1 00:01:26,520 --> 00:01:31,120 The volcanoes of today are mere feeble flickerings 2 00:01:31,120 --> 00:01:36,400 compared with those that dominated the world at the beginning of its history. 3 00:01:36,400 --> 00:01:40,600 Then, enormous sheets of lava welled out of the craters, 4 00:01:40,600 --> 00:01:44,680 titanic explosions blew whole mountains into fragments 5 00:01:44,680 --> 00:01:49,320 and scattered them as dust and ash over the surface of the land. 6 00:01:49,320 --> 00:01:53,440 That sort of activity continued for millions and millions of years, 7 00:01:53,440 --> 00:01:58,920 and I'm talking about a period that was 4,500 million years ago. 8 00:02:00,520 --> 00:02:04,440 The forces of erosion, frost and rain, snow and ice, 9 00:02:04,440 --> 00:02:07,120 shattered the volcanic rocks into fragments. 10 00:02:07,120 --> 00:02:10,960 Rivers carried them down piecemeal to the edges of the continents 11 00:02:10,960 --> 00:02:14,800 and deposited them as sands and gravels and muds. 12 00:02:17,760 --> 00:02:20,880 As the continents drifted over the globe and collided, 13 00:02:20,880 --> 00:02:25,360 new mountain ranges were built up and, in their turn, worn down. 14 00:02:31,760 --> 00:02:36,640 And throughout this immensity of time, the land remained sterile. 15 00:02:36,640 --> 00:02:39,800 Nowhere was there even the smallest of animals 16 00:02:39,800 --> 00:02:42,680 or the tiniest speck of green. 17 00:02:43,800 --> 00:02:48,320 If you condense the whole history of life, 18 00:02:48,320 --> 00:02:53,320 from its very beginnings until the present moment, into a year, 19 00:02:53,320 --> 00:02:56,920 then it wasn't until about the end of September 20 00:02:56,920 --> 00:03:01,240 that the first creatures of any size, jellyfish and so on, 21 00:03:01,240 --> 00:03:02,960 appeared in the sea. 22 00:03:02,960 --> 00:03:08,920 And it wasn't until the beginning of November that the first life, 23 00:03:08,920 --> 00:03:12,560 a few patches of green, appeared on land. 24 00:03:12,560 --> 00:03:16,000 Maybe at the edge of water, like this. 25 00:03:17,680 --> 00:03:20,600 These first plants were simple algae 26 00:03:20,600 --> 00:03:23,840 that had developed cell walls thick enough to enable them to survive 27 00:03:23,840 --> 00:03:26,960 on the moist boulders and gravels. 28 00:03:26,960 --> 00:03:31,040 Slowly, they spread over the lake beaches and sandspits, 29 00:03:31,040 --> 00:03:33,200 pioneers of the great revolution 30 00:03:33,200 --> 00:03:36,080 that was to lead to the greening of the earth. 31 00:03:48,040 --> 00:03:52,560 Moving out of water for the plants had presented a number of problems. 32 00:03:52,560 --> 00:03:55,760 One of the most serious was the question of support. 33 00:03:55,760 --> 00:04:01,240 In water, algae like this can grow into long strands, 34 00:04:01,240 --> 00:04:03,600 but robbed of the support of water, 35 00:04:03,600 --> 00:04:08,080 none has a sufficiently rigid stem to allow it to grow upright. 36 00:04:12,080 --> 00:04:15,720 So the first land plants had to remain lowly, 37 00:04:15,720 --> 00:04:20,640 forming flat skins like liverworts or cushions like mosses. 38 00:04:20,640 --> 00:04:25,160 All of them lived in wet, moist places and for a very good reason. 39 00:04:26,160 --> 00:04:29,720 Their ancestors, the algae, had reproduced in two ways, 40 00:04:29,720 --> 00:04:31,800 by budding and sexually, 41 00:04:31,800 --> 00:04:35,920 and the sexual method involved the sex cells actually swimming 42 00:04:35,920 --> 00:04:40,000 through water in order to find one another and fuse. 43 00:04:40,000 --> 00:04:44,720 Well, mosses retain very much the same sort of method. 44 00:04:44,720 --> 00:04:48,120 And it's this that keeps them tied to water. 45 00:04:48,120 --> 00:04:51,240 So they can only live in places where at the very least, 46 00:04:51,240 --> 00:04:53,960 it's wet during some time of the year, 47 00:04:53,960 --> 00:04:56,760 so that sexual reproduction can take place. 48 00:04:56,760 --> 00:05:01,680 Of course, in places like this, they are literally in their element. 49 00:05:17,960 --> 00:05:23,200 Mosses and liverworts like this both produce two kinds of sex cells. 50 00:05:25,880 --> 00:05:29,560 These outgrowths on the liverwort, only a few centimetres high, 51 00:05:29,560 --> 00:05:34,240 develop tiny mobile sperms which actively swim. 52 00:05:34,240 --> 00:05:38,640 These different growths contain larger static sex cells, the eggs. 53 00:05:39,680 --> 00:05:43,400 Under the microscope, you can see the eggs at the base of tiny tubules 54 00:05:43,400 --> 00:05:46,920 surrounded by a protective sheath of smaller cells. 55 00:05:50,200 --> 00:05:54,000 When the outgrowths are ripe and conditions sufficiently wet, 56 00:05:54,000 --> 00:05:56,080 fertilisation begins. 57 00:05:59,440 --> 00:06:01,600 The wriggling sperm are released 58 00:06:01,600 --> 00:06:05,080 and swim in the film of water that covers the plant. 59 00:06:18,200 --> 00:06:21,440 The sperm appears as a milky fluid. 60 00:06:36,240 --> 00:06:37,760 At the same time, 61 00:06:37,760 --> 00:06:41,240 the female part of the liverwort that bears the egg cells 62 00:06:41,240 --> 00:06:45,440 releases a special chemical that attracts the sperms. 63 00:06:47,480 --> 00:06:50,440 Eventually, they reach the female organs. 64 00:06:50,440 --> 00:06:53,600 Fertilisation occurs and the eggs develop, 65 00:06:53,600 --> 00:06:57,680 repeatedly dividing to produce a capsule full of microscopic grains - 66 00:06:57,680 --> 00:06:58,920 spores. 67 00:06:58,920 --> 00:07:03,640 When they are ripe and the weather is dry, the capsules burst. 68 00:07:10,000 --> 00:07:14,960 Each minute spore is capable of growing into a new liverwort plant. 69 00:07:19,160 --> 00:07:22,920 Mosses also reproduce by these two alternating methods. 70 00:07:22,920 --> 00:07:26,440 The sexual stage provides the variety of offspring necessary 71 00:07:26,440 --> 00:07:28,400 for continued evolution. 