Darwin Class Clips


Darwin

A selection of clips taken from BBC programmes about Darwin and evolutionary biology.


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Transcript


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Darwin was loath to admit his evolutionary view.

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He began breeding pigeons and joined fanciers clubs.

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He wanted to know how they created their extraordinary strangely feathered birds.

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Darwin bought and kept every known breed in England and many of the types he kept survive today.

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These were the sorts of fancy breeds that existed in Darwin's day.

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Here we have the English pouter, the biggest and tallest of the pouters. This big yellow one.

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He knew if these birds were wild they would have been classed as distinct species.

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Miniature, where it gets its name from. The pygmy.

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And the Jacobin, which is the exotic feathering...

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But all the fancy breeds were of one species.

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He crossed his tumblers and fantails to prove it.

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Different from the common garden fantails you see.

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And the runt...

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All had been bred over generations from one ancestral type.

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The breeders' craft was a mysterious business. More art than science.

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But Darwin knew that within it lay their secrets of selection.

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We're just waiting for... the markings are all right.

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We can already see at this stage how much better it is in length of leg.

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These minute differences are what we're looking for all the time.

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-So that's the champion?

-Hopefully, if everything carries on developing, yes.

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-At what age can you first spot the difference?

-As early as day one.

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We have two babies here one day old and you can see the difference.

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-From the same nest?

-Yeah.

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From day one you can see the difference in the beak.

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He found what he'd expected. The individual birds were composed

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of a myriad tiny variations, invisible to all but experienced fanciers.

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The selecting hand was artificial, but all nature must be like this.

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Nature was a supreme selector picking out those with an edge, discarding and killing the rest.

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Pigeon breeding gave Darwin the most graphic example of how new species originate.

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In Victorian times, the collecting of butterflies that showed any slight variation

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from the normal pattern was fashionable.

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It was popularly thought that such varieties were unimportant, they just died off.

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Darwin didn't think that at all.

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"These individual differences are of the highest importance for they're often inherited."

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And as the variation is inherited, Darwin thought wild animals,

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just like our domestic animals, had the potential to change, too.

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"According to my view, varieties are species in the process of formation."

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This was a startling idea.

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Although it was accepted that new species could appear and old ones disappear,

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these changes were commonly believed to be due to divine acts of creation or destruction.

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But Darwin believed he'd discovered a natural process by which

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a variety could evolve into a brand new species.

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He was supplanting God's work by a natural process.

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It was a dangerous idea.

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How exactly did Darwin think new species came into being?

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Before answering that, he had to propose a view of nature that went against a romanticised,

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Victorian ideal of how the natural world worked.

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"We behold the face of nature bright with gladness,

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"we forget that the birds idly singing around us mostly

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"live on insects or seeds and are thus constantly destroying life.

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"Or we forget how their eggs or nestlings are destroyed by birds or beasts of prey."

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He was suggesting that the tranquil beauty around us is largely an illusion.

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In the natural world, life is often a struggle just to survive, let alone breed.

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Of all the arguments raised against his ideas,

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nothing troubled Darwin more than that about the origin of the eye.

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"The belief that an organ so perfect as the eye could have been

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"formed by natural selection is enough to stagger anyone."

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It certainly staggered his critics.

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"It's only here or there that a second rate naturalist would

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"sympathise at all with such dreamy views."

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They simply couldn't believe that such an intricate mechanism could arise by any natural process.

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Darwin thought it could.

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"If numerous gradations from a simple eye to one complex and perfect can be shown to exist,

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"each grade useful to its possessor, then the difficulty of believing a complex eye could be formed

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"by natural selection shouldn't be considered as subversive of the theory."

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The earthworm has a layer of light, sensitive cells in its skin that can detect light from dark.

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It's the simplest eye possible and all that an earthworm needs.

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If a random variation should cause these cells to be set back in a pit,

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then the animal can detect the direction of light just as the limpet can.

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The snail has an additional refinement.

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A blob of mucus in the pit acts as a simple lens.

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The snail can seek a roughly focused image.

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If the lens then hardens, the vision becomes better.

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The conch has this kind of eye.

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Darwin argued that there were no limits to what such a process might ultimately produce.

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"A structure even as perfect as an eagle's eye might thus be formed."

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The eagle's vision is said to be

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eight times more acute than our own.

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It can spot prey at distances over which we would spot nothing.

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Darwin believed his theory could explain the entire variety of life on Earth.

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Through the adding up of tiny variations, fish would have evolved into amphibians.

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At every stage, the new form would be better adapted to an amphibious life than the last.

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In the struggle for life, the new kind would out compete the old and drive it to extinction.

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In the end result is a world today with fish and amphibians, but nothing in between.

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But don't the missing links turn up as fossils?

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"It's been asserted over and over again that geology yields no linking forms."

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Darwin's critics maintained he couldn't point to a single

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fossil intermediate between two different groups of living animals.

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He replied that few animals have ever become preserved as fossils.

