1 00:00:04,167 --> 00:00:07,842 ATTENBOROUGH: The natural world is full of extraordinary animals 2 00:00:08,047 --> 00:00:09,878 with amazing life histories. 3 00:00:10,887 --> 00:00:14,197 Yet, certain stories are more intriguing than most. 4 00:00:17,447 --> 00:00:20,200 The mysteries of a butterfly's life-cycle 5 00:00:20,927 --> 00:00:23,839 or the strange biology of the emperor penguin. 6 00:00:24,927 --> 00:00:29,125 some of these creatures were surrounded by myths and misunderstandings 7 00:00:29,207 --> 00:00:30,765 for a very long time. 8 00:00:31,807 --> 00:00:35,083 And some have only recently revealed their secrets. 9 00:00:36,367 --> 00:00:39,598 These are the animals that stand out from the crowd. 10 00:00:40,087 --> 00:00:44,319 The curiosities 1 find most fascinating of all. 11 00:00:52,767 --> 00:00:56,043 Animals are usually either male or female 12 00:00:56,607 --> 00:01:01,078 and usually they behave in a way that is characteristic of their gender. 13 00:01:01,807 --> 00:01:05,482 But, in nature, there are always curious exceptions. 14 00:01:07,007 --> 00:01:10,795 Female hyenas behave and look like males. 15 00:01:12,687 --> 00:01:17,078 And male seahorses play mother and physically give birth. 16 00:01:18,327 --> 00:01:20,841 Only now are we beginning to understand 17 00:01:20,927 --> 00:01:25,318 why these two animals seemed to have swapped their sexual identities. 18 00:01:32,567 --> 00:01:34,683 seahorses are fascinating. 19 00:01:35,047 --> 00:01:39,245 some are tiny and blend perfectly with their surroundings. 20 00:01:39,407 --> 00:01:43,844 Others can grow to an impressive 35 centimetres in size. 21 00:01:44,647 --> 00:01:47,844 They live in shallow waters, both tropical and temperate, 22 00:01:47,967 --> 00:01:49,286 across much of the world 23 00:01:49,367 --> 00:01:52,518 and have even been found in the Thames estuary near London. 24 00:01:53,167 --> 00:01:57,046 seeing one for the first time is a moment to remember. 25 00:01:57,927 --> 00:02:01,840 They are magical creatures with a truly fantastic appearance. 26 00:02:02,367 --> 00:02:05,803 They have the head of a horse, eyes like a chameleon, 27 00:02:05,887 --> 00:02:10,165 the prehensile tail of a monkey, armour that can change colour, 28 00:02:10,247 --> 00:02:13,398 and, perhaps most strangely of all, a pouch. 29 00:02:13,927 --> 00:02:17,203 Their unusual features inspired their name, hippocampus, 30 00:02:17,447 --> 00:02:20,883 a combination of two Greek words, hippo meaning ''horse'' 31 00:02:20,967 --> 00:02:23,322 and campus meaning ''sea monster.'' 32 00:02:24,287 --> 00:02:27,996 For centuries, they've been considered animals of myth and legend. 33 00:02:28,327 --> 00:02:34,163 And only today are we unravelling the true story of males that give birth. 34 00:02:36,847 --> 00:02:39,839 seahorses baffled early naturalists. 35 00:02:40,167 --> 00:02:43,762 Their unusual characteristics seem to make them misfits. 36 00:02:44,567 --> 00:02:48,879 But, after much debate, they were recognised as true bony fish. 37 00:02:49,927 --> 00:02:52,521 But their breeding habits were hardly fishy. 38 00:02:53,567 --> 00:02:58,402 Typically, female fish release large numbers of eggs into the sea 39 00:02:58,527 --> 00:03:00,757 that males must quickly fertilise. 40 00:03:01,687 --> 00:03:06,283 But a fish that kept its eggs in a pouch seemed scarcely believable. 41 00:03:07,607 --> 00:03:11,964 The seahorse's striking appearance has given it an almost magical status. 42 00:03:12,567 --> 00:03:16,037 Images and stories of a creature part horse, part fish 43 00:03:16,127 --> 00:03:18,960 have spanned the centuries across many cultures. 44 00:03:19,327 --> 00:03:23,764 Among the most famous are those belonging to Poseidon. 