What's the evolutionary advantage of

sleep?
I can understand big predators requiring sleep to conserve energy.
But why do humans need sleep? A group of humans who needed no or much less sleep could have easily outcompeted us.

THE REAL ANSWER FROM SOMEONE WHO KNOWS WHAT THEY'RE TALKING ABOUT

But first, I'll just say that OP/13 is arrogant, ignorant, immature and delusional. Good job basing that entire post on logical fallacy, notably ad hominem attacks, while completely avoiding the couple actual points 12 brought up (especially bullets 3+4).

Anyway, sleep is not a genetic trait. That is, it is not something defined in DNA and so it is not passed down genetically and not subject to evolution. There are genes that manipulate the sleeping process, stuff like circadian rhythm modulations and unihemispheric tendencies, but nothing like an on/off switch for the sleeping "trait".

Sleep is a physical need, like eating or drinking. It is a part of the metabolic cycle. As organisms developed larger brains, the brains simultaneously adapted to optimize time spent sleeping for memory processing and such. The reason why we "tune out" the environment when we sleep seems to be because the pathways responsible for sensory input and processing are also used in these processes.

There are many hypotheses dealing with the subject, but that's the gist of it. Sleep isn't an evolutionary matter, it's a biochemical matter. You would know at least that much even just reading the wikipedia article that was already given.

However, the notion that sleep itself harms survivability is just plain wrong. Animals do not need all 24 hours in a day to do their survival bit: eat, drink, shit, piss, fuck, etc. That stuff takes up maybe half of their time, if that. So for the rest of the day, it makes sense to conserve energy and not run around and risk getting injured or eaten.

And as has already been said in this thread, most species have sleeping behaviors that help protect them. Nesting/burrowing, unihemispheric sleep, social groups, etc. Also, many species actually maximize survivability by hiding and sleeping when most of their predators are active.

And while I'm here:
>Something that renders an organism unconscious and vulnerable to attack for extended periods of time does not stick around after it's outlived its usefulness.

No. Sorry, but you have once again shown that you do not, in fact, know what you're talking about. Seriously, pick up a book on the subject.

As I've already said, sleep isn't genetic. It's biochemical. But there are literally thousands of evolutionary traits that have "outlived their usefulness", many of which are potentially fatal. Off the top of my head:

Cetaceans (animals in the order Cetacea like whales and dolphins) still have lungs. Besides the obvious inconvenience of having to resurface often, they also suffer from a type of decompression sickness known as "the bends". This is where Nitrogen from the lungs is forced into the bloodstream as bubbles as a result of a rapid change in atmospheric pressure. This is, of course, easily fatal. After a certain depth (depending on the physiology of the species), great care must be taken not to surface too quickly. This is not a problem for species with gills, and numerous species have actually re-evolved gills after previously evolving lungs.

A much more complicated example along similar lines would be the human respiratory system, which retains numerous "features" that are quite dangerous. The larynx/pharynx area, for example. Swallowing prevents breathing, breathing prevents swallowing, and until recently with the development of the Heimlich Maneuver, choking was the leading cause of accidental death.

Another human example concerns vitamin C. Nearly every single organism on Earth, plant and animal alike can produce it internally via biogenesis. Humans are among the small handful of species that can't. The gene for a certain enzyme is defectively mutated. The only reason it hasn't been catastrophically fatal is because vitamin C is abundant in our food sources. The body can only store a very limited supply of vitamin C, and so it must be constantly ingested.

I could go on and on, but I've got shit to do and I've already wasted enough time today. The point is that even if the trait severely damages survivability, that doesn't mean Evolution will necessarily take care of it.