Very little was known about emperor penguins but there was another bird
0:24:57 > 0:25:01which could give Wilson some insights into their lives - the king penguin.
0:25:04 > 0:25:09Adult king penguins look very much the same as adult emperors.
0:25:09 > 0:25:11The main difference is in size.
0:25:11 > 0:25:15These kings are only about half as big as an emperor,
0:25:15 > 0:25:18and they live in the northern part of Antarctica.
0:25:20 > 0:25:23They breed in the middle of the Antarctic summer -
0:25:23 > 0:25:28November, December - and incubation takes about seven weeks.
0:25:28 > 0:25:31Wilson thought that emperors would do very much the same.
0:25:33 > 0:25:36But he was about to discover otherwise.
0:25:36 > 0:25:40The following spring, with the hope of collecting some penguin eggs,
0:25:40 > 0:25:43Wilson left for Cape Crozier as early as he dared.
0:25:46 > 0:25:49When he got there, however, much to his surprise,
0:25:49 > 0:25:52he found only well-grown chicks.
0:25:53 > 0:25:57After repeated calculations, he finally concluded that these
0:25:57 > 0:26:02penguins must lay their eggs in the middle of the Antarctic winter.
0:26:05 > 0:26:08That emperors should start breeding at the coldest
0:26:08 > 0:26:12and bleakest time of the year was an astonishing discovery.
0:26:12 > 0:26:15It seemed to defy all the rules of nature,
0:26:15 > 0:26:18and Wilson was indeed amazed.
0:26:20 > 0:26:24But it seems that this strange lifestyle does, in fact, make sense.
0:26:24 > 0:26:28Emperor penguins are big birds and the chicks take more than
0:26:28 > 0:26:31a year to grow large enough to be independent.
0:26:31 > 0:26:33By laying the eggs earlier in winter,
0:26:33 > 0:26:36emperors give their chicks a head start
0:26:36 > 0:26:38so that they first go to sea in the summer months
0:26:38 > 0:26:40when food is plentiful.
0:26:42 > 0:26:44But how do emperor penguins protect their eggs
0:26:44 > 0:26:46and chicks from the bitter cold?
0:26:50 > 0:26:53Neither kings nor emperors make a nest
0:26:53 > 0:26:55or lay their eggs on the ground.
0:26:55 > 0:26:58If they did, the eggs would freeze within minutes.
0:26:58 > 0:27:01Instead, they keep their eggs on the top of their feet
0:27:01 > 0:27:05and cover them with a feathered fold of skin from the abdomen,
0:27:05 > 0:27:06and inside that pouch
0:27:06 > 0:27:10the temperature is about 70 degrees warmer than it is outside.
0:27:14 > 0:27:17With temperatures of minus-60 degrees Celsius,
0:27:17 > 0:27:22and winds gusting at 200km/h, the birds huddle together for warmth.
0:27:28 > 0:27:31Even under these extremely difficult conditions,
0:27:31 > 0:27:33Wilson recorded everything he saw.
0:27:33 > 0:27:35WIND ROARS
0:27:35 > 0:27:38Able to work for only a few minutes at a time,
0:27:38 > 0:27:42he still managed to produce detailed notes and drawings that give us
0:27:42 > 0:27:45a first insight into the southern continent.
0:27:50 > 0:27:53This is the expedition's scientific report.
0:27:53 > 0:27:58And it contains most of Wilson's observations on the Antarctic.
0:27:58 > 0:28:01At a time when illustrations of animals were often
0:28:01 > 0:28:03drawn from dead specimens,
0:28:03 > 0:28:07Wilson drew his subjects live in the field wherever possible,
0:28:07 > 0:28:10to capture the true nature of the animal.
0:28:10 > 0:28:13Despite the extreme conditions under which he had to work,
0:28:13 > 0:28:16he made over 900 detailed drawings in the Antarctic.
0:28:23 > 0:28:28Wilson was an exceptional artist and a meticulous scientist
0:28:28 > 0:28:31and most of his observations have stood the test of time.
0:28:31 > 0:28:35But some things puzzled him more than others.
0:28:35 > 0:28:39He noted, for example, that the brooding of the chick was not
0:28:39 > 0:28:43just carried out by one bird or even by a single pair.
0:28:43 > 0:28:48It appeared as if numerous birds were taking turns in looking after
0:28:48 > 0:28:53the chick. Today, of course, we know that this is not quite correct.
0:28:53 > 0:28:57It's only the parents who care for both the egg and then the chick.
0:28:57 > 0:29:00RAPID STACCATO CAWING
0:29:00 > 0:29:02We now have a much better understanding of how
0:29:02 > 0:29:06emperor penguins breed, but Wilson's confusion as to
0:29:06 > 0:29:09who cares for the chicks is in fact quite understandable.