45 00:03:23,847 --> 00:03:27,556 This famous Greek god of the sea lived below the waves 46 00:03:27,647 --> 00:03:32,357 and his golden chariot was pulled by a pair of giant hippocampi. 47 00:03:33,047 --> 00:03:36,244 The seahorses' odd behaviour appeared mysterious, too. 48 00:03:36,687 --> 00:03:38,723 As early as the 3rd century BC, 49 00:03:38,807 --> 00:03:42,277 Aristotle noted in his book on the History of Animals 50 00:03:42,447 --> 00:03:45,564 that pipefish, close relatives to the seahorse, 51 00:03:45,967 --> 00:03:49,960 had a pouch that burst into two to release the young. 52 00:03:51,607 --> 00:03:55,759 These early observations of the pipefish's strange breeding behaviour 53 00:03:55,927 --> 00:04:00,955 helped to reveal the true story of the male seahorse's mysterious pouch. 54 00:04:02,007 --> 00:04:05,886 Just like seahorses, pipefish carry their eggs around with them. 55 00:04:07,047 --> 00:04:10,483 some species simply stick the eggs to the outside of their bodies. 56 00:04:11,687 --> 00:04:14,076 Others have a rudimentary pouch. 57 00:04:16,247 --> 00:04:19,637 These simpler techniques provide some clues 58 00:04:19,727 --> 00:04:24,596 as to how seahorses developed their more complex, closed pouch. 59 00:04:27,647 --> 00:04:31,720 But what Aristotle didn't know when he spotted the pipefish giving birth 60 00:04:31,807 --> 00:04:34,367 was that he was actually looking at a male. 61 00:04:35,207 --> 00:04:39,917 And this important detail was to remain undiscovered for hundreds of years. 62 00:04:44,607 --> 00:04:47,246 Although seahorses live in British waters, 63 00:04:47,407 --> 00:04:51,685 until Victorian times, few people, apart from fishermen, had ever seen them. 64 00:04:52,327 --> 00:04:57,355 In 1 859, a Mr Pinto brought four live seahorses back to London 65 00:04:57,447 --> 00:05:00,359 from the mouth of the river Tagus in Portugal. 66 00:05:01,247 --> 00:05:05,638 Pinto endured a sleepless, seven-day train journey through Europe, 67 00:05:05,727 --> 00:05:10,482 waking himself frequently to aerate the seahorses' water with a syringe. 68 00:05:11,207 --> 00:05:16,804 His seahorses survived and were installed in the new London Aquarium. 69 00:05:16,887 --> 00:05:18,718 They were an instant hit. 70 00:05:20,487 --> 00:05:22,955 seahorses were headline news. 71 00:05:23,207 --> 00:05:27,086 Mr Pinto's journey and their arrival made the front pages. 72 00:05:27,487 --> 00:05:30,081 Now, they could be seen in great detail 73 00:05:30,167 --> 00:05:33,125 and the study of their mysterious breeding began. 74 00:05:34,887 --> 00:05:39,517 1n that same year, what was described as ''a herd of baby seahorses'' 75 00:05:39,607 --> 00:05:42,246 was born in the British Midlands Aquarium. 76 00:05:42,687 --> 00:05:44,598 This caused quite a stir, 77 00:05:44,687 --> 00:05:49,158 as did the discovery that it was the male that gave birth to the young. 78 00:05:51,327 --> 00:05:55,798 But why seahorses swapped parenting roles remained a mystery 79 00:05:55,887 --> 00:05:58,799 and we're still searching for the answers today. 80 00:06:00,767 --> 00:06:02,883 Here at the London Zoo's Aquarium, 81 00:06:02,967 --> 00:06:06,755 over 1 50 years since the arrival of the first seahorses, 82 00:06:06,887 --> 00:06:10,197 a detailed study is revealing more about their reproduction 83 00:06:10,287 --> 00:06:12,437 and the unusual role of the male. 84 00:06:13,007 --> 00:06:17,398 These tanks are set like a seahorse dating centre. 85 00:06:17,807 --> 00:06:22,835 The first port of call is the courtship aquarium or ballroom tank. 86 00:06:23,607 --> 00:06:27,122 Here, a number of adult seahorses spend time getting to know each other 87 00:06:27,207 --> 00:06:29,482 as they look for compatible partners. 