Why haven't we evolved to see bacteria or viruses?

[Rodney182]

TL;DR

Why haven't we evolved to see bacteria or viruses? Are there any theories as to why?

Apologies if this is too basic of a question, but it's something I've wondered. We can potentially turn this thread into a discussion as to why or what theories there are, if any.

I understand that we have 'reactions' to bacteria (in the sense of when things are dirty, we want to stay away; I'm not sure how this works either.) and reactions to bugs (though I wonder if that's truly about the bacteria/virus aspect or the fact that some of them bite us and kill us that way) and I'm not really sure if that's truly the same. (If anything, it's kinda counterproductive in modern day society when I have to clean something and can't just run away from it haha.)

But why can't we just see them visually, so we know we've rinsed them off well enough or anything similar? So we would stay away from areas where there's tons of them (like crowds, or being able to spot bacteria when your friend is sick so you know what not to touch).

I suppose there's a counter-argument to make about how much that would drive us mad because it's constant threat, but couldn't we just adapt? Like how we know roads are dangerous, but we have enough experience crossing them that we're not worried about every single car because we trust our judgment of the situation?

I love evolutionary questions and theories; I think it's one of the main things that helped me understand why a lot of things in the world work the way that they do.

If anyone wants to explain, I'm open to hearing it! Thanks for reading.

 

[Matterwave]

Physics actually can contribute here. They are too small.

To resolve things through a lens of size $D$, the angular resolution limit estimate is $\theta\approx \lambda/D$.

If we plug in values for our eyes (pupils) we get roughly 1 arcminute. So at a meter we can resolve things about 0.2mm apart. A typical bacterium is 1-2 microns (0.001-0.002 mm). To see a bacterium at 1 meter we'd need eyes 100x bigger. A virus is even smaller, in the sub-micron scale so that's even worse. This is not factoring in anything related to focal length. And minimum resolution just means "I can see two dots instead of one".

But of course, if a lot of bacteria pile up, we can see the colonies. Have you seen a bacterium culture in a petri dish before?

 

[pinball1970]

TL;DR: Why haven't we evolved to see bacteria or viruses? Are there any theories as to why?

Apologies if this is too basic of a question, but it's something I've wondered. We can potentially turn this thread into a discussion as to why or what theories there are, if any.

I understand that we have 'reactions' to bacteria (in the sense of when things are dirty, we want to stay away; I'm not sure how this works either.) and reactions to bugs (though I wonder if that's truly about the bacteria/virus aspect or the fact that some of them bite us and kill us that way) and I'm not really sure if that's truly the same. (If anything, it's kinda counterproductive in modern day society when I have to clean something and can't just run away from it haha.)

But why can't we just see them visually, so we know we've rinsed them off well enough or anything similar? So we would stay away from areas where there's tons of them (like crowds, or being able to spot bacteria when your friend is sick so you know what not to touch).

I suppose there's a counter-argument to make about how much that would drive us mad because it's constant threat, but couldn't we just adapt? Like how we know roads are dangerous, but we have enough experience crossing them that we're not worried about every single car because we trust our judgment of the situation?

I love evolutionary questions and theories; I think it's one of the main things that helped me understand why a lot of things in the world work the way that they do.

If anyone wants to explain, I'm open to hearing it! Thanks for reading.

We evolved to see prey, mates, competitors, things we understand as danger.
There are physical limitations on small things as matter waves explanation of the human eye.
We can still smell, bad odour can mean rotting and spoiling. We all recognise certain aspects of smell including death and we would have been much better at it 1000s of years ago before we had morgues and funeral homes.
So how things/food and water look and smell would have given us some warnings.

 

[pinball1970]

TL;DR: Why haven't we evolved to see bacteria or viruses? Are there any theories as to why?

I suppose there's a counter-argument to make about how much that would drive us mad because it's constant threat, but couldn't we just adapt? Like how we know roads are dangerous, but we have enough experience crossing them that we're not worried about every single car because we trust our judgment of the situation?

Most microbes are harmless, many that are not we can deal with and some are opportunistic. There are microbes covering our skin, mucus membranes, hair and teeth. That's just on the outside.
Imagine seeing all of the staphylococcus sp all over your skin? All over a mates face and hair? Before kissing her? Probably run a mile!
Evolutionary limits on the physiology of the eye spared us some unpleasant biology.

