WEBVTT - Why Do Kangaroos Hop? 0:00:01.920 --> 0:00:04.320 Welcome to brain Stuff, a production of I Heart Radio, 0:00:06.160 --> 0:00:10.680 Hey brain Stuff Lauren bog Obam. Here. Rabbits, grasshoppers and 0:00:10.760 --> 0:00:15.200 frogs share a special spring in their steps, but Australia's 0:00:15.360 --> 0:00:19.600 native kangaroo out hops them all. Aresa cotton tail rabbit 0:00:19.640 --> 0:00:22.520 against a red kangaroo, and the rue would leap ahead 0:00:22.760 --> 0:00:25.320 up to thirty five miles per hour or about fifty 0:00:25.560 --> 0:00:28.360 kilometers per hour, more than twice the top speed of 0:00:28.400 --> 0:00:32.240 the rabbit. In fact, these marsupials are the only large 0:00:32.280 --> 0:00:37.519 mammals to use this pogo stick styled locomotion. The tall, furry, 0:00:37.600 --> 0:00:40.000 red and gray kangaroos that we know best are part 0:00:40.080 --> 0:00:43.880 of the family macro pott Today. These macro Pottids are 0:00:43.960 --> 0:00:48.239 so named for their large hind feet. They're marsupials, like 0:00:48.400 --> 0:00:53.040 possums and koalas, which all carry their offspring and pouches. Today, 0:00:53.200 --> 0:00:56.200 more than sixty species of the macro potted family exist, 0:00:56.520 --> 0:00:59.480 including the large redd and gray kangaroos down to the 0:00:59.520 --> 0:01:05.080 palm saised musky rat kangaroo. Fossil evidence dating back million 0:01:05.160 --> 0:01:09.360 years has revealed that kangaroo ancestors did not hop At 0:01:09.400 --> 0:01:13.440 that time. Rainforests covered most of Australia, and these predecessors 0:01:13.480 --> 0:01:17.080 most likely fed from fruits and leaves and could climb trees. 0:01:17.880 --> 0:01:21.679 One existing species, the tree kangaroo, still inhabits parts of 0:01:21.680 --> 0:01:25.200 the rainforests in Papua New Guinea. As the continents climate 0:01:25.200 --> 0:01:29.199 heated up, though, the rainforests gave way to dry, grassy plains, 0:01:29.319 --> 0:01:34.000 guiding the ruse to their current terrestrial existence, and what 0:01:34.160 --> 0:01:36.880 better way to cruise the plains than by leaps and bounds. 0:01:38.360 --> 0:01:40.320 If you were to take a close look at a 0:01:40.400 --> 0:01:44.880 kangaroo's hind foot very carefully out assume you'd noticed that 0:01:44.959 --> 0:01:49.640 its toes aren't like ours. Kangaroos have an enlarged fourth 0:01:49.680 --> 0:01:53.240 toe on each foot, starting from the inside of the foot. 0:01:53.600 --> 0:01:56.520 The kangaroo's first toe is tiny and may not even 0:01:56.520 --> 0:01:59.520 be present. The second and third toes are small and 0:01:59.560 --> 0:02:02.600 appeared to be fused together, although there are separate nails. 0:02:03.200 --> 0:02:05.920 The fourth toe is at the center of the hopping action. 0:02:06.560 --> 0:02:10.480 The kangaroos leg bone aligns with this oversized digit, allowing 0:02:10.520 --> 0:02:14.399 it to propel the foot off the ground. According to fossils, 0:02:14.400 --> 0:02:18.359 this adaptation of the enlarged fourth toe preceded the kangaroos 0:02:18.360 --> 0:02:22.320 hop The fifth toe provides additional support and thrust for 0:02:22.360 --> 0:02:25.440 the hop as well. Traveling up the foot to the 0:02:25.520 --> 0:02:28.920 hind leg, we hit the powerhouse of the kangaroos hop. 0:02:29.160 --> 0:02:33.120 The strong elastic tendons and its legs store energy for jumping. 0:02:33.919 --> 0:02:37.120 Think about sitting on top of a spring. If you 0:02:37.200 --> 0:02:39.880 press your weight down to compress the spring as much 0:02:39.880 --> 0:02:43.119 as possible, you'll get a decent bounce when you relax. 