88 00:06:30,047 --> 00:06:34,165 Breeding seahorses form lasting partnerships as mating pairs, 89 00:06:34,247 --> 00:06:36,807 and their long, elaborate courtship dances 90 00:06:36,887 --> 00:06:40,118 are a way of finding and securing a suitable mate. 91 00:06:43,287 --> 00:06:46,643 Dances like those of this Australian species 92 00:06:46,767 --> 00:06:49,759 can be complex and last several days. 93 00:06:51,927 --> 00:06:54,600 They help the couple synchronise their bodies 94 00:06:54,687 --> 00:06:57,440 so that the male's pouch is ready for the eggs. 95 00:07:00,167 --> 00:07:03,443 They also help to establish the couple's joint territory. 96 00:07:08,487 --> 00:07:11,877 seahorses were thought to be monogamous, but we now know that 97 00:07:11,967 --> 00:07:16,995 some are only exclusive couples for the duration of the breeding season. 98 00:07:17,087 --> 00:07:19,362 The female must choose the right male 99 00:07:19,447 --> 00:07:22,917 because she's going to pass over her precious eggs to him. 100 00:07:24,887 --> 00:07:27,447 Female seahorses do not have a pouch, 101 00:07:27,527 --> 00:07:30,678 so a strong pair bond with a male is very important 102 00:07:30,807 --> 00:07:32,684 as he will care for her eggs. 103 00:07:33,527 --> 00:07:36,280 This is the honeymoon tank. 104 00:07:36,647 --> 00:07:40,526 Seahorses that have shown an attraction for each other in the courtship tank 105 00:07:40,687 --> 00:07:44,919 are removed as a couple and given their own private space. 106 00:07:45,367 --> 00:07:48,040 In the wild, each pair has its own territory 107 00:07:48,127 --> 00:07:51,722 and these smaller tanks make captive breeding more successful. 108 00:07:51,807 --> 00:07:54,924 Here, the pair can synchronise their courtship. 109 00:07:55,527 --> 00:07:57,006 Timing is crucial. 110 00:07:57,127 --> 00:08:01,040 The female's eggs must be fully developed at exactly the same time 111 00:08:01,127 --> 00:08:03,641 that the male's pouch is ready to receive them. 112 00:08:06,727 --> 00:08:11,642 Once the female's eggs are ready, she hydrates them with sea water. 113 00:08:11,727 --> 00:08:15,003 They must then be laid within 24 hours. 114 00:08:16,127 --> 00:08:18,721 she transfers her eggs to her partner 115 00:08:18,807 --> 00:08:24,359 by inserting her egg-laying tube, or ovipositor, into the male's pouch. 116 00:08:27,087 --> 00:08:30,841 Once pregnant, the male attaches himself to one spot 117 00:08:30,927 --> 00:08:33,441 and the female visits him every day. 118 00:08:34,727 --> 00:08:39,323 she checks to see when he'll be ready for her next batch of eggs. 119 00:08:41,367 --> 00:08:44,882 One theory suggests that, because the male is incubating the eggs, 120 00:08:44,967 --> 00:08:47,003 the female has more time to feed, 121 00:08:47,167 --> 00:08:50,398 and can put energy into making new eggs more quickly. 122 00:08:53,127 --> 00:08:58,155 swapping roles may be a smart way to use their resources more efficiently. 123 00:09:03,327 --> 00:09:06,444 What goes on inside the pouch is still a mystery. 124 00:09:08,487 --> 00:09:12,002 The male may simply provide a closed incubator. 125 00:09:12,807 --> 00:09:15,719 Or the inner skin may develop extra blood vessels 126 00:09:15,807 --> 00:09:17,843 to give a more placenta-like connection. 127 00:09:18,287 --> 00:09:19,686 1t's not clear. 128 00:09:20,927 --> 00:09:24,886 During pregnancy and birth, the male's metabolism increases, 129 00:09:24,967 --> 00:09:30,439 but that's little wonder, for he may have up to 1,500 eggs in his pouch. 130 00:09:35,527 --> 00:09:39,645 The male seahorse gives birth to dozens of miniature babies, 131 00:09:39,767 --> 00:09:41,598 perfect in every detail. 132 00:09:42,287 --> 00:09:45,597 The free swimming young are put into separate crash tanks 133 00:09:45,687 --> 00:09:47,678 where they can be fed and cared for. 134 00:09:48,207 --> 00:09:51,995 The parent seahorses in this biological hotel 135 00:09:52,087 --> 00:09:56,000 remain in the honeymoon suite, ready to mate again. 