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The fossil record was like an incomplete book.

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"Only here and there a short chapter has been preserved

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"and of each page only here and there a few lines."

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Yet he was sure that in time

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intermediate forms would come to light.

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One year after The Origin Of Species was published,

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an extraordinary fossil was found in Germany.

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It had a mouthful of teeth like a reptile and feathers like a bird.

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This is Archaeopteryx.

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It's an animal intermediate between two living animal groups.

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Darwin felt this natural process would hinge on which animals

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survived the struggle for life to breed and which do not.

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"Individuals having any advantage, however slight, over others would

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have the best chance of surviving and procreating their kind."

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This gazelle may be just that bit fast or stronger than the rest.

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"The preservation of favourable individual differences and the destruction

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"of those which are injurious I've called natural selection or survival of the fittest."

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So here is the crux of Darwin's great theory.

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A natural law, survival of the fittest,

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determines which animals will live long enough to have offspring.

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If this natural selection were to go on constantly

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perhaps those tiny individual differences could add up, then wild species might change.

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"Natural selection is daily and hourly scrutinising

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"the slightest variations, rejecting those that are bad,

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"preserving and adding up all those that are good."

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This scrutiny may be constant, but the resulting change would be slow.

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The variation between individuals of a species

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are usually very slight

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yet the differences between one species and another

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may be very great, a lot of adding up of tiny differences

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would be needed to produce a new and different species.

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If he's looking a little smug, it may be with good reason.

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Joshua is the very first of a new kind of cat.

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You can stroke him all day long without risk of red eyes, sneezing or skin rash.

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In the UK alone, 8 million cats are kept as household pets,

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but many end up being given away because their presence

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can bring out an allergic reaction in their owners.

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It's the cat saliva which is responsible, or rather a protein within it called Fel d 1.

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The American scientists isolated two cats which were low in Fel d 1

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and bred them over several generations until the protein had virtually been eliminated.

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In doing so, they created cats which don't bring out allergies.

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The RSPCA has criticised the development saying selective

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breeding undermines the value of animal life.

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The company responsible is emphasising the benefits to people.

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I know how pet owners really are and in times of need and passion,

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whether it's depression or something traumatic, nothing

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substitutes the love of a pet.

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You can't put a price and it.

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But in fact they have. A moggy like this will set you back more than £2,000.

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There's already a long waiting list.

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Some living animals are so bizarre they seemed hard to explain by Darwin's theory.

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How can a tail like this evolve when it seems sure to slow its owners escape from predators?

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And wouldn't the same apply to the great cumbersome jaws of this stag beetle?

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Surely these are exactly the sort of things

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that would be weeded out in the struggle for life.

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Darwin said these kind of exaggerated features evolved by what he called sexual selection.

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"This form of selection depends on a struggle between the individuals

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"of one sex, generally the males, for the possession of the other sex.

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"The result isn't death, but few or no offspring."

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The struggle isn't violent.

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The males gather to show off their tails and the females choose which males to mate with.

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If, even with such long tail feathers, a male peacock is still strong enough

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to escape from predators then such feathers are a sure sign of a healthy male.

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From an ancestral form of peacock with short tail feathers,

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the females of each generation would have chosen the longest feathered males to mate with.

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In time, the feature would have become exaggerated

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to produce today's peacocks with their spectacular tails.

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Such a process would also explain the famous displays of male birds of paradise.

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But sexual selection isn't just about show.

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"In many cases victory depends on having a special weapons."

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Male stag beetles actually fight other males.

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The winner gets the female.

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So the biggest jawed males of each generation beat their rivals and have big-jawed offspring.

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The adding up of tiny advantages leads to animals superbly adapted to their own way of living.

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Given the number of offspring every living thing is able to produce,

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it's actually a good thing life is a struggle.

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"There's no exception to the rule that every organic being naturally increases at so high a rate

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"that if not destroyed the earth would soon be covered by the progeny of a single pair."

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The result of just a few successive generations, in which all offspring

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from one original pair survive to breed, would be dramatic.

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Temporary outbreaks of mice in Australia when food is abundant

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and predators scarce are living proof of that.

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The hard times will return, then the struggle will begin again

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and many animals will die before they can breed.

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The first challenge to overcome is the intense and unrelenting heat.

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Red kangaroos deal with the worst of this by finding shade

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and digging to find cooler earth below the sun-baked ground.

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Another trick is to conserve as much water as possible.

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When resting, they don't sweat.

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Instead, they lick their forearms so that saliva cools blood vessels close to the surface.

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Emus also cool down using surface blood vessels,

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increasing the flow to their long necks, long legs and big feet.

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Their flightless wings have unique double quilled feathers that

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protect them from the burning heat so they can brave the midday sun without shade.

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The second problem desert dwellers face here,

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unlike their rainforest past, is finding water.

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Emus are often forced to walk huge distances to find water

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as they need to drink every day.

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Red kangaroos can memorise pools they visited before,

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but they're better adapted to cope without a drink.

