Well put!
What would be in that space without this bit of tissue? A gap. A straight clean merger to the end of the eye? Would that actually be better? Perhaps this is better than nothing. Perhaps it is better at removing dust or protecting the eye than not having it. It could also be that it is benign, and there is no advantage to letting it become expressed smaller or larger in successive generations.
I’m going to take “no longer serve a purpose” with a grain of salt. There’s been quite a few things with our bodies that science initially thought might just be “evolutionary leftovers” that actually had significant functions for our bodies. Our appendix which most people thought was just there to occasionally try and kill you by bursting is now being found to harbor bacteria that can fight infections and could be a part of our immune system. There was a point where you heard about “junk DNA” being thrown around in articles while science was figuring out the ins and outs of our DNA before eventually finding that the “junk DNA” that had previously thought to do nothing it plays a critical role in holding our genome together (https://www.sciencealert.com/scientists-find-a-crucial-new-role-for-dna-we-once-considered-junk) by ensuring that chromosomes bundle correctly inside the nuclei of our cells. Without that function, cells die. Or gallbladder’s that I’ve had three friends have removed because of medical issues is now being studied because it appears it holds a backup of our gut’s bacteria so if our gut bacteria gets wiped out it can re-seed our gut with the proper bacteria.
Anyways, not trying to bag on scientists and science, just saying it’s a risky venture to say something doesn’t serve a purpose or is “junk”. Since some of those things we’ve thought were useless or not needed have since been found to play a role in our bodies that we would be worse off without.
I know of the vestigil organ humans have that USED to manufacture vit C.
Mammals; cool story.
But crocs have nictitating membranes they can see through.
I am jealous because that would be so handy for underwater swimming.
So, with a little DNA tweaking these features could be reactivated? That third eyelid could be real handy when Trumps oligarchs finish destroying the EPA. They’d keep the coal soot out of your eyes. Let’s hear it for the worthless pile of shitsacks in the Senate who rubber stamp every appointment their fuhrer makes regardless of how much they are dedicated to rolling back every bit of social progress that has been made in the last 100 years.
Birds too. Herons use the membrane to protect their eyes when fishing.
The Strike by Graham Moore, on Flickr
You can see it protecting the front half of the eye in this picture.
Pretty sure I saw that in action on The X Files.
Also useful when swimming out to check the mailbox after the West Antarctic Ice Sheet gives way.
see, this is one of those instances in which 240p just falls flat on its face
Wasn’t the appendix once considered a useless & worthless organ?
Depends how you define intelligence, some would say there’s been several successful ventures in that direction.
The outer edge is quite thin, it likely does a good job of deflecting debris that could otherwise get wedged behind the eye.
I can see how an extra horizontal eyelid would have pros and cons. I guess having something acting like a Third Eyelid Blind would give you a Semi-charmed Life.
Paleontologist Neil Shubin has a book - and a TV show - called “Your Inner Fish”, all about this kind of stuff.
Yeah, this is why I don’t really like the way vestigial structures are often described.
They are structures that no longer server their original purpose. One of the things that make vestigial structures interesting is that they often get repurposed. Lots of them do something. It may not be critically important, it may not be the “best” way to accomplish that job. If there is an easy adaptation from a existing structure that satisfies some selection pressure, frequently that is what will happen.
If you don’t already know this one, enjoy… (or not…)
https://rifters.com/real/Blindsight.htm
and more so in:
This. Vestigial does not mean “no longer serves a purpose”.
Vestigial organs are relics, reduced in function or even completely losing a function. Finding a novel function, or an expanded secondary function, does not make such organs non-vestigial.
I just discovered that I have the vestigial Palmaris Longus arm muscles and I was really good at climbing trees as a kid, I also really like banana’s. Dammit It all makes sence now, however i’ve never had the urge to fling my poop at anyone so it’s not all bad, lol.
