0:00:02 > 0:00:05The natural world is full of extraordinary animals
0:00:05 > 0:00:07with amazing life histories.
0:00:07 > 0:00:12Yet, certain stories are more intriguing than others'.
0:00:14 > 0:00:17The mysteries of a butterfly's life cycle,
0:00:17 > 0:00:20or the strange biology of the emperor penguin.
0:00:20 > 0:00:25Some of these creatures were surrounded by fantastic
0:00:25 > 0:00:27myths and misunderstandings.
0:00:29 > 0:00:32Others have only recently revealed their secrets.
0:00:32 > 0:00:37These are the creatures that stand out from the crowd.
0:00:37 > 0:00:41The curiosities that I find particularly fascinating.
0:00:50 > 0:00:52At the turn of the 19th century,
0:00:52 > 0:00:55a German horse called Hans hit the headlines.
0:00:55 > 0:00:57It was claimed that he could perform
0:00:57 > 0:01:00complicated mathematical calculations.
0:01:01 > 0:01:04And Chinese records tell of a species of bamboo
0:01:04 > 0:01:07that seems able to count the years,
0:01:07 > 0:01:11for all individual plants growing in different parts of the world
0:01:11 > 0:01:13flower at exactly the same time.
0:01:15 > 0:01:18Can a horse and a plant truly count?
0:01:21 > 0:01:25In 1891, a retired German mathematics teacher
0:01:25 > 0:01:30called Wilhelm von Osten decided to do a very unusual thing.
0:01:30 > 0:01:35He began to teach maths to his horse, Hans.
0:01:36 > 0:01:39After four years, Hans was presented to the public
0:01:39 > 0:01:42to demonstrate his remarkable abilities.
0:01:42 > 0:01:44To everyone's amazement,
0:01:44 > 0:01:47he was able to count the number of people in the audience,
0:01:47 > 0:01:51perform complex arithmetic, read a clock,
0:01:51 > 0:01:53recognise and identify playing cards,
0:01:53 > 0:01:56and he knew the calendar of the whole year.
0:01:56 > 0:02:00To signal the correct answer, Hans tapped his hoof.
0:02:00 > 0:02:03He was accurate and consistent,
0:02:03 > 0:02:08and was declared worldwide as the first horse genius.
0:02:08 > 0:02:11It all seemed incredible.
0:02:14 > 0:02:17Could Hans the horse really count?
0:02:17 > 0:02:21And why might animals need to do so anyway?
0:02:21 > 0:02:25Well, it could help them keep track of the number within a group.
0:02:27 > 0:02:30They might need to know how many offspring they have.
0:02:32 > 0:02:35And, for many animals, it's an advantage to know
0:02:35 > 0:02:39if one quantity is smaller or larger than another.
0:02:43 > 0:02:46ROARING SOUNDS
0:02:46 > 0:02:48Studies of lions in the Serengeti
0:02:48 > 0:02:51suggest that they're able to count roars
0:02:51 > 0:02:55in order to assess the size of a competing pride.
0:03:00 > 0:03:04They estimate the number of challengers from the sound
0:03:04 > 0:03:08of the incoming roars, and compare this to the size of their own pride.
0:03:11 > 0:03:15They will only decide to defend themselves if their pride is larger.
0:03:16 > 0:03:19But it seems their counting is limited
0:03:19 > 0:03:22to no more than five or six roars.
0:03:25 > 0:03:29Could Hans the horse be drawing on his wild instincts
0:03:29 > 0:03:31to use numbers in this way?
0:03:33 > 0:03:35Wild horses live in small bands
0:03:35 > 0:03:39that can join up to form big herds of more than 100 animals.
0:03:41 > 0:03:44They have a dominant stallion, and a firm pecking order.
0:03:44 > 0:03:48Horses are not territorial,
0:03:48 > 0:03:52and have no great need to know the exact numbers in their own herd.
0:03:52 > 0:03:54Or another.
0:03:54 > 0:03:58But they do sometimes make judgments about quantity
0:03:58 > 0:03:59when choosing food.
0:04:02 > 0:04:06This basic ability to judge differences in amounts
0:04:06 > 0:04:09is the first step in the skill of counting.
