Why birds do not fall while sleeping
news.cnrs.fr
news.cnrs.fr
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.
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.
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.
But to be honest, without light there isn't much humans can do at night.
The forgotten medieval habit of 'two sleeps'
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.
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?
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."
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.
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.
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.
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.
or it has evolved somewhere and we either don't know about it or the trait didn't survive
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.
Little chitin matchbox racecaroaches everywhere ..
It's why intelligent machines will absolutely destroy us when it comes to being "superior".
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/....
We do have an unconscious falling reflex, but that works by startling us awake! Actually doing movement planning requires a running brain.
Are they saying that birds are in a stable equilibrium while standing? I always assumed that some low level activity in the Cerebellum would actively stabilize them even during sleep.
If this is not the case, a dead parrot should be perfectly able to stand, right?
An interesting and somewhat related fact is that flying birds also sometimes sleep: https://www.audubon.org/news/scientists-finally-have-evidenc...
The short story (at least in the case of the frigatebirds they studied) is that they do hemispherical sleeping, where only one half of their brain is asleep. And also it seems they only sleep while climbing in a thermal updraft. The theory being that "gliding up" is the safest portion of their flight.
Relatadely there is a famous videoclip of a paraglider colliding with an eagle mid-flight. https://youtu.be/g8_hyqlQXpk?si=alAvnt4Xva4RGYw3 (The clip is quite scary, but both the pilot and the eagle seems to be fine at the end.)
It is speculated that the incident happened because the bird was "dozing off" mid-flight in the updraft too. Of course this is difficult to verify.
Obviously a wheel is the easiest design you can build based on tension given its symmetric nature.
https://www.youtube.com/watch?v=hkzeE6BVNIk [Super Ball Bot, NASA]
However, witnessing the rapid evolution of AI with just a few hundred GPUs, enough data, and power, I no longer wonder what a billion years of feedback loops and randomness can achieve.
Sure, you have dominant genes like eye colour. But evolutionary changes to a whole species are more about weeding out genes that cannot survive, right? Because if a species has no specific sexual selectors for breeding and all mutations survive and reproduce, then how does a specific gene thrive?
Edit: but chatting to my wife, she mentioned that species is a difficult concept, generally taken to be a generic group that actual mate in the wild. There are several different species that could technically produce offspring but through sexual selection, do not.
Now I wonder if internal structure of cells can be attributed to that too - i.e. organelles create zones where processes relying on fast random walk can work, enabling the cell itself to grow bigger.
A single training session will iterate more than the number of generations of all birds.
But that's not the right analogy. Evolution happens at the individual level, and even to some extent at the individual gamete level. So it's actually every single fecundated bird egg that ever existed, and even every single spermatozoon and egg cell every time two birds mated. Not to mention every division of every bacterial cell in every bird gut, since microflora are a key part of the organism too.
And even this is an undercount, since the DNA and gene expression of an individual actually changes during its lifetime, and those changes can be passed down to offspring through various mechanisms. So there is a constant process of evolution that even all cells inside a living organism go through, that we're still trying to fully understand.
That statements need a whole lot of backing. It contradicts the Central dogma of molecular biology [0]. The idea that an organism can pass on to its offspring physical characteristics that the parent organism acquired through use or disuse during its lifetime is called Lamarckism which was disproven more than a hundred years ago.
[0] https://en.wikipedia.org/wiki/Central_dogma_of_molecular_bio...
For an extremely simple example, if a female organism is exposed to significant doses of radiation, the DNA inside the egg cells it was born with will have a high chance of suffering mutations. If one of those eggs remains viable and later gets fertilized, the DNA of the offspring produced from it will be significantly different from the DNA that of offspring born before the radiation exposure.
There are other more subtle and more common processes, though. The most surprising one is that DNA methylation, a process in which environmental stimuli encountered in a living sexually mature individual affect gene expression, has been proven to be transmissible to offspring across several generations in certain species. This includes stimuli such as prolonged exposure to heat or cold, long-term starvation, and others. This is indeed a form of Lamarckism that has actually been proven to happen, though of course it involves much subtler changes than some of what Lamarck envisioned.