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They store more water in their bodies, in the muscles and their guts, than other mammals.

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And can withstand water loss that would easily kill a human.

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If there are plenty of green plants, the kangaroos' sole diet, they don't need to drink at all.

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But they can't always count on that.

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Red kangaroos have evolved broad padded feet designed not to damage new shoots,

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but still their biggest problem is finding enough to eat.

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They're experts in saving energy.

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They can survive on the bare minimum of food.

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Kangaroos, and all of Australia's marsupials,

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have a much lower metabolism than mammals in other parts of the world.

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This means they use less energy, whether resting or on the move,

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so they can live on less food than other mammals of their size.

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A vital adaptation to desert life.

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Today, they number 10 million.

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But the kangaroos' ability to scrimp and save is nothing

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compared to their neighbours.

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In nearby creeks and billabongs, freshwater crocodiles have barely

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changed since their rainforest days 50 million years ago.

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They feed on fish, insects, crustaceans and the occasional unwary bird.

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When times are good, they lay down fat in special stores along their tails.

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This, combined with an exceptionally low metabolism,

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far lower than the kangaroos', allows them to survive up to two years without a single meal.

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Among the towering cliffs, peaks and ridges of Ethiopia's Semien highlands,

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the so-called roof of Africa,

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Walia Ibex - Ethiopia's national symbol.

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They can exist in these precarious places and they do.

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But that's mainly because they have to.

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The cliffs are something like a kilometre high

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and they're almost sheer.

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That's where the Walia Ibex live

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and to see them in this enormous distance

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on these sheer cliffs is truly spectacular.

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I tried to film them years and years ago for another series and they proved too difficult.

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The Walia Ibex were much wider spread at one time throughout the mountains of Ethiopia

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and are related to the Ibexes of Europe.

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But as humans have spread through Ethiopia

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and the environment has dried out, the Walia Ibex has

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been pushed into the most marginal habitats it can find and some

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of the last remaining places humans can't get to

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are these incredible sheer cliffs

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and it's only just been with a lot of warfare

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in the last century in Ethiopia, the Italian invasion

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and then a big civil war, that the Walia Ibex became favourite food for soldiers.

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The Semien mountains saw a huge amount of fighting

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through the 1970s and 1980s and in that period

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the easiest food for a very cold soldier would have been to take a shot at one of the Walia Ibex.

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We saw the numbers decimated.

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The one thing the Walia has going for it is the habitat it lives in.

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These sheer, sheer cliffs.

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There are very few animals in the world that could live on precipices like the Walia.

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It has a little niche it can cling to,

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but it's such a fragile situation.

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600 animals for a large mammal is nothing.

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When you've no other habitats to spread in to, no other populations to interbreed with,

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no Walia Ibex in captivity,

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you'd better be sure you can protect that one last piece of cliff they have.

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Aborigines survive by their exceptional knowledge of the land

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and its secret sources of food and water.

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This priceless knowledge is inherited through storytelling.

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Stories that relate to the magical dream time are passed from generation to generation.

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They retrace the journeys of the ancestral beings as they wandered

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over the empty continent creating the world.

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In doing so, every feature of the land and its invaluable resources

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are recounted to enable future generations to survive here, too.

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But even if you know what food you're looking for,

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how do you find enough?

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The best strategy is to keep on the move and eat

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from a wide variety of sources - to avoid any becoming depleted.

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And an intimate knowledge of wildlife is essential.

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Eggs from the freshwater crocodile are usually laid in the holes within ten metres of water.

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After laying, the female leaves them unguarded, only returning when the baby has hatched.

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So with the right knowledge, it's safe to raid her nest.

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By breaking open the roots of certain bushes and trees, witchety grubs can be found.

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These plump white insects are larvae of the ghost moth -

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an important source of protein, said to taste like almonds.

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They're usually cooked in ashes but can easily be eaten raw.

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The trail of a certain ant leads to a sweeter delicacy.

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Digging a hole as deep as herself,

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this Aboriginal woman can access the underground nest of the honey ant.

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Some of the worker ants are fed on nectar by other members of the colony

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until their abdomens are so swollen they can barely move.

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They become living storage vessels, tucked away deep in the nest where

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other ants can feed on them in times of drought.

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By easing them gently out with a stick, others can feed on this sugar sauce too.

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As women are traditionally gatherers, it's their task

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to collect plant food which makes up half of their diet.

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They have a special technique to help it grow.

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Firestick farming, as it's called, works in two ways.

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First, it burns off the tall, dominant grasses

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allowing a range of edible plants to grow in their place.

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So there is not only in more food to eat, but it's easier to find.

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The Aborigines rely on their detailed knowledge of the land to see them through.

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Just like their predecessors 40,000 years ago, they know

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how to find water underground when their usual water holes dry up.

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The desert sand protects this water from evaporating and the grass acts as a filter.

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So, digging in the right place can produce a life-saving drink.

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And in desperate times, every drop of water helps.