0:02:43.800 --> 0:02:46.800 In the same way, whenever a kangaroo's feet hit the ground, 0:02:47.120 --> 0:02:51.280 its tendons compressed to gather elastic energy for the kangaroo 0:02:51.400 --> 0:02:56.639 to rebound. To stabilize that motion, the kangaroos sizeable tail 0:02:56.840 --> 0:02:59.880 acts as a counterbalance to its hind feet. If you 0:03:00.000 --> 0:03:02.880 watch a kangaroo hop in slow motion, you'll see that 0:03:02.919 --> 0:03:05.960 the tail moves down to almost meet the feet in 0:03:06.040 --> 0:03:10.120 mid air. As the marsupial lands, the tail rises again 0:03:11.000 --> 0:03:14.320 by transitioning from that horizontal position when the feet are 0:03:14.360 --> 0:03:17.680 on the ground to being quasi vertical during the hop, 0:03:17.800 --> 0:03:22.320 The tails downward thrust helps propel the kangaroo up. This 0:03:22.400 --> 0:03:25.160 counterbalance effect is similar to what happens when you ride 0:03:25.160 --> 0:03:28.840 a see saw. Put all of this together and what 0:03:28.880 --> 0:03:32.280 do you have the red kangaroo motors along at an 0:03:32.320 --> 0:03:35.080 average speed of fifteen to twenty miles per hour. That's 0:03:35.120 --> 0:03:39.000 about thirty two kilometers per hour. A single hop can 0:03:39.040 --> 0:03:41.880 propel it twenty five ft forward and six ft high. 0:03:42.280 --> 0:03:44.680 That's seven and a half meters forward and almost two 0:03:44.720 --> 0:03:48.320 meters high. Your backyard trampoline might be the closest way 0:03:48.360 --> 0:03:52.760 that you'll ever get to experience kangaroo travel. So what's 0:03:52.800 --> 0:03:56.320 the point of all of these ausee aerobatics. It's all 0:03:56.360 --> 0:04:01.960 about conservation. To figure out exactly why kangaroos hop, researcher 0:04:02.120 --> 0:04:05.840 Terence Dawson put rus on treadmills and measured their speeds 0:04:05.840 --> 0:04:10.720 and energy outputs. The result at higher speeds, kangaroo hopping 0:04:10.880 --> 0:04:13.960 ranks among the most energy efficient means of land travel 0:04:14.160 --> 0:04:18.160 in the animal kingdom. You see, when kangaroos speed up, 0:04:18.400 --> 0:04:21.360 they don't increase the frequency of their hops, but rather 0:04:21.520 --> 0:04:25.039 the range. The greater the range, the more energy they harness, 0:04:25.120 --> 0:04:28.400 and their muscles and tendons after they touched down With 0:04:28.480 --> 0:04:31.600 a heart twice as big as comparably sized mammals, a 0:04:31.720 --> 0:04:35.839 kangaroo has a naturally strong physical endurance, even their respiratory 0:04:35.880 --> 0:04:39.880 systems operate more effectively during this exercise. The motion of 0:04:40.000 --> 0:04:43.720 landing and jumping causes their stomach muscles to contract and expand, 0:04:44.120 --> 0:04:47.240 forcing air in and out of their lungs without expending 0:04:47.320 --> 0:04:51.400 extra energy to do so. At lower speeds, however, the 0:04:51.440 --> 0:04:55.359 efficiency drops off. When a kangaroo needs to graze or 0:04:55.440 --> 0:04:58.400 move slowly. It uses its tail as a fifth leg, 0:04:58.760 --> 0:05:02.440 balancing back on it, shifting forward with its smaller front legs. 0:05:02.720 --> 0:05:06.719 Referred to as pentapedal walking. The kangaroos don't walk on 0:05:06.720 --> 0:05:10.279 all fours because, except when swimming, they have trouble moving 0:05:10.320 --> 0:05:14.400 their hind legs independently of each other. But why walk 0:05:14.480 --> 0:05:22.320 when you can hop anyway? Today's episode was written by 0:05:22.360 --> 0:05:25.400 Christen Conger and produced by Tyler Clang. For more on 0:05:25.440 --> 0:05:27.479 this lots of other topics, you can hop around to 0:05:27.720 --> 0:05:30.279 visit how stuff works dot com. Brain Stuff is a 0:05:30.279 --> 0:05:32.840 production of I Heart Radio or more podcasts my heart 0:05:32.920 --> 0:05:35.920 Radio visit the iHeart Radio app, Apple Podcasts, or wherever 0:05:35.960 --> 0:05:37.360 you listen to your favorite shows.