72 00:07:28,400 --> 00:07:31,240 The asexual spores can be carried on the wind 73 00:07:31,240 --> 00:07:34,360 to distribute the plant over great distances. 74 00:07:34,360 --> 00:07:37,720 The spore capsules of mosses are very varied in shape, 75 00:07:37,720 --> 00:07:39,800 and they have the most ingenious ways 76 00:07:39,800 --> 00:07:42,520 of making sure that they only release their contents 77 00:07:42,520 --> 00:07:45,800 when the weather is suitably warm and dry. 78 00:08:01,240 --> 00:08:03,400 Many species have detachable caps 79 00:08:03,400 --> 00:08:06,760 which are blown off before the spores can be released. 80 00:08:07,920 --> 00:08:11,480 And beneath, a perforated lid, like a pepper pot. 81 00:08:11,480 --> 00:08:16,280 And the wind will now carry the microscopic spores for miles. 82 00:08:29,320 --> 00:08:31,520 With such mechanisms as these, 83 00:08:31,520 --> 00:08:35,280 the first plants colonised the moist places of the world, 84 00:08:35,280 --> 00:08:38,520 and green carpets bordered the lakes and rivers. 85 00:08:43,200 --> 00:08:48,320 Into these miniature jungles came the first land animals. 86 00:08:53,520 --> 00:08:56,920 Millipedes, then as now, were vegetarians, 87 00:08:56,920 --> 00:09:00,880 and they must have found plenty to eat among the mosses and liverworts. 88 00:09:00,880 --> 00:09:03,840 The biggest of them today are only a few inches long, 89 00:09:03,840 --> 00:09:08,640 but many ancient forms that pioneered life on land grew very much larger. 90 00:09:08,640 --> 00:09:11,440 One, indeed, was as long as a cow. 91 00:09:21,160 --> 00:09:24,040 Millipedes were descended from sea-living creatures 92 00:09:24,040 --> 00:09:27,680 very distantly related to crustaceans such as shrimps. 93 00:09:27,680 --> 00:09:32,120 From them, they inherited segmented bodies and an external skeleton 94 00:09:32,120 --> 00:09:34,160 which gave them the necessary support 95 00:09:34,160 --> 00:09:37,120 so they could move just as well in air, on land, 96 00:09:37,120 --> 00:09:39,280 as their ancestors had done in the sea. 97 00:09:42,960 --> 00:09:45,200 But breathing was another matter. 98 00:09:45,200 --> 00:09:48,680 Their ancestors had extracted dissolved oxygen from water 99 00:09:48,680 --> 00:09:51,400 with feathery gills alongside each leg. 100 00:09:51,400 --> 00:09:53,760 But such things wouldn't work in air. 101 00:09:53,760 --> 00:09:57,760 Instead, the first millipedes developed a system of branching tubes 102 00:09:57,760 --> 00:10:02,280 within each segment, along which air diffuses to all parts of the body 103 00:10:02,280 --> 00:10:05,600 so that the tissues can absorb oxygen directly. 104 00:10:05,600 --> 00:10:07,880 These tubes open to the outside 105 00:10:07,880 --> 00:10:11,080 through a tiny pore on the side of each segment. 106 00:10:18,960 --> 00:10:24,160 But the amiable browsing millipedes didn't have the land to themselves for long. 107 00:10:24,160 --> 00:10:26,480 Very soon after they had colonised it, 108 00:10:26,480 --> 00:10:29,800 hunters came up from the sea to prey on them. 109 00:10:32,200 --> 00:10:35,440 These hunters are still today active, mostly at night. 110 00:10:36,680 --> 00:10:38,400 The scorpions. 111 00:10:48,480 --> 00:10:52,080 They had evolved from a different group of segmented sea creatures, 112 00:10:52,080 --> 00:10:56,680 but, again, they had an external skeleton which worked very effectively on land. 113 00:10:56,680 --> 00:11:01,000 With powerful nipping claws and poisoned stings on their tails, 114 00:11:01,000 --> 00:11:04,160 scorpions are well-armed and ferocious, 115 00:11:04,160 --> 00:11:07,840 actively seeking out their prey wherever it may be hiding. 116 00:11:15,320 --> 00:11:18,960 Another closely related group became mainly day hunters 117 00:11:18,960 --> 00:11:20,880 in the miniature forests. 118 00:11:20,880 --> 00:11:22,400 The spiders. 119 00:11:26,880 --> 00:11:30,680 Although their sea-living ancestors had many pairs of legs, 120 00:11:30,680 --> 00:11:35,000 spiders and scorpions have only four pairs. Better for speed. 121 00:11:35,000 --> 00:11:38,560 And spiders have lost most signs of division in their bodies, 122 00:11:38,560 --> 00:11:42,080 except for some very primitive ones that live in Southeast Asia. 123 00:11:42,080 --> 00:11:47,200 Their abdomens show the last relics of that ancestral segmentation. 124 00:11:49,160 --> 00:11:52,720 Early in their history, the spiders developed glands in the abdomen 125 00:11:52,720 --> 00:11:54,880 with which they produce silk. 126 00:11:59,200 --> 00:12:03,040 They use it in hunting, sometimes laying long trip lines, 127 00:12:03,040 --> 00:12:05,680 sometimes constructing dense sheets. 128 00:12:05,680 --> 00:12:10,440 And they manipulate the threads with modified limbs, the spinnerets. 129 00:13:04,320 --> 00:13:08,800 By the time it's finished, any small creature trying to make its way here 130 00:13:08,800 --> 00:13:11,200 will blunder into a silken trap. 131 00:13:11,200 --> 00:13:15,160 And while it's still entangled, the spider will pounce on it. 132 00:13:21,960 --> 00:13:26,320 Reproduction for all these land creatures presented new problems. 133 00:13:26,320 --> 00:13:30,280 Without water to transport sperm to egg, there was nothing for it - 134 00:13:30,280 --> 00:13:32,880 male and female had to get together. 135 00:13:34,600 --> 00:13:37,680 For the millipede, this presented no real danger. 136 00:13:37,680 --> 00:13:39,240 They are vegetarians, 137 00:13:39,240 --> 00:13:43,640 so when individuals meet, neither risks being eaten by the other. 138 00:13:43,640 --> 00:13:47,400 Their difficulties are entirely ones of manipulation. 139 00:13:54,800 --> 00:13:57,720 The sex glands of both male and female 140 00:13:57,720 --> 00:14:00,760 are at the base of the second pair of legs. 141 00:14:00,760 --> 00:14:04,160 The male has reached forward with his seventh pair of legs 142 00:14:04,160 --> 00:14:08,080 and collected from his second segment a little packet of sperm. 