Dr. David Eagleman

And because the brain is a storyteller, we impose plot, meaning, and we have emotion that goes with that.

But the key is this is the brain's way of defending territory in the dark.

And so what we did then was,

is we examined very carefully 25 species of primates and looked at their brain plasticity.

And you can measure this with different proxies, like, you know, when they start to walk and when they get to reproduction age and so on.

And, you know, some creatures like the gray mouse lemur, which is a type of monkey,

You know, they are born, let's just say, pre-programmed.

You know, they pop out.

They're really quick to stop, you know, to wean and reach juvenile age and reproduce and so on.

Whereas you look at Homo sapiens, we're super slow.

We've got these extended infancies and we take a long time to learn how to walk and so on.

OK, because we're very plastic, we end up in the world half-baked.

Okay, well, it turns out if you plot how much REM sleep each of these animals get, the more plastic the animal, like homo sapiens, we've got tons of REM sleep.

And by the way, this is mostly in infancy.

Infants spend 50% of their time in REM sleep.

As you get older and your brain becomes less plastic, you have a drop-off in REM sleep.

And by the way, when you look across animal species of all types, you find that the animals that are born with extended infancies need to figure out how to do stuff in the world.

They all have much more REM sleep, like eight times more REM sleep than animals that are born essentially mature, like, you know, cows and giraffes and zebras and whatever.

You know, they show up, they start walking in 40 minutes and so on.

They have much less REM sleep than we do.