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Burrowing frogs can shut down body systems and live dormant underground for seven years.

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Even in the hottest months, they don't dry out because layers of dead skin act like cocoon.

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They stay alive this long by using water stored in their bladders after previous rains.

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And Aborigines know how to access this in an emergency.

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As temperatures in Australia rose, most of the rainforest trees died out,

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but one, the eucalyptus, adapted well to the new dry conditions

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and seized its chance to spread.

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There are now over 700 species of eucalypts in Australia's dry, dusty earth.

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To save precious nutrients, they grow fibrous leaves full of poisons

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so that like the Spinifex grass, nothing can eat them.

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But one animal has broken through its defences...

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..the Koala.

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In fact, it eats nothing else.

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Koalas have very long digestive tracts,

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full of specialised bacteria,

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which must be passed on to their young through their faeces.

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They carefully select leaves with the fewest tannins and the highest oil content.

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But despite munching through a kilo a day,

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they still gain very little energy.

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The price they pay for this poor diet is to sleep

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an epic 19 hours a day.

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Since they spend five hours feeding,

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there is little time for anything else.

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Koalas have another way to save energy.

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They are bears of very little brain.

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The brain consumes more energy than any other organ,

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so if all you do is eat and sleep, a small brain probably makes sense.

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But there is an upside to this poor diet.

0:28:390:28:42

The chemicals in the pungent leaves means koala flesh is not popular to eat.

0:28:420:28:49

So despite their sluggish way of life,

0:28:490:28:52

koalas can still sleep away their days in relative peace.

0:28:520:28:57

In the High Arctic, the Planet Earth team saw

0:29:040:29:10

polar bears behaving in ways they'd

0:29:100:29:13

never seen before.

0:29:130:29:15

Get your eye behind the viewfinder, the adrenalin starts rushing.

0:29:550:29:59

You know you're recording something so unusual, something so amazing

0:29:590:30:03

that very few people have ever seen before.

0:30:030:30:06

But you have to focus.

0:30:060:30:09

It is very rare to see a bear go after walruses

0:30:090:30:12

and to actually physically

0:30:120:30:14

jump on them and attack them, stalk them, hunt them.

0:30:140:30:18

Ten years ago, at the same time of year and at the same latitude,

0:31:030:31:08

this, as filmed in a BBC Wildlife Special

0:31:080:31:12

was what polar bears were doing.

0:31:120:31:14

The sea was frozen and the bears were hunting

0:31:170:31:21

less intimidating prey.

0:31:210:31:23

Not enormous walruses in defensive herds on dry land,

0:31:270:31:32

but small ring seals out on the ice.

0:31:320:31:36

We are rapidly losing ice cover.

0:31:520:31:55

It's happening as we speak.

0:31:550:31:57

The ice cap is getting thinner and in its extent, is greatly reduced,

0:31:570:32:01

and that icecap is the home of the polar bear.

0:32:010:32:04

So, they're finding the places they're accustomed to breeding and hunting are disappearing.

0:32:050:32:12

There's no doubt, people can see the ice breaking up,

0:32:120:32:16

they can see the glaciers retreating.

0:32:160:32:19

That's a real problem for the polar bears.

0:32:190:32:22

Polar bears are in deep trouble and there's lots of research to show that.

0:32:240:32:29

There are two possibilities, one, they go extinct

0:32:290:32:32

as they try desperately to find ice.

0:32:320:32:35

Or, they may go further south and come on to firm land.

0:32:350:32:39

Of course, their habits will have to change greatly.

0:32:390:32:43

Maybe they will evolve to do that?

0:32:430:32:46

It's got a very short time in which to do this,

0:32:460:32:48

if the projection is that

0:32:480:32:50

the polar icecap will have disappeared within 50 years,

0:32:500:32:53

we are expecting an awful lot

0:32:530:32:55

in the way of habitat change, annual movement change,

0:32:550:32:59

feeding habits, hunting techniques of a bear.

0:32:590:33:03

I think it's going to be very interesting to see if it can do that.

0:33:030:33:06

The estimates we have is that we might lose 35% of them over the next 50 years.

0:33:080:33:15

As that population starts to go down and their prey species move out,

0:33:150:33:19

it's going to be a tough adaptation for the polar bear.

0:33:190:33:24

No part of the Earth is more hostile to life than the frozen wastes around the Poles.

0:33:350:33:42

850 miles north of the Arctic Circle, this is Ellesmere Island.

0:33:420:33:48

No animal can live permanently on these ice fields.

0:33:480:33:51

And even plants face almost insuperable problems,

0:33:510:33:55

for the four things they must have are in cripplingly short supply.

0:33:550:34:00

Water, it's true there is a lot of frozen water all around me,

0:34:000:34:04

but water has to be liquid for plants to make any use of it.

0:34:040:34:09

Nutrients, there's virtually none in this frost-shattered rock.