143 00:14:08,080 --> 00:14:11,680 Now, if only he can get it into exactly the right position 144 00:14:11,680 --> 00:14:15,040 alongside the female's pouch in HER second segment, 145 00:14:15,040 --> 00:14:16,720 all will be well. 146 00:14:32,480 --> 00:14:34,480 And there it goes. 147 00:14:45,760 --> 00:14:49,280 The scorpion's sexual problems are much more complicated 148 00:14:49,280 --> 00:14:51,400 and potentially dangerous. 149 00:14:51,400 --> 00:14:55,280 They are hunters and have to make sure one doesn't regard the other 150 00:14:55,280 --> 00:14:57,520 not as a mate but as a meal. 151 00:14:57,520 --> 00:14:59,280 Courtship is necessary, 152 00:14:59,280 --> 00:15:02,160 ritualised in a number of set movements. 153 00:15:03,640 --> 00:15:07,160 First, those dangerous pincers have to be neutralised. 154 00:15:41,400 --> 00:15:46,080 Now, with the pincers held out of action, more rituals follow. 155 00:15:58,680 --> 00:16:01,840 The heads of male and female come close 156 00:16:01,840 --> 00:16:03,320 and even touch. 157 00:16:11,440 --> 00:16:14,520 Now a strange heaving back and forth, 158 00:16:14,520 --> 00:16:18,040 which will eventually lead to the actual transfer of sperm. 159 00:16:18,040 --> 00:16:21,080 The male's sex gland is on the underside of his body, 160 00:16:21,080 --> 00:16:24,800 and from it, he has deposited a packet of sperm on the ground. 161 00:16:24,800 --> 00:16:27,640 Now he has to tug the female into a position 162 00:16:27,640 --> 00:16:31,120 where her sexual pouch is directly above it. 163 00:16:40,480 --> 00:16:42,920 If this ritual is not performed correctly, 164 00:16:42,920 --> 00:16:46,400 the scorpion's hunting instincts will not be pacified. 165 00:16:46,400 --> 00:16:50,360 It's a delicate balance, and here it seems to be going wrong, 166 00:16:50,360 --> 00:16:52,520 because this probing with the sting 167 00:16:52,520 --> 00:16:55,520 is probably more to do with aggression than with mating. 168 00:17:23,520 --> 00:17:24,920 And they break. 169 00:17:25,920 --> 00:17:28,720 Spiders have the same kind of problem. 170 00:17:28,720 --> 00:17:31,920 They, too, are hunters, and a male advancing on a female 171 00:17:31,920 --> 00:17:36,520 has to make quite sure she knows who he is and what his intentions are. 172 00:17:36,520 --> 00:17:40,680 The female jumping spider has sharp eyes, eight of them. 173 00:17:40,680 --> 00:17:43,880 He signals with his front legs as though his life depended on it, 174 00:17:43,880 --> 00:17:45,960 which indeed it does. 175 00:17:57,360 --> 00:17:59,080 She signals back... 176 00:18:10,160 --> 00:18:12,120 ..and he is encouraged. 177 00:18:16,920 --> 00:18:18,280 At close range, 178 00:18:18,280 --> 00:18:22,120 the male begins to use tactile signals rather than visual ones. 179 00:18:22,120 --> 00:18:25,480 He must constantly convince the female of his good intentions, 180 00:18:25,480 --> 00:18:30,040 for he has to achieve a more intimate and direct contact with the female 181 00:18:30,040 --> 00:18:32,200 than the male scorpion did. 182 00:18:32,200 --> 00:18:35,640 He's prepared for this encounter by spinning a tiny web of silk 183 00:18:35,640 --> 00:18:39,240 on which he's dropped some sperm from a gland under his abdomen. 184 00:18:39,240 --> 00:18:43,080 And he's taken up the sperm in two special feelers, the palps. 185 00:18:43,080 --> 00:18:47,520 Now he must reach over the female to pump sperm from one palp 186 00:18:47,520 --> 00:18:50,080 into one of the female's sexual pouches. 187 00:18:50,080 --> 00:18:53,600 It's rather like liquid being squeezed out of an eye dropper. 188 00:18:54,760 --> 00:18:56,440 And there it goes. 189 00:18:58,120 --> 00:19:02,560 Now the spider changes position to pass sperm from the other palp 190 00:19:02,560 --> 00:19:04,680 into the female's other sexual opening. 191 00:19:11,720 --> 00:19:16,120 The wolf spider is a larger and particularly aggressive species. 192 00:19:16,120 --> 00:19:18,600 He too is courting a female. 193 00:19:18,600 --> 00:19:21,040 His problem is especially dangerous here, 194 00:19:21,040 --> 00:19:23,120 because the female lives in a burrow 195 00:19:23,120 --> 00:19:26,000 from which she emerges only on hunting forays. 196 00:19:26,000 --> 00:19:30,440 It's hardly surprising, therefore, that he approaches with the greatest caution. 197 00:19:43,040 --> 00:19:46,000 At first, he uses a kind of semaphore. 198 00:19:46,000 --> 00:19:49,600 If he doesn't keep this up, the female may mistake him for prey 199 00:19:49,600 --> 00:19:51,640 and rush out and pounce on him. 200 00:20:09,640 --> 00:20:13,520 Within the confines of the burrow, visual signals are difficult, 201 00:20:13,520 --> 00:20:18,400 and so the male changes to delicate and sensitive strokings with his front legs. 202 00:20:30,160 --> 00:20:34,720 At last, she receives him and he can take up his risky mating position, 203 00:20:34,720 --> 00:20:37,520 reaching right round to the female's abdomen. 204 00:20:41,240 --> 00:20:44,040 The early jungles, filled with such creatures, 205 00:20:44,040 --> 00:20:46,040 were still only a few inches high, 206 00:20:46,040 --> 00:20:50,160 no more than a thick, moist carpet draping the sandspits and boulders. 207 00:20:50,160 --> 00:20:55,320 For plants like mosses and liverworts were still the only ones on land. 208 00:20:57,800 --> 00:21:03,600 And this is just about as big as any moss in the world ever grows. 209 00:21:04,640 --> 00:21:08,080 A series of isolated stems. 210 00:21:08,080 --> 00:21:13,280 It has no real roots. It just absorbs what moisture it requires through its surface. 211 00:21:13,280 --> 00:21:17,240 And it doesn't have true leaves. They're just simple scales. 212 00:21:17,240 --> 00:21:22,440 And to see why it's so frail, one has to look inside the stem. 213 00:21:24,640 --> 00:21:27,760 Sliced and examined under the electron microscope, 214 00:21:27,760 --> 00:21:29,920 this is how it appears in section. 