Dr. David Eagleman

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.

So anyway, this is our hypothesis about why we dream, and it's the only hypothesis that makes quantitative predictions across species.

Yeah, and the important part here, of course, is they're more visually elaborate.

You know, there are dreams that people can have in deep sleep.

Obviously, the way...

that this gets studied, as you know, is you rouse the sleeper and you say, hey, what were you just dreaming about?

What were you just thinking about?

And so if you do that during REM sleep where their eyes are moving around, they'll say, whoa, I was just, you know, riding across a meadow on a camel and this is what was going on.

If you wake somebody during other stages of sleep, deep sleep, they'll, you know, they sometimes have something like, well, I was just considering this thing

feeling i had of whatever but it's not as visual it's not as rich by the way people who are blind still have dreams but their dreams are not visual they have a dream like oh i was you know feeling my way around the living room but all the furniture was rearranged and then i felt in the corner and it was a jaguar and the jaguar started chasing me and i was trying to get away from it and so on