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00:27THE END
00:57THE END
01:27The volcanoes of today are mere feeble flickerings compared with those that dominated the world at the beginning of its history.
01:37Then enormous sheets of lava welled out of the craters.
01:41Titanic explosions blew whole mountains into fragments and scattered them as dust and ash over the surface of the land.
01:50That sort of activity continued for millions and millions of years.
01:54I'm talking about a period that was four and a half thousand million years ago.
01:59The forces of erosion, frost and rain, snow and ice shattered the volcanic rocks into fragments.
02:08Rivers carried them down piecemeal to the edges of the continents and deposited them as sands and gravels and muds.
02:15As the continents drifted over the globe and collided, new mountain ranges were built up and in their turn worn down.
02:26And throughout this immensity of time, the land remained sterile.
02:38Nowhere was there even the smallest of animals or the tiniest speck of green.
02:42If you condense the whole history of life from its very beginnings until the present moment into a year,
02:54then it wasn't until about the end of September that the first creatures of any size, jellyfish and so on, appeared in the sea.
03:03And it wasn't until the beginning of November that the first life, a few patches of green, appeared on land,
03:14maybe at the edge of water like this.
03:18These first plants were simple algae that had developed cell walls thick enough to enable them to survive on the moist boulders and gravels.
03:28Slowly they spread over the lake beaches and the sand spits,
03:31pioneers of the great revolution that was to lead to the greening of the earth.
03:49Moving out of water for the plants had presented a number of problems,
03:53and one of the most serious was the question of support.
03:56In water, algae like this can grow into long strands.
04:02But robbed of the support of water, none of them has sufficient rigidity in its stem to allow it to grow upright.
04:09So the first land plants had to remain lowly, forming flat skins like liverworts or cushions like mosses.
04:21All of them lived in wet, moist places, and for a very good reason.
04:27Their ancestors, the algae, had reproduced in two ways, by budding and sexually.
04:32And the sexal method involved these sex cells actually swimming through water in order to find one another and fuse.
04:41Well, mosses retain very much the same sort of method.
04:45And it's this that keeps them tied to water.
04:49So they can only live in places where, at the very least, it's wet during some time of the year,
04:54so that sexal reproduction can take place.
04:57And, of course, in places like this, they are literally in their element.
05:19Mosses and liverworts like this both produce two kinds of sex cells.
05:24These outgrowths, on a liverwort only a few centimetres high, develop tiny mobile sperms which actively swim.
05:35These different growths contain larger static sex cells, the eggs.
05:40Under the microscope, you can see the eggs at the base of tiny tubules,
05:45surrounded by a protective sheath of smaller cells.
05:47When the outgrowths are ripe and conditions sufficiently wet, fertilisation begins.
06:00The wriggling sperm are released and swim in the film of water that covers the plant.
06:05The sperm appears as a milky fluid.
06:21At the same time, the female part of the liverwort that bears the egg cells
06:42releases a special chemical that attracts the sperms.
06:46Eventually, they reach the female organs.
06:51Fertilisation occurs and the eggs develop,
06:54repeatedly dividing to produce a capsule full of microscopic grains, spores.
07:00When they are ripe and the weather is dry, the capsules burst.
07:04Each minute spore is capable of growing into a new liverwort plant.
07:20Moss is also reproduced by these two alternating methods.
07:24The sexual stage provides the variety of offspring necessary for continued evolution.
07:28The asexual spores can be carried on the wind to distribute the plant over great distances.
07:35The spore capsules of mosses are very varied in shape,
07:39and they have the most ingenious ways of making sure that they only release their contents
07:43when the weather is suitably warm and dry.
07:46Many species have detachable caps, which are blown off before the spores can be released.
08:07And beneath, a perforated lid, like a pepper pot.
08:12And the wind will now carry the microscopic spores for miles.
08:16With such mechanisms as these, the first plants colonised the moist places of the world,
08:36and green carpets bordered the lakes and rivers.
08:38Into these miniature jungles came the first land animals.
08:54Millipedes, then as now, were vegetarians,
08:58and they must have found plenty to eat among the mosses and liverworts.
09:02The biggest of them today are only a few inches long,
09:04but many of the ancient forms that pioneered life on land grew very much larger.
09:09One, indeed, was as long as a cow.