0:34:090:34:14

Warmth and light,

0:34:140:34:15

for six months of the year it's dark,

0:34:150:34:18

and in the brief summer as now,

0:34:180:34:20

the sun doesn't rise high in the sky and devastating winds

0:34:200:34:24

can carry away what little warmth it brings.

0:34:240:34:27

And yet, there are plants here.

0:34:270:34:30

Some live...

0:34:300:34:32

actually inside the rock.

0:34:320:34:35

This thin green line is made by algae, microscopic plants.

0:34:400:34:46

They're so small they can live actually between the grains of the sandstone.

0:34:460:34:52

And there at least, they're out of this desiccating wind.

0:34:520:34:57

On the surface of the rocks there are lichens.

0:34:570:35:00

They grow incredibly slowly and may take 50 years to cover a square centimetre.

0:35:000:35:05

But they can survive even if there are only two days in the year when it's warm enough for them to grow.

0:35:050:35:12

In spite of these bleak conditions, there are in fact flowers to be found here.

0:35:120:35:17

But you have to look hard to find them.

0:35:170:35:20

Here's one.

0:35:220:35:24

It's a kind of mustard,

0:35:240:35:26

but it's much smaller than its more southerly relatives.

0:35:260:35:30

But by being so small, it manages to keep out of the crippling wind.

0:35:300:35:35

In mid-summer, for a few weeks, enough water melts from the glaciers

0:35:350:35:39

for streams to flow, then, miniature gardens burst into bloom.

0:35:390:35:46

The searing wind compels them all to keep close to the ground.

0:35:560:36:01

None keeps closer than this.

0:36:090:36:12

It is in fact a tree, a willow.

0:36:120:36:14

These are its catkins.

0:36:140:36:17

But the trunk grows horizontally instead of vertically

0:36:170:36:21

and it can stretch almost as far along the ground

0:36:210:36:23

as its more southerly relatives stand up above it.

0:36:230:36:27

Even so, it still produces enough leaves to sustain a few grazers -

0:36:270:36:34

musk ox.

0:36:340:36:36

The Arctic poppy, like all plants needs warmth to grow,

0:36:400:36:44

but it's unusually efficient at collecting it.

0:36:440:36:48

As the mid-summer sun skims round the horizon, all 360 degrees

0:36:480:36:53

in 24 hours without setting,

0:36:530:36:55

the poppy turns its flowers to track it.

0:36:550:36:58

The slanting sun may not be strong,

0:37:060:37:09

but it is at least continuous during the few weeks of high summer.

0:37:090:37:13

The heat of the poppy gathers by staring continuously at the sun enables it to develop the seeds

0:37:180:37:23

in the centre of each flower before summer comes to an end

0:37:230:37:27

and the sun disappears below the horizon for months.

0:37:270:37:31

On the high peaks of the Alps,

0:37:460:37:48

spring brings a greater benefit than it does in the Arctic.

0:37:480:37:52

The sun rises higher in the sky and is warm enough to melt all but the highest snowfields.

0:37:520:37:58

As it melts, it reveals the snow bell, already in flower.

0:37:590:38:04

The plant formed its flower buds last autumn,

0:38:070:38:10

before the increasing cold shut down all its activities for the winter.

0:38:100:38:15

The buds remained dormant until the spring sunshine filtering down through the snow triggered

0:38:150:38:21

them into action and they opened even before

0:38:210:38:25

the snowy blanket above them had melted.

0:38:250:38:28

In summer, the high meadows,

0:38:350:38:37

newly freed from snow, fill with flowers.

0:38:370:38:41

Because for so much of the time it's so cold,

0:38:420:38:44

the vegetation here decays only very slowly.

0:38:440:38:48

So a peaty soil forms, but it's only a thin layer over solid rock

0:38:480:38:53

and boulders and trees find it difficult to get root.

0:38:530:38:57

Not only that, but avalanches regularly sweep these slopes,

0:38:570:39:02

carrying away saplings before they can get firmly established.

0:39:020:39:07

So, shallow-rooted plants have these parts of the mountains

0:39:070:39:11

largely to themselves, and in summer they bring a rich display of colour.

0:39:110:39:16

But, for every 1000 ft you climb,

0:39:160:39:19

the average temperature drops by about three degrees.

0:39:190:39:23

Plants living in the high mountains

0:39:230:39:26

have to be able to survive extreme cold.

0:39:260:39:29

It's very important to keep out of the worst of the chilling winds,

0:39:290:39:33

and many plants here form small, rounded humps

0:39:330:39:36

and that brings them a number of advantages.

0:39:360:39:40

Growing into the shape of a cushion

0:39:440:39:46

is an excellent way of conserving heat.

0:39:460:39:49

And no plants do it more spectacularly than these growing

0:39:490:39:52

high in the mountains of Tasmania.

0:39:520:39:55

These are the largest cushion plants in the world.

0:39:550:39:58

They grow to over 12 ft across.

0:39:580:40:00

Any one square yard contains over 100,000 shoots.