0:29:09 > 0:29:11He observed numerous occasions
0:29:11 > 0:29:15when a youngster was accidentally dropped by its parent.
0:29:15 > 0:29:17In his report, he writes,
0:29:17 > 0:29:22"what we actually saw again and again was the wild dash made by adults,
0:29:22 > 0:29:25"each weighing anything up to 90 pounds, to take possession
0:29:25 > 0:29:30"of any chick that happened to find itself deserted on the ice.
0:29:30 > 0:29:34"It can be compared to nothing better than a football scrimmage."
0:29:36 > 0:29:38The birds Wilson had observed
0:29:38 > 0:29:41were in fact females who had lost their own egg or chick
0:29:41 > 0:29:45and were trying to adopt or kidnap any unattended youngsters.
0:29:47 > 0:29:52What he couldn't know was that these adoptions are never successful.
0:29:52 > 0:29:56A new parent rarely feeds its foster chick
0:29:56 > 0:29:58and simply broods it for a few days.
0:29:58 > 0:30:01After that, the youngster is abandoned again
0:30:01 > 0:30:03or dies of starvation.
0:30:11 > 0:30:14It's likely that the female eventually recognises that
0:30:14 > 0:30:16the adopted chick is not her own.
0:30:27 > 0:30:32Although Wilson had been the first man to find an emperor penguin colony,
0:30:32 > 0:30:36he had not been able to obtain any freshly laid eggs.
0:30:36 > 0:30:40These were particularly sought-after by scientists of the day.
0:30:41 > 0:30:45It was thought at that time that the emperor penguin was
0:30:45 > 0:30:46one of the most primitive birds
0:30:46 > 0:30:50and possibly a missing evolutionary link with dinosaurs.
0:30:51 > 0:30:55If embryos could be obtained at an early enough stage then maybe
0:30:55 > 0:30:59one would see reptilian scales or some other dinosaur features.
0:31:01 > 0:31:05So the emperor penguin egg was regarded as a great scientific prize.
0:31:11 > 0:31:13A few years later, Scott and Wilson
0:31:13 > 0:31:16planned a second expedition to the Antarctic.
0:31:16 > 0:31:19The main objective was to reach the South Pole,
0:31:19 > 0:31:22but Wilson was determined to bring back
0:31:22 > 0:31:24newly laid emperor penguin eggs.
0:31:25 > 0:31:29This time, he made plans to travel to Cape Crozier even earlier,
0:31:29 > 0:31:32so as not to miss the birds on eggs.
0:31:32 > 0:31:34BIRD CAWS
0:31:34 > 0:31:38He picked two men to accompany him, Bowers and Cherry-Garrard,
0:31:38 > 0:31:42and they set off in the pitch black of the winter.
0:31:43 > 0:31:49It was a journey of over 70 miles and they had to cover it on foot.
0:31:49 > 0:31:51For six painful weeks,
0:31:51 > 0:31:54the three men pulled their heavy sledges in complete darkness
0:31:54 > 0:31:59and howling gales at temperatures of minus-40 degrees centigrade.
0:31:59 > 0:32:02Never before had anyone travelled in such bitter cold
0:32:02 > 0:32:04or in such difficult conditions.
0:32:04 > 0:32:07They sometimes barely covered a mile a day.
0:32:07 > 0:32:10It was what Cherry-Garrard would later call
0:32:10 > 0:32:12"the worst journey in the world".
0:32:14 > 0:32:17Their clothes were iced up and their breath
0:32:17 > 0:32:19and sweat froze on their bodies.
0:32:22 > 0:32:26Each night, it took them an hour to chip into their sleeping bags,
0:32:26 > 0:32:28which were frozen solid.
0:32:31 > 0:32:35When they finally reached the penguin colony, they collected five eggs,
0:32:35 > 0:32:40with great difficulty, and put them inside their mittens for safety.
0:32:40 > 0:32:44The men staggered back to base camp close to death
0:32:44 > 0:32:46and only three eggs survived the journey.
0:32:46 > 0:32:48These are two of them.
0:32:51 > 0:32:54It was an extraordinary feat of determination
0:32:54 > 0:32:56by Wilson and his companions.
0:32:56 > 0:33:01The precious eggs were supposed to reveal the evolutionary links
0:33:01 > 0:33:02between reptiles and birds,
0:33:02 > 0:33:05but getting them had nearly killed the collectors.
0:33:08 > 0:33:09A few months later,
0:33:09 > 0:33:14Scott led his party on the final push to reach the South Pole.
0:33:14 > 0:33:18His team consisted of just five men,
0:33:18 > 0:33:20and Wilson was amongst them.