09:23Millipedes were descended from sea-living creatures
09:25very distantly related to crustaceans such as shrimps.
09:29From them, they inherited segmented bodies
09:31and an external skeleton which gave them the necessary support
09:35so that they could move just as well in air on land
09:38as their ancestors had done in the sea.
09:43But breathing was another matter.
09:46Their ancestors had extracted dissolved oxygen from water
09:49with feathery gills alongside each leg.
09:52But such things wouldn't work in air.
09:55Instead, the first millipedes developed a system of branching tubes
09:58within each segment, along which air diffuses to all parts of the body
10:03so that the tissues can absorb oxygen directly.
10:06These tubes open to the outside
10:08through a tiny paw on the side of each segment.
10:20But the amiable browsing millipedes
10:22didn't have the land to themselves for long.
10:24Very soon after they had colonised it,
10:27hunters came up from the sea to prey on them.
10:33These hunters are still today active mostly at night.
10:38The scorpions.
10:38They had evolved from a different group of segmented sea creatures,
10:53but again they had an external skeleton
10:55which worked very effectively on land.
10:57With powerful nipping claws and poisoned stings
11:00at the end of their tails,
11:02scorpions are well-armed and ferocious,
11:05actively seeking out their prey
11:07wherever it may be hiding.
11:16Another closely related group
11:18became mainly day hunters in the miniature forests.
11:22The spiders.
11:28Although their sea-living ancestors had many pairs of legs,
11:32spiders and scorpions have only four pairs.
11:35Better for speed.
11:35And spiders have lost most signs of division in their bodies
11:39except for some very primitive ones
11:41that live in Southeast Asia.
11:43Their abdomens show the last relics
11:45of that ancestral segmentation.
11:50Early in their history,
11:51the spiders developed glands in the abdomen
11:53with which they produce silk.
11:55They use it in hunting,
12:02sometimes laying long trip lines,
12:04sometimes constructing dense sheets.
12:06And they manipulate the threads
12:08with modified limbs, the spinnerets.
12:11and they use it in the mountains.
12:12They use it in the?-
12:13They use it in the baptist.
12:14They use it in the bedtime
12:15and the
12:33footsteps of the boatswain.
13:03By the time it's finished, any small creature trying to make its way here will blunder
13:10into a silken trap, and while it's still entangled, the spider will pounce on it.
13:23Reproduction for all these land creatures presented new problems.
13:27Without water to transport sperm to egg, there was nothing for it.
13:32Male and female had to get together.
13:36For the millipede, this presented no real danger.
13:39They are vegetarians, so when individuals meet, neither risks being eaten by the other.
13:45Their difficulties are entirely ones of manipulation.
13:56The sex glands of both male and female are at the base of the second pair of legs.
14:02The male has reached forward with his seventh pair of legs and collected from his second
14:06segment a little packet of sperm.
14:09Now if only you can get it into exactly the right position alongside the female's pouch
14:14in her second segment, all will be well.
14:16And there it goes.
14:21The scorpion's sexual problems are much more complicated and potentially dangerous.
14:28They are hunters and they have to make sure that one doesn't regard the other not as a
14:29mate, but as a meal.
14:30Courtship is necessary.
14:31They are hunters and they have to make sure that one doesn't regard the other not as a mate,
14:45but as a meal.
14:58Courtship is necessary, ritualised in a number of set movements.
15:04First, those dangerous pincers have to be neutralised.
15:34Now, with the pincers held out of action, more rituals follow.
16:00The heads of male and female come close together and even touch.
16:12Now a strange heaving back and forth, which will eventually lead to the actual transfer
16:18of sperm.
16:19The male's sex gland is on the underside of his body and from it he has deposited a packet
16:24of sperm on the ground.
16:26Now he has to tug the female into a position where her sexual pouch is directly above it.
16:41If this ritual is not performed correctly, the scorpion's hunting instincts will not
16:46be pacified.
16:48It's a delicate balance.
16:49And here it seems to be going wrong, because this probing with the sting is probably more
16:54to do with aggression than with mating.
17:01And they break.
17:26Spiders have the same kind of problem.
17:30They too are hunters and a male advancing on a female has to make quite sure that she
17:34knows who he is and what his intentions are.
17:38The female jumping spider has sharp eyes, eight of them, and he signals with his front legs
17:43as though his life depended on it, which indeed it does.
