Why birds do not fall while sleeping

I.e. why wasn't in simpler in evolutionary terms to come up with some mechanism where 1% of the brain was dedicated to the relatively simple task of "station keeping", while the rest of the brain could benefit from sleep?

I could just be misremembering things, so I’m not certain.

or it has evolved somewhere and we either don't know about it or the trait didn't survive

That said, this is not the whole story, because there are people with a rare genetic disorder called CIPA which completely prevents the feeling of pain, but they still reposition themselves, so besides pain, it is muscle fatigue (that prompts subconscious movements), autonomic reflexes, and well, sleep cycles or phases also lead to the body shifting positions unconsciously.

In any case, people with CIPA are at a much higher risk of developing complications related to immobility because they do not experience the typical discomfort (pain) that triggers movement.

I get some form of maintenance is needed, but 8h every day seems like an overkill for very significant disadvantages. Many other mammals require significantly less sleep.

Sleep according to sleep scientist matthew walker, isnt what it seems. If i remember correctly theres even more brain activity and it serves certain goals like behavior refinement, among other things not just refreshing yourself. There might not be more benefit by more sleep.

He mentions that sleep is so crucial that despite how vulnerable it makes organisms to be debilitated 8 or whatever many hours a day, what it provides more than counterbalances that massive evolutionary vulnerability.

Not everything is lost though, you can potentially learn it through repetition, you just have to do this in a half-awake state or in a state close to sleep. Do it often enough, and theoretically you may be able to perform the task during non-REM sleep.

I'd also wonder about creatures inhabiting extremely sparse environments like deep caves and undersea trenches, that spend most of their lives dormant and only seem to do anything at all when food happens to come around, which might only happen every few weeks or even every few years. They're probably not studied extensively enough to answer, but do they have anything like a sleep/wake cycle?

Some animals, mainly sharks which can't stop or they would be asphyxied, deal with that by having kind of 2 brains which are never both sleeping at the same time.

Neurotransmitters of sleep and wakefulness in flatworms https://pmc.ncbi.nlm.nih.gov/articles/PMC9216492/

"Sleep is a prominent behavioral and biochemical state observed in all animals studied, including platyhelminth flatworms."

"Dopamine and histamine decreased the time spent inactive and increased distance traveled, consistent with their wake-promoting effect in vertebrates and fruit flies; pyrilamine increased restfulness and GABA showed a nonsignificant trend towards promoting restfulness in a dose-dependent manner, in agreement with their sleep-inducing effect in vertebrates, fruit flies, and Hydra."

Persistence of Nocturnality in Decapitated and Bisected Flatworms https://pmc.ncbi.nlm.nih.gov/articles/PMC10278384/

"Here, we demonstrate that intact flatworms were predominantly active at night, with peaks in activity seen in the hours after lights-off and before lights-on. While decapitated and tailless flatworms could still move, both were less active than the original animal, and both segments retained a nocturnal lifestyle. Furthermore, decapitated flatworms, once regenerated, again showed a U-shaped pattern of nocturnal activity reminiscent of the two night-time peaks seen in the original animal. These results could be used to further investigate how regeneration may affect motor control and motor output, or to further investigate the presence of a clock in the flatworm brain."

"Nocturnal by nature, their rhythm persists even in the absence of photoperiodic cues, suggestive of an endogenous circadian clock (Omond et al., 2017). Even more interestingly, despite being closely related to other lophotrochozoans, that is, annelid (segmented) worms and mollusks (Tessmar-Raible, 2003), flatworms have secondarily lost their circulatory and respiratory systems, and endocrine glands. What remains is (1) a centralized nervous system, complete with bilobed brain (Roberts-Galbraith and Newmark, 2015); (2) a need for sleep that is regulated by sleep-wake history and induced by the evolutionarily conserved neurotransmitter gamma-aminobutyric acid, or GABA;"

A sleep-like state in Hydra unravels conserved sleep mechanisms during the evolutionary development of the central nervous system https://www.science.org/doi/10.1126/sciadv.abb9415

