1 00:00:02,000 --> 00:00:05,480 The natural world is full of extraordinary animals 2 00:00:05,480 --> 00:00:07,520 with amazing life histories. 3 00:00:07,520 --> 00:00:12,160 Yet, certain stories are more intriguing than others'. 4 00:00:14,160 --> 00:00:17,400 The mysteries of a butterfly's life cycle, 5 00:00:17,400 --> 00:00:20,600 or the strange biology of the emperor penguin. 6 00:00:20,600 --> 00:00:25,160 Some of these creatures were surrounded by fantastic 7 00:00:25,160 --> 00:00:27,520 myths and misunderstandings. 8 00:00:29,200 --> 00:00:32,440 Others have only recently revealed their secrets. 9 00:00:32,440 --> 00:00:37,240 These are the creatures that stand out from the crowd. 10 00:00:37,240 --> 00:00:41,720 The curiosities that I find particularly fascinating. 11 00:00:50,200 --> 00:00:52,160 At the turn of the 19th century, 12 00:00:52,160 --> 00:00:55,920 a German horse called Hans hit the headlines. 13 00:00:55,920 --> 00:00:57,800 It was claimed that he could perform 14 00:00:57,800 --> 00:01:00,400 complicated mathematical calculations. 15 00:01:01,600 --> 00:01:04,880 And Chinese records tell of a species of bamboo 16 00:01:04,880 --> 00:01:07,440 that seems able to count the years, 17 00:01:07,440 --> 00:01:11,360 for all individual plants growing in different parts of the world 18 00:01:11,360 --> 00:01:13,920 flower at exactly the same time. 19 00:01:15,200 --> 00:01:18,480 Can a horse and a plant truly count? 20 00:01:21,200 --> 00:01:25,120 In 1891, a retired German mathematics teacher 21 00:01:25,120 --> 00:01:30,880 called Wilhelm von Osten decided to do a very unusual thing. 22 00:01:30,880 --> 00:01:35,440 He began to teach maths to his horse, Hans. 23 00:01:36,640 --> 00:01:39,360 After four years, Hans was presented to the public 24 00:01:39,360 --> 00:01:42,320 to demonstrate his remarkable abilities. 25 00:01:42,320 --> 00:01:44,080 To everyone's amazement, 26 00:01:44,080 --> 00:01:47,360 he was able to count the number of people in the audience, 27 00:01:47,360 --> 00:01:51,000 perform complex arithmetic, read a clock, 28 00:01:51,000 --> 00:01:53,680 recognise and identify playing cards, 29 00:01:53,680 --> 00:01:56,640 and he knew the calendar of the whole year. 30 00:01:56,640 --> 00:02:00,840 To signal the correct answer, Hans tapped his hoof. 31 00:02:00,840 --> 00:02:03,760 He was accurate and consistent, 32 00:02:03,760 --> 00:02:08,600 and was declared worldwide as the first horse genius. 33 00:02:08,600 --> 00:02:11,200 It all seemed incredible. 34 00:02:14,400 --> 00:02:17,600 Could Hans the horse really count? 35 00:02:17,600 --> 00:02:21,400 And why might animals need to do so anyway? 36 00:02:21,400 --> 00:02:25,640 Well, it could help them keep track of the number within a group. 37 00:02:27,120 --> 00:02:30,240 They might need to know how many offspring they have. 38 00:02:32,120 --> 00:02:35,520 And, for many animals, it's an advantage to know 39 00:02:35,520 --> 00:02:39,120 if one quantity is smaller or larger than another. 40 00:02:43,040 --> 00:02:46,080 ROARING SOUNDS 41 00:02:46,080 --> 00:02:48,600 Studies of lions in the Serengeti 42 00:02:48,600 --> 00:02:51,800 suggest that they're able to count roars 43 00:02:51,800 --> 00:02:55,920 in order to assess the size of a competing pride. 44 00:03:00,840 --> 00:03:04,000 They estimate the number of challengers from the sound 45 00:03:04,000 --> 00:03:08,800 of the incoming roars, and compare this to the size of their own pride. 46 00:03:11,080 --> 00:03:15,680 They will only decide to defend themselves if their pride is larger. 47 00:03:16,840 --> 00:03:19,400 But it seems their counting is limited 48 00:03:19,400 --> 00:03:22,040 to no more than five or six roars. 49 00:03:25,040 --> 00:03:29,120 Could Hans the horse be drawing on his wild instincts 50 00:03:29,120 --> 00:03:31,000 to use numbers in this way? 51 00:03:33,160 --> 00:03:35,920 Wild horses live in small bands 52 00:03:35,920 --> 00:03:39,480 that can join up to form big herds of more than 100 animals. 