0:33:21 > 0:33:27On their return journey, all five men perished, succumbing to the cold
0:33:27 > 0:33:31and starvation just a few kilometres from their nearest food depot.
0:33:33 > 0:33:36In the end, Wilson's eggs didn't contribute as much
0:33:36 > 0:33:39to our understanding of the development of the penguin chick
0:33:39 > 0:33:42as he had hoped, but his beautiful drawings
0:33:42 > 0:33:47and meticulous observations are quite a different matter.
0:33:47 > 0:33:51They helped to unravel the biology of a bird that is able
0:33:51 > 0:33:54to rear its young in the depths of the polar winter.
0:33:59 > 0:34:01The emperor penguin amazes us
0:34:01 > 0:34:05by raising its chicks in the most inhospitable place on earth.
0:34:05 > 0:34:08But a small frog has a way of coping with the cold
0:34:08 > 0:34:11that seems to be beyond belief.
0:34:13 > 0:34:15This is a North American wood frog,
0:34:15 > 0:34:18and it lives as far north as the Arctic Circle,
0:34:18 > 0:34:21but, like all cold-blooded creatures,
0:34:21 > 0:34:24it can't generate its own heat and its body temperature rises
0:34:24 > 0:34:26and falls with the surroundings.
0:34:26 > 0:34:31So when conditions drop below zero the frog risks freezing.
0:34:31 > 0:34:35How does a creature like this survive the harsh winters?
0:34:38 > 0:34:42The skin of amphibians is thin and moist and this makes them
0:34:42 > 0:34:45particularly vulnerable to the cold.
0:34:45 > 0:34:50Any contact with ice can instantly trigger freezing within
0:34:50 > 0:34:55their bodies and, for most animals, this means almost certain death.
0:34:56 > 0:34:58When water freezes, it expands,
0:34:58 > 0:35:02and the sharp ice crystals can puncture blood vessels
0:35:02 > 0:35:06and break cell walls, causing irreparable damage.
0:35:06 > 0:35:09The animal's internal organs may never function properly again.
0:35:12 > 0:35:15So, how do frogs avoid freezing?
0:35:16 > 0:35:20Many sit out the winter by hibernating at the bottom of a pond.
0:35:20 > 0:35:23The surface may freeze but underneath the ice
0:35:23 > 0:35:26the temperature remains just above freezing.
0:35:27 > 0:35:31And most land-living amphibians seek out a sheltered spot
0:35:31 > 0:35:34on the ground to avoid the deadly frost.
0:35:38 > 0:35:43But, in the 18th century, Arctic travellers came back with tales
0:35:43 > 0:35:46so extraordinary they were scarcely believable.
0:35:48 > 0:35:52A British explorer called Samuel Hearne reported seeing
0:35:52 > 0:35:55frozen frogs among the piles of leaves in Arctic Canada.
0:35:58 > 0:36:01He went on to make an extraordinary claim.
0:36:01 > 0:36:05"Frogs of various colours are numerous in these parts.
0:36:05 > 0:36:09"I have frequently seen them dug up with moss,
0:36:09 > 0:36:11"frozen as hard as ice,
0:36:11 > 0:36:15"in which state the legs are as easily broken off as a pipe stem,
0:36:15 > 0:36:19"without giving the least sensation to the animals.
0:36:21 > 0:36:25"But, by wrapping them up in warm skins and exposing them
0:36:25 > 0:36:28"to a slow fire, they soon recover life
0:36:28 > 0:36:32"and the mutilated animal gains its usual activity."
0:36:35 > 0:36:40Frozen frogs that, if gently warmed by a fire, would come back to life.
0:36:40 > 0:36:42What truth could there be in this account?
0:36:42 > 0:36:44Well...
0:36:45 > 0:36:47..this is a marsh frog
0:36:47 > 0:36:50and it's found in ponds and marshes throughout
0:36:50 > 0:36:52central and northern Europe.
0:36:52 > 0:36:56It's lying completely immobile on my hand because it's frozen solid.
0:36:58 > 0:37:01From the outside, it feels much like a rock.
0:37:01 > 0:37:05And you might be forgiven for thinking it was dead.
0:37:05 > 0:37:09Well, watch what happens when I put it into a bowl of warm water.
0:37:17 > 0:37:21Although it appears dead and has in fact stopped breathing,
0:37:21 > 0:37:23the frog's heart is still beating.
0:37:23 > 0:37:25Only the outer layer has frozen.
0:37:25 > 0:37:27The vital organs inside are still undamaged.
0:37:31 > 0:37:35Lab experiments have shown that, in this state, the marsh frog
0:37:35 > 0:37:40can survive temperatures of two degrees below freezing.