0:04:09 > 0:04:13But what methods might animals use to assess numbers?
0:04:15 > 0:04:18There are several ways to keep count.
0:04:18 > 0:04:21We can count precisely to very high numbers,
0:04:21 > 0:04:24and have created number symbols that indicate exact amounts.
0:04:24 > 0:04:29So, we know that the number five, for example, indicates five objects.
0:04:29 > 0:04:31Even if we can't see them.
0:04:31 > 0:04:35Perhaps animals judge quantity in a similar way,
0:04:35 > 0:04:38and have their own pictorial shapes perhaps, in mind,
0:04:38 > 0:04:40that match an amount.
0:04:40 > 0:04:44Another idea is that animals judge differences in amount
0:04:44 > 0:04:45as an accumulation,
0:04:45 > 0:04:48just like filling a measuring tube with a liquid.
0:04:48 > 0:04:52Alternatively, the mind may have memory slots
0:04:52 > 0:04:54that store a limited number of objects
0:04:54 > 0:04:58in the same way as a filing cabinet stores cards.
0:04:58 > 0:05:01So, there could be several different ways in which animals
0:05:01 > 0:05:03judge quantity or amounts.
0:05:06 > 0:05:11Hans the horse appeared to count very precisely to high numbers.
0:05:11 > 0:05:15This seems an improbable feat for any animal.
0:05:17 > 0:05:21But, recently, an extraordinary discovery showed that an insect
0:05:21 > 0:05:24with a brain a fraction of the size of a horse's,
0:05:24 > 0:05:27can count with great accuracy.
0:05:27 > 0:05:28The ant.
0:05:32 > 0:05:34Ants are social animals that use scent trails
0:05:34 > 0:05:38and visual reference points to find their way around.
0:05:39 > 0:05:42But, in the desert, where scent evaporates,
0:05:42 > 0:05:44and the landscape is featureless,
0:05:44 > 0:05:47they nonetheless seem able to navigate successfully.
0:05:52 > 0:05:57In 2007, researchers investigated how Tunisian desert ants
0:05:57 > 0:06:01find their way home from foraging trips across barren plains.
0:06:01 > 0:06:06It's known that ants can measure and integrate two parameters -
0:06:06 > 0:06:08direction, and distance of travel.
0:06:08 > 0:06:13The desert sun helps an ant orientate its direction.
0:06:13 > 0:06:15But how do they measure distance?
0:06:15 > 0:06:20Experiments were performed to manipulate the ant's stride length
0:06:20 > 0:06:24to see if they were counting the number of footsteps that they took.
0:06:24 > 0:06:26Based on a featureless environment,
0:06:26 > 0:06:31ants learned to travel home to a set point.
0:06:32 > 0:06:37Then, stilt-like extensions were glued to their legs
0:06:37 > 0:06:39to lengthen their stride.
0:06:39 > 0:06:42These ants took the right number of steps,
0:06:42 > 0:06:45but, because of the increased leg length,
0:06:45 > 0:06:48they marched right past their goal.
0:06:48 > 0:06:52So, ants are able to log the number of steps that they take,
0:06:52 > 0:06:56perhaps not counting them in the way that we do,
0:06:56 > 0:06:58but they do have an internal counter.
0:07:02 > 0:07:05Unlike ants, horses have no need to count their steps,
0:07:05 > 0:07:09so it's unlikely that they have an internal pedometer.
0:07:09 > 0:07:13But they can, nonetheless, assess quantity.
0:07:14 > 0:07:16Wild horses are highly social.
0:07:16 > 0:07:19And, if one is harassed by flies,
0:07:19 > 0:07:23it will seek to join the largest available group for protection.
0:07:23 > 0:07:29So, horses can estimate numbers and recognise differences in size.
0:07:29 > 0:07:31But this is a much simpler ability
0:07:31 > 0:07:34than the counting that Hans the horse was doing.
0:07:37 > 0:07:41There seem to be no limit to the complexity of the calculations
0:07:41 > 0:07:45that Hans could compute, and his answers were precise.
0:07:45 > 0:07:48For many, this seemed too extraordinary to be true.
