[dystroy]

We don't know exactly why nature can't do otherwise, but any complex brain has to sleep.

Some animals, mainly sharks which can't stop or they would be asphyxied, deal with that by having kind of 2 brains which are never both sleeping at the same time.

[Aardwolf]

It would be so useful if one half could sleep, and then the other half, so you never have to be truly sleep