0:40:000:40:04

So I guess this one cushion around me contains several million.

0:40:040:40:09

This rounded shape does more than just reduce wind chill.

0:40:100:40:15

The air temperature around me here at about 3,500 ft high

0:40:150:40:20

is only a degree or so above freezing.

0:40:200:40:22

But if I take this temperature probe, put it on the surface of this cushion,

0:40:220:40:26

I can see that there, it is several degrees warmer.

0:40:260:40:30

The cushion in fact acts as a solar panel,

0:40:300:40:32

absorbing heat directly from the sun.

0:40:320:40:35

So that even on very cold days, providing it's not covered with snow

0:40:350:40:39

and is exposed to direct sunshine, it can photosynthesise and grow.

0:40:390:40:44

The plants that form these spectacular cushions

0:40:440:40:47

come from several different families.

0:40:470:40:50

Sedges and rushes, daisies and dandelions.

0:40:500:40:53

One cushion may contain several species tightly packed together

0:40:530:40:58

and growing to exactly the same height.

0:40:580:41:00

For one kind to grow higher than those around it would be suicidal.

0:41:000:41:05

In the New Zealand Alps, one of these cushion-forming species

0:41:060:41:10

also protects itself by developing a blanket of hair.

0:41:100:41:15

This tall pillar growing on Mount Kenya

0:41:150:41:18

also covers itself in a blanket.

0:41:180:41:21

It's a giant lobelia.

0:41:210:41:23

Its long leaves are fringed with dense hairs.

0:41:240:41:27

Its flowers are hidden away from the frost beneath this downy covering.

0:41:270:41:33

There's no point in having bright petals if they can't be seen, and these are just simple tubes.

0:41:330:41:38

But the lobelia's pollinator, a sunbird, knows where they are

0:41:380:41:43

and how to reach them.

0:41:430:41:44

During the day, it can get quite warm.

0:41:450:41:48

For Mount Kenya stands almost exactly on the equator.

0:41:480:41:51

But up here, at 14,000 ft, once the sun goes down it gets bitterly cold,

0:41:510:41:57

and then the lobelia will have real need of its hairy blanket.

0:41:570:42:01

There are other giants here, too.

0:42:020:42:04

Tree groundsels, relatives of the little yellow weed that grows in European gardens.

0:42:040:42:10

They have a different way of dealing with the cold nights.

0:42:100:42:14

Their dead leaves remain attached

0:42:140:42:16

to the stem so that they act like lagging and prevent the liquids

0:42:160:42:20

in the pipes running up inside the trunk from freezing solid.

0:42:200:42:24

Conditions here can change with extraordinary speed.

0:42:240:42:28

One moment the equatorial sun is blazing down from a cloudless sky,

0:42:280:42:33

the next, a chilling wind begins to blow and the great mountain

0:42:330:42:37

collects a cloud cover.

0:42:370:42:39

As well as the tree groundsel, there's another member of the family

0:42:430:42:47

that grows close to the ground like a cabbage.

0:42:470:42:51

As night falls,

0:42:510:42:52

it makes its own preparations for surviving the bitter cold.

0:42:520:42:57

The most precious and vulnerable part of the plant is the bud

0:42:590:43:03

in its centre, from which all growth comes.

0:43:030:43:06

That must be protected at all costs and folding the thick leaves over it does the trick.

0:43:060:43:11

The birdcage plant lives in California.

0:43:210:43:24

But the desert dunes are always moving and a sheltered site

0:43:240:43:27

can suddenly become intolerably exposed -

0:43:270:43:30

so the plant must find a new place.

0:43:300:43:33

This plant is now dead.

0:43:510:43:53

But within it, there is still life.

0:43:530:43:57

These tiny particles are the next generation.

0:43:590:44:02

Each is a miracle of packaging because each, after all, contains

0:44:020:44:07

complete genetic instructions for rebuilding an adult plant like this.

0:44:070:44:13

And it's precisely because these grains are so small

0:44:130:44:16

that it is in this form that most plants do most of their travelling.

0:44:160:44:21

Some of these genetic particles, in fact, are microscopic.

0:44:210:44:24

The smallest of all belong to fungi.

0:44:260:44:29

Fungi are not, to be accurate, plants at all. They belong to a kingdom all their own.

0:44:290:44:34

But the particles they produce, called spores, are in many ways similar to seeds.

0:44:340:44:41

A single puffball produces so many that someone has calculated that if,

0:44:450:44:49

for two generations, every spore

0:44:490:44:51

grew into an adult, the resultant mass of puffballs would be 800 times

0:44:510:44:57

the volume of the Earth.

0:44:570:44:58

Like the birdcage plant, a puffball can be carried along by the wind.

0:45:010:45:05

But the real long-distance travelling is done by the spores

0:45:050:45:09

that are knocked from it in clouds, like smoke.

0:45:090:45:12

In autumn, other, smaller fungi appear on the woodland floor.

0:45:230:45:29

Earth stars.

