Speaker 1: Welcome to brain stuff from how stuff works, Hey, brain
Speaker 1: stuff lorn Voga bom here. Snakes and lizards are both
Speaker 1: card carrying members of the order Squamata. But while lizards
Speaker 1: skinner and dash on fully formed legs, snakes opt for
Speaker 1: a legless slither. Just why and how these animals took
Speaker 1: such different evolutionary paths is a matter of scientific debate. However,
Speaker 1: one thing is for sure. Some snakes still carry the
Speaker 1: genetic coating that would allow them to develop legs and feet.
Speaker 1: So why don't these snakes sprout limbs and start strutting
Speaker 1: through the bush. The genetic machinations behind this process are
Speaker 1: essentially switched to the off position thanks to multiple genetic
Speaker 1: mutations that occurred more than a hundred million years ago.
Speaker 1: Those mutations affected a particular gene, the sonic hedgehog gene,
Speaker 1: which is responsible for the development of limbs. And before
Speaker 1: you ask, yes, that is actually the genes official name
Speaker 1: so called because of its spiky appear it's The sonic
Speaker 1: hedgehog gene is not only vital for limbs, it also
Speaker 1: provides guides for organs and their placement within growing animals.
Speaker 1: In lizards, the sonic hedgehog gene is active and results
Speaker 1: in legs and feet. In snakes, it's deactivated. A study
Speaker 1: published in Nature Communications in sixteen showed how changes in
Speaker 1: the reptile genome ultimately resulted in obvious transformations in the
Speaker 1: creatures phenotype, which are the physical traits that come from
Speaker 1: expressions of certain genes. In short, genetic mutations caused some
Speaker 1: lizards to do away with their appendages, becoming steaks, while
Speaker 1: still retaining the echoes of those leggy genes in their DNA.
Speaker 1: In order to pinpoint changes in genetic sequences, the researchers
Speaker 1: compare genomes from steaks with those of other reptiles and
Speaker 1: vertebrates that do have complete limbs. They relied particularly on
Speaker 1: the genome of the tagou lizard. Scientists have completely sequenced
Speaker 1: its genome. Lizards happened to have DNA regulatory sequencers called
Speaker 1: enhancers that can flip certain genes and off during a
Speaker 1: creature's development. The sonic hedgehog gene needs those enhancers for
Speaker 1: limbs to fully develop, which is how lizards wind up
Speaker 1: with four legs, but in snakes, this enhancer was removed
Speaker 1: from DNA sequences during evolution, and it's now virtually but
Speaker 1: not completely eliminated, even from primitive snakes. In some snakes,
Speaker 1: traces of the enhancer are still there, along with another
Speaker 1: gene called h o x D, which is responsible for
Speaker 1: guiding the development of feet. Some python embryos even develop
Speaker 1: partial leg bones and footplates in the egg, but these
Speaker 1: features disintegrate long before the justating creature hatches. Still there
Speaker 1: are leftover signs that not all snakes are ready to
Speaker 1: be done with the idea of sprinting along. Think of
Speaker 1: all the tiny athletic shoes. If you peer closely at
Speaker 1: the underside of these snakes, you'll see little nubs on
Speaker 1: their bellies, vestigial remnants of legs that could have been
Speaker 1: All of this means that with just a few genetic mutations,
Speaker 1: some types of primitive snakes might be able to develop
Speaker 1: limbs that essentially be activating features that are already tucked
Speaker 1: away in their DNA, just waiting for the right variables
Speaker 1: to trigger their development. But bonus fact of the episode,
Speaker 1: snakes don't necessarily need feet to catch you. The black
Speaker 1: mamba is one of the world's deadliest snakes due to
Speaker 1: its neuro and cardio toxic venom. It can reach up
Speaker 1: to fourteen feet long that's over four meters, and can
Speaker 1: slither about twelve miles per hour. That's nineteen kilometers per hour,
Speaker 1: which is faster than most people can run. But don't
Speaker 1: worry too much. They're largely shy and are more likely
Speaker 1: to flee instead of fight. Though, if you accidentally corner
Speaker 1: a large gray snake that rears back and hisses showing
Speaker 1: a black inner mouth, go ahead and back off. Today's
Speaker 1: episode was written by Dathan Chandler and produced by Tyler Clay.
Speaker 1: Brain Stuff is a production of i Heeart Media's How
Speaker 1: Stuff Works. For more on this and lots of other
Speaker 1: well evolved topics, visit our home planet, how stuff Works
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