17:58And he brings three signals back.
18:11And he is encouraged.
18:18At close range, the male begins to use tactile signals rather than visual ones.
18:23He must constantly convince the female of his good intentions, for he has to achieve a much
18:28more intimate and direct contact with the female than the male scorpion did.
18:33He's prepared for this encounter by spinning a tiny web of silk on which he's dropped some
18:37sperm from a gland under his abdomen.
18:40And he's taken up the sperm in two special feelers, the palps.
18:44Now he must reach over the female so that he can pump sperm from one palp into one of the
18:49female's sexual pouches.
18:51It's rather like liquid being squeezed out of an eyedropper.
18:56And there it goes.
18:59Now the spider changes position to pass sperm from the other palp into the female's other
19:04sexual opening.
19:13The wolf spider is a larger and particularly aggressive species.
19:17He too is courting a female.
19:20His problem is especially dangerous here because the female lives in a burrow from which she emerges
19:25only on hunting forays.
19:27It's hardly surprising therefore that he approaches with the greatest caution.
19:44At first he uses a kind of semaphore.
19:47If he doesn't keep this up, the female may mistake him for prey and rush out and pounce
19:52on him.
20:11Within the confines of the burrow visual signals are difficult.
20:14And so the male changes to delicate and sensitive strokings with his front legs.
20:21At last she receives him and he can take up his risky mating position, reaching right round
20:37to the female's abdomen.
20:42The early jungles filled with such creatures were still only a few inches high.
20:47No more than a thick moist carpet draping the sand spits and boulders.
20:51For plants like mosses and liverworts were still the only ones that existed on land.
20:59And this is just about as big as any moss in the world ever grows.
21:06A series of isolated stems.
21:09It has no real roots.
21:11It just absorbs what moisture it requires through its surface.
21:14And it doesn't have true leaves.
21:16They're just simple scales.
21:18To see why it's so frail, one has to look inside the stem.
21:26Sliced and examined under the electron microscope, this is how it appears in section.
21:31The cells are thin-walled with no rigidity to them, unable to support a tall plant.
21:37But that structure was soon to be strengthened.
21:41In the course of time, some plants developed that were able to grow upright and several feet
21:46tall, and the fossilized remains of some of the earliest of them have been found in the
21:51rocks of these bleak Welsh hillsides.
21:55To find fossils, you sometimes have to use violent methods.
22:16And here are some, they're just thin branching filaments, but they'll show up even better if I
22:43went this slab.
22:48They look like tiny moss filaments.
22:51But when these flattened, 400 million year old stems are sectioned, the electron microscope
22:56reveals quite different cells.
22:59These have much thicker walls forming tubes in the stem, a plumbing system of which the
23:04plant draws water.
23:06And these new cells give the stem strength and the ability to grow tall.
23:11And these very similar cells come not from a fossil plant, but from a living one, from
23:18this plant, which grows on another Welsh hillside.
23:21It may look superficially like a moss.
23:24In fact, its common name is club moss.
23:26But actually, it's fundamentally different.
23:29By virtue of those tough, thick cells in its stem, it's much more rigid than any moss.
23:36Today, it only grows to that sort of height.
23:39But in the past, it grew to the size of trees and formed great forests.
23:46There were soon many kinds of plant with the new cell walls.
23:50And some of them, the horsetails, are still common all over the world.
23:54The highest in South America reaches three or four metres.
23:57And 300 million years ago, they grew to 30 metres, 90 feet tall.
24:03Then as now, they developed a hard outer skin to prevent desiccation.
24:08Under the microscope, you can see minute pores through which the plant breathes, taking in
24:13carbon dioxide and giving out oxygen.
24:17And there was a third kind of plant that grew with the giant horsetails and the club moss
24:20trees in those first forests, tree ferns.
24:31But height for the horsetail and the tree fern accentuated yet again the problem of achieving
24:38sexual union with a male cell that has to swim.
24:44How could a microscopic cell swim from the top of that tree fern to the top of that one?
24:51Impossible.
24:52The structures that are up there produce spores.
24:57Reproductive cells that do not require fertilisation in order to develop.
25:01Just like those in the little capsules developed by mosses.
25:06The ferns produce their spores from little structures beneath the fronds.
25:12Their shape and arrangement varies with each fern species.
25:19The ferns produce their spores at the bottom of the top of that tree ferns.
