Why Don't Snakes Have Legs?

So why don't these snakes sprout limbs and start strutting through the bush. The genetic machinations behind this process are essentially switched to the off position thanks to multiple genetic mutations that occurred more than a hundred million years ago. Those mutations affected a particular gene, the sonic hedgehog gene,

which is responsible for the development of limbs. And before you ask, yes, that is actually the genes official name so called because of its spiky appear it's The sonic hedgehog gene is not only vital for limbs, it also provides guides for organs and their placement within growing animals. In lizards, the sonic hedgehog gene is active and results

in legs and feet. In snakes, it's deactivated. A study published in Nature Communications in sixteen showed how changes in the reptile genome ultimately resulted in obvious transformations in the creatures phenotype, which are the physical traits that come from expressions of certain genes. In short, genetic mutations caused some lizards to do away with their appendages, becoming steaks, while still retaining the echoes of those leggy genes in their DNA.

In order to pinpoint changes in genetic sequences, the researchers compare genomes from steaks with those of other reptiles and vertebrates that do have complete limbs. They relied particularly on the genome of the tagou lizard. Scientists have completely sequenced its genome. Lizards happened to have DNA regulatory sequencers called enhancers that can flip certain genes and off during a

creature's development. The sonic hedgehog gene needs those enhancers for limbs to fully develop, which is how lizards wind up with four legs, but in snakes, this enhancer was removed from DNA sequences during evolution, and it's now virtually but not completely eliminated, even from primitive snakes. In some snakes, traces of the enhancer are still there, along with another gene called h o x D, which is responsible for

guiding the development of feet. Some python embryos even develop partial leg bones and footplates in the egg, but these features disintegrate long before the justating creature hatches. Still there are leftover signs that not all snakes are ready to be done with the idea of sprinting along. Think of

all the tiny athletic shoes. If you peer closely at the underside of these snakes, you'll see little nubs on their bellies, vestigial remnants of legs that could have been All of this means that with just a few genetic mutations, some types of primitive snakes might be able to develop limbs that essentially be activating features that are already tucked away in their DNA, just waiting for the right variables to trigger their development. But bonus fact of the episode,

snakes don't necessarily need feet to catch you. The black mamba is one of the world's deadliest snakes due to its neuro and cardio toxic venom. It can reach up to fourteen feet long that's over four meters, and can slither about twelve miles per hour. That's nineteen kilometers per hour, which is faster than most people can run. But don't worry too much. They're largely shy and are more likely

to flee instead of fight. Though, if you accidentally corner a large gray snake that rears back and hisses showing a black inner mouth, go ahead and back off. Today's episode was written by Dathan Chandler and produced by Tyler Clay. Brain Stuff is a production of i Heeart Media's How Stuff Works. For more on this and lots of other well evolved topics, visit our home planet, how stuff Works

dot com. And for more podcasts from my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H