The bird eye was pushed to an evolutionary extreme
quantamagazine.org
quantamagazine.org
More generally, human cancers cells often seem like they've rolled-back to an earlier, atavistic set of behaviors.
I wonder if that's a "direction" of random mutations which is less-likely to be attacked by the immune system, because it leads to things that are less-alien because they were normal at one point. (Or may still be normal in limited contexts.)
Ex:
> The hallmarks of cancer are not the acquisition of novel behaviors due to genomic mutation but rather the re-deployment of ancient, unicellular programs that support survival of the cell at the expense of the host and break the contract of cooperation required for multicellular life.
https://www.sciencedirect.com/science/article/abs/pii/S00796...
https://www.hopkinsmedicine.org/news/newsroom/news-releases/...
https://www.amazon.com/Red-Queen-Evolution-Human-Nature/dp/0...
This is one of the most fascinating books I've ever read.
Fascinating mental shift to explain things like the menstrual cycle (why would we want an environment that can be fully shed every month? Isn’t that crazy expensive?)
https://aeon.co/essays/why-pregnancy-is-a-biological-war-bet...
Any ideas how to raise babies more efficent?
Evolution does not optimize for the individual, but the species.
As the RQ shows, this process often leads to a dead end. Such as a short term success for cancer, but no long term success. Deadly infections lose their deadliness over time, as killing the host does not lead to propagation.
Evolution often falls into a local optima, which will inevitably lead to extinction.
Covid seems to have its mortality dramatically shrunk.
Our genomes are full of bits and pieces of ancient disease DNA. Our bodies are full of bugs that have evolved into peaceful coexistence. Some bugs even became part of us (mitochondria).
That does not support your argument that there is a adaptive advantage for reduced deadliness. The fact that it was exceedingly deadly to non co-evolved hosts indicates it was not the disease that became less deadly, but that the co-evolved hosts developed better defenses.
> Our bodies are full of bugs that have evolved into peaceful coexistence.
That is a argument that there is a continuous adaptive advantage to reduced deadliness down to ~0%. Again, Rabies had and continues to have a nearly 100% fatality rate in co-evolved hosts for thousands of years. Smallpox had a 10-30% fatality rate. Any magical inherent adaptive advantage for reduced deadliness failed to materialize to continue pushing down their deadliness.
Or put another way, a disease can have a 30% mortality rate and still do a really bang-up job at propagation with limited adaptive pressure to reduce that further for thousands of years. Peaceful coexistence is more likely a artifact of the specific dynamic than any sort of meaningful fundamental advantage to reduced deadliness.
That's a good argument, but it is not proof that there wasn't some adaptation of smallpox to Europeans. The immune systems of Europeans and Indians diverged 10,000 years ago.
> Rabies had and continues to have a nearly 100% fatality rate in co-evolved hosts for thousands of years.
I doubt that there were large enough epidemics of rabies to influence its evolution.
> Peaceful coexistence is more likely a artifact of the specific dynamic than any sort of meaningful fundamental advantage to reduced deadliness.
Killing your host does not help propagation of the disease. Causing your host to cough and sneeze is a great way to propagate.
That's hard to reconcile everything else we know: The baby needs a healthy mother in order to survive until and past childbirth and to be healthy itself. For the mother, for multiple reasons, nothing is more important than the baby's survival and well-being. Humans generally care for and will help and sacrifice for other humans, most especially those in their clan (however that's defined) and with their genes.
Don't confuse terms like "parasite" with implying evil or malicious intent.
Contrast with squid eyes, that have nerves underneath the light sensitive cells. No blind spots, better light sensitivity.
I never knew, but it explains why when you close to fainting you lose your vision. Or when you are working at high heart rate close to your maximum. It works as a kind of a warning sign, than you are probably shouldn't try it that hard.
> The lack of blood vessels could also offer birds the advantage of better vision.
Now they are ready to reintroduce blood vessels back, but this time behind the retina.
I'm not sure how fainting works, but fainting looks to me like an energy crisis, so kinda not surprising the results are the same.
