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  • Hank Green: What you're about to see in this SciShow Dose may shock you. There are about

  • 8600 animals in the world that are electroreceptive. They can feel electric fields. Like the sense

  • of touch, eletroreceptivity carries information about the shape, size, and texture of things

  • in the environment, and like hearing or vision, it works at a distance, but what it actually

  • feels like is something that we will never be able to even imagine.

  • For electroreceptive animals, electric currents and electric fields are as real and immediate

  • as color or music are for us. Most electroreceptive animals are amphibians or fish, though there

  • are rare exceptions, including the duck-billed platypus, because everything that could possibly

  • be weird about the platypus is weird. Electroreceptivity has evolved over and over again, totally independently,

  • in a global act of convergent evolution. Animals that live and hunt in murky water where they

  • might not be able to see or hear very well gain advantage if they can feel their surroundings

  • through special electroreceptive cells in their skin. And a few animals take it even

  • further. There are 716 known species of fish capable of electrogenesis, the creation of

  • electric fields and even strong electric shocks. And these fish don't have a common ancestor

  • either. Biologists believe that electrogenesis has evolved separately at least 11 different

  • times in places as isolated from each other as the African interior, the Amazon basin,

  • and the coral-rich waters of Australia.

  • The most famous electric fish is the electric eel, which is electric but is not an eel--it's

  • actually a kind of knifefish that lives in South America and can produce an electric

  • shock up to 600 volts--enough to hurt, but not seriously injure, something as big as

  • a human, but if you're an itty bitty tiny fish trying to go about your daily business

  • of swimming and eating and not dying, yeah, 600 volts is the last problem you'll ever

  • have.

  • All cells in living things produce an electric charge; it's a normal part of cell biology.

  • They do this by pumping positive ions of metals like sodium, potassium, and calcium outside

  • the cell membrane. So the outside of your cells are slightly positive compared to the

  • insides. Every cell in your body has a resting voltage of about 0.085 volts. Of course, my

  • cells aren't organized in a way that would let me add those voltages together, but this

  • fish have special cells called electrocytes, they're stacked in long chains like the batteries

  • inside a flashlight. And each one of those cells is connected on one side to a nerve

  • fiber. When an electric eel charges up, its brain sends a signal down those nerve fibers.

  • When the signal hits the electrocytes, little pores open up in their cell membranes, allowing

  • those positive ions to rush into the cell. Each cell becomes like a little tiny battery.

  • Instead of having a negative inside and a positive outside, the cell now has a negative

  • left side and a positive right side. And just like in a battery, electrons flow between

  • the two ends to equalize the charge. Since the cells are stacked in chains, positive

  • to negative to positive and so on, the voltage of each cell adds up with every other cell

  • in the chain. String enough of those chains together and fire them all at once, and bleaughh,

  • underwater barbecue.

  • But this arrangement of electrocytes doesn't have to be used offensively, and in most electric

  • fish, it isn't. Instead, they create a constant electric field around themselves, usually

  • with the power of only a few millivolts. They use this to sense their immediate environments

  • so they know when food or predators are nearby, even in total darkness. And some species of

  • fish use these electric fields to like, communicate with each other. Using distinct patterns of

  • discharges, they can signal aggression, submission, alarm, even courtship. When they're ready

  • to mate, the males and females of many kinds of electric fish will perform electric duets.

  • Electric boogie!

  • So if you feel like you're missing out, you might be wondering, why didn't we evolve to

  • create awesome electric fields that we can control with our minds? Well, because we can

  • see and hear. Seeing and hearing may seem kind of boring compared to being like, electric

  • fish Magneto, but they use a lot less energy than electrogenesis. Plus, one of the most

  • common questions people ask about electric eels is 'why don't they electrocute themselves?'

  • The answer being that they do. When an electric eel fires, you can actually see it flinch.

  • I don't know about you, but I think I'll stick with my senses since they don't actually cause

  • physical pain to use.

  • Thanks for watching this electrifying SciShow Dose, and if you'd like to help us keep sharing

  • natural wonders like this, go to Subbable.com/SciShow to find out how you can help us keep our batteries

  • charged, and don't forget to go to YouTube.com/SciShow and subscribe.

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