53 00:03:41,160 --> 00:03:44,960 They have a dominant stallion, and a firm pecking order. 54 00:03:44,960 --> 00:03:48,120 Horses are not territorial, 55 00:03:48,120 --> 00:03:52,640 and have no great need to know the exact numbers in their own herd. 56 00:03:52,640 --> 00:03:54,360 Or another. 57 00:03:54,360 --> 00:03:58,080 But they do sometimes make judgments about quantity 58 00:03:58,080 --> 00:03:59,760 when choosing food. 59 00:04:02,680 --> 00:04:06,600 This basic ability to judge differences in amounts 60 00:04:06,600 --> 00:04:09,080 is the first step in the skill of counting. 61 00:04:09,080 --> 00:04:13,360 But what methods might animals use to assess numbers? 62 00:04:15,920 --> 00:04:18,080 There are several ways to keep count. 63 00:04:18,080 --> 00:04:21,200 We can count precisely to very high numbers, 64 00:04:21,200 --> 00:04:24,680 and have created number symbols that indicate exact amounts. 65 00:04:24,680 --> 00:04:29,640 So, we know that the number five, for example, indicates five objects. 66 00:04:29,640 --> 00:04:31,480 Even if we can't see them. 67 00:04:31,480 --> 00:04:35,120 Perhaps animals judge quantity in a similar way, 68 00:04:35,120 --> 00:04:38,240 and have their own pictorial shapes perhaps, in mind, 69 00:04:38,240 --> 00:04:40,320 that match an amount. 70 00:04:40,320 --> 00:04:44,200 Another idea is that animals judge differences in amount 71 00:04:44,200 --> 00:04:45,560 as an accumulation, 72 00:04:45,560 --> 00:04:48,560 just like filling a measuring tube with a liquid. 73 00:04:48,560 --> 00:04:52,000 Alternatively, the mind may have memory slots 74 00:04:52,000 --> 00:04:54,800 that store a limited number of objects 75 00:04:54,800 --> 00:04:58,120 in the same way as a filing cabinet stores cards. 76 00:04:58,120 --> 00:05:01,800 So, there could be several different ways in which animals 77 00:05:01,800 --> 00:05:03,880 judge quantity or amounts. 78 00:05:06,560 --> 00:05:11,520 Hans the horse appeared to count very precisely to high numbers. 79 00:05:11,520 --> 00:05:15,560 This seems an improbable feat for any animal. 80 00:05:17,440 --> 00:05:21,800 But, recently, an extraordinary discovery showed that an insect 81 00:05:21,800 --> 00:05:24,600 with a brain a fraction of the size of a horse's, 82 00:05:24,600 --> 00:05:27,000 can count with great accuracy. 83 00:05:27,000 --> 00:05:28,720 The ant. 84 00:05:32,000 --> 00:05:34,920 Ants are social animals that use scent trails 85 00:05:34,920 --> 00:05:38,120 and visual reference points to find their way around. 86 00:05:39,200 --> 00:05:42,200 But, in the desert, where scent evaporates, 87 00:05:42,200 --> 00:05:44,200 and the landscape is featureless, 88 00:05:44,200 --> 00:05:47,600 they nonetheless seem able to navigate successfully. 89 00:05:52,080 --> 00:05:57,520 In 2007, researchers investigated how Tunisian desert ants 90 00:05:57,520 --> 00:06:01,600 find their way home from foraging trips across barren plains. 91 00:06:01,600 --> 00:06:06,080 It's known that ants can measure and integrate two parameters - 92 00:06:06,080 --> 00:06:08,840 direction, and distance of travel. 93 00:06:08,840 --> 00:06:13,240 The desert sun helps an ant orientate its direction. 94 00:06:13,240 --> 00:06:15,760 But how do they measure distance? 95 00:06:15,760 --> 00:06:20,920 Experiments were performed to manipulate the ant's stride length 96 00:06:20,920 --> 00:06:24,800 to see if they were counting the number of footsteps that they took. 97 00:06:24,800 --> 00:06:26,960 Based on a featureless environment, 98 00:06:26,960 --> 00:06:31,560 ants learned to travel home to a set point. 99 00:06:32,560 --> 00:06:37,760 Then, stilt-like extensions were glued to their legs 100 00:06:37,760 --> 00:06:39,480 to lengthen their stride. 101 00:06:39,480 --> 00:06:42,720 These ants took the right number of steps, 102 00:06:42,720 --> 00:06:45,440 but, because of the increased leg length, 103 00:06:45,440 --> 00:06:48,520 they marched right past their goal. 104 00:06:48,520 --> 00:06:52,920 So, ants are able to log the number of steps that they take, 105 00:06:52,920 --> 00:06:56,240 perhaps not counting them in the way that we do, 106 00:06:56,240 --> 00:06:58,920 but they do have an internal counter. 