I don't think that's the right way to think about it. Genetic variation originates at an individual level, but "evolution" (differentiated survival of genetic variants) mostly happens at population level after genetic changes have spread among the population. In particular this is the case with "punctuated equilibrium" that has been observed in the fossil record (long periods of stability, interspersed with short periods of rapid change).
What happens is that many genetic variations are subtle and don't have an immediate survival benefit to the individual, so will just accumulate in the population as a whole as they are spread by breeding. Once in a while some environmental change occurs (famine, drought, disease, new predator, etc/etc) that may make a set of accumulated genetic changes, previously benign, now become more important to survival. With multiple sub-populations of the same species that have genetically drifted apart over multiple generations, some will now become more successful than others in this new (changed environment) evolutionary landscape.
Ultimately this sub-population genetic drift may lead to inability of these sub-populations (e.g. plains elephants vs forest elephants) to interbreed, and then no-going-back speciation has occurred, and further drift is guaranteed (due to no interbreeding to merge genetic changes).
I should have expressed myself more carefully. What I am thinking of is that each individual is essentially one training step, where the current model is confronted with the training data (in this case, the entire environment, including other members of the population). Or even multiple moments over the life of the individual might be considered distinct training steps, where the model is adjusted in minute ways (epigenetics) based on certain events.
Of course, this makes less sense for species that are highly communal, such as bees, ants, or termites, where the fitness of an entire population is highly interconnected, and even severe maladaptations in an individual can nevertheless be an improvement to the fitness of the overall population (e.g. sterility in the vast majority of individual bees and ants is not a detriment, when it is a fatal flaw in almost all other animals).
LLM training is training an organism to "survive" in an environment consisting of languages/lexicons.
Not getting eaten by a tiger is equivalent to being able to produce a semantically and logically correct sentence.
If suppose evolution were to occur , then many wrong and absurd things would emerge or they would not have come into existence. But there is no disorder or mistake in the past or present and everything seems to be created perfectly.
"We see that in its existence, its attributes, and its lifetime, while hesitant among innumerable possibilities, that is, among truly numerous ways and aspects, each thing follows a well-ordered way in regard to its being in innumerable respects. Its attributes also are given it in a particular way. All the attributes and states which it changes throughout its life are specified in the same fashion. This means it is impelled on a wise way amid innumerable ways through the will of one who specifies, the choice of one who chooses, and the creation of a wise Creator. He clothes it with well-ordered attributes and states. Then it is taken out of isolation and made part of a compound body, and the possibilities increase, for they may be found in that body in thousands of ways. Whereas among those fruitless possibilities, it is given a particular, fruitful state, whereby important results and benefits are obtained from that body, and it is made to carry out important functions. Then the body is made a component of another body. Again the possibilities increase, for it could exist in thousands of ways. Thus, it is given one state among those thousands of ways. And through that state it is made to perform important functions; and so on. It progressively demonstrates more certainly the necessary existence of an All-Wise Planner. It makes known that it is being impelled by the command of an All-Knowing Commander. Body within body, each has a function, a well-ordered duty, in all the compounds that one within the other themselves become components of larger compounds, and has relationships particular to each, in the same way that a soldier has a function and well-ordered duty in his squad, his company, his battalion, his regiment, his division, and his army, and a relationship particular to each of these sections, one within the other. A cell from the pupil of your eye has a duty in your eye and a relationship with it, and has wise functions and duties in your head as a whole and a relationship with it. If it confuses these the tiniest jot, the health and organization of the body will be spoilt. It has particular functions with regard to each of the veins, the sensory and motor nerves, and even the body as a whole, and wise relations with them. That specified state has been given it within thousands of possibilities through the wisdom of an All-Wise Maker.
In just the same way, each of the creatures in the universe testifies to the Necessarily Existent One through the particular being, the wise form, the beneficial attributes given it among numerous possibilities. So too when they enter compounds, those creatures proclaim their Maker with a different tongue in each compound. Step by step till the greatest compound, through their relations, functions, and duties, they testify to the necessary existence, choice, and will of their All-Wise Maker. Because the one who situates a thing in all the compounds while preserving its wise relations, must be the Creator of all the compounds. That is to say, it is as though one single thing testifies to Him with thousands of tongues. Thus, from the point of view of contingency, the testimony to the existence of the Necessarily Existent One is as numerous, not as the number of beings in the universe, but as the attributes of beings and the compounds they form..."