25:22The ferns produce their spores from little structures.
25:24So the square itself is a pyramid of white and the two Laurens.
25:26The ferns produce of water.
25:27The ferns ry»vee.
25:28Because Kandis, the sky of the earth.
25:29The water is a premature Drink.
25:3010 years old.
25:31The ferns produce of water.
25:32The forest is a ihrer вице, which is little to the earth.
25:33The ferns produce of water.
25:34The ferns moving from little structures.
25:36The earth is a mountainous resource.
25:38It's a mountainous source.
25:40It's a mountainous mountainous.
25:40It's a mountainous moment.
25:41It's a mountainous area.
25:42It's a mountainous.
25:45The ferns have an repeating.
25:45Furns, like mosses, release their spores when the weather is dry and the wind can carry
25:57them far and wide. Some fern spores are produced in cups at the end of curled strips, one side
26:03of which is woody and the other thin-walled. As these cups dry, they shrivel, pulling back
26:08the strip until the tension is too much. The strip snaps back and the spores are catapulted
26:13free. The spores have tiny spines and ridges on them that help them catch the wind. A
26:33few will fall on moist ground and then germinate to produce a different kind of plant altogether.
26:40This is the stage in the fern's life cycle that bears the sex cells, and this has had
26:44to remain small and close to the ground in order that its sperm can swim from plant to
26:49plant. When wet weather comes, the male organs release the sperm, which swim by threshing
26:56their thread-like tails. Hundreds of thousands are produced from the underside of the flat
27:05plant and are carried away by the rainwater. Eventually, some reach the female organs of
27:19the plant and swim up the tubes that lead to the egg cells. After fertilization, a new growth
27:33develops from the egg, sending up a tiny stalk.
27:40a new growth cycle. These green shoots eventually grow tall and complete the cycle, becoming once
28:03more a familiar spore-bearing fern. Then, about 400 million years ago, as the forest began
28:10to rise, new animals appeared. These were descendants of the ancestral millipedes, and several kinds
28:20still survive today. This is a bristle tail, and it lives in soil worldwide. And this, the silverfish,
28:26that now often lives in houses. Faster than millipedes, they have fewer body segments and even fewer legs,
28:33just three pairs. They all feed on vegetable matter. But as plants grew taller, so leaves and spores became more
28:41inaccessible, and these little creatures doubtless clambered up the stems and trunks after them.
28:47The journey up must have been fairly easy, but getting down again, sometimes over upward-pointing spikes, may have been more laborious.
29:04Maybe that was the reason for a dramatic development. Some little creatures developed wings for flying from plant to plant.
29:14Just how wings evolved, we can't be certain. But they may have first developed as tiny lobes on the back.
29:24Dragonflies today develop their wings in just this way, repeating millions of years of evolution in just one night.
29:44But it is a dream of almost three years of spring.
29:45Let's give our wings in just a long way.
29:47Dragonflies
29:49Dragonflies
29:52Dragonflies
29:54Dragonflies
29:56Dragonflies
29:59Dragonflies
30:01Dragonflies
30:02Dragonflies
30:04Dragonflies
30:07Dragonflies
30:08The wings are stretched taut by blood pumping into the veins.
30:38Later, the blood is drawn back into the body and the gauzy wings slowly dry and harden.
31:08Flight is the great achievement of the insects.
31:20They were the first creatures to take to the air and they were to have it almost to themselves
31:24for 100 million years.
31:27Dragonflies were among the first fliers and they are still superb aeronauts.
31:39They can reach speeds of 20 miles, 30 kilometers an hour.
31:42They hunt in the air, holding their legs cooked in front of them like a basket.
31:47They even mate on the wing.
31:57The females lay their eggs in water.
32:03Their young, wingless larvae will grow up on the bottom of the pond, breathing through
32:08feathery gills and feeding on other small, water-living creatures until the time comes
32:13for them too to climb up a reed and spread their wings.
32:16The dragonflies' smaller relatives, damselflies, also haunt ponds.
32:24The wings of these insects beat so rapidly that only a slow motion camera can show clearly
32:30how they fly.
32:31This is the action slowed down 120 times.
32:35The insect gets lift on the downbeat of the wing by twisting it so that the leading edge
32:40is inclined downwards.
