WEBVTT - Why Don't Snakes Have Legs?

0:00:02.040 --> 0:00:06.840
<v Speaker 1>Welcome to brain stuff from how stuff works, Hey, brain

0:00:06.920 --> 0:00:10.360
<v Speaker 1>stuff lorn Voga bom here. Snakes and lizards are both

0:00:10.360 --> 0:00:14.080
<v Speaker 1>card carrying members of the order Squamata. But while lizards

0:00:14.080 --> 0:00:17.040
<v Speaker 1>skinner and dash on fully formed legs, snakes opt for

0:00:17.079 --> 0:00:20.800
<v Speaker 1>a legless slither. Just why and how these animals took

0:00:20.800 --> 0:00:25.239
<v Speaker 1>such different evolutionary paths is a matter of scientific debate. However,

0:00:25.440 --> 0:00:28.760
<v Speaker 1>one thing is for sure. Some snakes still carry the

0:00:28.760 --> 0:00:31.880
<v Speaker 1>genetic coating that would allow them to develop legs and feet.

0:00:32.840 --> 0:00:36.120
<v Speaker 1>So why don't these snakes sprout limbs and start strutting

0:00:36.159 --> 0:00:39.839
<v Speaker 1>through the bush. The genetic machinations behind this process are

0:00:39.880 --> 0:00:43.160
<v Speaker 1>essentially switched to the off position thanks to multiple genetic

0:00:43.280 --> 0:00:46.040
<v Speaker 1>mutations that occurred more than a hundred million years ago.

0:00:47.200 --> 0:00:51.120
<v Speaker 1>Those mutations affected a particular gene, the sonic hedgehog gene,

0:00:51.400 --> 0:00:54.680
<v Speaker 1>which is responsible for the development of limbs. And before

0:00:54.720 --> 0:00:57.760
<v Speaker 1>you ask, yes, that is actually the genes official name

0:00:58.000 --> 0:01:01.880
<v Speaker 1>so called because of its spiky appear it's The sonic

0:01:01.920 --> 0:01:04.760
<v Speaker 1>hedgehog gene is not only vital for limbs, it also

0:01:04.800 --> 0:01:08.240
<v Speaker 1>provides guides for organs and their placement within growing animals.

0:01:08.720 --> 0:01:11.880
<v Speaker 1>In lizards, the sonic hedgehog gene is active and results

0:01:11.880 --> 0:01:16.240
<v Speaker 1>in legs and feet. In snakes, it's deactivated. A study

0:01:16.240 --> 0:01:19.800
<v Speaker 1>published in Nature Communications in sixteen showed how changes in

0:01:19.800 --> 0:01:23.600
<v Speaker 1>the reptile genome ultimately resulted in obvious transformations in the

0:01:23.600 --> 0:01:26.880
<v Speaker 1>creatures phenotype, which are the physical traits that come from

0:01:26.880 --> 0:01:31.160
<v Speaker 1>expressions of certain genes. In short, genetic mutations caused some

0:01:31.280 --> 0:01:34.479
<v Speaker 1>lizards to do away with their appendages, becoming steaks, while

0:01:34.560 --> 0:01:37.679
<v Speaker 1>still retaining the echoes of those leggy genes in their DNA.

0:01:39.160 --> 0:01:42.480
<v Speaker 1>In order to pinpoint changes in genetic sequences, the researchers

0:01:42.480 --> 0:01:45.440
<v Speaker 1>compare genomes from steaks with those of other reptiles and

0:01:45.520 --> 0:01:49.160
<v Speaker 1>vertebrates that do have complete limbs. They relied particularly on

0:01:49.200 --> 0:01:52.440
<v Speaker 1>the genome of the tagou lizard. Scientists have completely sequenced

0:01:52.440 --> 0:01:57.520
<v Speaker 1>its genome. Lizards happened to have DNA regulatory sequencers called

0:01:57.600 --> 0:02:00.840
<v Speaker 1>enhancers that can flip certain genes and off during a

0:02:00.880 --> 0:02:04.960
<v Speaker 1>creature's development. The sonic hedgehog gene needs those enhancers for

0:02:05.080 --> 0:02:07.680
<v Speaker 1>limbs to fully develop, which is how lizards wind up