107 00:07:02,000 --> 00:07:05,920 Unlike ants, horses have no need to count their steps, 108 00:07:05,920 --> 00:07:09,800 so it's unlikely that they have an internal pedometer. 109 00:07:09,800 --> 00:07:13,640 But they can, nonetheless, assess quantity. 110 00:07:14,640 --> 00:07:16,760 Wild horses are highly social. 111 00:07:16,760 --> 00:07:19,040 And, if one is harassed by flies, 112 00:07:19,040 --> 00:07:23,720 it will seek to join the largest available group for protection. 113 00:07:23,720 --> 00:07:29,080 So, horses can estimate numbers and recognise differences in size. 114 00:07:29,080 --> 00:07:31,520 But this is a much simpler ability 115 00:07:31,520 --> 00:07:34,920 than the counting that Hans the horse was doing. 116 00:07:37,840 --> 00:07:41,200 There seem to be no limit to the complexity of the calculations 117 00:07:41,200 --> 00:07:45,160 that Hans could compute, and his answers were precise. 118 00:07:45,160 --> 00:07:48,720 For many, this seemed too extraordinary to be true. 119 00:07:48,720 --> 00:07:52,680 In 1904, the German Board of Education was so intrigued 120 00:07:52,680 --> 00:07:55,640 that they formed a 13-strong commission 121 00:07:55,640 --> 00:08:00,400 to look closely at how Hans could perform such amazing feats. 122 00:08:00,400 --> 00:08:04,080 They wondered if Hans' owner was using trickery 123 00:08:04,080 --> 00:08:05,680 to feed him the answers. 124 00:08:06,720 --> 00:08:07,920 To test this, 125 00:08:07,920 --> 00:08:11,440 other members of the board were given questions and answers 126 00:08:11,440 --> 00:08:13,040 to pose to Hans. 127 00:08:13,040 --> 00:08:17,520 Incredibly, Hans still answered correctly. 128 00:08:17,520 --> 00:08:19,840 Eminent psychologist Oskar Pfungst 129 00:08:19,840 --> 00:08:22,880 then came to investigate Hans' skills further. 130 00:08:22,880 --> 00:08:27,000 And confirmed that he appeared to understand numerology, 131 00:08:27,000 --> 00:08:31,800 and the abstract idea of counting words associated with numbers. 132 00:08:35,200 --> 00:08:38,360 For Hans to perform complex mathematics, 133 00:08:38,360 --> 00:08:39,720 he would need to understand 134 00:08:39,720 --> 00:08:42,160 much more than just differences in quantities. 135 00:08:45,520 --> 00:08:48,800 He would need to recognise the fact that two 136 00:08:48,800 --> 00:08:50,760 is smaller than six. 137 00:08:52,000 --> 00:08:54,120 And that specific number symbols 138 00:08:54,120 --> 00:08:56,920 always go with the corresponding amounts. 139 00:08:58,520 --> 00:09:02,600 To count, he would also need to realise that numbers occur 140 00:09:02,600 --> 00:09:05,320 in a set, repeatable sequence. 141 00:09:05,320 --> 00:09:07,760 And that the last number counted 142 00:09:07,760 --> 00:09:10,400 represents the total of the whole set. 143 00:09:11,720 --> 00:09:16,080 In effect, that he'd answered the question, "How many do you have?" 144 00:09:19,080 --> 00:09:22,160 It seems that many animals have a sense of number, 145 00:09:22,160 --> 00:09:25,400 but few are conscious of an exact total. 146 00:09:26,440 --> 00:09:30,080 For most animals, the ability to recognise an amount, 147 00:09:30,080 --> 00:09:33,160 and to compare it to others, is all they need. 148 00:09:33,160 --> 00:09:37,360 Usually, a crude estimate, between more or less, 149 00:09:37,360 --> 00:09:40,160 or larger and smaller, is enough. 150 00:09:41,800 --> 00:09:44,080 But could horses be an exception? 151 00:09:44,080 --> 00:09:47,560 Could they have advanced counting skills? 152 00:09:51,720 --> 00:09:54,760 In 2009, experiments showed 153 00:09:54,760 --> 00:09:57,800 that horses could count to a certain level. 