I've had two complete blackouts due to Ventricular Fibrillation, and one near blackout where the VF stopped after nine seconds (as reported by my ICD). In my experience, vision and thinking seem to stop at the same time, with increased dizziness being the first functional effect (after perhaps 7-8 seconds). My ICD is set to fire at 14 seconds, by which time I'm guaranteed unconscious and won't feel the painful shock. It takes 2-3 seconds to recognise the warning signs (painless fluttering sensation in my chest), so there are 4-5 seconds of normal consciousness when I can try to make sure I fail safe. Like sitting down.
This is why I don't drive anymore.
I'm not sure how VF works, but maybe the deficit of oxygen develops much faster, so it leads to complete blackout in seconds?
> there are 4-5 seconds of normal consciousness when I can try to make sure I fail safe. Like sitting down.
Fainting and workout take more time. Definitely more. When I fainted it took tens few minutes from the moment I broke my leg. When I ride my bike up to a hill with all my might, it takes a couple of minutes to see darkness in my eyes.
When I was in college, running on the track, I decided to see how fast I could run by ignoring the stress and pain. My vision began rolling and surging in a weird way impossible to describe. I stopped and laid down on the ground, unable to do anything but pant.
I realized that what I had done was extremely stupid and never did it again.
Ha! It’s the same thing.
The distinction is very sharp and clear: adaptation is not a mere property discovered in the organism, but an exciting post-hoc human classification of evolutionary history. It's powered by the grand human psyche doing what it does best: projecting competitive, status-oriented social psychology onto non-human biological processes.
If you ever wondered "how dare biology fail to conform to a clear narrative easily processed by the human mind?", adaptation fixes exactly that.
That would have favored eyes built for sharper vision at the expense of higher metabolic demands.
The different evolutionary track may come from the fact that theropods stood upright on two legs, so they could scan farther across the landscape. Also, they were active during the day. Early mammals, by contrast, were mostly nocturnal, so hearing and smell mattered more than sharp vision.
Interestingly, humans have some of the best vision in the animal kingdom and humans are both upright standing and diurnal, i.e. active in the daytime.
In Central Europe, most of the big game (boars, deer etc.), but also foxes and hares have become nocturnal. The great exception is the Exclusion Zone around Chernobyl, where they all have reverted to diurnal life and tourists will quite often encounter something like a fox walking right in the middle of a road, looking at them with curiosity.
Everywhere else, that would be sign of rabies, but there, it is the original normal behavior.
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1. While checking Wikipedia to confirm my belief about feathers, I found that the consensus among paleontologists was that tyrannosaurs had superb vision, better than humans, in fact.
It feels like most people mix the two things up: excellent vision and predatory response. An eagle can absolutely see a mouse hiding in the bushes, not moving. But a moving prey is what triggers their predatory response. Plausibly… they probably don’t attack a non-moving mouse because it could be a dead mouse.
Human vision evolved for different things. Our ancestors were tree-dwelling and optimized for depth perception, social cues and color acuity. So it’s just a different strategy.
I was always amazed at the idea of a Radar, how it can detect objects at large distances by using reflected EM radiation, then I remember that eyes are just a RADAR and I am 10x amazed by the fact....
https://www.nature.com/articles/s41586-025-09978-w
Damsgaard, C., Skøtt, M.V., Williams, C.J.A. et al. Oxygen-free metabolism in the bird inner retina supported by the pecten. Nature 650, 657–663 (2026).
I'm not sure why this is easier, but I'm guessing it has to do with how much oxygen you need for aerobic glycolysis. In blood, glucose just exists in the plasma by itself, oxygen has to be carried by red blood cells. Without blood vessels it's probably difficult to get enough oxygen through diffusion into the inner retina.
Fun fact: the human cornea also doesn't have blood vessels. Instead oxygen diffuses from the atmosphere into it and from the aqueous humor - a fluid? behind the cornea. The aqueous humor is also where the cornea (and the lens) get nutrients from.
Yep, your cornea basically breathes!
Ever
> sometimes
Always
You can see the effect in how prey is eaten after a hunt. A mammalian sprint-predator like a cheetah has to catch its breath before eating what it has just caught. Its avian equivalent, like a Peregrine falcon, can immediately start eating.
How could it?