So turn your vision again: do you see any flaw? Then turn your vision a second time; your vision will come back to you in a state dazzled and truly defeated(Quran)
state and point out, however much the human gaze tries to find faults, it can find none anywhere, and returns worn out to its dwelling, the eye, and says to the fault-finding mind who sent it: “I am worn out for nothing; there are no faults.” This shows that the order and regularity are most perfect
Counterpoint: allergies, birth deformities, cancer
Hill climbing obviously gets stuck easily in 2 or 3 dimensions. So our intuition ain't reliable.
Also our intuition about overfitting from lower-dimensional representations seems to be less of an issue at high dimensions.
LLM Algorithms don't "evolve" when trained, they just fit data in a pre-existing and hardwired "DNA". More GPU, data, energy consumption etc. simply means different weights (parameters) for the same fixed algorithm. Training involves no feedback loop on the algorithm design itself. The biological analogy is like what happens when you starve or overfeed somebody: They become skinny or obese (but they will not pass on that attribute to their offspring).
The algorithm's DNA is explicitly designed and put in place by human intelligence. When thinking of the observed "evolution" of algorithms we need to include the sum total of the people involved in algorithmic design and deployment, their cognitive toolkit, incentives etc. Now that part is definitely "evolving" (various mathematical, technical or economic breakthroughs), not biologically of course, but culturally.
So-called AI Winters (and other AI Seasons) are indeed evidence of this collective cultural movement. You could say that the invention / adoption of the multilayered neural net pattern has led to a sort of Cambrian explosion similar to going from single cell to multicellular organisms.
Take humans, for example. You can block your trachea and die through the simple act of eating. An intelligent (and omniscient) designer could have avoided that by better designing our overall our overall structure.
Or take the fact or ear bones are modified jaw bones. Or if you believe in intelligent design, ask why our intelligent designer thought it wise to link our jaw to our ears so that it’s hard to hear things when you’re chewing.
1. The designer does not have to be "omniscient" only intelligent. Some people believe in it's omniscience but I don't think it's a requirement.
2. How do you know that our trachea is not an optimal design when you take into account all the tradeoffs?
3. You're surrounded by items created by intelligent design (us) and all of them have flaws, reused parts and tend to break. Obviously you wouldn't argue based on this that they weren't designed by intelligent beings.
Because if we were designed from scratch we could have been designed in any optimal shape or form.
> You're surrounded by items created by intelligent design (us) and all of them have flaws, reused parts and tend to break. Obviously you wouldn't argue based on this that they weren't designed by intelligent beings.
Show me an intelligent designer who can literally design the universe, but is still not intelligent enough to avoid these flaws even we can recognize. I don’t think we are intelligent enough to design a completely novel life form, let alone as many as exist on earth in all their forms.
This is all beside the point that there’s no evidence of any kind for intelligent design, only supposition based on nothing more than intuition and feelings.
Would a perfectly and optimally designed being get no diseases? won't die? won't fall?
If we ever make silicone man that runs on sunlight then I'll say, "ah, this looks like a being created by a moral intelligent designer".
It's going to be pretty revealing when a creature with such "lowborne morals" as ourselves creates a being that can function and operate without the explicit need to kill something every ~7 days to survive.
But yes, there are a million ways in which the human biology is imperfect.
If our bodies are temples, then whoever made us is probably Nurgle. Nothing else really explains the reproductive organs sharing space with the waste removal ports.
Only if you assume the designer had infinite time, knowledge and resources. But life on Earth did not have to be created by some omnipotent god who created universe. It only requires more advanced intelligence than us. Although theoretically even we may reach this level in the future with advances in bioengineering.
> This is all beside the point that there’s no evidence of any kind for intelligent design, only supposition based on nothing more than intuition and feelings.
Depending on what you consider "evidence" the same sentence could be said for evolution. There are many arguments in favor of intelligent design like for example no viable mechanism of randomly evolving genetic code. I wouldn't say it's as open and shut case as you make it seem.
No need to be so coy. Who/what else do proponents of intelligent design believe designed us if not an omnipotent, omniscient, God? Ancient aliens? Deep Thought?
If there’s some other scientific theory of “intelligent design” you’re referring to, please enlighten me as I’m not aware of it.