32:42But at the bottom of each stroke, the wing is twisted back so that it is effective on
32:47the upstroke as well.
32:49It's an intricate set of mechanical movements which man has never matched in the air.
32:54Here, the insect is hovering.
32:57The wings sweep alternately backwards and forwards, again changing angle at the end of each sweep
33:03in order to obtain lift on both strokes.
33:06Man has achieved something similar with a helicopter whose blades rotate.
33:11The insect can't rotate its wings, but it's evolved a set of movements which are even more complex.
33:24The principal navigational equipment of the dragonflies and damselflies are their superb eyes.
33:34Because they're so dependent on them, dragonflies normally fly only during the day.
33:43Today's splendid species are among the biggest of insects.
33:46But when the insects first colonized the air and had it to themselves, the dragonflies grew gigantic.
33:52And one appeared that had a wingspan of 70 centimetres, over two feet, the largest insect that has ever existed.
34:02While all this was happening some 300 million years ago, the plants themselves were on the brink of an important advance.
34:11This tiny sexual stage of the fern's life cycle is obviously very vulnerable.
34:17It can only live in moist conditions like these.
34:19And down on the ground, it's easily cropped by plant-eating animals.
34:24It would obviously be much safer if this stage could take place up in the top of the tree.
34:30But that would require some way of transferring the sex cells from tree to tree.
34:37Well, they could be blown there by the wind.
34:39But there was then, as there is now, also a regular traffic in between the tops of the trees.
34:46Insects that go up there to seek the spores as food and fly from one tree to another.
34:52They could take them.
34:54And that's what happened.
34:55New plants appeared in which the sexual generation remained fixed to the asexual tree stage.
35:02And one of the first of them was a plant like this, a cycad.
35:09Cycads bear two kinds of cones, each of which represent, in effect, part of the tiny sexual stage that once grew down on the ground.
35:18The male cones produce pollen, the grains of which germinate to produce the male cells.
35:23And the female cones contain the large egg cells.
35:29Insects help to transport the pollen from the male cone to the female.
35:34And there it produces a tube down which swims the sperm.
35:37At its tip, within the female cone, a drop of water appears.
35:45And in that, the sperm swims, re-enacting the journeys made through the primordial seas by the sperm cells of their algal ancestors.
35:54Only after several days does it fuse with the egg.
35:59This cycad leaf is about 200 million years old.
36:03That's to say, it was fossilised around the end of November in the Life on Earth year.
36:09And at that time, a new and revolutionary plant had appeared that was growing alongside these cycads.
36:16It was the conifer.
36:18And this is one of its trunks.
36:21It's not wood, as you might think, but solid stone.
36:24I'm in the middle of one of the most spectacular deposits of plant fossils in the whole world.
36:36The petrified forest in Arizona.
36:40These conifers grew to over 200 feet tall.
36:44And they stood in thick, dense, dark forests alongside the swamps where the cycads grew.
36:50And when the trunks fell, they often dropped into a river which swept them down here so that they formed great log jams around here.
37:00And then the river muds and sands and silts buried them.
37:05And the silts eventually formed mudstones like those over there.
37:09And when the mudstones eroded away, as they have done here, they re-exposed these trunks that had been turned to stone.
37:17Yes.
37:17å•¥
37:18ORGAN PLAYS
37:48ORGAN PLAYS
38:18ORGAN PLAYS
38:30Conifers are built on very similar lines to the cycads,
38:35except that they have both the male and the female cone on the same tree.
38:40These are the male cones, and they use wind to transport their pollen.
38:47But in order to make sure that such a haphazard method of fertilisation is successful,
38:52they have to produce pollen in huge quantities.
38:55One cone may produce several million grains,
38:59and there are many thousands of cones on an average-sized tree.
39:02The female cones are fewer in number and also grow on the same branches.
39:13They are small globes in conspicuous positions on the tips of shoots,
39:17where they have a good chance of receiving pollen.
39:19Pollen falling on the female cone is only the beginning of a very long process.
39:33It takes a whole year for the pollen grains to grow down to the eggs.
39:38And at the end of that year, the cone looks like that.
39:41But even that's not the end of things.
39:43During the next year, the cone grows still more.
39:48It develops wrappings around the fertilised eggs,
39:51and then it dries out and opens up
39:53and out drop small, neatly packaged brown objects, seeds.