154 00:09:57,800 --> 00:10:00,480 I'm going to take false apples, 155 00:10:00,480 --> 00:10:03,440 ones that don't have a smell which might confuse the issue, 156 00:10:03,440 --> 00:10:05,360 and show the horse one... 157 00:10:06,720 --> 00:10:08,040 ..two... 158 00:10:08,040 --> 00:10:09,400 ..three... 159 00:10:10,640 --> 00:10:12,800 ..four in here. 160 00:10:12,800 --> 00:10:15,760 And one, two... 161 00:10:15,760 --> 00:10:17,360 ..in there. 162 00:10:17,360 --> 00:10:19,400 Now, then, which do you want? 163 00:10:23,720 --> 00:10:25,120 Thank you. 164 00:10:26,320 --> 00:10:27,760 Yes. 165 00:10:27,760 --> 00:10:29,400 Four. 166 00:10:31,000 --> 00:10:33,240 Repeated tests of 14 horses 167 00:10:33,240 --> 00:10:36,120 found that they consistently selected buckets 168 00:10:36,120 --> 00:10:38,840 that contained a higher number of apples. 169 00:10:38,840 --> 00:10:41,120 But that sense of number was limited - 170 00:10:41,120 --> 00:10:44,440 they could only keep track of numbers up to about six, 171 00:10:44,440 --> 00:10:46,160 and no higher. 172 00:10:46,160 --> 00:10:47,640 So, it seemed incredible 173 00:10:47,640 --> 00:10:51,560 that Hans the horse had such advanced counting skills. 174 00:10:51,560 --> 00:10:55,520 Perhaps he was being helped or trained in some way by his owner? 175 00:10:57,760 --> 00:11:02,120 There is little doubt that most horses are very intelligent animals. 176 00:11:02,120 --> 00:11:04,360 And, if they're given clear signals, 177 00:11:04,360 --> 00:11:08,440 they can indeed learn to perform complicated routines. 178 00:11:11,480 --> 00:11:14,040 Hans the horse was schooled for many years, 179 00:11:14,040 --> 00:11:17,680 so, perhaps, he had developed an advanced understanding of numbers 180 00:11:17,680 --> 00:11:20,360 when given clear instructions by his owner. 181 00:11:25,480 --> 00:11:26,800 In the wild, 182 00:11:26,800 --> 00:11:31,320 horses communicate with each other by using quite a rich body language. 183 00:11:33,120 --> 00:11:38,600 Wild Mustang use a complex silent one that scientists call Equus. 184 00:11:41,400 --> 00:11:43,480 It consists of a series of gestures, 185 00:11:43,480 --> 00:11:46,600 that are much like signing for the deaf. 186 00:11:48,680 --> 00:11:51,240 Every part of the horse conveys meaning. 187 00:11:51,240 --> 00:11:55,440 Especially the ears, tongues, lips, shoulders, and necks. 188 00:11:57,400 --> 00:12:00,040 They have the sensitivity and intelligence 189 00:12:00,040 --> 00:12:04,560 to interpret the tiniest of gestures, even breathing patterns. 190 00:12:04,560 --> 00:12:07,960 And, from this, they can judge each other's intentions. 191 00:12:11,440 --> 00:12:14,440 And it's this ability to sense subtle changes 192 00:12:14,440 --> 00:12:17,280 in physical and emotional states of those around them, 193 00:12:17,280 --> 00:12:20,040 that has made horses so responsive to training. 194 00:12:23,800 --> 00:12:28,000 So, did Hans the horse really understand numbers, 195 00:12:28,000 --> 00:12:29,840 or was something fishy going on? 196 00:12:31,360 --> 00:12:34,480 In 1907, after further research, 197 00:12:34,480 --> 00:12:37,280 Professor Oskar Pfungst discovered 198 00:12:37,280 --> 00:12:39,920 that Hans could only get the correct answer 199 00:12:39,920 --> 00:12:42,040 if the questioner knew the answer, 200 00:12:42,040 --> 00:12:45,640 and then, only if he could see his face. 201 00:12:45,640 --> 00:12:48,000 That was a significant discovery. 202 00:12:52,520 --> 00:12:56,840 I have my own clever horse, her name is Millie. 203 00:12:56,840 --> 00:13:00,480 Millie, what is two plus two? 204 00:13:02,120 --> 00:13:05,640 HORSE SCRAPES HOOF FOUR TIMES 205 00:13:05,640 --> 00:13:07,280 There you are. 206 00:13:07,280 --> 00:13:09,960 All right, let me ask you something more difficult, Millie. 207 00:13:09,960 --> 00:13:14,360 Millie, what is eight plus two minus seven? 208 00:13:15,400 --> 00:13:18,520 HORSE SCRAPES HOOF THREE TIMES 209 00:13:18,520 --> 00:13:21,000 Yes! Well done, Millie! 210 00:13:22,160 --> 00:13:23,480 There you are. 211 00:13:23,480 --> 00:13:26,400 Millie is, indeed, a clever horse, 212 00:13:26,400 --> 00:13:28,920 and appears to be able to do arithmetic. 