> Depending on what you consider "evidence" the same sentence could be said for evolution.
There is empirical evidence for evolution.
The examples you quote do look like a problem today, but I think they must have worked to some benefit to bring us here.
If anything, your optimal design is just another mutation that may or may not survive time.
Which is the absurdity I’m pointing out.
Of course you can. We could regenerate limbs like a lizard’s tail, keep growing teeth like a shark, not require so many different types of foods to survive healthily… The list goes on and on.
I disagree, evolution is not perfect nor intelligent (as far as we know). It's never the "best design" that survives, it's always "good enough for now", merely better than other solutions at the time. A billion years of good enough is not necessarily the best it can be theoretically.
I'm sure we can find examples of living processes that are dumb and inefficient, with obvious room for improvement, but have survived for millenia simply because it was good enough.
The fact that conditions change doesn’t make your current form ideal.
Speaking of conditions.
In 5 billion years there will be no need for natural selection cause Earth will dip into the exploding Sun and evolution game will be over. Nothing will keep working. Even in 1B years it will be pretty hot outside. We’ll have no time for that “optimal” crap anymore, starting now tbh, considering our stupid tribal nature and the complexity of overcoming it.
Btw, if we fail to continue our current civilization, there will be no another civilization, cause we’ve drained all under-your-feet resources long ago. The next civilization will be forever farmers slowly burned by a star.
We absolutely can escape this fate by finding something much better than a bare minimum.
Edit: messed up numbers, fixed
Please point to a theory of intelligent design that is verifiable and doesn’t involve magic.
Iow, it’s not only robust enough, but just robust enough and never pretended to be ideal or durable, except for few accidental cases like sharks, crocs and turtles. Who surely can suffer from long-term non-killing issues but cannot whine to their GP about it.
The examples you quote do look like a problem today, but I think they must have worked to some benefit to bring us here.
Nah, it’s a vast space. There may be natural trade-offs, but there’s no force to solve an issue in the best way possible. It solves randomly and if that creates a non-fatal problem - bad luck, now we just have it. You’ll always have a set of non-fatal problems just under fatality, and also a set of fatal problems just under a reproduction disabling line.
Personally, and in hindsight ofc, I find abiogenesis much more miraculous than the life/evolution following it, cause the latter was sort of obvious and almost indestructible by its nature after it all started. It sort of just happens unamazingly in the complexity space it is lazily exploring (which itself is amazing that it exists).
Only intelligent agents can explore it with a goal different from (but still including) stable reproduction.
No, the other consequence of evolution is that whatever we are today is not enough to kill us. Some of the things in our bodies and behavior are just useless, but not bad enough that they endanger our life and cut the genetic deviation responsible for it, so it just keeps on being there.
There's no good reason we still have 5 fingers on feet, but they're also not bad enough that having them all would endanger us as as species, so they just stay there.
There are parts that might be a million years old, but everything is in a state of flux at all times. Things are changing all the time. Evolution is a process with no end goal.
And just because that got us here today doesn't mean it's the best design. If that's the case, cats are equally the best design. As are dogs, and elephants, and mosquitos, and platypuses. Evolution is the ultimate form of the adage, "You don't have to be faster than the bear, just faster than your friend". Good enough works well enough.
We are effectively held together with duct tape and string. Our eyes are wrong, our backs are wrong, our throats, nerves, circulatory, etc. are all wrong in some manner. And some of the fixes are simple. There is no reason for our ocular nerve to start from the inside of the eye. It just happened that way. And it worked well enough.
You can use a lead pipe to hammer nails, that didn't make it a good choice.
Design is all about tradeoffs.
It starts with a discussion about the miseries people suffer and if they have any utility at all. Is pain a useful warning of problems or could that information be gotten across in a better way?
It ends with the two characters agreeing that neither believes in God, with one not believing in a good and kind God and the other not believing in an evil malevolent God.
That is basically the entire premise of intelligent design. Not that there is no evolution, but that it is a guided process.
Half a billion, afaik. And also how technology matters. Oxygenless ~3.5B years were boring as hell.