40:00They contain the first kind of plant eggs
40:02to have been fertilised without the help of water.
40:13Ancient, though, the conifers' technique of reproduction is,
40:30it has proved a huge success.
40:32Today, about a third of the forests of the entire world are formed by conifers.
40:38Furs, larches, cedars, pines, they're all members of this group.
40:43The biggest living organism of any kind is a conifer,
40:57the giant sequoia of California,
41:00that grows to 112 metres, 367 feet high.
41:05Some have a diameter of 12 metres, 40 feet.
41:13Conifers have a special way of healing wounds to their trunks.
41:33They seal them with resin.
41:35When it first flows, it's runny, but it soon forms a sticky lump,
41:39which not only covers the wound, but incidentally acts as an insect.
41:43Lumps of resin from the ancient coniferous forests survive as amber,
41:52and in them are insects, as perfect now as the day
41:55when they blundered into the resin 100 million years ago.
42:08From fossils like these, we know that the insects by that time
42:12had developed into an enormous variety of forms
42:15that swarmed through the trees and over the ground,
42:18feeding on every part of the plants,
42:20pollen and fruit, leaves and wood, root and branch,
42:23just as they do today.
42:30Bugs stab stems with stiletto-like mouthparts to reach the sap.
42:34There are over 3,000 species of aphids alone,
42:44tapping this ready source of food in plants all over the world.
42:47All they have to do is to pierce the plant vessels.
42:50They don't even need to suck,
42:52such as the pressure of the sap within the stem.
42:57Locusts and grasshoppers chew the leaves.
43:00Beetles munch through cuticles and even manage to digest wood.
43:10Some insects not only eat plants,
43:13but in order to hide themselves while they're doing so,
43:16they've come to look like plants,
43:18like leaves and sticks.
43:19Hunters from the ground pursued the insects up into the trees.
43:35Spiders.
43:37But lying in ambush on trunks and on leaves has its limitations.
43:42Most insects fly.
43:43Spiders never developed wings,
43:49so they were unable to pursue their prey into the air.
43:52Instead, they set traps for them.
44:03The silk that they had spread in sheets and trip lines on the ground,
44:07they now wove into nets,
44:09setting them across the insect flyways.
44:13comida sitting in jakh!
44:16It was very weak,
44:16so they showed theirå‘€!
44:17It was very weak as plants.
44:18They didn't see.
44:20It was a ranch każde garden,
44:22so they took some fireionove быв her.
44:23Such a place.
44:23These Africans appeared.
44:25They ripped and praised the pig cualquier couple of these plants.
44:29Someone else could sneak in the shade.
44:30The Fourier hides is the Vikt chịu.
44:32Their weather patterns.
44:33Their spending time has been healthy.
44:34They're lessons to eat eventually.
44:35Seag towel is the bearing because of Isaiah carrying this resume.
44:37Their description is strong fuel for certain images,
44:38and anticipate theänner.
44:39It was streamlined in the East ItsNewbanian sea.
44:42The Said were different,
44:43With these elegant and varied constructions,
45:04spiders began to take a heavy toll of flying insects,
45:07and today spiders are one of the most effective predators on the insect populations.
45:13The insects themselves developed their flying skills in many different ways.
45:31The two pairs of wings used by the dragonflies and their relatives
45:34were also used by other insects.
45:36This is a lace wing.
45:43But this design was modified by other insects.
45:48The caddisfly, not needing the speed of a dragonfly to catch prey,
45:52overlapped its two pairs of wings, producing a unified surface area.
45:58On the other hand, bees must have compact wings,
46:02which can be neatly folded back when visiting flowers or in the hive.
46:06To get the right lift, their smaller wings must beat faster.
46:10They look as though they only have one pair of wings,
46:15but in fact they have two.
46:17They are hitched together to form what is virtually a single surface
46:20by a line of hooks along the front edge of the back wing.
46:27Other insects spend more time among dense foliage.
46:31The front wings of this bug have thickened bases to them,
46:35which strengthen them and give some protection to the rear ones when folded.
46:38Beetles have gone one stage further.
46:42Many burrow through litter and dense vegetation,
46:45and their front wings have become totally converted into protective covers.
46:49In order to lift the heavy body during flying,
46:52the operational wings have to be large.
46:55If they are to be protected when not in use,
46:57they have to be folded,
46:59and the trick is done with spring-loaded joints in the veins of the wings.