0:07:48 > 0:07:52In 1904, the German Board of Education was so intrigued
0:07:52 > 0:07:55that they formed a 13-strong commission
0:07:55 > 0:08:00to look closely at how Hans could perform such amazing feats.
0:08:00 > 0:08:04They wondered if Hans' owner was using trickery
0:08:04 > 0:08:05to feed him the answers.
0:08:06 > 0:08:07To test this,
0:08:07 > 0:08:11other members of the board were given questions and answers
0:08:11 > 0:08:13to pose to Hans.
0:08:13 > 0:08:17Incredibly, Hans still answered correctly.
0:08:17 > 0:08:19Eminent psychologist Oskar Pfungst
0:08:19 > 0:08:22then came to investigate Hans' skills further.
0:08:22 > 0:08:27And confirmed that he appeared to understand numerology,
0:08:27 > 0:08:31and the abstract idea of counting words associated with numbers.
0:08:35 > 0:08:38For Hans to perform complex mathematics,
0:08:38 > 0:08:39he would need to understand
0:08:39 > 0:08:42much more than just differences in quantities.
0:08:45 > 0:08:48He would need to recognise the fact that two
0:08:48 > 0:08:50is smaller than six.
0:08:52 > 0:08:54And that specific number symbols
0:08:54 > 0:08:56always go with the corresponding amounts.
0:08:58 > 0:09:02To count, he would also need to realise that numbers occur
0:09:02 > 0:09:05in a set, repeatable sequence.
0:09:05 > 0:09:07And that the last number counted
0:09:07 > 0:09:10represents the total of the whole set.
0:09:11 > 0:09:16In effect, that he'd answered the question, "How many do you have?"
0:09:19 > 0:09:22It seems that many animals have a sense of number,
0:09:22 > 0:09:25but few are conscious of an exact total.
0:09:26 > 0:09:30For most animals, the ability to recognise an amount,
0:09:30 > 0:09:33and to compare it to others, is all they need.
0:09:33 > 0:09:37Usually, a crude estimate, between more or less,
0:09:37 > 0:09:40or larger and smaller, is enough.
0:09:41 > 0:09:44But could horses be an exception?
0:09:44 > 0:09:47Could they have advanced counting skills?
0:09:51 > 0:09:54In 2009, experiments showed
0:09:54 > 0:09:57that horses could count to a certain level.
0:09:57 > 0:10:00I'm going to take false apples,
0:10:00 > 0:10:03ones that don't have a smell which might confuse the issue,
0:10:03 > 0:10:05and show the horse one...
0:10:06 > 0:10:08..two...
0:10:08 > 0:10:09..three...
0:10:10 > 0:10:12..four in here.
0:10:12 > 0:10:15And one, two...
0:10:15 > 0:10:17..in there.
0:10:17 > 0:10:19Now, then, which do you want?
0:10:23 > 0:10:25Thank you.
0:10:26 > 0:10:27Yes.
0:10:27 > 0:10:29Four.
0:10:31 > 0:10:33Repeated tests of 14 horses
0:10:33 > 0:10:36found that they consistently selected buckets
0:10:36 > 0:10:38that contained a higher number of apples.
0:10:38 > 0:10:41But that sense of number was limited -
0:10:41 > 0:10:44they could only keep track of numbers up to about six,
0:10:44 > 0:10:46and no higher.
0:10:46 > 0:10:47So, it seemed incredible
0:10:47 > 0:10:51that Hans the horse had such advanced counting skills.
0:10:51 > 0:10:55Perhaps he was being helped or trained in some way by his owner?
0:10:57 > 0:11:02There is little doubt that most horses are very intelligent animals.
0:11:02 > 0:11:04And, if they're given clear signals,
0:11:04 > 0:11:08they can indeed learn to perform complicated routines.
0:11:11 > 0:11:14Hans the horse was schooled for many years,
0:11:14 > 0:11:17so, perhaps, he had developed an advanced understanding of numbers
0:11:17 > 0:11:20when given clear instructions by his owner.
0:11:25 > 0:11:26In the wild,
0:11:26 > 0:11:31horses communicate with each other by using quite a rich body language.
