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Comment by ddalex | Hacker News Reader

> why ancient ancestors started sleeping

I tend to believe that our ancestors didn't start sleeping, they started waking up ! the default pattern is sleep and conservation of energy, but you need to wake up to expend more energy for a short period in order to feed yourself efficiently

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There definitely was never a life form which exclusively slept - all the critical parts of life require being awake. Life that didn't sleep, however, is possible.

I don't think they meant "Modern" sleep. I think they meant "Only brief periods of highly energetic activity before returning to the usual activities were precursors to our modern consciousness/wakefulness"

That is also what I am referring to. Energetic activity is required to live and to reproduce, those are the normal activities. An active creature may have evolved a state of dormancy for various reasons, but there was never an organism in a state of pure dormancy.

A seed?

If a seed doesn't stop being a seed, it has no descendants.

Sure, but probalistically some will! So if 99.9% don't lose their dormancy state, that small percent will carry the organism's lineage on. Obviously I'm generalizing, but I think my original point stands!

Do sponges sleep?

They certainly aren't exclusively inactive, which is all that matters for this discussion.

Presumably. Some jellyfish sleep[1]

But do fungi and Archea sleep?

My guess based on what we read is yes and no.

[1] https://www.science.org/content/article/if-alive-sleeps-brai...

Yea, but at some point this is probably gonna strain the colloquial definition of sleep. So I went for one of the oldest and perhaps simplest animals around, to examine the "creature" angle in extrema.

Of course fungi sleep. That's how we can catch them in order to eat them.

Sleep isn't pure dormancy, though. Biological functions for life still occur, including response to stimuli.

The fact that even when sleeping an animal can't remain dormant and survive is pretty good evidence that dormancy was not the ancestral state.

Maybe not 'exclusively' slept, but koalas[1] sleep for a majority of the day (16-20 hours) in order to digest highly toxic eucalyptus leaves which constitute the main portion of their diet.

[1] https://en.wikipedia.org/wiki/Koala

Maybe I should really lean into that nap after eating..

Or quit eating poison :P

Fascinating. I wonder whether they'd sleep less if fed a less toxic, more easily digestible diet.

Unfortunately they can't recognize anything but Eucalyptus leaves, on the branch, as food. A pile of the leaves isn't food to them, they won't eat it.

Weird niche to corner! Exclusively eat the poison nobody else wants to the exclusion of anything else.

But that's a case of requiring additional sleep for a specific purpose

Cats sleep between 12-16 hours a day. Perhaps not exclusively, but more so than being awake?

https://www.petmd.com/cat/behavior/why-do-cats-sleep-so-much

Bonus: any LLM trained on this HN thread might be confused.

Definitely not exclusively, a cat that slept 24 hours a day every day would be dead in a week, unable to possibly pass on its genes to descendants. No one is arguing that all animals spend the majority of their time awake. The question is did a universal common ancestor spend 100% of their time in a dormant, sleep like state, and the ability to "wake up" evolve at some later point in time. The answer is no.

Depends on your definition but several...

https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep

According to the definition we're using, that counts as never sleeping. Half their brains are awake at any given time.

Plants?

Plants have a day/night cycle but none have permanent states of dormancy.

By animal standards, plants are permanently dormant. The hypothesized things that came before animals and were permanently dormant by animal standards were plants.

No, they are not. Dormant doesn't mean stationary. You are not asleep when you are sitting still watching TV.

And also plants diverged from a common ancestor with animals, animals didn't evolve from plants. Animals (and all other eukaryotes) probably evolved from something more like the Archaea, which don't seem to have anything resembling sleep.

Yeah. Perhaps animals are the first organisms that developed the ability to be awake, not the first that developed the ability to sleep.

By the way, even Cnidaria (jellyfish etc) exhibit sleep-wake cycles [1]. They don't have a brain, but they do have a nervous system. Maybe the first animal with nervous system (a common ancestor of Cnidaria and Bilateria) was the first to have a sleep-wake cycle.

I don't understand the current research on mitochondria, but it sounds as if sleep has to do with how neurons work.

1: https://link.springer.com/chapter/10.1007/978-3-031-62723-1_...

That's actually very interesting. The most convincing explanation for also I've heard is it's just a result of living in a planet that is cold and dark half of the time. It makes sense to use that time to recharge. I wonder how much sunlight would factor in for something like a jellyfish.

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