0:02:07.680 --> 0:02:11.400
<v Speaker 1>with four legs, but in snakes, this enhancer was removed

0:02:11.400 --> 0:02:15.280
<v Speaker 1>from DNA sequences during evolution, and it's now virtually but

0:02:15.400 --> 0:02:20.200
<v Speaker 1>not completely eliminated, even from primitive snakes. In some snakes,

0:02:20.240 --> 0:02:23.200
<v Speaker 1>traces of the enhancer are still there, along with another

0:02:23.240 --> 0:02:26.240
<v Speaker 1>gene called h o x D, which is responsible for

0:02:26.360 --> 0:02:30.160
<v Speaker 1>guiding the development of feet. Some python embryos even develop

0:02:30.200 --> 0:02:32.959
<v Speaker 1>partial leg bones and footplates in the egg, but these

0:02:33.000 --> 0:02:37.639
<v Speaker 1>features disintegrate long before the justating creature hatches. Still there

0:02:37.680 --> 0:02:40.600
<v Speaker 1>are leftover signs that not all snakes are ready to

0:02:40.600 --> 0:02:43.320
<v Speaker 1>be done with the idea of sprinting along. Think of

0:02:43.400 --> 0:02:46.640
<v Speaker 1>all the tiny athletic shoes. If you peer closely at

0:02:46.639 --> 0:02:49.359
<v Speaker 1>the underside of these snakes, you'll see little nubs on

0:02:49.400 --> 0:02:52.399
<v Speaker 1>their bellies, vestigial remnants of legs that could have been

0:02:53.919 --> 0:02:56.840
<v Speaker 1>All of this means that with just a few genetic mutations,

0:02:56.880 --> 0:02:59.400
<v Speaker 1>some types of primitive snakes might be able to develop

0:02:59.440 --> 0:03:02.680
<v Speaker 1>limbs that essentially be activating features that are already tucked

0:03:02.680 --> 0:03:05.399
<v Speaker 1>away in their DNA, just waiting for the right variables

0:03:05.400 --> 0:03:09.440
<v Speaker 1>to trigger their development. But bonus fact of the episode,

0:03:09.600 --> 0:03:12.880
<v Speaker 1>snakes don't necessarily need feet to catch you. The black

0:03:12.919 --> 0:03:15.120
<v Speaker 1>mamba is one of the world's deadliest snakes due to

0:03:15.200 --> 0:03:17.920
<v Speaker 1>its neuro and cardio toxic venom. It can reach up

0:03:17.919 --> 0:03:20.680
<v Speaker 1>to fourteen feet long that's over four meters, and can

0:03:20.720 --> 0:03:24.200
<v Speaker 1>slither about twelve miles per hour. That's nineteen kilometers per hour,

0:03:24.400 --> 0:03:27.320
<v Speaker 1>which is faster than most people can run. But don't

0:03:27.400 --> 0:03:30.440
<v Speaker 1>worry too much. They're largely shy and are more likely

0:03:30.520 --> 0:03:34.079
<v Speaker 1>to flee instead of fight. Though, if you accidentally corner

0:03:34.160 --> 0:03:36.960
<v Speaker 1>a large gray snake that rears back and hisses showing

0:03:36.960 --> 0:03:44.920
<v Speaker 1>a black inner mouth, go ahead and back off. Today's

0:03:44.960 --> 0:03:47.600
<v Speaker 1>episode was written by Dathan Chandler and produced by Tyler Clay.

0:03:48.000 --> 0:03:49.960
<v Speaker 1>Brain Stuff is a production of i Heeart Media's How

0:03:50.000 --> 0:03:52.000
<v Speaker 1>Stuff Works. For more on this and lots of other

0:03:52.040 --> 0:03:54.760
<v Speaker 1>well evolved topics, visit our home planet, how stuff Works

0:03:54.760 --> 0:03:57.360
<v Speaker 1>dot com. And for more podcasts from my heart Radio,

0:03:57.600 --> 0:04:00.280
<v Speaker 1>visit the i heart Radio app, Apple Podcasts, or wherever

0:04:00.400 --> 0:04:12.840
<v Speaker 1>you listen to your favorite shows. H