[omgitstom]

"Sleeping animals are incredibly vulnerable to attacks, with no obvious benefit to make up for it — at best, they waste precious hours that could be used finding food or seducing a mate; at worst, they could get eaten."

It seems pretty obvious that sleep had an evolutionary advantage to conserve energy when the species couldn't be productive. For example, human sleep during the night because we can't forage / hunt / find a mate during the night because our vision requires light.

[SamBam]

"Pretty obvious" answers never hold up much to scrutiny, or the questions wouldn't be actively studied.

Many animals are nocturnal. They eat and mate during the night, and sleep during the day. From your theory, what reason do they have to sleep during the day? They could be doing all sorts of productive things in the light -- more mating, making homes, defending themselves and their babies from predators, migrating, etc etc.

Yet they need to sleep during the day. Why?

[Florin_Andrei]

It looks like some pretty heavy optimizations are needed if you want to be successful in one of those environments (daytime vs nighttime). Visual perception has to be fine-tuned for one of those environments. Perhaps thermal regulation is different too.

So I guess one possible explanation is that too many fine-tunings are required to work well in one environment, to allow the organism to be a good performer in both. So the logical choice is to withdraw from the other environment - just don't participate.

[thanksforcoming]

The parent comment only mentioned humans being diurnal, not other animals.

There's a number of strong evolutionary forces that explain nocturnality: niche differentiation, crypsis, a predation arms-race, water conservation, etc.

https://en.wikipedia.org/wiki/Nocturnality#Survival_adaptati...

[SamBam]

I'm not sure your point about humans vs other animals.

Are you suggesting sleep evolved for a different reason in humans than it did for our ancestors and the millions of other species that sleep?

[gnaritas]

That doesn't seem obvious at all, it presumes sleeping is about conserving energy and that's an unwarranted assumption and baseless assumption. Sleep very well could be a requirement for brains to work they way they do. If you are deprived of sleep you will shortly go crazy; sleep isn't about saving energy.

If you see anything that seems obvious, you can bet science already checked that out and moved past it and that it's more complicated than that.

Anytime your beliefs conflict with science, you should immediately question your beliefs, not the science. The odds are absurdly high, near a virtual certainty, that your beliefs are wrong; never assume science is missing the obvious (unless you're a scientist and it's your field of study, then you might be onto something but you're still probably wrong).

[outworlder]

Yeah. For starters, there is a whole bunch of toxins that build up when you don't sleep enough. But it can't be the whole story, as why wouldn't we have mechanisms to remove those and keep the brain functioning?

It can't be all about memory retention. There are some fascinating studies on how some groups of neurons repeat the same patterns they did when the organism was awake, presumedly for long-term storage. But why can't storage happen while awake?

There must be a reason why these "brain batch processes" run while most of the brain is shutdown.

[brazzledazzle]

I've found that it's best to not think that evolution optimizes for the best thing but rather that it optimizes for "good enough". Sometimes they are one and the same but they don't have to be.

Sleep could have started as a rudimentary adaptation to one thing and ended up being refined and coopted for other things.

[Freestyler_3]

Evolution is diverse, if all living things need sleep then I think its A: something that is absolutely needed, without it you wont survive [guaranteed] B: A left over from our common ancestor

[Noseshine]

    > why wouldn't we have mechanisms to remove those and keep the brain functioning?

I don't know if it's in the links below, but I remember hearing a talk that the flushing required physical changes inside the brain: Widening of channels (by neurons getting smaller and making room, if I remember that correctly?). So normal function can't go on while the flushing process is being performed.

https://www.nih.gov/news-events/news-releases/brain-may-flus...

https://www.nih.gov/news-events/nih-research-matters/how-sle...

Since we have distinct sleep phases we may not have just one "sleep", (very) different things going on at different phases.

[jpttsn]

Science can often be helped by some questioning, esp. from scientists outside the field of study.

[jsprogrammer]

>If you see anything that seems obvious, you can bet science already checked that out and moved past it and that it's more complicated than that.

Science doesn't do anything. Even if it did, you should be able to look the obvious results up and figure out where current research has taken your question.

[erdevs]

Many nocturnal animals have eyes and utilize vision of light. Also, many animals who wake during the day and utilize vision of light also frequently hunt at night (eg see lions during hotter seasons).

It may well be that specializing systems such that they perform well during daylight only could lead to greater advantage than maintaining additional mechanisms for performing well at night also (or vice versa), and that sleeping during the downtime in order to conserve energy might confer supplemental advantage in this scheme. But we don't know if this explains all sleep, in all species.

Even if we did, then sleep in animals which perform reasonably well at any time of day would still be unexplained. Common ancestry wherein sleep evolved earlier may explain that, but we don't have that evidence as far as I know.

As such, it doesn't seem this is quite so easy to conclude about, let alone obviously so.

[duaneb]

> For example, human sleep during the night because we can't forage / hunt / find a mate during the night because our vision requires light.

What makes you think the causality is in that direction? This is clearly a teleological argument (read: assumes that everything has a function, which is contradictory to the way evolution works, where the only function is to help your genes propagate).

[bbctol]

Taken on its own, unconsciousness is a massive evolutionary setback--an explanation like "conserves energy" doesn't cut it, when there are plenty of nocturnal predators around. Why didn't humans evolve to lie down at night, with their heartrate and breathing slow, but remain fully aware of their surroundings? That would make survival to reproduction age a lot simpler.

[callesgg]

No, there is animals that sleep during the day and can see perfectly good during the night.

[gonehome]

As other commenters has said it's not that obvious.

I suspect it's more that sleep is a necessary requirement for consciousness, but it's not clear why. Maybe recalculating weights for the neural net based on new input data requires 'downtime'.

There was some earlier evidence that 'cleanup' is happening the brain or some chemical pathways were being reversed. Either way behavioral speculation based on evolution isn't very good science.

[outworlder]

> because our vision requires light

Even on a new moon, there's plenty of starlight. Nocturnal animals are able to take advantage of that.

[dominotw]

>because our vision requires light.

doesn't that assume that requiring light came before sleeping at night. It could be the opposite, our vision requires light because we sleep at night?

[dsr_]

Optical vision does not seem to require sleep:

https://en.wikipedia.org/wiki/Sleep_in_fish