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Comment by fifilura | Hacker News Reader

I wonder why humans can't see infrared?

Seems like it would have been a good survivability enhancement that evolution could have taken care of?

Humans are diurnal. We foraged for fruit during the day and slept when the sun went down, so it's not very clear that being able to see infrared would help.

Plus evolution doesn't work by automatically adding the best body enhancements like a superhero. It might have happened that the genes for making red cones got duplicated (making one person a tetrachromat) and then that person had lots of children and those genes gradually evolved into infrared receptors and were successful, and the mutation was not too much of a burden in other ways. Or that's all very very unlikely and it simply didn't happen.

> Humans are diurnal. We foraged for fruit during the day and slept when the sun went down

Moonlight is plenty bright enough to see by, many people (eg: Sama-Bajau) catch non fruit food (such as squid) at night with a small oil | candle light and have done so for longer than European recorded history.

Aboriginal hunters in Australia catch particular animals that come out in the cool of the night using the moon to see by.

And do not forget the good old THC night vision enhancer.

https://www.sciencedirect.com/science/article/abs/pii/S03788...

But also see this

https://www.nature.com/articles/s41598-021-81070-5

YMMV

Animals who see infrared are cold blooded. My guess is that the hardware that evolution can easily produce to detect and process infrared gets flooded by the heat of warmblooded animal and is therefore not effective for them.

We could in theory avoid the problem if our eyes were at the top of antennas.

But yeah, genetic evolution does not explore states widely different from its origin. The more complex an organism, the more "conservative" the entire process is, and we are quite complex.

Most animals don't see into thermal IR ranges eitehr but the ones closer to the visible spectrum.

The amount of rod and cone cells in your eye fill all available space. Introducing an IR sensitive cell type would take away space from existing cells, limiting their usefulness. Having night vision would mean sacrificing something else. IR frequencies would also require larger sensor cells due to their larger wavelength.

As a side note, men generally have a higher ratio of rod cells, allowing them to see in the dark. While women have a higher ratio of cone cells, allowing them to better distinguish colors. Apparently, these tradeoffs were important enough to cause for specialization in our DNA.

People with tetrachromacy have 4 cones Don’t know if that extra color perception, negatively influence other aspects of their vision

Also a lot of the IR spectrum is absorbed by water, so it wouldn't pass through the eyeball.

> fill all available space

Couldn't we have evolved physically larger eyes to accommodate additional "visual apparatus" though?

Yes, but you will find a similar analogy here. Balancing tradeoffs is a central feature of evolution.

It would also be great if we had eyes in the back of our heads to see 360 degrees.

Oh, and we should be able to hear above 20,000hz in order to detect small prey more easily.

If we don’t have a particular adaptation there are a few basic explanations:

- it just wasn’t on the path: the RNG just simply didn’t produce this outcome

- it was on the path but it was sacrificed for something else (for humans this is typically our big, energy hungry brains)

- it was on the path but just didn’t offer a selection advantage

A scenario I just came up with: Half of all humans had IR vision, but when we got control of fire, they were outcompeted by those who weren’t “blinded” by the IR output of the flames.

Someone once told me that the visible frequency range matches the spectrum for which water is transparent.

This person also said that this is an indicator of life evolving in water. That seems unsatisfactory though since it has been a long while on land.

The human visible frequencies also match the frequencies where the sun has most of its output.

Moreover, they also match the frequencies for which the atmosphere is transparent.

Regardless of how long life has evolved on land, our eyes are filled with (mostly) water - so any frequencies that can't pass through water would be scattered and absorbed by the goop inside of your eyeball.

That makes sense. I should have thought of that myself. :-) Thanks!

Evolution is the king of good enough. Things that work but have issues usually don't get 'revised'. For one of the funniest examples check out the recurrent laryngeal nerve which connects from your spine very close to your brain to your voice box... with a short little detour all the way down into your neck under your aortic arch back up to your voice box. [0] The main theory is it's a vestige of ancient fish anatomy and even shows up in GIRAFFES where it's over 4 meters long because it takes the same detour all the way down the neck.

[0] https://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve#/med...

Wow! Thanks for sharing.

For the optic nerves in humans, a similar questiom comes -- Why does it connect to the rear side of the brain when the front is much closer! This perhaps relates animals having their eyes on the sides of the head and a relatively small brain positioned in a way that the eyes were closer to the rear side of the brain.

I'm far from an evolutionary biologist but AFAIK the majority of our brain is a late addition in the scheme of our evolution from sludge to human and vision is connected to one of the older parts and the new parts are up towards the front. Another case of the iterative nature of evolution, the frontal cortex where most emotion processing happens came about and enlarged a lot through the evolution of chimps that eventually branched off into humans.

Can you imagine going through the design (well, not really design, but for the purpose of the joke…) of human eyes, like a code review?

- Nice resolution, really impressive stuff

- Can we fit in some more frequencies?

- Wait, are all the cells backwards?!?

And the massive blind spot that is handled by just having our brain be unable to notice it

"We'll patch it in firmware."

The image recognition algorithm is probably good enough to fill it in at the application layer anyway, so if the firmware patches don’t make it in we’ll see if anybody complains.

The firmware patch is wild. I carefully positioned a sign post so the sign was in my blind spot, and was amazed that I saw the full post clearly without the sign on it, just as if it had been photoshopped out. It is truly crazy how much our brains process the images we see, yet we assume we are looking directly at a representation of reality.

That applies to the minimal field of vision too.

But now advances in technology allow us to extend our sensory capabilities beyond natural limits

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