0:11:33 > 0:11:38Wild Mustang use a complex silent one that scientists call Equus.
0:11:41 > 0:11:43It consists of a series of gestures,
0:11:43 > 0:11:46that are much like signing for the deaf.
0:11:48 > 0:11:51Every part of the horse conveys meaning.
0:11:51 > 0:11:55Especially the ears, tongues, lips, shoulders, and necks.
0:11:57 > 0:12:00They have the sensitivity and intelligence
0:12:00 > 0:12:04to interpret the tiniest of gestures, even breathing patterns.
0:12:04 > 0:12:07And, from this, they can judge each other's intentions.
0:12:11 > 0:12:14And it's this ability to sense subtle changes
0:12:14 > 0:12:17in physical and emotional states of those around them,
0:12:17 > 0:12:20that has made horses so responsive to training.
0:12:23 > 0:12:28So, did Hans the horse really understand numbers,
0:12:28 > 0:12:29or was something fishy going on?
0:12:31 > 0:12:34In 1907, after further research,
0:12:34 > 0:12:37Professor Oskar Pfungst discovered
0:12:37 > 0:12:39that Hans could only get the correct answer
0:12:39 > 0:12:42if the questioner knew the answer,
0:12:42 > 0:12:45and then, only if he could see his face.
0:12:45 > 0:12:48That was a significant discovery.
0:12:52 > 0:12:56I have my own clever horse, her name is Millie.
0:12:56 > 0:13:00Millie, what is two plus two?
0:13:02 > 0:13:05HORSE SCRAPES HOOF FOUR TIMES
0:13:05 > 0:13:07There you are.
0:13:07 > 0:13:09All right, let me ask you something more difficult, Millie.
0:13:09 > 0:13:14Millie, what is eight plus two minus seven?
0:13:15 > 0:13:18HORSE SCRAPES HOOF THREE TIMES
0:13:18 > 0:13:21Yes! Well done, Millie!
0:13:22 > 0:13:23There you are.
0:13:23 > 0:13:26Millie is, indeed, a clever horse,
0:13:26 > 0:13:28and appears to be able to do arithmetic.
0:13:28 > 0:13:33That's because, in fact, she can react to very subtle signals.
0:13:33 > 0:13:36If I take my hand off her and step forward...
0:13:37 > 0:13:39..she paws.
0:13:40 > 0:13:43And, if I step back, she stops.
0:13:43 > 0:13:49So, eventually, it was shown that Hans was not a mathematician genius,
0:13:49 > 0:13:53he was just extremely skilled at following body language.
0:13:53 > 0:13:57Particularly those facial signals that questioners might give
0:13:57 > 0:14:01when they reach the right answer to the question.
0:14:01 > 0:14:04Some animals can, of course, count.
0:14:04 > 0:14:05Ants can.
0:14:05 > 0:14:09But, for most animals, knowing the difference between more or less
0:14:09 > 0:14:11is all they need for survival.
0:14:14 > 0:14:19Hans the horse baffled all the experts for many years.
0:14:19 > 0:14:22But true counting is, in fact, a complex concept
0:14:22 > 0:14:25that few animals grasp.
0:14:26 > 0:14:29There is a plant, however,
0:14:29 > 0:14:32that may be able to do so in a surprising way.
0:14:38 > 0:14:41It's the fastest-growing plant on earth.
0:14:41 > 0:14:44A type of grass we know as bamboo.
0:14:45 > 0:14:50Remarkably, some species only flower every 30 or 60 years.
0:14:50 > 0:14:55Others do so in cycles of over 100 years.
0:14:57 > 0:15:00But how do these plants measure time?
0:15:00 > 0:15:02Can they count down the years?
0:15:05 > 0:15:08Flowers that bloom in the spring, like these,
0:15:08 > 0:15:12are triggered to do so by a rise in temperature
0:15:12 > 0:15:15and an increase in the length of the days.
0:15:15 > 0:15:19But bamboos flower on an entirely different system.
0:15:19 > 0:15:21They don't do so annually,
0:15:21 > 0:15:25but at intervals which far exceed the length of a human life.
0:15:30 > 0:15:33The function of flowers is to reproduce.
