1 00:00:01,920 --> 00:00:04,320 Speaker 1: Welcome to brain Stuff, a production of I Heart Radio, 2 00:00:06,160 --> 00:00:10,680 Speaker 1: Hey brain Stuff Lauren bog Obam. Here. Rabbits, grasshoppers and 3 00:00:10,760 --> 00:00:15,200 Speaker 1: frogs share a special spring in their steps, but Australia's 4 00:00:15,360 --> 00:00:19,600 Speaker 1: native kangaroo out hops them all. Aresa cotton tail rabbit 5 00:00:19,640 --> 00:00:22,520 Speaker 1: against a red kangaroo, and the rue would leap ahead 6 00:00:22,760 --> 00:00:25,320 Speaker 1: up to thirty five miles per hour or about fifty 7 00:00:25,560 --> 00:00:28,360 Speaker 1: kilometers per hour, more than twice the top speed of 8 00:00:28,400 --> 00:00:32,240 Speaker 1: the rabbit. In fact, these marsupials are the only large 9 00:00:32,280 --> 00:00:37,519 Speaker 1: mammals to use this pogo stick styled locomotion. The tall, furry, 10 00:00:37,600 --> 00:00:40,000 Speaker 1: red and gray kangaroos that we know best are part 11 00:00:40,080 --> 00:00:43,880 Speaker 1: of the family macro pott Today. These macro Pottids are 12 00:00:43,960 --> 00:00:48,239 Speaker 1: so named for their large hind feet. They're marsupials, like 13 00:00:48,400 --> 00:00:53,040 Speaker 1: possums and koalas, which all carry their offspring and pouches. Today, 14 00:00:53,200 --> 00:00:56,200 Speaker 1: more than sixty species of the macro potted family exist, 15 00:00:56,520 --> 00:00:59,480 Speaker 1: including the large redd and gray kangaroos down to the 16 00:00:59,520 --> 00:01:05,080 Speaker 1: palm saised musky rat kangaroo. Fossil evidence dating back million 17 00:01:05,160 --> 00:01:09,360 Speaker 1: years has revealed that kangaroo ancestors did not hop At 18 00:01:09,400 --> 00:01:13,440 Speaker 1: that time. Rainforests covered most of Australia, and these predecessors 19 00:01:13,480 --> 00:01:17,080 Speaker 1: most likely fed from fruits and leaves and could climb trees. 20 00:01:17,880 --> 00:01:21,679 Speaker 1: One existing species, the tree kangaroo, still inhabits parts of 21 00:01:21,680 --> 00:01:25,200 Speaker 1: the rainforests in Papua New Guinea. As the continents climate 22 00:01:25,200 --> 00:01:29,199 Speaker 1: heated up, though, the rainforests gave way to dry, grassy plains, 23 00:01:29,319 --> 00:01:34,000 Speaker 1: guiding the ruse to their current terrestrial existence, and what 24 00:01:34,160 --> 00:01:36,880 Speaker 1: better way to cruise the plains than by leaps and bounds. 25 00:01:38,360 --> 00:01:40,320 Speaker 1: If you were to take a close look at a 26 00:01:40,400 --> 00:01:44,880 Speaker 1: kangaroo's hind foot very carefully out assume you'd noticed that 27 00:01:44,959 --> 00:01:49,640 Speaker 1: its toes aren't like ours. Kangaroos have an enlarged fourth 28 00:01:49,680 --> 00:01:53,240 Speaker 1: toe on each foot, starting from the inside of the foot. 29 00:01:53,600 --> 00:01:56,520 Speaker 1: The kangaroo's first toe is tiny and may not even 30 00:01:56,520 --> 00:01:59,520 Speaker 1: be present. The second and third toes are small and 31 00:01:59,560 --> 00:02:02,600 Speaker 1: appeared to be fused together, although there are separate nails. 32 00:02:03,200 --> 00:02:05,920 Speaker 1: The fourth toe is at the center of the hopping action. 33 00:02:06,560 --> 00:02:10,480 Speaker 1: The kangaroos leg bone aligns with this oversized digit, allowing 34 00:02:10,520 --> 00:02:14,399 Speaker 1: it to propel the foot off the ground. According to fossils, 35 00:02:14,400 --> 00:02:18,359 Speaker 1: this adaptation of the enlarged fourth toe preceded the kangaroos 36 00:02:18,360 --> 00:02:22,320 Speaker 1: hop The fifth toe provides additional support and thrust for 37 00:02:22,360 --> 00:02:25,440 Speaker 1: the hop as well. Traveling up the foot to the 38 00:02:25,520 --> 00:02:28,920 Speaker 1: hind leg, we hit the powerhouse of the kangaroos hop. 39 00:02:29,160 --> 00:02:33,120 Speaker 1: The strong elastic tendons and its legs store energy for jumping. 40 00:02:33,919 --> 00:02:37,120 Speaker 1: Think about sitting on top of a spring. If you 41 00:02:37,200 --> 00:02:39,880 Speaker 1: press your weight down to compress the spring as much 42 00:02:39,880 --> 00:02:43,119 Speaker 1: as possible, you'll get a decent bounce when you relax. 