Evolution "optimizes" (as far as local hill climbing can go) fitness, which is the ability to produce viable offspring. Genes get mutated and then combined (in sexual species) and passed to offspring via reproduction ... that's the process that results in biological evolution, which is the change over time of the presence of alleles in a population. That's it -- there's no secret "evolution" sauce or engine. The optimization for fitness occurs through the environment affecting the relative survivability of traits--traits that increase survivability become more common in the population--this part is tautological.
They start out saying oxygen vessels partially and subtly occludes vision.
So the bird's eye doesn't suffer from this disadvantage.
In other words: It uses 15x more energy but presumably also sees 15x sharper and more into the distance than our human eye.
Sounds proportional at most, but certainly not inefficient for the bird's purposes?
> anaerobic glycolysis that is significantly less efficient than oxygen-powered metabolism
> Oxygen molecules make energy production in cells extremely efficient.
> the presence of oxygen makes energy extraction from a single glucose molecule 15 times as efficient, and sometimes more.
> This energetic ability is powered by an inefficient metabolism.
> This suggested that the strange structure wasn’t bringing oxygen into the bird’s retina; rather, it was helping to pump glucose in, thereby enabling the less efficient anaerobic process.
> Though we normally can’t perceive them, these vessels always occlude a portion of what we see, and for an important reason.
Efficiency is input / output, not just input.
15x input / 15x output is just as efficient as 1x input / 1x output.
I'm not moving goalposts. My 2nd comment just adds detail, which i hoped the reader would manage to infer based on my 1st one. That's all.
My point is it's like saying a car is more inefficient than a bicycle because it uses (more) fuel... totally ignoring that it also gets you much further and that too much faster.
Whereas a valid, to me, criticism would be that a particular car is less efficient than another car bc it burns more gas, when both do about as good a job.
Scientists noted that the bird eye produces good results with a less efficient process. This article is only about the explanation for that. Presumably they would have been just as interested if a human level eye also operated without oxygen.
Aren't crocodiles and dinosaurs seperarte branches ?
> the dinosaurs had split from crocodiles
Birds and crocodiles are both archosaurs (which includes all dinosaurs as well as crocodiles) and are each others' closest living relatives.
I believe that birds brains are kind of uniquely advanced too. Lightweight (in terms of mass) structured differently to mammalian brains... I've heard a definition of sight as "a bit of the brain popping out for a look". I wonder if the same brain density tricks bird brains use are used in some parts of their vision system. This is all as my memory serves. Feel free to correct any mistakes in my understanding.
There's some very interesting work happening to understand their calls too. If (my) memory serves, there able to identify particular call types quite well now.
If someone calls you a "bird brain", perhaps that could be taken as a complement! Trying to do more with less!
Fascinating to also think that birds are of course evolved dinosaurs. Raptors of the sky. It would be fascinating to link whats being looked at here with any kind of data that can be pulled from fossil evidence (though there might not be much...). I wonder which unique bird genetic traits were useful or super enhanced dinosaur traits.
...I think the strong but light bone structure was something inherited from the dinosaurs too? Fascinating creatures.
On the face of it, seems sensible that avian evolution has spent many genetic GPU cycles to generate advanced vision needed to fly and hunt from the air.... One wonders which "subroutines" have been reused from dino-days, as mentioned.
There's a robin who often sits in the fig tree in my back yard, giving friendly little chirps whenever I'm near. (I have no way of knowing whether it's the same robin from day to day, but if it's different robins then they all seem to be on the same wavelength.)
Anyhow, today a neighborhood cat came to the back door, and was aggressively friendly when I opened it. Clearly offering affection in exchange for... what? I've never given this cat anything before, apart from a friendly pat. Meanwhile the robin was overhead in the fig tree, giving totally different chirps than I'm used to. Clearly "warning!" "danger!" chirps. It was amazing how unambiguous they were.
I was puzzled who the robin's audience for this was, however. I'd never noticed it freaking out about cats before. Was it trying to warn me for some reason? Trying to warn other nearby birds? I couldn't see any. I thought that maybe it was just shouting at the cat out of general pique.
Then the cat led me to the answer. Turns out it had trapped an (uninjured) baby squirrel behind a planter box near my door. It couldn't reach the squirrel, and the squirrel couldn't escape. The cat seemed to be under the impression that since we were now friends, I could move the planter box and help it to get the baby squirrel. Sadly I had to disappoint it, and after unexpectedly acrobatic shenanigans, I facilitated the squirrel's escape instead.