215 00:21:29,920 --> 00:21:33,360 The cells are thin-walled with no rigidity to them, 216 00:21:33,360 --> 00:21:35,560 unable to support a tall plant. 217 00:21:35,560 --> 00:21:38,400 But that structure was soon to be strengthened. 218 00:21:39,960 --> 00:21:44,280 In the course of time, some plants developed that WERE able to grow upright 219 00:21:44,280 --> 00:21:45,680 and several feet tall. 220 00:21:45,680 --> 00:21:49,160 And the fossilised remains of some of the earliest of them 221 00:21:49,160 --> 00:21:53,760 have been found in the rocks of these bleak Welsh hillsides. 222 00:21:53,760 --> 00:21:55,600 To find fossils, 223 00:21:55,600 --> 00:21:59,640 you sometimes have to use violent methods. 224 00:22:33,080 --> 00:22:35,040 And here are some. 225 00:22:35,040 --> 00:22:38,840 They're just thin branching filaments, 226 00:22:38,840 --> 00:22:41,600 but they'll show up even better 227 00:22:41,600 --> 00:22:43,480 if I wet this slab. 228 00:22:47,160 --> 00:22:49,640 They look like tiny moss filaments, 229 00:22:49,640 --> 00:22:53,720 but when these flattened, 400-million-year-old stems are sectioned, 230 00:22:53,720 --> 00:22:57,680 the electron microscope reveals quite different cells. 231 00:22:57,680 --> 00:23:01,200 These have much thicker walls, forming tubes in the stem. 232 00:23:01,200 --> 00:23:04,600 A plumbing system, up which the plant draws water. 233 00:23:04,600 --> 00:23:07,680 And these new cells give the stem strength 234 00:23:07,680 --> 00:23:10,320 and the ability to grow tall. 235 00:23:10,320 --> 00:23:14,880 These very similar cells come not from a fossil plant 236 00:23:14,880 --> 00:23:17,520 but from a living one, from this plant, 237 00:23:17,520 --> 00:23:20,200 which grows on another Welsh hillside. 238 00:23:20,200 --> 00:23:22,880 It may look superficially like a moss. 239 00:23:22,880 --> 00:23:25,560 In fact, its common name is clubmoss, 240 00:23:25,560 --> 00:23:28,360 but actually, it's fundamentally different. 241 00:23:28,360 --> 00:23:32,120 By virtue of those tough, thick cells in its stem, 242 00:23:32,120 --> 00:23:34,880 it's much more rigid than any moss. 243 00:23:34,880 --> 00:23:38,800 Today, it only grows to that sort of height. 244 00:23:38,800 --> 00:23:44,160 But in the past, it grew to the size of trees and formed great forests. 245 00:23:45,400 --> 00:23:48,920 There were soon many kinds of plant with the new cell walls, 246 00:23:48,920 --> 00:23:52,800 and some of them, the horsetails, are still common worldwide. 247 00:23:52,800 --> 00:23:56,440 The highest, in South America, reaches three or four metres, 248 00:23:56,440 --> 00:24:01,160 but 300 million years ago, they grew to 30 metres, 90-feet tall. 249 00:24:01,160 --> 00:24:06,520 Then, as now, they developed a hard outer skin to prevent desiccation. 250 00:24:06,520 --> 00:24:09,760 Under the microscope, you can see minute pores 251 00:24:09,760 --> 00:24:11,600 through which the plant breathes, 252 00:24:11,600 --> 00:24:15,400 taking in carbon dioxide and giving out oxygen. 253 00:24:15,400 --> 00:24:19,040 And there was a third kind of plant that grew with the giant horsetails 254 00:24:19,040 --> 00:24:21,960 and the clubmoss trees in those first forests - 255 00:24:21,960 --> 00:24:23,600 tree ferns. 256 00:24:30,200 --> 00:24:35,720 But height for the horsetail and the tree fern accentuated yet again 257 00:24:35,720 --> 00:24:39,080 the problem of achieving sexual union 258 00:24:39,080 --> 00:24:42,240 with a male cell that has to swim. 259 00:24:43,280 --> 00:24:47,920 How could a microscopic cell swim from the top of THAT tree fern 260 00:24:47,920 --> 00:24:51,040 to the top of that one? Impossible. 261 00:24:51,040 --> 00:24:55,200 The structures that ARE up there produce spores, 262 00:24:55,200 --> 00:25:00,000 reproductive cells that do not require fertilisation in order to develop, 263 00:25:00,000 --> 00:25:03,680 just like those in the little capsules developed by mosses. 264 00:25:05,040 --> 00:25:09,440 The ferns produce their spores from structures beneath the fronds. 265 00:25:10,720 --> 00:25:14,320 Their shape and arrangement varies with each fern species. 266 00:25:50,840 --> 00:25:52,560 Ferns, like mosses, 267 00:25:52,560 --> 00:25:55,320 release their spores when the weather is dry, 268 00:25:55,320 --> 00:25:57,480 and the wind can carry them far and wide. 269 00:25:57,480 --> 00:26:01,240 Some fern spores are produced in cups at the end of curled strips, 270 00:26:01,240 --> 00:26:04,160 one side of which is woody and the other thin-walled. 271 00:26:04,160 --> 00:26:07,840 As these cups dry, they shrivel, pulling back the strip 272 00:26:07,840 --> 00:26:10,920 until the tension is too much, the strip snaps back 273 00:26:10,920 --> 00:26:13,200 and the spores are catapulted free. 274 00:26:22,120 --> 00:26:27,080 The spores have tiny spines and ridges that help them catch the wind. 275 00:26:32,440 --> 00:26:34,800 A few will fall on moist ground 276 00:26:34,800 --> 00:26:38,720 and then germinate to produce a different kind of plant altogether. 277 00:26:38,720 --> 00:26:42,560 This is the stage in the fern's life cycle that bears the sex cells. 278 00:26:42,560 --> 00:26:45,720 And this has had to remain small and close to the ground 279 00:26:45,720 --> 00:26:50,160 in order that its sperm can swim from plant to plant. 280 00:26:50,160 --> 00:26:53,720 When wet weather comes, the male organs release the sperm 281 00:26:53,720 --> 00:26:56,880 which swim by thrashing their thread-like tails. 282 00:27:00,640 --> 00:27:04,680 Hundreds of thousands are produced from the underside of the flat plant 283 00:27:04,680 --> 00:27:07,320 and are carried away by the rainwater. 284 00:27:15,840 --> 00:27:19,240 Eventually, some reach the female organs of the plant 285 00:27:19,240 --> 00:27:22,720 and swim up the tubes that lead to the egg cells. 