43 00:02:43,800 --> 00:02:46,800 Speaker 1: In the same way, whenever a kangaroo's feet hit the ground, 44 00:02:47,120 --> 00:02:51,280 Speaker 1: its tendons compressed to gather elastic energy for the kangaroo 45 00:02:51,400 --> 00:02:56,639 Speaker 1: to rebound. To stabilize that motion, the kangaroos sizeable tail 46 00:02:56,840 --> 00:02:59,880 Speaker 1: acts as a counterbalance to its hind feet. If you 47 00:03:00,000 --> 00:03:02,880 Speaker 1: watch a kangaroo hop in slow motion, you'll see that 48 00:03:02,919 --> 00:03:05,960 Speaker 1: the tail moves down to almost meet the feet in 49 00:03:06,040 --> 00:03:10,120 Speaker 1: mid air. As the marsupial lands, the tail rises again 50 00:03:11,000 --> 00:03:14,320 Speaker 1: by transitioning from that horizontal position when the feet are 51 00:03:14,360 --> 00:03:17,680 Speaker 1: on the ground to being quasi vertical during the hop, 52 00:03:17,800 --> 00:03:22,320 Speaker 1: The tails downward thrust helps propel the kangaroo up. This 53 00:03:22,400 --> 00:03:25,160 Speaker 1: counterbalance effect is similar to what happens when you ride 54 00:03:25,160 --> 00:03:28,840 Speaker 1: a see saw. Put all of this together and what 55 00:03:28,880 --> 00:03:32,280 Speaker 1: do you have the red kangaroo motors along at an 56 00:03:32,320 --> 00:03:35,080 Speaker 1: average speed of fifteen to twenty miles per hour. That's 57 00:03:35,120 --> 00:03:39,000 Speaker 1: about thirty two kilometers per hour. A single hop can 58 00:03:39,040 --> 00:03:41,880 Speaker 1: propel it twenty five ft forward and six ft high. 59 00:03:42,280 --> 00:03:44,680 Speaker 1: That's seven and a half meters forward and almost two 60 00:03:44,720 --> 00:03:48,320 Speaker 1: meters high. Your backyard trampoline might be the closest way 61 00:03:48,360 --> 00:03:52,760 Speaker 1: that you'll ever get to experience kangaroo travel. So what's 62 00:03:52,800 --> 00:03:56,320 Speaker 1: the point of all of these ausee aerobatics. It's all 63 00:03:56,360 --> 00:04:01,960 Speaker 1: about conservation. To figure out exactly why kangaroos hop, researcher 64 00:04:02,120 --> 00:04:05,840 Speaker 1: Terence Dawson put rus on treadmills and measured their speeds 65 00:04:05,840 --> 00:04:10,720 Speaker 1: and energy outputs. The result at higher speeds, kangaroo hopping 66 00:04:10,880 --> 00:04:13,960 Speaker 1: ranks among the most energy efficient means of land travel 67 00:04:14,160 --> 00:04:18,160 Speaker 1: in the animal kingdom. You see, when kangaroos speed up, 68 00:04:18,400 --> 00:04:21,360 Speaker 1: they don't increase the frequency of their hops, but rather 69 00:04:21,520 --> 00:04:25,039 Speaker 1: the range. The greater the range, the more energy they harness, 70 00:04:25,120 --> 00:04:28,400 Speaker 1: and their muscles and tendons after they touched down With 71 00:04:28,480 --> 00:04:31,600 Speaker 1: a heart twice as big as comparably sized mammals, a 72 00:04:31,720 --> 00:04:35,839 Speaker 1: kangaroo has a naturally strong physical endurance, even their respiratory 73 00:04:35,880 --> 00:04:39,880 Speaker 1: systems operate more effectively during this exercise. The motion of 74 00:04:40,000 --> 00:04:43,720 Speaker 1: landing and jumping causes their stomach muscles to contract and expand, 75 00:04:44,120 --> 00:04:47,240 Speaker 1: forcing air in and out of their lungs without expending 76 00:04:47,320 --> 00:04:51,400 Speaker 1: extra energy to do so. At lower speeds, however, the 77 00:04:51,440 --> 00:04:55,359 Speaker 1: efficiency drops off. When a kangaroo needs to graze or 78 00:04:55,440 --> 00:04:58,400 Speaker 1: move slowly. It uses its tail as a fifth leg, 79 00:04:58,760 --> 00:05:02,440 Speaker 1: balancing back on it, shifting forward with its smaller front legs. 80 00:05:02,720 --> 00:05:06,719 Speaker 1: Referred to as pentapedal walking. The kangaroos don't walk on 81 00:05:06,720 --> 00:05:10,279 Speaker 1: all fours because, except when swimming, they have trouble moving 82 00:05:10,320 --> 00:05:14,400 Speaker 1: their hind legs independently of each other. But why walk 83 00:05:14,480 --> 00:05:22,320 Speaker 1: when you can hop anyway? Today's episode was written by 84 00:05:22,360 --> 00:05:25,400 Speaker 1: Christen Conger and produced by Tyler Clang. For more on 85 00:05:25,440 --> 00:05:27,479 Speaker 1: this lots of other topics, you can hop around to 86 00:05:27,720 --> 00:05:30,279 Speaker 1: visit how stuff works dot com. Brain Stuff is a 87 00:05:30,279 --> 00:05:32,840 Speaker 1: production of I Heart Radio or more podcasts my heart 88 00:05:32,920 --> 00:05:35,920 Speaker 1: Radio visit the iHeart Radio app, Apple Podcasts, or wherever 89 00:05:35,960 --> 00:05:37,360 Speaker 1: you listen to your favorite shows.