0:45:310:45:33

Their appearance, just after they have emerged above ground,

0:45:360:45:39

gives little hint of how complex they will become.

0:45:390:45:42

As the damp autumn airs blow through the leafless woods,

0:45:420:45:46

the earth stars begin to transform themselves.

0:45:460:45:50

They open at this time of year to take advantage of the falling rain.

0:46:230:46:28

A drip gives them all the energy they need

0:46:360:46:38

to propel their spores into the air.

0:46:380:46:41

A snow leopard, the rarest of Himalayan animals.

0:47:050:47:10

The Planet Earth team spent months

0:47:110:47:14

just trying to glimpse a snow leopard, and more months to film one.

0:47:140:47:20

How do you conserve a creature that you're lucky even to see?

0:47:230:47:27

How do these scientists, or how do these conservationists know

0:47:290:47:34

where this animal is, how many there are, and what their behaviour is?

0:47:340:47:39

Someone told me that there were 3000 between China and Afghanistan.

0:47:390:47:44

Now, I mean, we've had a very tough time identifying three.

0:47:440:47:49

There is a threat to its existence,

0:47:510:47:53

simply because not enough is known about it.

0:47:530:47:57

We really don't know where it thrives.

0:47:570:48:01

Because it's isolated, you expect that a lot of wildlife is there.

0:48:020:48:06

How much of it and what are the elements affecting it are unknown.

0:48:060:48:10

In the distant reaches of Outer Mongolia,

0:49:030:49:06

one of the planet's great migrations is underway.

0:49:060:49:10

Few people ever see this extraordinary annual event.

0:49:110:49:16

Mongolian gazelle. 2 million are thought to live here.

0:49:190:49:22

But what will happen to the gazelle in 15 years?

0:49:250:49:29

And if they go the way of the saiga, will it matter?

0:49:290:49:32

Should we concentrate only on the most important species?

0:49:320:49:36

If so, which ones are the most important?

0:49:370:49:41

We need every species.

0:49:420:49:45

We need a great diversity of species.

0:49:450:49:48

We need every species

0:49:500:49:53

because...

0:49:530:49:54

when you start decreasing the numbers of species,

0:49:540:49:58

especially in an environment

0:49:580:50:00

which has adapted to a high level of diversity,

0:50:000:50:03

you'll start reducing the stability of the area.

0:50:030:50:08

I think any extinction that is before its time matters.

0:50:090:50:14

If one was to pick two groups, it's at the very top and the very bottom.

0:50:140:50:18

You know, the creatures that keep the planet going

0:50:180:50:21

and the big organisms that keep our souls and imaginations on fire.

0:50:210:50:27

The tiger, probably the best known poem in the English language,

0:50:270:50:31

Blake's Tiger Tiger, which

0:50:310:50:32

every child can recite and every child understands what it means.

0:50:320:50:36

"Tiger Tiger, burning bright, In the forests of the night."

0:50:360:50:40

They know that it's not just dark forest.

0:50:400:50:42

It's to do with the pulse of life.

0:50:420:50:45

If we lose these majestic creatures,

0:50:450:50:48

with their sense of power and ancestry and their possibility

0:50:480:50:54

of power over us sometimes, then I think

0:50:540:50:57

we are diminished by that, as well as the ecosystem.

0:50:570:51:03

If you go to a village in India

0:51:030:51:05

and you start talking to them about saving the tiger,

0:51:050:51:08

people will say to you, "How can you talk about saving the tiger when

0:51:080:51:13

"we've got starving people here?"

0:51:130:51:15

I think the way conservation was developed over the last 50 years,

0:51:150:51:21

we have focused our energy into trying to convince people

0:51:220:51:26

that things like tigers are inherently important.

0:51:260:51:29

Ultimately, if our movement is not relevant to the lives of real people

0:51:290:51:34

dealing with real issues, we're just going to be preaching to the choir.

0:51:340:51:38

My concern is the great indifference that most people have toward

0:51:380:51:43

the species of lesser creatures

0:51:430:51:45

that they'd never noticed or dismissed as bugs and weeds.

0:51:450:51:48

That's where the bulk of life on Earth exists.

0:51:480:51:52

When you magnify one of these organisms

0:51:520:51:57

to human size and approach it as an independent,

0:51:570:52:02

highly-complicated entity on Earth,

0:52:020:52:05

then you see it as the equal of a large mammal.

0:52:050:52:10

The organisms that matter, perhaps most of all, are the plants.

0:52:130:52:18

Many of them very unglamorous, hard-working, fantastically common.

0:52:180:52:23

Of course, without which,

0:52:230:52:24

there would be no way in which the energy of the sun

0:52:240:52:27

was translated into available energy for all other organisms.

0:52:270:52:33

Each of these creatures plays a role in its ecosystem.

0:52:330:52:36

Some of those roles quite important.

0:52:360:52:38

If you think in terms of a brick wall,

0:52:380:52:40

we are systematically knocking out bricks.