213 00:13:28,920 --> 00:13:33,040 That's because, in fact, she can react to very subtle signals. 214 00:13:33,040 --> 00:13:36,680 If I take my hand off her and step forward... 215 00:13:37,680 --> 00:13:39,240 ..she paws. 216 00:13:40,840 --> 00:13:43,280 And, if I step back, she stops. 217 00:13:43,280 --> 00:13:49,160 So, eventually, it was shown that Hans was not a mathematician genius, 218 00:13:49,160 --> 00:13:53,760 he was just extremely skilled at following body language. 219 00:13:53,760 --> 00:13:57,480 Particularly those facial signals that questioners might give 220 00:13:57,480 --> 00:14:01,320 when they reach the right answer to the question. 221 00:14:01,320 --> 00:14:04,000 Some animals can, of course, count. 222 00:14:04,000 --> 00:14:05,440 Ants can. 223 00:14:05,440 --> 00:14:09,440 But, for most animals, knowing the difference between more or less 224 00:14:09,440 --> 00:14:11,440 is all they need for survival. 225 00:14:14,920 --> 00:14:19,360 Hans the horse baffled all the experts for many years. 226 00:14:19,360 --> 00:14:22,640 But true counting is, in fact, a complex concept 227 00:14:22,640 --> 00:14:25,080 that few animals grasp. 228 00:14:26,920 --> 00:14:29,040 There is a plant, however, 229 00:14:29,040 --> 00:14:32,080 that may be able to do so in a surprising way. 230 00:14:38,360 --> 00:14:41,240 It's the fastest-growing plant on earth. 231 00:14:41,240 --> 00:14:44,320 A type of grass we know as bamboo. 232 00:14:45,760 --> 00:14:50,840 Remarkably, some species only flower every 30 or 60 years. 233 00:14:50,840 --> 00:14:55,880 Others do so in cycles of over 100 years. 234 00:14:57,760 --> 00:15:00,320 But how do these plants measure time? 235 00:15:00,320 --> 00:15:02,560 Can they count down the years? 236 00:15:05,560 --> 00:15:08,400 Flowers that bloom in the spring, like these, 237 00:15:08,400 --> 00:15:12,120 are triggered to do so by a rise in temperature 238 00:15:12,120 --> 00:15:15,160 and an increase in the length of the days. 239 00:15:15,160 --> 00:15:19,000 But bamboos flower on an entirely different system. 240 00:15:19,000 --> 00:15:21,280 They don't do so annually, 241 00:15:21,280 --> 00:15:25,560 but at intervals which far exceed the length of a human life. 242 00:15:30,600 --> 00:15:33,280 The function of flowers is to reproduce. 243 00:15:33,280 --> 00:15:36,760 Bright, sweet-smelling blooms attract insects, 244 00:15:36,760 --> 00:15:40,760 which carry pollen from one plant to another, and so fertilise them. 245 00:15:44,120 --> 00:15:48,120 The flowers of bamboos are unassuming and drab. 246 00:15:48,120 --> 00:15:52,360 Because they're pollinated not by insects, but by the wind. 247 00:15:54,840 --> 00:15:58,480 Most grasses, indeed, have flowers that are so small 248 00:15:58,480 --> 00:16:00,400 that they tend to go unnoticed. 249 00:16:04,320 --> 00:16:06,760 Since their pollen is carried by the wind, 250 00:16:06,760 --> 00:16:10,120 they have no need for spectacular blooms. 251 00:16:20,640 --> 00:16:24,600 Bamboos are the largest members of the grass family, 252 00:16:24,600 --> 00:16:29,360 and they were introduced to Britain from Asia during the 1800s. 253 00:16:29,360 --> 00:16:31,960 Many were planted here in Kew. 254 00:16:31,960 --> 00:16:37,120 But, for over 100 years, nobody ever saw them flower. 255 00:16:43,080 --> 00:16:47,240 Bamboos grow in tropical or subtropical climates. 256 00:16:47,240 --> 00:16:51,160 They are, in fact, one of the most widespread plants. 257 00:16:51,160 --> 00:16:55,960 But, despite this, few people ever see them flower. 258 00:16:55,960 --> 00:17:00,120 The reason is, they only do so very rarely. 259 00:17:00,120 --> 00:17:04,320 We know this because early collectors and scholars 260 00:17:04,320 --> 00:17:08,880 have kept careful records that, in some cases, extend over centuries. 261 00:17:10,800 --> 00:17:13,960 Some are still preserved at Kew Gardens in London, 262 00:17:13,960 --> 00:17:17,680 which houses one of the largest historical collections of plants 263 00:17:17,680 --> 00:17:19,320 in the world. 