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The evolution of eyes (nationalgeographic.com)
152 points by sajid 11 months ago | hide | past | web | favorite | 36 comments

I'm surprised they didn't mention jumping spiders (Salticidae), which are notable because they are inverts, have the ability to see an unusual number of colors, and unlike the mantis shrimp can be trained on them. Also another advantage is they can be rewarded with sugar water. Evolutionarily, their eyesight is a marvel. No other spiders really have anything approaching it.


I have a couple as pets (https://medium.com/@melissamcewen/how-i-ended-up-with-pet-ju...) and sometimes have managed to get them interested in videos of other bugs but I'd like to develop something geared just towards them. There are a couple of things like this used in the lab, but nothing open sourced that I know of.

Wow what a rabbit hole you've sent me down. Check out this diagram of the jumping spiders (almost) completely 360 field of view. https://en.wikipedia.org/wiki/Jumping_spider#/media/File:Jum...

Have you been able to breed them?

Yeah, but no longer, it was very time consuming to care for them all. You have to care for them daily and a lot of them die anyway.

Very nice write-up. You have inspired me to look into building a terrarium and keeping some spiders. I had a Green Lynx Hunter outside my backdoor for awhile and he was so nice to watch.

Also, I hate to be "that guy" but I found a few grammatical errors towards the end of your post. The first being with "No, not poisonous, but all spiders produced venom..."(produced > produce) and "Their are no jumping spiders that have venom"(Their > There). /grammar policing over :P Otherwise awesome article, thanks for the inspiration!

Oh thanks! I fixed them.

unlike the mantis shrimp can be trained on them

Interesting, IIRC mantis shrimp are considered one of the more intelligent forms of arthropod. Perhaps it's just not the correct sensory system to communicate with them through. Evolution is certainly capable of honing an organ system's acuity independently from the organism's brain/CNS.

On a related note, it's amazing how many times eyes have seemed to independently evolve. And once they do occur in a species, it takes a lot of evolutionary pressure to get rid of them. Troglobites or stygobites generally still have atrophied vestigial eyes, despite being adapted to a purely subterranean environment. It would seem with the relatively stable ecosystem a cave would provide, stabilizing selection over a long while would select for no eyes. However vestigial eyes are still common, which I suspect implies the metabolic cost to fitness ratio of eyes must be strongly in favor of having eyes, even if barely functional.

Yeah I wouldn't be surprised if they were a bit more intelligent than jumping spiders through it's hard to judge relative intelligence in animals like these. For mantis shrimp color training probably doesn't resemble anything they encounter in the wild. For jumping spiders, they use colors for sexual selection in most species and also color is a major signal for "poisonous" in their prey — i'm not sure that's the case with mantis shrimp.

You are right, it is difficult to compare intelligence here, because it's predicated on some objective measure of intelligence. It's also difficult because the ways intelligence can manifest can look very different depending on the instance. Perhaps a more general term like "sophisticated" would be appropriate, seeing as they've adapted highly complex responses to a very dynamic and complex environment.

Biology as a field is riddled with these definition based problems, because the phenomena it's used to describe are just so intricate. Another similar problem is the "species problem," where we find countless attempts at an objective and universal definition for differentiating species, but little consensus.

In the case of mantis shrimp it's probably the stimulus being too foreign to the organism for it to have a meaningful response, like you said. So it's probably just ignoring the stimulus until it to goes away.

It may also be the organism's adaptation to an environment with many diverse predators (like a shallow water reef would have). So any unusual stimulus is automatically interpreted as threatening. If they have a tendency to freeze when exposed to acute stress, it may just be their manifestation of the fight-or-flight response. This could probably be measured by comparing nervous system arousal between threatening and foreign stimulus.

This is one of my fav papers: How (not) to train your spider: successful and unsuccessful methods for studying learning http://www.tandfonline.com/doi/abs/10.1080/03014223.2015.112...

