Actually, we can conclude that there must be a good reason why the average human needs eight hours of sleep, as opposed to four hours or two hours or half an ho

Actually, we can conclude that there must be a good reason why the average human needs eight hours of sleep, as opposed to four hours or two hours or half an hour. Now, maybe you're trying to say that some accident in early evolution sent us down this particular branch, and now we can't get there from here. That's true, and it's really fascinating. That was indeed the idea behind my previous post. Rather the same thing happens with humans only changing teeth once a lifetime instead of continuously. There is some evidence that changing once doesn't give us an evolutionary advantage, but is simply a leftover from some ancestor's trait way back. (I'll see if I can find the reference). I'm not saying that humans might not need their sleep (we die if we are sleep deprived), but that, based on the fact that we sleep, you can't claim that sleeping creatures have an advantage over hypothetical non-sleeping creatures. Maybe it's just something that stuck and doesn't do enough harm to kill us all out.