Did you hear about the octopus that slipped out of its tank, into a drain pipe, and made a break for the sea? Or what about the cephalopod that figured out how to open those child-proof pill bottles? Which, let's be honest, even adult humans have a hard time doing sometimes. It;s fair to say that octopuses are smart. But when we talk about intelligence of other animals, we tend to fall into the trap of comparing them to humans -testing for everything from the size of their brains, to qualities like emotions and learning abilities. 

But octopuses are very different from people, I don't know if you've noticed. On the evolutionary tree, they are a long way off from us. And they're probably way more complex than we might realize or understand. 

So your brain is in your head. And so are the brains of other animals that we consider intelligent, like dogs and dolphins and chimps and crows. Octopuses have central brains in their heads as well, and we have some anatomical similarities. For example, their brains generate similar electrical patterns as vertebrates, and they seem to have specialized brain areas for things like learning and memory storage. They also seem to have a dominant, or preferred, eye - which is an example of lateralization, similar to the way people are right- or left-handed.

But the weird thing is, about two-thirds of their neurons are in their arms. Each arm literally has a mind of its own, to do its own problem solving and act independently, while the other arms are doing something completely different. 

In a 2013 research study, scientists isolated arms from dead octopuses in order to test those neural responses. They found that the isolated arms recoiled from being pinched, or from touching tap water or acetic acid. This suggests that they might have some kind of nociceptors, or special neurons that sense danger and pain, like the ones that make us pull our hand back when touching a hot stove. But, unlike humans, their arms can respond to these kind of stimuli without being attached to a central brain. Other experiments have found that the severed arms wriggle around, and even grab onto food.

So, anatomically, octopuses are some pretty cool invertebrates. But what about their behavior? Octopuses have been observed using tools, like picking up two coconut halves to use as a mobile home, and manipulating objects in a way that looks a lot like playing. 

One 1993 study published in the Journal of Comparative Psychology even suggested that octopuses seem to display distinct personalities, reacting to food and threats in individual, but consistent ways. One octopus might be consistently curious and daring, while another is careful and shy. Another study, in 2001, seemed to show that young octopuses changed their behavior over the course of weeks, becoming more alert to danger and learning from their environment. 

So octopuses do seem to have some sort of advanced cognition, learning and changing their behaviors over time. Even though we might see a lot of ourselves in the behavior of octopuses, we certainly didn't get there on the same path. Our vertebrate evolutionary branch split from the mollusks about 1.2 billion years ago, so humans and octopus intelligence evolved completely separately. 

Scientist have a lot of different theories to try and explain how humans evolved intelligence, and one of them relates to our social lifestyle. Basically, forming long-lasting relationships could've meant better survival. But octopuses don't have that specific evolutionary pressure, they only live for a couple of years and are almost always alone. 

So, how did these creatures evolve their intelligence and central brain - while other mollusks, like oysters, didn't? Well, i might have something to do with the most obvious thing that separates an octopus from an oyster, the shell! At some point in their evolution, the octopus's ancestors probably traded the safety of a shell for freedom. 

Suddenly, they could move around and forage for food, using  variety of hunting skills. But they also had to worry about becoming dinner, which led to all kinds of strategies to avoid being eaten, like hiding, camouflage, tool use and speed. And all that self-preservation requires some sort of intelligence. The smarter octopuses would've had a better chance of survival. 

Octopuses might not look like us, move like us, live like us, or probably even think like us. But they have somehow evolved intelligence in ways we're only beginning to understand. 

Thank you for watching this episode of SciShow, which was brought to you by our patron on Patreon. If you would like to help support this show, so you can learn more cool things about octopuses just go to Patreon.com/SciShow. And don't forget to go to YouTube.com/SciShow and subscribe!