[roomey]

It must give an evolutionary advantage, or we wouldn't sleep.

It may be hard to pin point exactly what advantage, but as we do it, it must have given us an advantage!

[dougmwne]

Especially considering that it is so widespread in nearly every creature with a brain. And it’s not simply a period of motionless energy conservation but has very specific neural patterns. The science is definitely zeroing in on a connection to learning.