0:15:33 > 0:15:36Bright, sweet-smelling blooms attract insects,
0:15:36 > 0:15:40which carry pollen from one plant to another, and so fertilise them.
0:15:44 > 0:15:48The flowers of bamboos are unassuming and drab.
0:15:48 > 0:15:52Because they're pollinated not by insects, but by the wind.
0:15:54 > 0:15:58Most grasses, indeed, have flowers that are so small
0:15:58 > 0:16:00that they tend to go unnoticed.
0:16:04 > 0:16:06Since their pollen is carried by the wind,
0:16:06 > 0:16:10they have no need for spectacular blooms.
0:16:20 > 0:16:24Bamboos are the largest members of the grass family,
0:16:24 > 0:16:29and they were introduced to Britain from Asia during the 1800s.
0:16:29 > 0:16:31Many were planted here in Kew.
0:16:31 > 0:16:37But, for over 100 years, nobody ever saw them flower.
0:16:43 > 0:16:47Bamboos grow in tropical or subtropical climates.
0:16:47 > 0:16:51They are, in fact, one of the most widespread plants.
0:16:51 > 0:16:55But, despite this, few people ever see them flower.
0:16:55 > 0:17:00The reason is, they only do so very rarely.
0:17:00 > 0:17:04We know this because early collectors and scholars
0:17:04 > 0:17:08have kept careful records that, in some cases, extend over centuries.
0:17:10 > 0:17:13Some are still preserved at Kew Gardens in London,
0:17:13 > 0:17:17which houses one of the largest historical collections of plants
0:17:17 > 0:17:19in the world.
0:17:22 > 0:17:26This is a specimen of the giant timber bamboo.
0:17:26 > 0:17:29Phyllostachys bambusoides.
0:17:29 > 0:17:35It was collected, as this label shows, in China in 1855.
0:17:36 > 0:17:39At the time, bamboo was clearly in flower.
0:17:39 > 0:17:41There they are.
0:17:41 > 0:17:43Quite small and obscure.
0:17:43 > 0:17:46Much like those of other grasses.
0:17:46 > 0:17:49And then, in the 1960s,
0:17:49 > 0:17:52Phyllostachys bambusoides bloomed again.
0:17:52 > 0:17:54And here is the evidence.
0:17:54 > 0:17:58This specimen is from 1961.
0:17:59 > 0:18:02These are just the records from European collectors.
0:18:02 > 0:18:07Chinese and Japanese accounts go back much further, over 1,000 years.
0:18:07 > 0:18:12Together, these records show that Phyllostachys bambusoides
0:18:12 > 0:18:16flowers in cycles of around 110 years.
0:18:20 > 0:18:22And there was another surprise.
0:18:24 > 0:18:28Phyllostachys is native to China and Japan.
0:18:28 > 0:18:30But, in the 19th century,
0:18:30 > 0:18:34it was introduced to other countries as an ornamental garden plant.
0:18:36 > 0:18:39And when it flowered, most recently in the 1960s,
0:18:39 > 0:18:42it came into bloom not just in its native Asia,
0:18:42 > 0:18:46but all around the world at the same time.
0:18:50 > 0:18:52It's a most bizarre life cycle.
0:18:54 > 0:18:57How do bamboos flower at the same time
0:18:57 > 0:18:59when separated by thousands of miles?
0:19:02 > 0:19:07The unusually long flowering cycle of bamboo was well-known in China.
0:19:07 > 0:19:11But there were other stories about its flowering
0:19:11 > 0:19:14that were picked up by European visitors trading in the Orient.
0:19:18 > 0:19:23Bamboo was valued by local people for its sturdiness and durability.
0:19:24 > 0:19:27The bamboo was held in such respect
0:19:27 > 0:19:30that it featured prominently in the paintings and calligraphy
0:19:30 > 0:19:33of ancient Chinese and Japanese artists.
0:19:36 > 0:19:41Although the bamboo is deeply rooted in local cultures,
0:19:41 > 0:19:46one part of the plant has instilled fear since the earliest times.
0:19:49 > 0:19:53An old Chinese proverb says when the bamboo flowers,
0:19:53 > 0:19:56it means either pestilence or famine.