The robin, meanwhile, ceased its warning chirps the moment it saw that I was aware of the baby squirrel. Then it watched the ensuing affair unfold, from the safety of the fig tree. Once the squirrel was safe and the cat had left disappointed, the robin looked at me, gave a few of its usual happy chirps, and flew away.
If I go outside and the crows are going crazy, something interesting is happening.
Mostly it is hawks, and the crows will chase and dive bomb them.
Once I came outside and the crows were going nuts, but not flying. And right in the middle of the driveway was a bobcat. no wonder.
a 60 fps computer display for pigeon vision is like a sequential slideshow it's much too slow to blur into what they would perceive as motion
many species of birds when they switch posture the motion is so fast it is imperceptible to the human eye it's like switching from one still frame to another
humans have perhaps 1/10th the temporal granularity that pigeons have
this leads me to the conclusion that if birds have a subjective experience it has a very different tempo than for humans or indeed most mammals
Cats also seem to have faster reactions that might be overlooked by our perceptive frame rate (imo, tested after recording interactions and reinterpreting them). Beyond eyesight, I suspect human breathing can be too noisy for their ears (consistent hissing).
Some human musicians and composers have played with similar themes, increasing or decreasing tempos by huge amounts. Examples of slow pieces include As Slow As Possible by John Cage, with a performance begun in 2001 due to end in 2640, and Longplayer by Jem Finer, which lasts 1,000 years. Musician and YouTube Adam Neely has an episode addressing the fastest tempos discernable by humans. At the upper range, the inter-beat range simply merges into a new soundform, at about 15--20 Hz, the lower bound of human audio perception.
There are similarities between the warm-bloodedness of mammals and birds that might not be coincidences.
An alternative possibility is that some ancestor of all extant amniotes already had some kind of warm-bloodedness.
Later, in the ancestors of crocodiles, turtles and lizards (including snakes), the capacity for generating heat has been abandoned, in order to save energy and allow them to survive with much less food than birds and mammals.
There is some evidence in favor of this hypothesis, besides the similarities in temperature regulation between birds and mammals.
For instance, in contrast with the amphibians, the lizards, snakes, crocodiles and turtles are dependent on high internal temperatures for their bodies to function correctly. Because they cannot generate internally the required heat, they must take it from the environment, so most of them can live only in warmer climates and they may need every day to do things like basking in solar light, before any sustained activity.
It is also known that already the ancestors of pterosaurs and dinosaurs had their bodies covered by some kind of hair, which might have had the purpose of thermal insulation. Later, that hair has evolved into the feathers of birds and of those dinosaurs more closely related to them, while in the biggest dinosaurs the hair or the feathers were lost, like also in elephants and other such big animals where cooling becomes the problem, not heating.
At least for some dinosaur or pterosaur fossils bone growth patterns are consistent with high body temperature. In the line of synapsid amniotes leading to mammals, high body temperature also appeared earlier than any ancestor of the extant mammals, but it is not known when exactly this happened.
In conclusion, perhaps warm-bloodedness (homeothermy) has appeared independently in the ancestors of birds and of mammals, but perhaps not, it could have also appeared before the split of amniotes into these 2 branches.
In general, this is the most difficult in guessing the past evolution, when you have a feature that exists only in some of the descendants of a common ancestor, is this because of independent gains of that feature, or because all the groups that do not have the feature have lost it.
Most mistakes made in the past about the evolution of living beings have been caused by underestimating the probability of multiple losses, because it was wrongly believed that evolution goes from simple to complex. Now we know that losses and simplifications are extremely frequent, typically more frequent than the development of complex features, which happens independently more seldom than assumed in the past.
(source - worked at a raptor conservancy). It depends on which bird. Some are really smart and can learn tricks (e.g. retrieving specific objects) for food rewards. They can work out simple puzzles, such as finding food hidden under sliding blocks. Crested Caracaras are examples in my experience.
Others are much less intelligent, in particular owls, who aren't particularly wise. They have great instinctive behaviours but can't solve puzzles. This is partly because, for their vision, a lot of their skull is filled with eye rather than brain - owl eyes are tubular rather than eyeballs and can't move in their sockets, hence the 270 degree neck turning.