136 00:09:56,727 --> 00:10:01,323 These are some of last year's youngsters and they've grown enormously. 137 00:10:01,767 --> 00:10:04,759 Next year, they'll be breeding themselves. 138 00:10:08,127 --> 00:10:12,803 swapping the parental roles seems to work well for seahorses. 139 00:10:13,767 --> 00:10:18,682 1n warm conditions, a male can give birth every 28 to 30 days. 140 00:10:19,287 --> 00:10:23,644 But of the thousands of fry produced each year, only a few survive. 141 00:10:24,367 --> 00:10:27,757 There is no safe creche in the open sea. 142 00:10:29,247 --> 00:10:33,365 To succeed, seahorse parents must work well together. 143 00:10:33,647 --> 00:10:35,239 Yet, in this partnership, 144 00:10:35,327 --> 00:10:40,196 the female seems to have the freedom to swim, feed and patrol her territory 145 00:10:40,287 --> 00:10:43,040 which is normally the prerogative of the male. 146 00:10:45,767 --> 00:10:51,080 So, is the male seahorse a slave to a gallivanting female? 147 00:10:51,487 --> 00:10:54,797 Well, latest research suggests not 148 00:10:54,887 --> 00:10:58,197 and shows that some males may have more control over breeding 149 00:10:58,287 --> 00:10:59,436 than first thought. 150 00:10:59,527 --> 00:11:04,123 If small or poor quality eggs are deposited into their pouches, 151 00:11:04,247 --> 00:11:06,841 some males will absorb them. 152 00:11:07,487 --> 00:11:12,083 Such males appear to be choosy about how they invest their time and energy. 153 00:11:12,727 --> 00:11:17,482 And some females, in entrusting their eggs to males, are being cheated. 154 00:11:18,527 --> 00:11:20,518 But the male seahorse can't be duped, 155 00:11:20,767 --> 00:11:23,759 as having a pouch means that he can always be certain 156 00:11:23,887 --> 00:11:28,005 that all the baby seahorses he gives birth to are his own. 157 00:11:30,247 --> 00:11:34,160 so, male and female seahorses have swapped their roles. 158 00:11:34,527 --> 00:11:38,281 The male is the mother and he gives birth to the babies. 159 00:11:40,487 --> 00:11:44,366 Another animal with unusual parenting habits is the hyena. 160 00:11:44,607 --> 00:11:48,885 Here it's the female that looks and behaves more like a male. 161 00:11:49,487 --> 00:11:52,718 Why have female hyenas become so masculine? 162 00:11:56,647 --> 00:11:59,525 These are African spotted hyenas, 163 00:11:59,807 --> 00:12:03,163 creatures that have an undeservedly bad reputation 164 00:12:03,247 --> 00:12:05,158 and a very strange biology. 165 00:12:05,647 --> 00:12:09,083 In the wild, they live in clans of up to 80 individuals 166 00:12:09,167 --> 00:12:11,442 and the females dominate the males. 167 00:12:11,927 --> 00:12:17,399 The females are big, aggressive and look physically almost exactly like males. 168 00:12:20,287 --> 00:12:23,643 Unravelling why the female is like this has not been easy 169 00:12:23,727 --> 00:12:26,719 as it's difficult to tell the difference between the sexes. 170 00:12:28,847 --> 00:12:31,919 The females male appearance is made all the more convincing 171 00:12:32,007 --> 00:12:33,645 by her reproductive organs. 172 00:12:34,207 --> 00:12:37,244 They're external and very similar to a male's. 173 00:12:39,767 --> 00:12:45,797 Understanding hyena biology has helped to explain the female's masculinity 174 00:12:46,007 --> 00:12:49,477 and the species' reputation as aggressive scavengers. 175 00:12:50,647 --> 00:12:55,960 But in the past, these strange traits gave hyenas a very bad image. 176 00:12:57,407 --> 00:12:59,967 In the first century, Pliny the Elder 177 00:13:00,047 --> 00:13:03,642 described the hyenas and did them a great disservice. 178 00:13:03,807 --> 00:13:04,922 This is what he wrote. 