For those unaware: Earth not always had O2 in its athmosphere - O2 is a result of one kind of ubiquitous goo that was emitting it as a byproduct. And while it oxidized what it could on the surface, it killed almost every goo, cause it is a poison. Then (and that is still an unproven theory) oxygen-breathing evolved and allowed for fast movement and carnivory, which started arms race of tracking and evasion, coordination, vision, swarming, etc. 0.5B years later here we are.
Btw, there were even higher peaks of oxygen concentration that allowed for animal-sized insects to exist. A time insectophobes wouldn’t want to live in.
Scientists know that dragonflies with wing spans as wide as a hawk's and cockroaches big enough to take on house cats lived during the Paleozoic era (245-570 million years ago). At the same time, mammoth millipedes longer than a human leg skittered across prehistoric soil.
https://youtu.be/oY32HPQrhYg?si=z0QO821u3-E5sJ6l&t=480 (about millipedes from 8:00)
The thing with evolution is that it is robust. Even after the human species collapses (with everything it manages to bring down with it), evolution will still work.
Modern humans have been very quick at many things, but at the cost of breaking the conditions of their survival. One may say "that's wrong, with enough GPU a solution will appear", but on the other hand maybe we have already passed the tipping point where we actually cannot solve it anymore.
It might be more readable on low-res screens that hint the strokes to a full pixel width, but on Retina screens it's simply too hard to read.
Thin weights like that are meant for display uses (titles, posters, etc.), not body text.
Kangaroos?
Also, I see both of my dogs standing on 2 legs every day, often walking short distances like that. According to wikipedia this only happens when they are trained to do it (?!) but we never trained them and they've been doing it since a few months old. Maybe I should update https://en.wikipedia.org/wiki/Bipedalism to indicate training may not be required for temporary bipedal behavior in some dogs.
That is against wikipedia's rules and thus will get reverted. You have to have a secondary source, not a primary source, and you're currently a primary source.
https://en.wikipedia.org/wiki/Wikipedia:No_original_research
Whether it gets reverted essentially depends on whether someone would bother before it gets lost in the depths of the change history and how the GP chooses to respond if someone did.
What has 4 legs in the morning, 2 in the afternoon, and 3 in the evening?
The key here is how relaxed is the interpretation of "permanent".
To answer the question: a yacht race?
(Aside from AI Yacht's, of course: https://www.youtube.com/watch?v=U79-kDQnbPE )
Now, nobody is completing that race in one day, but that’s a different issue.
~ https://en.wikipedia.org/wiki/Oedipus_Rex
( spoiler: he loved his mother )
Only the healthy adult form is taken into account generally, you wouldn't say that dragonflies are mainly swimming animals for example, even if they do spend most of their life underwater as larvae.
The point here is that kangaroos that are capable of bipedal motion will always choose quadrupedal motion at low speeds. While humans who can walk will always choose to walk when possible.
I think I’ve done that once in the last 10 years, and I spend a fair bit of time in the woods.
A table. My table. To solve this stupid riddle, I remove 2 of its legs before afternoon and screw one of them back on before the evening.
Sphinx, I dare you to refute me.
Many of the animal sanctuaries in zoos in Australia actually have little signs telling visitors not to be disappointed if they don't see the animals actually hopping: "Laying down and sunbathing, and the slow walk with their tail is a sign of relaxation and a lack of stress on the animal."
When birds relax, their feet curl in a similar way, and this provides enough grip that if they're on a perch, they will automatically hold on as easily as if they're awake.
There's a bit more to it, as the way the tendons in their feet and legs are attached, the foot will automatically grasp when the ankle is bent, so it's a much stronger grip than our floppy relaxed fingers would provide. Here's a quick rundown with a good gif illustrating how it works. https://windycityparrot.com/birds-sleep-standing-one-leg/ They also have an extra balance organ between their hips that help them sray upright, so the whole anatomy lends itself to sleeping like this.
Additionally, when we're awake and moving, we're constantly on our feet, so our feet and legs will get tired and need a rest. However, our arms don't generally get tired just from walking around, right?
Birds are the opposite. They spend a lot of time flying, and their feet are mostly relaxed and resting while they're in the air. It's the wings and chest muscles that get tired.
So sleeping on their feet has a whole other connotation to them.
But some birds can use tricks to fly without flapping, and I'm pretty sure some birds can sleep aloft.
https://news.mit.edu/2017/engineers-identify-key-albatross-m...