264 00:17:22,520 --> 00:17:26,440 This is a specimen of the giant timber bamboo. 265 00:17:26,440 --> 00:17:29,680 Phyllostachys bambusoides. 266 00:17:29,680 --> 00:17:35,480 It was collected, as this label shows, in China in 1855. 267 00:17:36,640 --> 00:17:39,680 At the time, bamboo was clearly in flower. 268 00:17:39,680 --> 00:17:41,280 There they are. 269 00:17:41,280 --> 00:17:43,560 Quite small and obscure. 270 00:17:43,560 --> 00:17:46,880 Much like those of other grasses. 271 00:17:46,880 --> 00:17:49,440 And then, in the 1960s, 272 00:17:49,440 --> 00:17:52,920 Phyllostachys bambusoides bloomed again. 273 00:17:52,920 --> 00:17:54,760 And here is the evidence. 274 00:17:54,760 --> 00:17:58,160 This specimen is from 1961. 275 00:17:59,880 --> 00:18:02,760 These are just the records from European collectors. 276 00:18:02,760 --> 00:18:07,880 Chinese and Japanese accounts go back much further, over 1,000 years. 277 00:18:07,880 --> 00:18:12,560 Together, these records show that Phyllostachys bambusoides 278 00:18:12,560 --> 00:18:16,760 flowers in cycles of around 110 years. 279 00:18:20,200 --> 00:18:22,000 And there was another surprise. 280 00:18:24,200 --> 00:18:28,040 Phyllostachys is native to China and Japan. 281 00:18:28,040 --> 00:18:30,080 But, in the 19th century, 282 00:18:30,080 --> 00:18:34,160 it was introduced to other countries as an ornamental garden plant. 283 00:18:36,000 --> 00:18:39,600 And when it flowered, most recently in the 1960s, 284 00:18:39,600 --> 00:18:42,720 it came into bloom not just in its native Asia, 285 00:18:42,720 --> 00:18:46,240 but all around the world at the same time. 286 00:18:50,160 --> 00:18:52,840 It's a most bizarre life cycle. 287 00:18:54,000 --> 00:18:57,200 How do bamboos flower at the same time 288 00:18:57,200 --> 00:18:59,680 when separated by thousands of miles? 289 00:19:02,440 --> 00:19:07,680 The unusually long flowering cycle of bamboo was well-known in China. 290 00:19:07,680 --> 00:19:11,040 But there were other stories about its flowering 291 00:19:11,040 --> 00:19:14,840 that were picked up by European visitors trading in the Orient. 292 00:19:18,440 --> 00:19:23,400 Bamboo was valued by local people for its sturdiness and durability. 293 00:19:24,800 --> 00:19:27,080 The bamboo was held in such respect 294 00:19:27,080 --> 00:19:30,840 that it featured prominently in the paintings and calligraphy 295 00:19:30,840 --> 00:19:33,480 of ancient Chinese and Japanese artists. 296 00:19:36,960 --> 00:19:41,040 Although the bamboo is deeply rooted in local cultures, 297 00:19:41,040 --> 00:19:46,400 one part of the plant has instilled fear since the earliest times. 298 00:19:49,280 --> 00:19:53,440 An old Chinese proverb says when the bamboo flowers, 299 00:19:53,440 --> 00:19:56,120 it means either pestilence or famine. 300 00:19:57,320 --> 00:20:01,640 In 1898, a medical officer called John Mitford Atkinson, 301 00:20:01,640 --> 00:20:04,560 based at a government hospital in Hong Kong, 302 00:20:04,560 --> 00:20:08,240 sent some bamboo seeds to the keeper of the horarium here at Kew. 303 00:20:08,240 --> 00:20:10,240 And, with it, this letter. 304 00:20:10,240 --> 00:20:12,200 In it, he writes that, 305 00:20:12,200 --> 00:20:16,000 "Oddly enough, in the years that the bamboo flowered, 306 00:20:16,000 --> 00:20:19,840 "plague epidemics seemed always to ravage the colony." 307 00:20:21,040 --> 00:20:24,400 So, could there perhaps be some truth in these old sayings? 308 00:20:29,600 --> 00:20:31,640 So, here was another mystery. 309 00:20:33,360 --> 00:20:37,920 Not only does the bamboo flower very rarely, but when it does, 310 00:20:37,920 --> 00:20:40,760 it seemingly causes death and famine. 311 00:20:45,680 --> 00:20:48,560 The bamboo's life cycle is truly puzzling. 312 00:20:49,640 --> 00:20:53,720 How can a plant survive by only flowering every 100 years? 