0:19:57 > 0:20:01In 1898, a medical officer called John Mitford Atkinson,
0:20:01 > 0:20:04based at a government hospital in Hong Kong,
0:20:04 > 0:20:08sent some bamboo seeds to the keeper of the horarium here at Kew.
0:20:08 > 0:20:10And, with it, this letter.
0:20:10 > 0:20:12In it, he writes that,
0:20:12 > 0:20:16"Oddly enough, in the years that the bamboo flowered,
0:20:16 > 0:20:19"plague epidemics seemed always to ravage the colony."
0:20:21 > 0:20:24So, could there perhaps be some truth in these old sayings?
0:20:29 > 0:20:31So, here was another mystery.
0:20:33 > 0:20:37Not only does the bamboo flower very rarely, but when it does,
0:20:37 > 0:20:40it seemingly causes death and famine.
0:20:45 > 0:20:48The bamboo's life cycle is truly puzzling.
0:20:49 > 0:20:53How can a plant survive by only flowering every 100 years?
0:20:56 > 0:20:59The answer, it seems, can be found underground.
0:21:05 > 0:21:08This is the rhizome of a bamboo.
0:21:08 > 0:21:12It extends in all directions from the plant.
0:21:12 > 0:21:14Putting down roots, and sending up shoots.
0:21:14 > 0:21:17It's a very efficient way of spreading.
0:21:17 > 0:21:19As gardeners know to their cost,
0:21:19 > 0:21:22because you plant one patch of bamboo,
0:21:22 > 0:21:25and before you know where you are, it's taken over the entire garden.
0:21:28 > 0:21:31It's a way of spreading that has its advantages.
0:21:33 > 0:21:37Bamboos don't have to flower and seed every year.
0:21:37 > 0:21:42Instead, they grow a whole network of underground rhizomes,
0:21:42 > 0:21:45and put their energy straight into producing fast-growing
0:21:45 > 0:21:47and strong shoots.
0:21:53 > 0:21:56The stems emerge from the ground at their full width,
0:21:56 > 0:21:59and shoot to the sky like a periscope.
0:22:02 > 0:22:05In just a few weeks, they reach their full height.
0:22:07 > 0:22:11After this, they don't get any taller or thicker.
0:22:11 > 0:22:15They simply expand outwards, like a family or colony.
0:22:21 > 0:22:24This is a giant bamboo.
0:22:25 > 0:22:30Some species can reach the extraordinary height of 30 metres,
0:22:30 > 0:22:33and, to achieve that in a single season,
0:22:33 > 0:22:38they have to grow at the phenomenal rate of a metre a day.
0:22:38 > 0:22:41You can literally see them grow.
0:22:44 > 0:22:46But, when it comes to flowering,
0:22:46 > 0:22:49bamboos are one of the slowest.
0:22:49 > 0:22:53What could be the reason for this long interval?
0:22:57 > 0:23:01In Southeast Asia, there are trees that may give us a clue.
0:23:03 > 0:23:06They're called dipterocarps and, like bamboos,
0:23:06 > 0:23:09they also flower and seed synchronously,
0:23:09 > 0:23:11but on a shorter timescale.
0:23:12 > 0:23:16They produce seeds en masse every two to seven years.
0:23:21 > 0:23:24And when they do, they swamp the forest floor
0:23:24 > 0:23:27with an abundant supply of food.
0:23:28 > 0:23:31This attracts small mammals from all around.
0:23:36 > 0:23:40By fruiting at the same time, the trees ensure that,
0:23:40 > 0:23:44despite the many predators, some of the seeds will survive,
0:23:44 > 0:23:47and grow into new seedlings.
0:23:52 > 0:23:55Bamboo seeds are also highly nutritious,
0:23:55 > 0:23:58and lots of animals like to feed on them.
0:23:58 > 0:24:01Rats, mice, birds, monkeys, even elephants.
0:24:01 > 0:24:05They all devour huge numbers of the seeds, given the chance.
0:24:05 > 0:24:08So, bamboos may fare better
0:24:08 > 0:24:11if they synchronise their reproduction to flower and seed
0:24:11 > 0:24:13at the same time.