Because it has all the failed methods for training them that never got published. Some of them are unintentionally hilarious too. > In our laboratory, we also used sprays of water as an aversive stimulus—spiders that moved into one side of an arena received a spray of water. In pilot trials, there was no evidence of learning: spiders ran wildly when sprayed and then stopped to groom themselves. If accidentally sprayed too heavily, they became trapped by the water droplet.

I think more papers like this should exist.

> it's amazing how many times eyes have seemed to independently evolve

And yet some claim that eyes couldn't have evolved, in the face of so much evidence.

People claim the world is flat. People with stupid ideas who reject all contrary evidence are extremely common in all walks of life.

Look at the champion of the anti-vaccine movement, the "progressive" Jenny McCarthy. (And they gave her a seat on The View!) Stupidity knows no race or creed.

You've been posting mostly comments that violate the guidelines. They ask, among other things, for us to comment civilly and substantively and avoid generic flamebait. Could you please change this?


I love jumping spiders. I sometimes feed them little droplets of honey from a toothpick (I leave it along their path) and they sometimes spend a few minutes drinking from it.

I also play with them and get them to chase a laser pointer, being careful to keep it away from their eyes.

Will spiders actually chase a laser pointer? Or was that last part a joke?

It's not my video, but here's an example:


Jumping spiders are simply amazing. Everything about them changed my perspective on spiders and arachnids, and I can no longer say I hate spiders.

> say I hate spiders.

Well, you hate them (and snakes) because evolutionary you're supposed to [for survival].

I just this morning on the train finished the rather enjoyable Children of Time by Adrian Tchaikovsky, which features a planet of sentient Portia Labiatas. Then came your comment and your lovely Medium article, which made me realize that the author had not overstated the characteristics of these animals at all. You may enjoy the book if you like sci-fi.

Keep in mind that they see a different spectrum. Any video you want to show them may need to be projected with special software or hardware to make those images look like bugs.

(It's not necessarily true, but worth thinking about.)

Even if they saw the same spectrum - if they have more cones, their sight won't be RGB-based, and so an RGB screen would look kinda posterized (eg the famous Obama 'HOPE' poster)

This is actually touching on a deep observation I've spent many years thinking about.

A hypothetical perfectly-realistic CG rendering would need to be perfectly realistic to animals as well as humans. Then you "capture" the realistic rendering using a virtual camera, which happens to look real for humans.

It's computationally infeasible, but the strategy seems correct.

(No one has ever achieved a perfectly realistic 100% synthetic video of complex scenes. It's good to keep such mountains on your radar -- someone will conquer it one day, but how? Could it be you?)

> A hypothetical perfectly-realistic CG rendering would need to be perfectly realistic to animals as well as humans.

That's not necessarily a true assumption - unless you mean realistic as in an exact light-propagation simulator, not realistic as in fooling humans. On the nanometer-scale there are things that happen with refraction that would probably be more accurately done if using wavelengths and photon energy as the units, start-to-finish. But at the end of the day, the models we use for rendering are already extremely effective - the uncanny valley arises with how we use them.

> No one has ever achieved a perfectly realistic 100% synthetic video of complex scenes

I get what you're saying, but that's a little bit subjective, like the turing test. Some people see some CGI scenes in movies and are shocked to find out they weren't real. Some people see a real scene and complain about how bad the CGI is! An interesting litmus test is Moff Tarkin. Some people were shocked they found a perfect lookalike, and had no clue it was CG. Some people were apalled at how poorly it was done.

It's important to qualify the claim:

- 100% CG: no mixing in real life footage.

- video. No still frames.

- reasonably complex scenes. Think nature documentary.

- reasonably long: 30 seconds or more.

- not a degenerate scene: it would be bogus if the camera was fixed, staring at a tree stump.

