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If you spook a spitting cobra, it might literally shoot venom at your eyes... And our ancestors might have caused them to do this, evolutionarily speaking.

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[♪ INTRO].

Spook a spitting cobra, and it might literally shoot venom at your eyes. And it turns out that’s probably not by accident, evolutionarily speaking.

These animals might actually have evolved this defensive tactic directly in response to our ancestors! Of the more than 600 venomous snakes in the world, only three small groups have long-range weapons. African spitting cobras, Asian spitting cobras, and rinkhals are the only ones that can spit a painful concoction when threatened.

Though… technically, they don’t spit. They forcefully eject venom from their fangs. By rapidly moving muscles in the head and neck, their modified teeth can spew venom as far as two and a half meters with impressive accuracy.

And they aim right at the eyes of the perceived threat. All of which is actually kind of weird, considering the reason these snakes have venom in the first place is to subdue prey. Most cobra venom contains a wide range of toxins that paralyze and sometimes kill their meal outright.

But spitting cobra venom is different. In particular, they’ve bumped up toxins called phospholipase A2s, or PLA2s for short. These don’t make their venom any deadlier.

Instead, they seem to work with other toxins already present to make it more painful. And what’s really cool is that the structures for spitting and this PLA2-rich, super-painful venom evolved three separate times. It’s an incredible example of convergent evolution: the evolution of similar traits by distinct groups of living things.

And it’s probably the result of these snakes facing similar challenges in their environment. Like, a common enemy perhaps…. And yes, I’m talking about the group of apes known as hominins, the ones that include us and our extinct human relatives.

You see, apes in general: not big fans of snakes. And they tend to gang together and attack things they find threatening. It’s a defensive strategy usually called mobbing… for obvious reasons.

But it also means that apes can exert a selective pressure on snakes. And things only got worse for the snakes once our lineage of apes started walking upright. Suddenly we could see farther, and our hands were freed up… for better rock-throwing and other long-range attacks.

Plus, we got smarter, and often use that intelligence to make more effective weapons. And this just might have been what drove these snakes to sling their venom in the first place. For a 2021 study published in Science, researchers used the differences between the toxins in their venoms and snake fossils to peer back in time and estimate when these lineages probably evolved the ability to spit.

And, as far as we can tell, the evolution of venom-spitting in different places basically coincided with when strolling apes became a thing there. Like, African spitting cobras seem to have shown up on the scene around 6.7 to 10.7 million years ago, not long after the first walking hominins did. And the appearance of Asian spitting cobras matches up with the arrival of.

Homo erectus in Asia, around 2.5 to 4.2 million years ago. While it’s hard to conclusively prove this kind of thing, it’s a compelling hypothesis. And so far, everything lines up really well.

So, with where we’re sitting now, it looks like our bipedal pals of the past are why some snakes spit at us today! Thanks for watching this episode of SciShow! If you enjoyed learning about these amazing snakes,.

I bet you’ll love our episode about 6 other awesome snake species. And if you need a bit more science in your life in general, be sure to subscribe and ring the notification bell! We put out a new episode every day, so there’s always something cool to check out. [♪ OUTRO].