179 00:13:05,807 --> 00:13:10,323 ''Hyenas are like a cross between a dog and a wolf. 180 00:13:10,407 --> 00:13:14,241 ''They break everything with their teeth, swallow it with a gulp, 181 00:13:14,367 --> 00:13:16,676 ''and masticate it in the belly. 182 00:13:17,167 --> 00:13:22,036 ''They are believed to become male and female in alternate years. 183 00:13:22,687 --> 00:13:27,124 ''They can imitate the human voice, calling a shepherd by name 184 00:13:27,207 --> 00:13:30,995 ''so that he comes outside where they tear him to pieces. 185 00:13:31,487 --> 00:13:36,925 ''Any animal that a hyena looks at three times will be unable to move.'' 186 00:13:37,607 --> 00:13:42,078 That tainted image of hyenas was perpetuated for many years to come 187 00:13:42,167 --> 00:13:45,796 and they were branded as evil, dangerous creatures. 188 00:13:48,087 --> 00:13:50,601 Hyenas are not, of course, evil. 189 00:13:50,687 --> 00:13:55,556 But their competitive nature and unusual eating habits make them appear fearsome. 190 00:13:56,487 --> 00:13:58,364 They're specialist feeders. 191 00:13:58,447 --> 00:14:00,961 They crush, eat and digest bones 192 00:14:01,047 --> 00:14:04,722 that other creatures can't tackle and so leave behind. 193 00:14:05,927 --> 00:14:10,796 And this diet has a significant effect on the female's appearance 194 00:14:10,887 --> 00:14:12,684 and her family relationships, 195 00:14:12,887 --> 00:14:15,003 especially those with her cubs. 196 00:14:17,007 --> 00:14:21,080 1n the early 1 9th century, an unusual discovery in Britain 197 00:14:21,167 --> 00:14:25,080 excited one man to look more closely at the hyena's diet. 198 00:14:26,847 --> 00:14:28,485 In 1 822, 199 00:14:28,567 --> 00:14:32,480 a rather eccentric but very eminent geologist called William Buckland 200 00:14:33,047 --> 00:14:35,003 made a significant discovery 201 00:14:35,087 --> 00:14:38,284 that was to further the modern understanding of hyenas. 202 00:14:39,367 --> 00:14:41,562 Quarry workers in Kirkdale, Yorkshire 203 00:14:41,767 --> 00:14:46,283 had come across a cave that contained a large number of bones. 204 00:14:46,927 --> 00:14:48,838 Buckland was very excited 205 00:14:48,927 --> 00:14:52,317 and rushed to see the remains before they were disturbed any further. 206 00:14:52,607 --> 00:14:55,041 And he found that mud deposits in the cave 207 00:14:55,127 --> 00:14:59,086 had preserved the bones of over 22 different species of animals 208 00:14:59,167 --> 00:15:05,766 including tiger, bear, wolf, elephant and, significantly, hyenas, 209 00:15:06,007 --> 00:15:11,525 which Buckland described as littering the cave like the bones in a dog kennel. 210 00:15:12,367 --> 00:15:16,519 This is one of the actual hyena jaws that Buckland found. 211 00:15:17,047 --> 00:15:20,119 It belonged to a young but ancient hyena. 212 00:15:20,607 --> 00:15:24,316 There are also a lot of these on the cave floor. 213 00:15:24,687 --> 00:15:29,886 They are coprolites, or fossilized faeces, from hyenas. 214 00:15:30,567 --> 00:15:32,000 They contain bone fragments 215 00:15:32,087 --> 00:15:34,726 that have passed through the hyena's digestive tract 216 00:15:35,047 --> 00:15:39,006 and so showed that they were successful bone crushers. 217 00:15:41,487 --> 00:15:46,322 Buckland's discovery of so many bones in what he believed to be a hyena's den 218 00:15:46,607 --> 00:15:49,804 indicated that they were very successful hunters. 219 00:15:50,207 --> 00:15:53,483 Contrary to popular belief, they scavenge very little 220 00:15:53,687 --> 00:15:56,679 and kill over 80% of their own food. 221 00:15:59,607 --> 00:16:03,646 A lone hyena can easily kill a wildebeest or a topi 222 00:16:03,727 --> 00:16:08,926 and, with teamwork, they will tackle bigger animals, like zebra and giraffe. 