286 00:27:30,240 --> 00:27:33,840 After fertilisation, a new growth develops from the egg, 287 00:27:33,840 --> 00:27:35,760 sending up a tiny stalk. 288 00:27:57,920 --> 00:28:02,600 These green shoots eventually grow tall and complete the cycle, 289 00:28:02,600 --> 00:28:06,600 becoming, once more, a familiar spore-bearing fern. 290 00:28:09,720 --> 00:28:12,760 Then, about 400 million years ago, 291 00:28:12,760 --> 00:28:16,320 as the forests began to rise, new animals appeared. 292 00:28:16,320 --> 00:28:19,320 These were descendants of the ancestral millipedes, 293 00:28:19,320 --> 00:28:22,240 and several kinds still survive today. 294 00:28:22,240 --> 00:28:26,800 This is a bristletail and it lives in soil worldwide. 295 00:28:28,360 --> 00:28:32,760 And this, the silverfish, that now often lives in houses. 296 00:28:32,760 --> 00:28:35,760 Faster than millipedes, they have fewer body segments 297 00:28:35,760 --> 00:28:39,560 and even fewer legs - just three pairs. 298 00:28:39,560 --> 00:28:41,800 They all feed on vegetable matter. 299 00:28:41,800 --> 00:28:46,920 But as plants grew taller, so leaves and spores became more inaccessible. 300 00:28:46,920 --> 00:28:49,200 And these little creatures doubtless 301 00:28:49,200 --> 00:28:52,120 clambered up the stems and trunks after them. 302 00:28:53,560 --> 00:28:56,160 The journey up must have been fairly easy, 303 00:28:56,160 --> 00:29:00,080 but getting down again, sometimes over upward-pointing spikes, 304 00:29:00,080 --> 00:29:01,840 may have been more laborious. 305 00:29:03,840 --> 00:29:07,840 Maybe that was the reason for a dramatic development. 306 00:29:09,120 --> 00:29:13,960 Some little creatures developed wings for flying from plant to plant. 307 00:29:16,960 --> 00:29:20,400 Just how wings evolved we can't be certain, 308 00:29:20,400 --> 00:29:24,400 but they may have first developed as tiny lobes on the back. 309 00:29:24,400 --> 00:29:28,320 Dragonflies today develop their wings in just this way, 310 00:29:28,320 --> 00:29:32,360 repeating millions of years of evolution in just one night. 311 00:30:31,440 --> 00:30:35,880 The wings are stretched taut by blood pumping into the veins. 312 00:30:43,320 --> 00:30:46,480 Later, the blood is drawn back into the body 313 00:30:46,480 --> 00:30:49,800 and the gauzy wings slowly dry and harden. 314 00:31:15,680 --> 00:31:18,840 Flight is the great achievement of the insects. 315 00:31:18,840 --> 00:31:21,400 They were the first creatures to take to the air 316 00:31:21,400 --> 00:31:26,080 and they were to have it almost to themselves for 100 million years. 317 00:31:32,720 --> 00:31:35,400 Dragonflies were among the first flyers, 318 00:31:35,400 --> 00:31:37,720 and they are still superb aeronauts. 319 00:31:37,720 --> 00:31:41,440 They can reach speeds of 20 miles, 30 kilometres an hour. 320 00:31:41,440 --> 00:31:43,200 They hunt in the air, 321 00:31:43,200 --> 00:31:46,560 holding their legs crooked in front of them like a basket. 322 00:31:46,560 --> 00:31:48,320 They even mate on the wing. 323 00:31:56,400 --> 00:31:58,920 The females lay their eggs in water. 324 00:32:01,600 --> 00:32:06,000 Their young, wingless larvae will grow up on the bottom of the pond, 325 00:32:06,000 --> 00:32:08,000 breathing through feathery gills 326 00:32:08,000 --> 00:32:11,200 and feeding on other small water-living creatures 327 00:32:11,200 --> 00:32:14,640 until the time comes for them too to climb up a reed 328 00:32:14,640 --> 00:32:16,320 and spread their wings. 329 00:32:18,120 --> 00:32:23,440 The dragonflies' smaller relatives, damselflies, also haunt ponds. 330 00:32:23,440 --> 00:32:26,280 The wings of these insects beat so rapidly 331 00:32:26,280 --> 00:32:30,480 that only a slow-motion camera can show clearly how they fly. 332 00:32:30,480 --> 00:32:34,640 This is the action slowed down 120 times. 333 00:32:34,640 --> 00:32:38,600 The insect gets lift on the downbeat of the wing by twisting it, 334 00:32:38,600 --> 00:32:41,640 so that the leading edge is inclined downwards. 335 00:32:41,640 --> 00:32:45,240 But at the bottom of each stroke the wing is twisted back 336 00:32:45,240 --> 00:32:48,120 so that it is effective on the upstroke as well. 337 00:32:48,120 --> 00:32:51,000 It's an intricate set of mechanical movements 338 00:32:51,000 --> 00:32:53,640 which man has never matched in the air. 339 00:32:53,640 --> 00:32:55,680 Here, the insect is hovering. 340 00:32:55,680 --> 00:32:59,320 The wings sweep alternately backwards and forwards, 341 00:32:59,320 --> 00:33:01,920 again changing angle at the end of each sweep 342 00:33:01,920 --> 00:33:04,880 in order to obtain lift on both strokes. 343 00:33:04,880 --> 00:33:07,560 Man has achieved something similar with a helicopter, 344 00:33:07,560 --> 00:33:09,640 whose blades rotate. 345 00:33:09,640 --> 00:33:12,240 The insect can't rotate its wings, 346 00:33:12,240 --> 00:33:16,000 but it's evolved a set of movements which are even more complex. 347 00:33:27,640 --> 00:33:31,880 The principal navigational equipment of dragonflies and damselflies 348 00:33:31,880 --> 00:33:33,680 are their superb eyes. 349 00:33:33,680 --> 00:33:35,680 Because they're so dependent on them, 350 00:33:35,680 --> 00:33:38,600 dragonflies normally fly only during the day. 351 00:33:41,880 --> 00:33:45,680 Today's splendid species are among the biggest of insects, 352 00:33:45,680 --> 00:33:49,480 but when the insects first had the air to themselves, 353 00:33:49,480 --> 00:33:51,880 the dragonflies grew gigantic 354 00:33:51,880 --> 00:33:56,280 and one appeared that had a wingspan of 70cm, over two feet. 355 00:33:56,280 --> 00:33:59,040 The largest insect that has ever existed. 356 00:34:01,680 --> 00:34:05,360 While all this was happening, some 300 million years ago, 357 00:34:05,360 --> 00:34:09,800 the plants themselves were on the brink of an important advance. 