313 00:20:56,000 --> 00:20:59,720 The answer, it seems, can be found underground. 314 00:21:05,000 --> 00:21:08,040 This is the rhizome of a bamboo. 315 00:21:08,040 --> 00:21:12,120 It extends in all directions from the plant. 316 00:21:12,120 --> 00:21:14,760 Putting down roots, and sending up shoots. 317 00:21:14,760 --> 00:21:17,600 It's a very efficient way of spreading. 318 00:21:17,600 --> 00:21:19,880 As gardeners know to their cost, 319 00:21:19,880 --> 00:21:22,080 because you plant one patch of bamboo, 320 00:21:22,080 --> 00:21:25,640 and before you know where you are, it's taken over the entire garden. 321 00:21:28,360 --> 00:21:31,840 It's a way of spreading that has its advantages. 322 00:21:33,480 --> 00:21:37,240 Bamboos don't have to flower and seed every year. 323 00:21:37,240 --> 00:21:42,000 Instead, they grow a whole network of underground rhizomes, 324 00:21:42,000 --> 00:21:45,680 and put their energy straight into producing fast-growing 325 00:21:45,680 --> 00:21:47,840 and strong shoots. 326 00:21:53,000 --> 00:21:56,520 The stems emerge from the ground at their full width, 327 00:21:56,520 --> 00:21:59,880 and shoot to the sky like a periscope. 328 00:22:02,880 --> 00:22:05,840 In just a few weeks, they reach their full height. 329 00:22:07,720 --> 00:22:11,200 After this, they don't get any taller or thicker. 330 00:22:11,200 --> 00:22:15,960 They simply expand outwards, like a family or colony. 331 00:22:21,720 --> 00:22:24,280 This is a giant bamboo. 332 00:22:25,480 --> 00:22:30,520 Some species can reach the extraordinary height of 30 metres, 333 00:22:30,520 --> 00:22:33,760 and, to achieve that in a single season, 334 00:22:33,760 --> 00:22:38,280 they have to grow at the phenomenal rate of a metre a day. 335 00:22:38,280 --> 00:22:41,680 You can literally see them grow. 336 00:22:44,840 --> 00:22:46,960 But, when it comes to flowering, 337 00:22:46,960 --> 00:22:49,520 bamboos are one of the slowest. 338 00:22:49,520 --> 00:22:53,120 What could be the reason for this long interval? 339 00:22:57,320 --> 00:23:01,280 In Southeast Asia, there are trees that may give us a clue. 340 00:23:03,240 --> 00:23:06,200 They're called dipterocarps and, like bamboos, 341 00:23:06,200 --> 00:23:09,360 they also flower and seed synchronously, 342 00:23:09,360 --> 00:23:11,120 but on a shorter timescale. 343 00:23:12,400 --> 00:23:16,640 They produce seeds en masse every two to seven years. 344 00:23:21,560 --> 00:23:24,920 And when they do, they swamp the forest floor 345 00:23:24,920 --> 00:23:27,040 with an abundant supply of food. 346 00:23:28,640 --> 00:23:31,800 This attracts small mammals from all around. 347 00:23:36,760 --> 00:23:40,360 By fruiting at the same time, the trees ensure that, 348 00:23:40,360 --> 00:23:44,920 despite the many predators, some of the seeds will survive, 349 00:23:44,920 --> 00:23:47,120 and grow into new seedlings. 350 00:23:52,240 --> 00:23:55,360 Bamboo seeds are also highly nutritious, 351 00:23:55,360 --> 00:23:58,440 and lots of animals like to feed on them. 352 00:23:58,440 --> 00:24:01,600 Rats, mice, birds, monkeys, even elephants. 353 00:24:01,600 --> 00:24:05,800 They all devour huge numbers of the seeds, given the chance. 354 00:24:05,800 --> 00:24:08,160 So, bamboos may fare better 355 00:24:08,160 --> 00:24:11,640 if they synchronise their reproduction to flower and seed 356 00:24:11,640 --> 00:24:13,360 at the same time. 357 00:24:13,360 --> 00:24:16,400 By overwhelming their enemies with food, 358 00:24:16,400 --> 00:24:20,000 they can ensure that at least some of their seeds will survive. 359 00:24:21,960 --> 00:24:26,040 Once bamboos fell into this flowering cycle, 360 00:24:26,040 --> 00:24:29,960 any that flowered too early would lose all their seeds to predators. 361 00:24:34,800 --> 00:24:37,880 In years when bamboos do flower, 362 00:24:37,880 --> 00:24:41,480 there is often a boom in rodent populations. 363 00:24:44,440 --> 00:24:47,840 But once the small mammals have stripped the forest of seeds, 364 00:24:47,840 --> 00:24:52,560 they swarm into fields and villages to devour people's crops and grain. 