The overall thrust of these criteria is that no one, anywhere, has achieved fully realistic CG video. And this is easy to demonstrate. If we had that capability, you'd be able to fool people in a double blind test so that they wouldn't be able to pick out real video from fakes any better than random chance. In a scientific setting, a nature video will wipe the floor with our best CG video ten out of ten times.

Thanks for qualifying more. I'm surprised you didn't mention having humans in the video as a point - since that's pretty much what we're best at detecting fakes.

I believe the technology already is at a point for us to do this. The technology isn't the barrier to meet your criteria as much as the attention to detail. For a rendered video scene to look good, the main issue is the animation.

Still image renders are already at the point of fooling humans if enough time went into it. Then the remaining issue is the animation. Animation requires incredible attention to detail - some of which can be improved by a more nuanced understanding of the physics involved (eg water simulation or bird flight).

> no one, anywhere, has achieved fully realistic CG video

According to your specific criteria for realistic CG video.

But I still would argue the technology is already there. They just haven't made your video yet because realistic CG is done in movies. And movies aren't prioritizing meeting that specific criteria. But the talent and technology is there.

What about scenes like this from the Jungle Book?


Of course it breaks your rubric for having the boy be real. But get rid of the boy, and less stylized setting (high saturation and fog and smooth tracking camera), people would absolutely be fooled in at least some of the scenes in that clip.

> In a scientific setting, a nature video will wipe the floor with our best CG video ten out of ten times.


Spectral rendering [1] could possibly fulfill that role, given a proper mapping to the specific color receptors of those animals.

[1] https://en.m.wikipedia.org/wiki/Spectral_rendering

yeah there are a bunch of factors you have to think about when presenting them with video in experiments. Luckily it's been done enough that there is lots of documentation on the subject http://www.sciencedirect.com/science/article/pii/S0003347205...

Have you read the book Children of Time? It's a sci-fi novel with (sentient) jumping spiders as protagonists.

I was literally about to reccomend this book! It's very good!

One of my favorite eye related articles talks about The Hobbit and why 48FPS looks so bad to some people: http://accidentalscientist.com/2014/12/why-movies-look-weird...

It turns out our eyes vibrate a bit(~80HZ) to get a higher information density by injecting noise, increasing sampling above the discrete quantization[1]. His theory is that 48FPS ends up being really close to the nyquist limit and wreaks all sorts of havok on how we process the film.

[1] https://electronics.stackexchange.com/questions/69748/using-...

Oh my god that uncanny valley graph from Wired :D

I've always wondered what having eyes in the back (or side) of your head would be like. Two eyes in the front is kind of like a cockpit, you see forward and have to turn. Would having an eye in the back of your head be... Behind you? Would you be aware of the blind spots around the side of your head?

We are very ingrained in having forward facing sight, I think the mere idea of having eyes in a different position is pretty incomprehensible to us

Lots of birds and fish have eyes on the side (https://en.wikipedia.org/wiki/Bird_vision#Extraocular_anatom...), and they seem to be doing okay. Presumably you lose depth perception, so you can't hunt things, only run away.

Would probably depend on what kind of eyes and how they integrated into our overall visual perception. We might only subconsciously recognize motion behind us. See, e.g., http://www.nytimes.com/2008/12/23/health/23blin.html

What we _think_ we see and what we're actually seeing seems to be quite different. We both see more and see less than we believe. I imagine more eyes might significantly increase that complexity and nuance.

Richard Dawkins has talked about this fascinating subject several times in interviews (and in his books). It is a beautiful demonstration of how complexity and seemingly magical things can emerge from small changes over large periods of time. e.g: https://www.youtube.com/watch?v=fzERmg4PU3c

Although this is rather dated, if you liked that article you may also like Richard Dawkins' talk on the evolution of the eye: https://www.youtube.com/watch?v=2X1iwLqM2t0

It's pretty cool seeing a much younger energetic Richard Dawkins talk about how the eye evolved multiple times.

Maybe human eyes will evolve to better read smaller characters over a bigger area like the ever expanding phone screens

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