358 00:34:09,800 --> 00:34:14,160 This tiny sexual stage of the fern's life cycle 359 00:34:14,160 --> 00:34:16,000 is obviously very vulnerable. 360 00:34:16,000 --> 00:34:19,080 It can only live in moist conditions like these, 361 00:34:19,080 --> 00:34:23,360 and down on the ground it's easily cropped by plant-eating animals. 362 00:34:23,360 --> 00:34:27,200 It would obviously be much safer if this stage could take place 363 00:34:27,200 --> 00:34:29,480 up in the top of the tree. 364 00:34:29,480 --> 00:34:34,440 But that would require some way of transferring the sex cells 365 00:34:34,440 --> 00:34:36,080 from tree to tree. 366 00:34:36,080 --> 00:34:39,080 Well, they could be blown there by the wind. 367 00:34:39,080 --> 00:34:40,800 But there was then, as there is now, 368 00:34:40,800 --> 00:34:44,520 also a regular traffic in-between the tops of the trees. 369 00:34:44,520 --> 00:34:49,000 Insects that go up there to seek the spores as food 370 00:34:49,000 --> 00:34:51,240 and fly from one tree to another. 371 00:34:51,240 --> 00:34:54,440 They could take them. And that's what happened. 372 00:34:54,440 --> 00:34:58,960 New plants appeared in which the sexual generation remained fixed 373 00:34:58,960 --> 00:35:01,560 to the asexual tree stage. 374 00:35:01,560 --> 00:35:05,520 And one of the first of them was a plant like this, 375 00:35:05,520 --> 00:35:07,600 a cycad. 376 00:35:07,600 --> 00:35:10,480 Cycads bear two kinds of cones, 377 00:35:10,480 --> 00:35:14,960 each of which represent, in effect, part of the tiny sexual stage 378 00:35:14,960 --> 00:35:17,200 that once grew down on the ground. 379 00:35:17,200 --> 00:35:19,600 The male cones produce pollen, 380 00:35:19,600 --> 00:35:22,720 the grains of which germinate to produce the male cells, 381 00:35:22,720 --> 00:35:26,360 and the female cones contain the large egg cells. 382 00:35:28,440 --> 00:35:32,760 Insects help to transport the pollen from the male cone to the female, 383 00:35:32,760 --> 00:35:36,760 and there it produces a tube down which swims the sperm. 384 00:35:40,040 --> 00:35:43,840 At its tip, within the female cone, a drop of water appears, 385 00:35:43,840 --> 00:35:46,480 and in that the sperm swims, 386 00:35:46,480 --> 00:35:49,920 re-enacting the journeys made through the primordial seas 387 00:35:49,920 --> 00:35:53,120 by the sperm cells of their algal ancestors. 388 00:35:53,120 --> 00:35:56,560 Only after several days does it fuse with the egg. 389 00:35:58,800 --> 00:36:02,600 This cycad leaf is about 200 million years old. 390 00:36:02,600 --> 00:36:06,040 That's to say it was fossilised around the end of November 391 00:36:06,040 --> 00:36:08,200 in the Life On Earth year. 392 00:36:08,200 --> 00:36:12,560 And at that time a new and revolutionary plant had appeared 393 00:36:12,560 --> 00:36:15,440 that was growing alongside these cycads. 394 00:36:15,440 --> 00:36:19,760 It was the conifer, and this is one of its trunks. 395 00:36:19,760 --> 00:36:23,520 It's not wood, as you might think, but solid stone. 396 00:36:28,840 --> 00:36:33,160 I'm in the middle of one of the most spectacular deposits 397 00:36:33,160 --> 00:36:35,760 of plant fossils in the whole world. 398 00:36:35,760 --> 00:36:38,720 The Petrified Forest in Arizona. 399 00:36:38,720 --> 00:36:43,360 These conifers grew to over 200 feet tall 400 00:36:43,360 --> 00:36:48,400 and they stood in thick, dense, dark forests alongside the swamps 401 00:36:48,400 --> 00:36:50,080 where the cycads grew. 402 00:36:50,080 --> 00:36:53,840 And when the trunks fell, they often dropped into a river 403 00:36:53,840 --> 00:36:55,800 which swept them down here 404 00:36:55,800 --> 00:36:59,160 so that they formed great logjams around here. 405 00:36:59,160 --> 00:37:03,720 And then the river muds and sands and silts buried them. 406 00:37:03,720 --> 00:37:08,440 And the silts eventually formed mudstones like those over there. 407 00:37:08,440 --> 00:37:12,640 When the mudstones eroded away, as they have done here, 408 00:37:12,640 --> 00:37:16,520 they re-exposed these trunks that have been turned to stone. 409 00:38:29,760 --> 00:38:33,800 Conifers are built on very similar lines to the cycads, 410 00:38:33,800 --> 00:38:39,400 except that they have both the male and the female cone on the same tree. 411 00:38:41,080 --> 00:38:43,320 These are the male cones, 412 00:38:43,320 --> 00:38:46,320 and they use wind to transport their pollen. 413 00:38:46,320 --> 00:38:51,320 But to ensure that such a haphazard method of fertilisation is successful, 414 00:38:51,320 --> 00:38:54,480 they have to produce pollen in huge quantities. 415 00:38:54,480 --> 00:38:57,920 One cone may produce several million grains, 416 00:38:57,920 --> 00:39:01,640 and there are many thousands of cones on an average-sized tree. 417 00:39:07,360 --> 00:39:12,280 The female cones are fewer in number and grow on the same branches. 418 00:39:12,280 --> 00:39:16,040 They're small globes in conspicuous positions on the tips of shoots, 419 00:39:16,040 --> 00:39:18,960 where they have a good chance of receiving pollen. 420 00:39:26,800 --> 00:39:29,640 Pollen falling on the female cone 421 00:39:29,640 --> 00:39:32,640 is only the beginning of a very long process. 422 00:39:32,640 --> 00:39:37,000 It takes a whole year for the grains to grow down to the eggs, 423 00:39:37,000 --> 00:39:40,280 and at the end of that year the cone looks like that. 424 00:39:40,280 --> 00:39:42,760 But even that's not the end of things. 425 00:39:42,760 --> 00:39:46,800 During the next year, the cone grows still more, 426 00:39:46,800 --> 00:39:50,080 it develops wrappings around the fertilised eggs 427 00:39:50,080 --> 00:39:53,040 and then it dries out and opens up. 428 00:39:53,040 --> 00:39:57,440 Out drop small, neatly packaged brown objects. 429 00:39:57,440 --> 00:39:58,800 Seeds. 430 00:39:58,800 --> 00:40:02,720 They contain the first kind of plant eggs to have been fertilised 431 00:40:02,720 --> 00:40:04,680 without the help of water. 