0:37:43 > 0:37:45Yes! It's lifted itself up, it's moving.
0:37:45 > 0:37:47Look at this.
0:37:48 > 0:37:51There, it's moving its right leg.
0:37:51 > 0:37:56Within a few minutes the frog has awakened to life once again.
0:37:58 > 0:38:02This is surely one of the most extraordinary miracles of nature.
0:38:04 > 0:38:09Nonetheless, the marsh frog can only survive a few hours of freezing.
0:38:09 > 0:38:12Anything more would mean certain death.
0:38:14 > 0:38:17Where it lives, it rarely faces extreme winters
0:38:17 > 0:38:21and is protected from the worst by the insulating water.
0:38:23 > 0:38:26So what about Samuel Hearne's story?
0:38:26 > 0:38:30Could some frogs survive longer periods of freezing?
0:38:30 > 0:38:33Another account from North America would seem to suggest so.
0:38:35 > 0:38:39In the 19th century, a naturalist called John Burroughs
0:38:39 > 0:38:42found a wood frog underneath the leaf litter
0:38:42 > 0:38:44at the beginning of the winter.
0:38:44 > 0:38:46Burroughs was surprised,
0:38:46 > 0:38:49but reasoned that the frog must know that a mild winter was on the way
0:38:49 > 0:38:53and had therefore not bothered to bury itself deeper.
0:38:55 > 0:38:57In fact, a very severe winter followed.
0:39:00 > 0:39:03Wondering about his frog, Burroughs went back to the same spot
0:39:03 > 0:39:07in spring and found the animal seemingly unharmed.
0:39:09 > 0:39:12The wood frog must have spent the entire winter above ground
0:39:12 > 0:39:15and survived temperatures that should have killed it.
0:39:16 > 0:39:19How did the tiny frog do it?
0:39:21 > 0:39:26The wood frog is not strong and large enough to dig itself into the ground,
0:39:26 > 0:39:30so it has to sit out the winter beneath the leaf litter.
0:39:30 > 0:39:33But this doesn't provide sufficient protection against the cold.
0:39:33 > 0:39:36So, how does this small frog survive?
0:39:37 > 0:39:39Today, we know the truth,
0:39:39 > 0:39:43and if Burroughs had done so he would have been astounded.
0:39:45 > 0:39:49It's only recently that we've discovered just how the wood frog
0:39:49 > 0:39:53avoids the usually fatal consequences of freezing.
0:39:54 > 0:39:59As winter sets in, the frog prepares for an extraordinary change.
0:40:07 > 0:40:11First, it draws water out of its cells into spaces where it
0:40:11 > 0:40:13will do less damage if it freezes.
0:40:14 > 0:40:18At the same time, its liver produces large amounts of sugar
0:40:18 > 0:40:20that act as antifreeze.
0:40:20 > 0:40:24This is pumped through the body to slow down the freezing.
0:40:30 > 0:40:35Now the entire frog slowly freezes from the outside inwards.
0:40:47 > 0:40:50And finally, the heart stops.
0:40:50 > 0:40:52The frog isn't dead,
0:40:52 > 0:40:55but it's probably about as close as you can get.
0:40:56 > 0:40:5970% of its body is frozen.
0:40:59 > 0:41:02And it can remain like this for several weeks on end.
0:41:11 > 0:41:13Then, as the air warms up again,
0:41:13 > 0:41:16a miraculous transformation takes place.
0:41:18 > 0:41:23The ice melts and the frog's body thaws and suddenly
0:41:23 > 0:41:25the heart sprouts back to life.
0:41:30 > 0:41:34Unlike the marsh frog, the deeply frozen wood frog needs
0:41:34 > 0:41:37several hours before it can resume normal activity.
0:41:42 > 0:41:46The wood frog's ability to survive in a frozen state
0:41:46 > 0:41:48has fascinated scientists.
0:41:48 > 0:41:52Could this one day help enhance our own medical understanding?
0:41:54 > 0:41:58We still don't understand completely how the wood frogs survive
0:41:58 > 0:42:01something that would kill most animals.
0:42:01 > 0:42:04What we do know is that, when freezing occurs slowly
0:42:04 > 0:42:09and in the right places, it appears to do less damage.
0:42:09 > 0:42:12This little frog seems to have mastered the problem
0:42:12 > 0:42:15by controlling how and where ice forms in its body.
0:42:17 > 0:42:21The emperor penguin's ability to breed during the Antarctic winter
0:42:21 > 0:42:24is a remarkable feat of endurance,
0:42:24 > 0:42:28but for a small frog to freeze solid and come back to life
0:42:28 > 0:42:33must surely be one of the most astonishing curiosities of nature.