223 00:16:09,847 --> 00:16:11,963 They do scavenge as well, 224 00:16:12,047 --> 00:16:15,244 but it's more usual for lions to steal from hyenas 225 00:16:15,367 --> 00:16:17,278 rather than the other way around. 226 00:16:18,247 --> 00:16:21,080 Female hyenas have become big and strong 227 00:16:21,207 --> 00:16:24,404 and compete for food with other members of their clan. 228 00:16:24,567 --> 00:16:29,243 Nothing goes to waste. They can eat even the thickest of bones. 229 00:16:30,087 --> 00:16:34,080 Buckland was fascinated by the marks on the bones from the cave 230 00:16:34,167 --> 00:16:37,125 but found it hard to believe that hyenas had made them. 231 00:16:37,287 --> 00:16:39,562 He wanted to be sure of his findings 232 00:16:39,647 --> 00:16:41,717 and understand how their jaws, 233 00:16:41,807 --> 00:16:45,038 with their strange, massive teeth, actually worked. 234 00:16:46,327 --> 00:16:50,036 Hyenas are African or Asiatic animals. 235 00:16:50,207 --> 00:16:54,200 So, Buckland's discovery of hyena bones in an English cave 236 00:16:54,287 --> 00:16:56,482 was strange, to put it mildly. 237 00:16:57,127 --> 00:16:59,322 As a man of science, he wanted to confirm 238 00:16:59,407 --> 00:17:01,284 that the skull he had collected from Kirkdale 239 00:17:01,367 --> 00:17:03,403 was definitely from a hyena 240 00:17:03,487 --> 00:17:07,526 and that it had made the marks on the many fractured bones. 241 00:17:08,407 --> 00:17:10,284 To try and prove his case, 242 00:17:10,487 --> 00:17:13,843 he asked a friend, William Burchell, an African traveller, 243 00:17:13,927 --> 00:17:17,124 to send a young hyena back to England from the Cape. 244 00:17:17,967 --> 00:17:20,720 He planned to kill it and compare its skull and teeth 245 00:17:20,807 --> 00:17:22,365 with the specimens in the cave. 246 00:17:22,887 --> 00:17:26,516 The young hyena that arrived at the docks was already tame 247 00:17:26,607 --> 00:17:30,805 and had become a great favourite with the sailors, who christened him Billy. 248 00:17:32,407 --> 00:17:36,480 Billy became quite a celebrity and was as tame as a pet dog. 249 00:17:37,007 --> 00:17:40,920 No one could bring themselves to sacrifice him for the sake of science. 250 00:17:41,127 --> 00:17:46,076 1nstead, a search of British museums produced a hyena skull 251 00:17:46,207 --> 00:17:48,198 and Billy's life was spared. 252 00:17:49,007 --> 00:17:52,522 Buckland was then able to compare the new and old skulls 253 00:17:52,647 --> 00:17:53,921 and they matched. 254 00:17:54,247 --> 00:17:57,796 Billy also helped to clarify the fractures on the bones. 255 00:17:57,927 --> 00:17:59,724 He was fed ox bones. 256 00:18:00,327 --> 00:18:01,601 This was one. 257 00:18:02,047 --> 00:18:06,484 And Buckland compared it with one that was found in the cave 258 00:18:06,767 --> 00:18:08,485 and they closely match. 259 00:18:09,687 --> 00:18:12,645 This ability to crack massive bones 260 00:18:12,727 --> 00:18:16,276 explains why female hyenas look like bristling males. 261 00:18:16,727 --> 00:18:21,357 1t's also tied up intricately with the relationship they have with their cubs. 262 00:18:22,647 --> 00:18:27,004 Cubs are born underground and are fed on their mother's rich milk. 263 00:18:29,327 --> 00:18:32,319 At about three months of age, they emerge from the den 264 00:18:32,487 --> 00:18:35,638 and continue to suckle for almost another two years. 265 00:18:36,407 --> 00:18:38,204 Their mother helps feed the youngsters 266 00:18:38,287 --> 00:18:41,563 as they can't yet crack and crush bones for themselves. 267 00:18:42,207 --> 00:18:46,246 Even at almost a year in age, when they're big enough to join the kill, 268 00:18:46,327 --> 00:18:49,399 their teeth and jaws are still not sufficiently developed 269 00:18:49,487 --> 00:18:51,443 to tackle big bones. 