432 00:40:25,920 --> 00:40:29,040 Ancient though the conifers' technique of reproduction is, 433 00:40:29,040 --> 00:40:31,480 it has proved a huge success. 434 00:40:31,480 --> 00:40:36,640 Today, about a third of the forests in the world are formed by conifers. 435 00:40:36,640 --> 00:40:41,720 Firs, larches, cedars, pines. They're all members of this group. 436 00:40:53,160 --> 00:40:56,720 The biggest living organism of any kind is a conifer, 437 00:40:56,720 --> 00:40:59,200 the giant sequoia of California 438 00:40:59,200 --> 00:41:04,040 that grows to 112 metres - 367 feet high. 439 00:41:04,040 --> 00:41:08,440 Some have a diameter of 12 metres, 40 feet. 440 00:41:27,640 --> 00:41:31,760 Conifers have a special way of healing wounds to their trunks. 441 00:41:31,760 --> 00:41:34,120 They seal them with resin. 442 00:41:34,120 --> 00:41:38,320 When it first flows, it's runny, but it soon forms a sticky lump 443 00:41:38,320 --> 00:41:42,840 which not only covers the wound but incidentally acts as an insect trap. 444 00:41:46,080 --> 00:41:50,840 Lumps of resin from the ancient coniferous forests survive as amber, 445 00:41:50,840 --> 00:41:53,080 and in them are insects, 446 00:41:53,080 --> 00:41:56,120 as perfect now as the day when they blundered into the resin 447 00:41:56,120 --> 00:41:58,200 100 million years ago. 448 00:42:07,200 --> 00:42:11,080 From fossils like these, we know that the insects by that time 449 00:42:11,080 --> 00:42:14,080 had developed into an enormous variety of forms 450 00:42:14,080 --> 00:42:16,840 that swarmed through the trees and over the ground, 451 00:42:16,840 --> 00:42:19,160 feeding on every part of the plants. 452 00:42:19,160 --> 00:42:22,640 Pollen and fruit, leaves and wood, root and branch, 453 00:42:22,640 --> 00:42:24,240 just as they do today. 454 00:42:28,720 --> 00:42:33,800 Bugs stab stems with stiletto-like mouthparts to reach the sap. 455 00:42:39,120 --> 00:42:42,600 There are over 3,000 species of aphids alone, 456 00:42:42,600 --> 00:42:46,560 tapping this ready source of food in plants all over the world. 457 00:42:46,560 --> 00:42:49,440 All they have to do is to pierce the plant vessels. 458 00:42:49,440 --> 00:42:54,320 They don't even need to suck, such is the pressure of the sap within the stem. 459 00:42:55,920 --> 00:42:59,520 Locusts and grasshoppers chew the leaves. 460 00:43:04,440 --> 00:43:09,400 Beetles munch through cuticles and even manage to digest wood. 461 00:43:09,400 --> 00:43:12,080 Some insects not only eat plants, 462 00:43:12,080 --> 00:43:14,880 but in order to hide while doing so 463 00:43:14,880 --> 00:43:18,920 they've come to look like plants, like leaves and sticks. 464 00:43:29,200 --> 00:43:33,400 Hunters from the ground pursue the insects up into the trees. 465 00:43:34,480 --> 00:43:35,720 Spiders. 466 00:43:37,000 --> 00:43:41,320 But lying in ambush on trunks and on leaves has its limitations. 467 00:43:41,320 --> 00:43:42,960 Most insects fly. 468 00:43:45,760 --> 00:43:47,880 Spiders never developed wings, 469 00:43:47,880 --> 00:43:51,040 so they were unable to pursue their prey into the air. 470 00:43:51,040 --> 00:43:53,360 Instead, they set traps for them. 471 00:44:01,960 --> 00:44:06,200 The silk that they had spread in sheets and trip lines on the ground 472 00:44:06,200 --> 00:44:08,320 they now wove into nets, 473 00:44:08,320 --> 00:44:11,160 setting them across the insect flyways. 474 00:44:59,760 --> 00:45:02,800 With these elegant and varied constructions, 475 00:45:02,800 --> 00:45:06,680 spiders began to take a heavy toll of flying insects 476 00:45:06,680 --> 00:45:10,040 and today spiders are one of the most effective predators 477 00:45:10,040 --> 00:45:12,040 on the insect populations. 478 00:45:24,280 --> 00:45:29,440 The insects developed their flying skills in many different ways. 479 00:45:29,440 --> 00:45:33,280 The two pairs of wings used by the dragonflies and their relatives 480 00:45:33,280 --> 00:45:36,880 were also used by other insects. This is a lacewing. 481 00:45:43,240 --> 00:45:46,800 But this design was modified by other insects. 482 00:45:46,800 --> 00:45:51,160 The caddis-fly, not needing the speed of a dragonfly to catch prey, 483 00:45:51,160 --> 00:45:55,880 overlapped its two pairs of wings, producing a unified surface area. 484 00:45:57,480 --> 00:46:01,160 On the other hand, bees must have compact wings 485 00:46:01,160 --> 00:46:05,760 which can be neatly folded back when visiting flowers or in the hive. 486 00:46:05,760 --> 00:46:09,640 To get the right lift, their smaller wings must beat faster. 487 00:46:10,880 --> 00:46:14,000 They look as though they only have one pair of wings, 488 00:46:14,000 --> 00:46:15,920 but in fact they have two. 489 00:46:15,920 --> 00:46:19,680 They're hitched together to form what is virtually a single surface 490 00:46:19,680 --> 00:46:23,160 by a line of hooks along the front edge of the back wing. 491 00:46:26,760 --> 00:46:30,280 Other insects spend more time among dense foliage. 492 00:46:30,280 --> 00:46:33,720 The front wings of this bug have thickened bases to them 493 00:46:33,720 --> 00:46:38,000 which strengthen them and protect the rear ones when folded. 494 00:46:38,000 --> 00:46:40,440 Beetles have gone one stage further. 495 00:46:40,440 --> 00:46:43,400 Many burrow through litter and dense vegetation, 496 00:46:43,400 --> 00:46:48,200 and their front wings have become converted into protective covers. 497 00:46:48,200 --> 00:46:51,400 In order to lift the heavy body during flying, 498 00:46:51,400 --> 00:46:54,360 the operational wings have to be large. 499 00:46:54,360 --> 00:46:58,000 If they're to be protected when not in use, they have to be folded, 500 00:46:58,000 --> 00:47:01,080 and the trick is done with spring-loaded joints 501 00:47:01,080 --> 00:47:03,080 in the veins of the wings. 