0:24:13 > 0:24:16By overwhelming their enemies with food,
0:24:16 > 0:24:20they can ensure that at least some of their seeds will survive.
0:24:21 > 0:24:26Once bamboos fell into this flowering cycle,
0:24:26 > 0:24:29any that flowered too early would lose all their seeds to predators.
0:24:34 > 0:24:37In years when bamboos do flower,
0:24:37 > 0:24:41there is often a boom in rodent populations.
0:24:44 > 0:24:47But once the small mammals have stripped the forest of seeds,
0:24:47 > 0:24:52they swarm into fields and villages to devour people's crops and grain.
0:24:54 > 0:24:56The rats carry dangerous diseases,
0:24:56 > 0:25:00and the result is often death and starvation among people.
0:25:02 > 0:25:05So, paradoxically, the bamboo,
0:25:05 > 0:25:09which provides an essential livelihood for so many people,
0:25:09 > 0:25:12at times causes death and devastation.
0:25:15 > 0:25:18When Atkinson made a connection between bamboo flowering
0:25:18 > 0:25:22and plague epidemics in Hong Kong during the 19th century,
0:25:22 > 0:25:26he had little idea of the true reasons behind this.
0:25:26 > 0:25:28But, as it turns out, he was right.
0:25:28 > 0:25:32And the old Chinese proverb contained a deadly prophecy.
0:25:36 > 0:25:39While the reason behind the synchronous flowering
0:25:39 > 0:25:41may have been explained,
0:25:41 > 0:25:45it's still a mystery as to how bamboos actually do it.
0:25:45 > 0:25:48Could the plants be counting down the years
0:25:48 > 0:25:51in order to all flower at the same time?
0:25:51 > 0:25:57It seems the answer may, once again, lie within their roots.
0:25:58 > 0:26:00The bamboo's unusual way of reproducing
0:26:00 > 0:26:03via a network of underground rhizomes
0:26:03 > 0:26:08means that most plants are, ultimately, from the same mother plant.
0:26:08 > 0:26:11These clumps have been shared across the world,
0:26:11 > 0:26:14and although they're now in different locations,
0:26:14 > 0:26:16they still carry the same genetic make-up.
0:26:16 > 0:26:21They are effectively clones of the parent plant.
0:26:21 > 0:26:25And it may be that they have some kind of internal memory
0:26:25 > 0:26:27that is also passed on.
0:26:31 > 0:26:36Scientists believe that the bamboo's roots contain some kind of clock
0:26:36 > 0:26:40that enables them to count the passing of the years.
0:26:40 > 0:26:44How they do that is still a mystery.
0:26:44 > 0:26:48But, nonetheless, there is an animal that might give us a clue.
0:26:52 > 0:26:58Periodical cicadas in North America spend 17 years underground,
0:26:58 > 0:27:01feeding on the sap from tree roots.
0:27:04 > 0:27:06Within the space of a few days,
0:27:06 > 0:27:10the whole population emerges in their millions.
0:27:11 > 0:27:12Their mission is to breed.
0:27:17 > 0:27:21But what triggers the cicadas to all emerge at exactly the same time
0:27:21 > 0:27:23every 17 years?
0:27:27 > 0:27:28We know that, when feeding underground,
0:27:28 > 0:27:32they can detect changes in the tree sap each spring,
0:27:32 > 0:27:34and so tell the passing of a year.
0:27:38 > 0:27:42Could it be that bamboos also count the years in this way?
0:27:46 > 0:27:51It's possible that bamboos register the passing of the seasons
0:27:51 > 0:27:54in a similar way by changes in their sap.
0:27:54 > 0:27:56We just don't know.
0:27:56 > 0:27:59But, while the exact mechanism remains a mystery,
0:27:59 > 0:28:05it may well prove that these time-measuring plants, bamboos,
0:28:05 > 0:28:09are the master mathematicians of the non-human world.
0:28:12 > 0:28:15True counting is very rare in nature.
0:28:17 > 0:28:20But some animals and plants achieve numerical feats
0:28:20 > 0:28:23that are astonishing in their own right.