 

[DaveC426913]

But why can't we just see them visually, so we know we've rinsed them off well enough or anything similar? So we would stay away from areas where there's tons of them (like crowds, or being able to spot bacteria when your friend is sick so you know what not to touch).

We can do that a lot better than seeing them. We sense their by-products with our noses.

Noses were the first sensory organ to evolve because that's the one that finds food and avoids toxins.

The question is more informative if we turn it on its head: why, if our primitive ancestor can already smell what to eat and what to avoid, did they need to evolve eyes?

 

[renormalize]

Imagine seeing all of the staphylococcus sp all over your skin? All over a mates face and hair? Before kissing her? Probably run a mile!
Evolutionary limits on the physiology of the eye spared us some unpleasant biology.

Good point! It's analogous to what we'd have to get used to if our eyes were sensitive to ultraviolet, thereby rendering us able to see the sun damage in people's skin:

(from https://www.dailymail.com/health/ar...ultraviolet-portraits-reality-sun-damage.html)

 

[BillTre]

why, if our primitive ancestor can already smell what to eat and what to avoid, did they need to evolve eyes?

To get more information about one's environment (in a tradeoff with the costs to the organism for getting that capability).
In a SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis, its an opportunity.
Vision gives rapid warnings of distant threats and alerts to distant opportunities.

 

[OmCheeto]

Fun question. One problem with seeing them is how many there are.

From the intro of an article by the Central Dental Associates:

How Many Bacteria are Secretly Living Inside Your Mouth?​

March 13, 2021​

...​

How Many Bacteria are Present?​

It’s nearly impossible to accurately determine how many bacteria are present inside the mouth at any given time, but some estimates are as high as 20 billion. Additionally, researchers have determined that there are 500 to 650 species.​

...​

[ref]​

20 billion is roughly twice as many as there are humans on earth. Even if you could see each bacteria as clearly as you could see a human, that would take you forever to avoid the bad ones. And given they're all in such a small area, I have this feeling it would be a useless superhuman ability.

There's a fun image of a petri dish after an 8 year old played outside for a bit, indicating it's not just our mouths that are full of these bugs: Image

 

[pinball1970]

We can do that a lot better than seeing them. We sense their by-products with our noses.

Noses were the first sensory organ to evolve because that's the one that finds food and avoids toxins.

The question is more informative if we turn it on its head: why, if our primitive ancestor can already smell what to eat and what to avoid, did they need to evolve eyes?

You didn't read my post?

 

[256bits]

TL;DR: Why haven't we evolved to see bacteria or viruses? Are there any theories as to why?

Like how we know roads are dangerous, but we have enough experience crossing them that we're not worried about every single car because we trust our judgment of the situation?

And yet. incidents of pedestrians trusting their judgement and getting hit by a moving vehicle does happen.

Deer and moose seem to dart out in front of moving vehicles. They know the vehicle is something, maybe it is moving towards them due to sound, but visually there are few clues to what the vehicle is doing and how fast it is travelling - no car head movements or running legs.
People do the same - they see the car, process something in their brain for some seconds and then dart out in front and get hit. Judgement was not working. There is no dedicated jay-walking processing centre within the brain. If there was one, you would have to eat more to supply energy to keep the centre functional. In which case foraging for longer periods for food brings extra risk of becomming prey yourself.

If the eye has evolved to see smallish things such as bacteria, the brain would have to keep up with extra visual processing trying to discern the different types of bacteria. That would take extra energy needing extra foraging, with accompanying extra risk of becoming prey, inter species conflict, injury, or starvation during scarce food supply.
To keep brain energy levels down, perhaps instead something else would have to give such as taste and smell. Perhaps the creativity and adaptable tool use of the brain could go. Rather than a human looking and acting the way you do now, you would be a saucer eyed creature wolfing down food like a dog does without the favourable sensations that smell and taste provide, or just a simple creature looking around at bacteria, which are everywhere and unavoidable, for whatever reason.

Odd about pets and how they evolved a bit differently.
Cat - sniffs at new food, walks away = i don't like it.
Dog - stinkiest morcel of rancid food = this is great! ( They will even enjoy rolling on a decaying animal carcass )