270 00:18:53,047 --> 00:18:56,642 The skull of a young hyena is quite different from that of an adult. 271 00:18:57,087 --> 00:19:02,400 It's got a flat top, narrow cheeks and relatively small teeth. 272 00:19:02,967 --> 00:19:08,439 An animal with a skull like this would not be able to crush and eat big bones. 273 00:19:08,767 --> 00:19:12,885 It takes almost three years for a young hyena's skull to grow to full size 274 00:19:12,967 --> 00:19:14,798 and reach mechanical maturity. 275 00:19:15,047 --> 00:19:16,878 And this is the result. 276 00:19:17,327 --> 00:19:20,444 This skull has a large, vaulted forehead 277 00:19:20,527 --> 00:19:23,599 that dissipates biting stress, carrying it away from the face. 278 00:19:24,087 --> 00:19:26,806 It's also got wide arches at its sides 279 00:19:26,927 --> 00:19:29,122 for the attachment of powerful jaw muscles 280 00:19:29,327 --> 00:19:34,321 and robust pre-molars that have specialised crack-resistant enamel. 281 00:19:34,607 --> 00:19:39,840 jaws like these can crack the dense bones of zebra and even giraffe. 282 00:19:42,807 --> 00:19:47,597 Developing this substantial specialised eating equipment takes time. 283 00:19:47,727 --> 00:19:52,562 so it may be several years before a young hyena can feed independently. 284 00:19:52,767 --> 00:19:57,238 This puts pressure on their mothers to become dominant and aggressive. 285 00:19:58,767 --> 00:20:02,362 They need to fight to get enough food for their cubs. 286 00:20:02,447 --> 00:20:05,245 The female's status in the clan's hierarchy 287 00:20:05,327 --> 00:20:07,921 will directly affect the survival of her young. 288 00:20:08,407 --> 00:20:12,320 The biggest, oldest, most established females are the most dominant 289 00:20:12,407 --> 00:20:14,363 and take a bigger share of the kill. 290 00:20:15,087 --> 00:20:17,476 so food and the need to fight for it 291 00:20:17,567 --> 00:20:21,162 has made females look and behave like aggressive males. 292 00:20:21,527 --> 00:20:24,724 But it has also had a strange side effect. 293 00:20:25,287 --> 00:20:30,122 Female hyenas have large amounts of the male hormone testosterone 294 00:20:30,207 --> 00:20:34,166 and consequently develop male-like reproductive organs. 295 00:20:34,847 --> 00:20:36,200 This can be a problem. 296 00:20:36,287 --> 00:20:39,802 Having a long, thin birth canal makes mating very difficult 297 00:20:39,887 --> 00:20:43,357 and both mothers and cubs sometimes die during birth. 298 00:20:45,247 --> 00:20:47,886 The female's strange gender swap 299 00:20:47,967 --> 00:20:50,606 is one of the most unusual in the animal kingdom 300 00:20:51,047 --> 00:20:54,517 and new science has now made sense of the old clues 301 00:20:54,607 --> 00:20:56,165 and solved this mystery. 302 00:20:57,127 --> 00:20:59,641 Hyenas are very intriguing animals. 303 00:21:00,327 --> 00:21:05,196 William Buckland's early observations of their bones and his hyena experiments 304 00:21:05,327 --> 00:21:10,162 started a study of these creatures that was to reveal their fascinating biology. 305 00:21:11,127 --> 00:21:14,164 Hyenas may have a frightening reputation 306 00:21:14,247 --> 00:21:17,159 but their odd characteristics all have a reason. 307 00:21:17,527 --> 00:21:20,519 The story of their aggression and bizarre bodies 308 00:21:20,607 --> 00:21:24,395 is intimately tied up with their food and the survival of their cubs. 309 00:21:25,247 --> 00:21:28,717 They've evolved a perfectly formed bone-breaking jaw, 310 00:21:28,887 --> 00:21:31,560 but the time it takes to grow has resulted 311 00:21:31,647 --> 00:21:35,879 in one of the most unusual but dedicated mothers in the animal kingdom. 312 00:21:36,767 --> 00:21:38,962 so, to become the best parents 313 00:21:39,047 --> 00:21:44,167 female hyenas have become more male and male seahorses more motherly.