502 00:47:05,000 --> 00:47:09,160 Once in the air, the wing covers have to be held up out of the way. 503 00:47:09,160 --> 00:47:13,360 But they may also help a little in flight, acting as stabilisers, 504 00:47:13,360 --> 00:47:15,760 preventing rolling and yawing. 505 00:47:15,760 --> 00:47:18,680 Like many insects, this beetle increases lift 506 00:47:18,680 --> 00:47:21,880 by clapping its wings together at the top of the upstroke, 507 00:47:21,880 --> 00:47:24,880 thereby improving airflow over the wings. 508 00:47:29,240 --> 00:47:32,600 The chafer is the heavyweight of the insect fliers. 509 00:47:32,600 --> 00:47:36,640 Its wings beat comparatively slowly, about 40 times a second. 510 00:47:36,640 --> 00:47:39,320 And it's the least agile of insects in the air, 511 00:47:39,320 --> 00:47:43,040 ponderous and unable easily to bank and swerve. 512 00:47:43,040 --> 00:47:46,160 It holds its wing covers out of the way along its back 513 00:47:46,160 --> 00:47:49,200 and balances itself with outstretched legs. 514 00:47:49,200 --> 00:47:51,960 Its wing structure is tremendously strong, 515 00:47:51,960 --> 00:47:54,080 in order to support a heavy insect, 516 00:47:54,080 --> 00:47:57,680 and yet flexible enough to change its angle on each stroke 517 00:47:57,680 --> 00:48:01,400 and even fold back on itself when the insect stops flying. 518 00:48:07,080 --> 00:48:09,200 Even that feat is overshadowed 519 00:48:09,200 --> 00:48:12,360 by the achievement of the most skilled aeronauts of all, 520 00:48:12,360 --> 00:48:13,960 the flies. 521 00:48:13,960 --> 00:48:17,280 This one, the hoverfly, is perhaps the champion. 522 00:48:17,280 --> 00:48:20,640 It uses only one pair of wings, the front ones, 523 00:48:20,640 --> 00:48:24,560 which it keeps in perfect condition with frequent cleaning. 524 00:48:24,560 --> 00:48:27,720 It can hang absolutely stationary in the air, 525 00:48:27,720 --> 00:48:30,480 and does so even when it mates. 526 00:48:30,480 --> 00:48:35,000 It can compensate for any sudden current of wind to hold its position. 527 00:48:35,000 --> 00:48:39,240 It can fly backwards and dart off at great speed in any direction. 528 00:48:39,240 --> 00:48:40,960 And to perform these manoeuvres 529 00:48:40,960 --> 00:48:46,280 it beats its wings at the astonishing speed of 175 beats a second. 530 00:48:46,280 --> 00:48:50,360 A normal slow-motion camera still shows the wings as a blur. 531 00:48:52,040 --> 00:48:56,800 They control flight with a device which can be seen clearly in another fly, 532 00:48:56,800 --> 00:48:59,400 the crane-fly, or daddy-long-legs. 533 00:48:59,400 --> 00:49:02,880 Those two objects, like drumsticks, swinging up and down, 534 00:49:02,880 --> 00:49:07,440 are their back pair of wings after millions of years of evolution. 535 00:49:07,440 --> 00:49:10,520 They're jointed to the body just as the rear wings are, 536 00:49:10,520 --> 00:49:12,720 and they act like gyroscopes. 537 00:49:12,720 --> 00:49:17,360 By beating very fast, and here they're slowed down 120 times, 538 00:49:17,360 --> 00:49:20,240 they give the fly stability in the air. 539 00:49:20,240 --> 00:49:24,120 For, like gyroscopes in the automatic controls of an aeroplane, 540 00:49:24,120 --> 00:49:28,000 they enable the fly to be aware of the attitude of its body in the air 541 00:49:28,000 --> 00:49:31,520 and to detect when there's been any change in the flight path. 542 00:49:35,360 --> 00:49:38,840 Houseflies also have these "drumsticks", 543 00:49:38,840 --> 00:49:40,560 though they're much smaller. 544 00:49:40,560 --> 00:49:43,840 It's these that enable flies to perform such extraordinary 545 00:49:43,840 --> 00:49:46,080 and tantalising aerobatics. 546 00:49:48,640 --> 00:49:52,240 And the same organs perform similar functions for the hoverfly, 547 00:49:52,240 --> 00:49:55,480 giving it that superb flight control. 548 00:50:10,120 --> 00:50:15,280 The design of the insect body is particularly suited not to great size 549 00:50:15,280 --> 00:50:17,280 but to miniaturisation. 550 00:50:17,280 --> 00:50:21,960 The hoverfly is one of the most intricately constructed insects of all. 551 00:50:21,960 --> 00:50:25,040 A marvel of microscopic machinery 552 00:50:25,040 --> 00:50:27,920 that's built up from an egg in a few days 553 00:50:27,920 --> 00:50:30,480 and is often crushed beneath a thumb. 554 00:50:34,920 --> 00:50:36,840 The main developments of the insects 555 00:50:36,840 --> 00:50:40,720 took place at a comparatively early stage in the history of life on earth. 556 00:50:40,720 --> 00:50:44,800 At the time when these petrified forest trees were alive, 557 00:50:44,800 --> 00:50:46,680 200 million years ago, 558 00:50:46,680 --> 00:50:49,840 every single main type of insect that we know today 559 00:50:49,840 --> 00:50:51,640 was already in existence. 560 00:50:51,640 --> 00:50:55,600 Here, for example, is a piece of petrified wood, 561 00:50:55,600 --> 00:51:01,040 and before it was turned to stone some beetle had bored holes into it, 562 00:51:01,040 --> 00:51:04,280 just as beetles bore into dead wood today. 563 00:51:04,280 --> 00:51:07,560 And now the stage was set for a revolution, 564 00:51:07,560 --> 00:51:11,000 and one in which the insects were to play a crucial part. 565 00:51:11,000 --> 00:51:15,320 Charles Darwin called its history "an abominable mystery". 566 00:51:15,320 --> 00:51:19,280 Even today, we've only got a sketchy idea of just what happened. 567 00:51:19,280 --> 00:51:22,760 But some of the plants developed flowers. 568 00:51:22,760 --> 00:51:25,920 The woodlands and the lakes bloomed 569 00:51:25,920 --> 00:51:28,360 and colour came to the earth. 570 00:52:57,680 --> 00:52:59,720 Flowers became beautiful, 571 00:52:59,720 --> 00:53:03,880 not to delight the eye of man, but to attract insects. 572 00:53:03,880 --> 00:53:07,960 This led to some of the most intimate of all the relationships 573 00:53:07,960 --> 00:53:12,040 that have evolved between plants and insects - pollination.