365 00:24:54,080 --> 00:24:56,680 The rats carry dangerous diseases, 366 00:24:56,680 --> 00:25:00,880 and the result is often death and starvation among people. 367 00:25:02,360 --> 00:25:05,000 So, paradoxically, the bamboo, 368 00:25:05,000 --> 00:25:09,120 which provides an essential livelihood for so many people, 369 00:25:09,120 --> 00:25:12,480 at times causes death and devastation. 370 00:25:15,600 --> 00:25:18,520 When Atkinson made a connection between bamboo flowering 371 00:25:18,520 --> 00:25:22,160 and plague epidemics in Hong Kong during the 19th century, 372 00:25:22,160 --> 00:25:26,080 he had little idea of the true reasons behind this. 373 00:25:26,080 --> 00:25:28,880 But, as it turns out, he was right. 374 00:25:28,880 --> 00:25:32,560 And the old Chinese proverb contained a deadly prophecy. 375 00:25:36,880 --> 00:25:39,680 While the reason behind the synchronous flowering 376 00:25:39,680 --> 00:25:41,440 may have been explained, 377 00:25:41,440 --> 00:25:45,520 it's still a mystery as to how bamboos actually do it. 378 00:25:45,520 --> 00:25:48,920 Could the plants be counting down the years 379 00:25:48,920 --> 00:25:51,880 in order to all flower at the same time? 380 00:25:51,880 --> 00:25:57,000 It seems the answer may, once again, lie within their roots. 381 00:25:58,200 --> 00:26:00,400 The bamboo's unusual way of reproducing 382 00:26:00,400 --> 00:26:03,040 via a network of underground rhizomes 383 00:26:03,040 --> 00:26:08,120 means that most plants are, ultimately, from the same mother plant. 384 00:26:08,120 --> 00:26:11,320 These clumps have been shared across the world, 385 00:26:11,320 --> 00:26:14,040 and although they're now in different locations, 386 00:26:14,040 --> 00:26:16,880 they still carry the same genetic make-up. 387 00:26:16,880 --> 00:26:21,000 They are effectively clones of the parent plant. 388 00:26:21,000 --> 00:26:25,880 And it may be that they have some kind of internal memory 389 00:26:25,880 --> 00:26:27,960 that is also passed on. 390 00:26:31,160 --> 00:26:36,680 Scientists believe that the bamboo's roots contain some kind of clock 391 00:26:36,680 --> 00:26:40,880 that enables them to count the passing of the years. 392 00:26:40,880 --> 00:26:44,280 How they do that is still a mystery. 393 00:26:44,280 --> 00:26:48,360 But, nonetheless, there is an animal that might give us a clue. 394 00:26:52,600 --> 00:26:58,560 Periodical cicadas in North America spend 17 years underground, 395 00:26:58,560 --> 00:27:01,360 feeding on the sap from tree roots. 396 00:27:04,720 --> 00:27:06,880 Within the space of a few days, 397 00:27:06,880 --> 00:27:10,120 the whole population emerges in their millions. 398 00:27:11,120 --> 00:27:12,880 Their mission is to breed. 399 00:27:17,200 --> 00:27:21,680 But what triggers the cicadas to all emerge at exactly the same time 400 00:27:21,680 --> 00:27:23,840 every 17 years? 401 00:27:27,160 --> 00:27:28,960 We know that, when feeding underground, 402 00:27:28,960 --> 00:27:32,680 they can detect changes in the tree sap each spring, 403 00:27:32,680 --> 00:27:34,960 and so tell the passing of a year. 404 00:27:38,440 --> 00:27:42,480 Could it be that bamboos also count the years in this way? 405 00:27:46,320 --> 00:27:51,000 It's possible that bamboos register the passing of the seasons 406 00:27:51,000 --> 00:27:54,520 in a similar way by changes in their sap. 407 00:27:54,520 --> 00:27:56,000 We just don't know. 408 00:27:56,000 --> 00:27:59,360 But, while the exact mechanism remains a mystery, 409 00:27:59,360 --> 00:28:05,280 it may well prove that these time-measuring plants, bamboos, 410 00:28:05,280 --> 00:28:09,200 are the master mathematicians of the non-human world. 411 00:28:12,240 --> 00:28:15,720 True counting is very rare in nature. 412 00:28:17,000 --> 00:28:20,600 But some animals and plants achieve numerical feats 413 00:28:20,600 --> 00:28:23,600 that are astonishing in their own right.