Given natural selection is true, why do we still have genetic eye sight issues? Because I would think bad eye sight would get you killed (or at least the inability to eat) in a hunter gatherer society.
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Bad eyesight wouldn’t get you killed nor stop you from eating. You’d need to have _really_ bad eyesight (as in, pretty much blindness), _and_ not live in any kind of society for bad eyesight to be lethal.
Our eyes are incredibly precise things. It does not take much to disrupt their function. Evolution is full of little tweaks and changes. If we wiped out everyone with bad eyesight, more would just be born. Fewer, but we can’t expect to get that number close to zero.
However, there is another issue. Modern eyesight issues, even with a genetic factor, are largely caused by the environment. These “bad” genes are only bad in a modern world and did not cause bad eyesight earlier in humanity.
Who’s to say that ancient eyesight was really horrendous relative to today and that natural selection has been improving eyesight for eons.
Also note that eye issue would impact people differently. A craftsman will suffer greatly from farsightedness. A hunter would have few if any serious issues from not being able to see close up.
Bad eyesight and bad enough eyesight to get you killed are two very different things. Humans have also been able to care for their sick for a very long time, leading to and increase in those who would have been too sick to pass on their genes.
Humans are social animals, so if one has bad eyesight, all of the others who see the hungry lion are warn and protect the one who didn’t see it.
I personally do not like the phrase, “Survival of the fittest” ‘cause it’s too easy to misunderstand. It should be replaced by something like, “Survival of the just barely adequate.”
A rabbit that can outrun a fox by a mile has no greater evolutionary advantage than one that outruns by an inch.
Our eyes are good enough so this is evidence that improving it provides no benefit in offspring.
A population that has an improvement here is no better off.
My eyesight (pre lasik) was 20/400. I wouldn’t have seen a predator until it was right in my face, and I’d have been useless as a hunter.
Always wondered why this wouldn’t have been selected against pre civilization.
So obviously is someone’s eye sight is so bad they cant even function that would have been a problem but one thing to keep in mind regarding “bad eyesight” is that a lot of it only matters now a days.
We have written language, so you need to be able to read really tiny characters some of which look almost exactly the same. If you never need to read (something that most people never did until the last 200 years or so) that’s a non-issue.
Well what about seeing stuff that’s far away? I mean…why would that matter? It wasn’t until recently (again, about 200 years ago tops) someone would find themselves using a vehicle that’s even fast enough that seeing something clearly from several 100 meters is *that* big of a deal. Again, there wasn’t exactly written language you need to read from a sign.
For example, I have glasses but the only thing that I really need them for is driving, and even then only at night and even *then* really only when I don’t already know where to go and need to read signs.
In addition to what the others have said, bear in mind that basically every single trait is influenced by environmental factors. In this case, there’s some evidence that not being exposed to enough sunlight when in childhood will cause your eyeballs to develop nearsighted! So whether your eyesight is good or bad is not just a matter of genes. Hunter gatherer societies spend a lot more time outdoors than modern humans who go from their homes to a school building or work building every day.
Say it with me everybody: humans evolved to take care of our sick, wounded, disabled, and old. “Humans are social creatures” doesn’t mean we like to see our friends sometimes, it means we are evolutionarily inclined to develop and maintain complex webs of social interdependency. Being born blind wasn’t a death sentence for early humans because you would have been surrounded by people who wanted you to be alive, even if that meant sharing the food on their plate. That’s one of the reason we like dogs and cats so much: they also prefer to live in social groups.
Evolution stands still for no one, baby! Lions are hella inbred but they all have perfect teeth because they need those to live. Humans, by contrast, no longer need good eyesight or straight teeth to survive so those traits no longer leads to people dying prematurely.
It’s the same thing with how women’s hips are getting narrower due to the invention of safe C-sections. Evolution usually moves real slow, but it can be relatively fast sometimes, e.g. elephants born without tusks tend to survive because a predator species (humans) are hunting them for the ivory.
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