47:03Once in the air, the wing covers have to be held up out of the way,
47:10but they may also help a little in flight,
47:13acting as stabilisers, preventing rolling and yawing.
47:17Like many insects, this beetle increases lift
47:19by clapping its wings together at the top of the upstroke,
47:23thereby improving airflow over the wings.
47:25The chaffer is the heavy weight of the insect flyers.
47:33Its wings beat comparatively slowly, about 40 times a second,
47:37and it's the least agile of insects in the air,
47:40ponderous and unable easily to bank and swerve.
47:44It holds its wing covers out of the way along its back
47:47and balances itself with outstretched legs.
47:49Its wing structure is tremendously strong
47:53in order to support a heavy insect,
47:55and yet flexible enough to change its angle on each stroke
47:58and even fold back on itself when the insect stops flying.
48:08Even that feat is overshadowed by the achievement
48:11of the most skilled aeronauts of all, the flies.
48:15This one, the hoverfly, is perhaps the champion.
48:18It uses only one pair of wings, the front ones,
48:21which it keeps in perfect condition with frequent cleaning.
48:25It can hang absolutely stationary in the air
48:28and does so even when it mates.
48:31It can compensate for any sudden current of wind
48:34to hold its position.
48:36It can fly backwards and dart off at great speed in any direction.
48:40And to perform these manoeuvres,
48:42it beats its wings at the astonishing speed
48:44of 175 beats a second,
48:47a normal slow-motion camera still shows the wings as a blur.
48:51They control their flight with a device
48:55which can be seen most clearly in another fly,
48:57the crane fly or daddy long legs.
49:00Those two objects, like drumsticks, swinging up and down,
49:04are the remains of their back pair of wings
49:06after millions of years of evolution.
49:08They're jointed to the body, just as the real wings are,
49:11and they act like gyroscopes.
49:13By beating very fast,
49:15and here they're slowed down 120 times,
49:18they give the fly stability in the air.
49:21For like gyroscopes and the automatic controls of an aeroplane,
49:25they enable the fly to be aware of the attitude of its body in the air
49:28and to detect when there's been any change in the flight path.
49:32House flies also have these drumsticks,
49:39though they're much smaller.
49:42It's these that enable flies to perform such extraordinary and tantalising aerobatics.
49:49And the same organs perform similar functions for the hoverfly,
49:53giving it that superb flight control.
49:56The design of the insect body is particularly suited,
50:15not to great size, but to miniaturisation.
50:18And the hoverfly is one of the most intricately constructed insects of all,
50:23a marvel of microscopic machinery
50:26that's built up from an egg in a few days
50:28and is often crushed beneath a thumb.
50:35The main developments of the insects
50:37took place at a comparatively early stage in the history of life on Earth.
50:42At the time when these petrified forest trees were alive 200 million years ago,
50:47every single main type of insect that we know today was already in existence.
50:52Here, for example, is a piece of petrified wood.
50:56And before it was turned to stone, some beetle had bored holes into it,
51:02just as beetles bore into dead wood today.
51:04And now the stage was set for a revolution,
51:08and one in which the insects were to play a crucial part.
51:12Charles Darwin called its history an abominable mystery,
51:16and even today we've only got a sketchy idea of just what happened.
51:20But some of the plants developed flowers.
51:24The woodlands and the lakes bloomed,
51:26and colour came to the earth.
51:28ORCHESTRA PLAYS
51:42ORCHESTRA PLAYS
51:46ORCHESTRA PLAYS
51:50ORCHESTRA PLAYS
52:10ORCHESTRA PLAYS
52:13ORGAN PLAYS
52:43Flowers became beautiful, not to delight the eye of man, but to attract insects.
53:04And this led to some of the most intimate of all the relationships that have evolved between plants and insects.
53:12Pollination.
53:13Pollination.
53:14Pollination.
53:15Pollination.
53:16Pollination.
53:17Pollination.
53:18Pollination.
53:19Pollination.
53:20Pollination.
53:21Pollination.
53:22Pollination.
53:23Pollination.
53:24Pollination.
53:25Pollination.
53:26Pollination.
53:27Pollination.
53:28Pollination.
53:29Pollination.
53:30Pollination.
53:31Pollination.
53:32Pollination.
53:33Pollination.
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