Humans are proud of a lot of things, from particle accelerators to poetry to Pokemon.

All of them made possible because of something humans value extremely highly:

Intelligence.

We think of intelligence as a trait like height or strength,

but when we try to define it, things get fuzzy.

In a nutshell, intelligence is a mechanism to solve problems.

Especially the problem of staying alive, which involves finding food and shelter,

fighting sexual competitors, or fleeing from predators.

Intelligence is not a single thing;

it includes the ability to gather knowledge, to learn, be creative, form strategies, or engage in critical thinking.

It manifests itself in a huge variety of behaviors.

From hardwired or instinct like reactions to different degrees of learning, to some sort of awareness.

But not all scientists agree where it begins or what even should count as intelligence.

To make this even more complicated,

intelligence is also connected to consciousness since awareness is helpful for problem-solving.

But we're exploring consciousness in other videos, so today we'll leave it aside.

Okay,

Intelligence isn't exactly clear-cut, so maybe we can think of it as more like a flexible set of skills:

A toolbox.

Basic tools.

The most basic tools in the intelligence toolbox are the ability to gather information, to save it, and to use it to learn.

Information about the world is gathered through senses such as vision, sound, smell, touch or taste,

and helps us navigate and react to the external world appropriately.

But living things also need to keep track of the state of their own bodies,

monitoring things like hunger and fatigue.

Information is the basis of action for all living things,

and without it, you're at the mercy of your surroundings, unable to react appropriately, or flexibly.

Information is much more powerful if we can keep and save it, so the second tool is memory.

Memory is the ability to save and recall information,

so a living being doesn't have to start from scratch every time it perceives something relevant.

Memories can be about events, places, and associations, but also behaviors like hunting or foraging methods.

Some of these, like flying, have to be repeated over and over until they're mastered.

This is what we call learning, the process of putting together a sequence of thoughts or actions.

Basically a string of repeatable behaviors that can be varied and adapted.

These three tools enable seemingly stupid creatures to act in surprisingly intelligent ways.

The acellular slime mold, which is basically just a single huge slimy cell,

shows behavior similar to an animal with a simple brain.

When put in a maze with food at one end,

the slime mold explores its surroundings, and marks its path with slime trails,