"Hydra sleep was shaped by homeostasis and necessary for cell proliferation, but it lacked free-running circadian rhythms. Instead, we detected 4-hour rhythms that might be generated by ultradian oscillators underlying Hydra sleep. Microarray analysis in sleep-deprived Hydra revealed sleep-dependent expression of 212 genes, including cGMP-dependent protein kinase 1 (PRKG1) and ornithine aminotransferase. Sleep-promoting effects of melatonin, GABA, and PRKG1 were conserved in Hydra. However, arousing dopamine unexpectedly induced Hydra sleep. Opposing effects of ornithine metabolism on sleep were also evident between Hydra and Drosophila, suggesting the evolutionary switch of their sleep-regulatory functions. Thus, sleep-relevant physiology and sleep-regulatory components may have already been acquired at molecular levels in a brain-less metazoan phylum and reprogrammed accordingly."

The Jellyfish Cassiopea Exhibits a Sleep-like State https://www.cell.com/current-biology/fulltext/S0960-9822(17)...

"In Cnidaria, neurons are organized into a non-centralized radially symmetric nerve net [11, 13, 15–17] that nevertheless shares fundamental properties with the vertebrate nervous system: action potentials, synaptic transmission, neuropeptides, and neurotransmitters [15–20]. It was reported that cnidarian soft corals [21] and box jellyfish [22, 23] exhibit periods of quiescence, a pre-requisite for sleep-like states, prompting us to ask whether sleep is present in Cnidaria. Within Cnidaria, the upside-down jellyfish Cassiopea spp. displays a quantifiable pulsing behavior, allowing us to perform long-term behavioral tracking. Monitoring of Cassiopea pulsing activity for consecutive days and nights revealed behavioral quiescence at night that is rapidly reversible, as well as a delayed response to stimulation in the quiescent state. When deprived of nighttime quiescence, Cassiopea exhibited decreased activity and reduced responsiveness to a sensory stimulus during the subsequent day, consistent with homeostatic regulation of the quiescent state. Together, these results indicate that Cassiopea has a sleep-like state, supporting the hypothesis that sleep arose early in the metazoan lineage, prior to the emergence of a centralized nervous system."

OPINION - Exploring phylogeny to find the function of sleep https://www.nature.com/articles/s41583-018-0098-9

"Indeed, it is interesting to consider sleep in animals that lack neurons altogether, such as sponges and the Placozoan species Trichoplax adhaerens. T. adhaerens have gland cells that are likely to contain and secrete neuropeptides91. Despite lacking neurons and muscle, T. adhaerens sense and respond to their environment and move and eat via the coordinated action of their cilia92,93,94. Sponges also lack muscles and neurons but carry genes encoding synaptic scaffold proteins95, can contract coordinately with a diurnal rhythm96 and can respond to their environment97. Evidence that Placozoa spp. or Porifera spp. have a sleep state would demonstrate that sleep is not just for organisms with neurons and would also suggest that non-neuronal cells can organize sleep behaviour." "Many plants synthesize melatonin99, although its function in plants is not elucidated100. Cassiopea jellyfish species live in a symbiotic relationship with single-cell photosynthetic algae, which provide carbohydrate fuel to these jellyfish. Do these algae also ‘sleep’ at night when photosynthetic activity is absent? Mammals are colonized with intestinal microbiota, the composition of which changes with sleep deprivation101. Should these microorganisms be considered to be sleepers? If, at its core, sleep were serving a metabolic function (see below), it is not inconceivable that plants, algae and single-cell prokaryotes will also ultimately be considered to sleep."

But to be honest, without light there isn't much humans can do at night.

Supposedly this is how dolphins sleep, shutting off part of the brain and using the other half to swim.

https://us.whales.org/whales-dolphins/how-do-dolphins-sleep/....

The 24-hour dark-light cycle on Earth is the most energetically significant thing that happens here, and species capitalize on the parts of the day that play to their strengths.

Animals also burn less calories when asleep, meaning they need less food to survive. Any change to sleep less would need to have major benefits of offset the loss of this benefit, as well as only being possible if the "maintenance" need for sleep were reduced or eliminated.

The forgotten medieval habit of 'two sleeps'

Little chitin matchbox racecaroaches everywhere ..

We do have an unconscious falling reflex, but that works by startling us awake! Actually doing movement planning requires a running brain.

It's why intelligent machines will absolutely destroy us when it comes to being "superior".