0:52:400:52:42

Sooner or later the wall collapses.

0:52:420:52:45

This is biodiversity.

0:53:350:53:38

The planet's full wide range of life-forms.

0:53:380:53:41

And it benefits every single species, including the human one.

0:53:410:53:46

How?

0:53:460:53:47

The whole planet Earth is a system

0:53:470:53:50

and we, human species,

0:53:500:53:53

are only a very small part of the system.

0:53:530:53:57

There are literally millions of species out there.

0:53:570:53:59

We may not know them.

0:53:590:54:01

We may not know their value.

0:54:010:54:03

But we want to conserve them.

0:54:030:54:06

There are a very wide range of practical reasons

0:54:080:54:11

as to why we need to conserve this planet's biodiversity.

0:54:110:54:14

For a start, all our food ultimately derives from biological systems.

0:54:140:54:18

So do a lot of our medicines.

0:54:180:54:19

A lot of our industrial products are based upon chemicals

0:54:190:54:23

we've taken from nature, for example.

0:54:230:54:25

Biodiversity is very much part, therefore, of the global economy.

0:54:250:54:29

Very much part of our wellbeing.

0:54:290:54:31

I don't think there's a single compelling

0:54:310:54:34

reason of an economic kind

0:54:340:54:38

that compels us to preserve biological diversity.

0:54:380:54:42

Insofar as there are reasons, one says, we want to preserve all this

0:54:420:54:47

gene pool because maybe we can use it.

0:54:470:54:50

Very human-centred.

0:54:500:54:51

Maybe we can be clever enough to just understand the molecules ourselves.

0:54:510:54:56

The second says, we depend on the services ecosystems give - pollinating,

0:54:560:55:02

cleaning water...

0:55:020:55:05

and as we reduce the number of species, we can't be sure they will continue to deliver those services.

0:55:050:55:11

Maybe we could be clever enough to live in an impoverished world.

0:55:120:55:16

The third reason is a straight ethical reason that says we have a responsibility of stewardship.

0:55:160:55:22

And how strong that is depends on the luxury you have to enjoy it.

0:55:240:55:28

The head count of the Amur leopard is disturbing.

0:55:410:55:45

Because of habitat loss and poaching,

0:55:450:55:49

there are just 30 left in the wild.

0:55:490:55:52

With extinction so close, conservation becomes desperate.

0:55:560:56:01

Here in New Orleans, the Audubon zoo, we have a pair of the Amur leopards.

0:56:080:56:12

Our long-term strategy with them is to work with what we call

0:56:120:56:16

the species survival plan.

0:56:160:56:18

The Amur leopard is one of the high-priority animals.

0:56:180:56:22

What's happened recently, and some of the work we're doing involving cloning, has allowed

0:56:270:56:33

us to now not necessarily take eggs and sperm but we're able

0:56:330:56:38

to take tissue samples from these animals.

0:56:380:56:41

Put this tissue sample in a culture and where it was once maybe 100 cells,

0:56:410:56:44

we can now grow thousands of cells.

0:56:440:56:46

Each one of those cells contains the complete copy of DNA of this animal.

0:56:460:56:53

So we can freeze these cells.

0:56:530:56:56

Let's say 50 years from now, scientists go into those liquid nitrogen containers and they

0:56:560:57:02

pull out the DNA from tigers, Amur leopards, rhinos.

0:57:020:57:07

That DNA is alive and it's able to be used to produce

0:57:070:57:12

embryos that then could result in babies - in offspring.

0:57:120:57:16

So, what I'm hoping we leave in our lifetime is this living library for the future.

0:57:160:57:21

50 years from now, the scientists can say, "Oh my gosh, we're about to lose

0:57:210:57:27

"this little rusty-spotted cat from Sri Lanka or the Amur leopard, but do you know what? We have the DNA.

0:57:270:57:33

"We have the science to at least be able to bring the numbers up of the species so they won't go extinct."

0:57:330:57:40

We have to be careful about producing

0:57:400:57:42

something which is a facsimile of a wild animal,

0:57:420:57:46

from something which is able to exist in the wild.

0:57:460:57:49

One of the problems of keeping animals in conventional zoos, the

0:57:500:57:54

selective pressures are very great

0:57:540:57:56

and you're actually moving that animal towards domestication.

0:57:560:58:01

It may look the same, but it may not have the skills

0:58:010:58:04

or the behavioural attributes or physiology to survive in the wild.

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You know it's funny when people say, we may be playing God, we may be

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controlling and taking charge of kind of these species' destinies.

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But you know, man played God a long time ago.

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I think, and I believe, God gave us stewardship over these animals.

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What we're doing is using the capabilities that we have

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as humans to not destroy animals any longer but to try to protect them,

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to preserve them and bring them back.

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Subtitles by Red Bee Media Ltd

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E-mail [email protected]

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A selection of clips taken from BBC programmes about Darwin and evolutionary biology. The programme includes material on adaptation and natural selection.


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