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You can get a $100 60-day credit on a new Linode account at linode.com/scishow. Most animals are rocking some wildly complex bodies, with electrical signals constantly shooting around and carrying messages to and from the brain.

Not only does that information reveal the world around us, it lets our brains act as the command center for each of our trillions of cells. But all the way on the other end of the complexity spectrum, there’s the sponge … one of the simplest animals in existence. No brain.

No nervous system. They just sway in the current and eat whatever food flows through them. And yet, these simple animals may have evolved their own unique way of transmitting information through their bodies … using light. [Intro music] Sponges were some of the first animals ever.

The oldest ones lived around 800 million years ago. Since then, they’ve evolved into more than 8,000 different species with all kinds of weird shapes and sizes, but their general body plan has stayed really simple. Unlike most animals, they don’t have any organs or even tissues.

Instead, they’re made of groups of cells packed together that perform different functions. And all this is organized without a brain telling cells what to do! The sponge’s genes just give each cell its marching orders, and the cells carry out their specific roles.

But even though sponges don’t have a nervous system, they act like animals that do. For instance, they respond to light in their environment. Some sponges will contract or their metabolism will change in response to different light levels.

Even some non-animal life is capable of this, so it’s not /that/ impressive. But the ability to “see” without eyes, nerves, or a brain is a little alien at first glance. Sponges manage to pass information through their bodies so that groups of cells can act in sync.

After giving up on finding a nervous system, scientists went looking for another way that sponges could be doing that. And in the early 2000s, they found a clue. A group of researchers was studying a deep-sea sponge called the Venus’ flower basket.

It’s known for its lacy skeleton, made up of fibers called spicules. They can come across as pretty delicate looking, and that might be because these spicules are mostly made of silica…the main ingredient we use to make glass. The researchers found that these glass fibers are basically natural fiber-optic cables.

They’re strangely similar to the one humans use to do super important things these days, like share memes on the internet. Now, finding a sponge with a fiber optic skeletal structure wasn't entirely a surprise. About a decade earlier, scientists had come across some light-transmitting spicules in a different sponge species, living in the waters around Antarctica.

In that case, the spicules stuck straight out from the sponge’s body, and they had algae clustered around the base. The researchers figured that the spicules were directing sunlight down to photosynthesizing organisms that lived within the sponge. But Venus’ flower baskets live in the deep sea, where there is practically no sunlight.

Maybe it was just a coincidence that these sponges also had evolved fibers that happened to transmit light. But some researchers started to consider another idea: Maybe sponges were using a system of light and glass fibers in place of a nervous system. And in 2009, another piece of the puzzle seemed to fall into place.

A different team of researchers found at least one sponge species that creates its own light. It has proteins called luciferases that give off a flash when they react with oxygen. Now, that on its own isn’t so special.

Lots of sea creatures are bioluminescent, meaning they create their own light. But inside this sponge, the cells creating the light were clustered around spicules. So, it looked like the sponge was creating flashes of light and channeling it through its spicules.

The question was just… where was it going? If sponges were really shooting light through a system of glass fibers and using this as a quasi nervous system, something had to be on the receiving end. Something had to be intercepting that light and responding to that signal.

And before long, the team found that something. They discovered that sponges have special cells with proteins called cryptochromes that get activated by light. Researchers think that light hitting a cryptochrome produces hormone-like molecules, and these act as chemical messengers.

These molecules move through the body much more slowly than nerve signals. But like nerve signals, they can also trigger certain behaviors in cells. Like, they can make cells contract or kick their metabolism into gear, all in response to what’s going on in the sponge’s environment.

In other words, a combination of bioluminescent cells, glass fibers, and cryptochromes could be acting like a unique kind of sensory system, not yet observed anywhere else in nature. So far, this whole idea is still hypothetical. It hasn’t been tested with experiments.

But the fact that it’s even plausible is kind of mind-blowing. Essentially, this ancient animal with no nervous system might be moving electromagnetic signals around its body in the form of light… kind of like us complicated creatures who send electrical impulses through a system of nerves. Sponges probably aren’t using this system to ponder the importance of their day-to-day experiences, let alone the meaning of life.

But in a weird way, this knock-off version of a nervous system does let them process information about the world. Which somehow makes these animals seem both weirdly familiar /and/ surprisingly alien. This episode of SciShow is supported by

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