REM sleep may be required for maintaining the cortex in complex nervous systems.

“you could argue that well for the same reason that the cockroach can survive the nuclear disaster the avian mammalian pathway is more evolved neuronal e presumably and therefore probably requires something essential in rem that when it deprives you it takes away your super power which is a cortex and I think that's exactly what it is which is when you look at anything that has essentially a complex nervous system maybe that's where the pressure for this thing called REM sleep emerged”