November 16, 2020
"For some reason, animals keep evolving into things that look like crabs, independently, over and over again."
"What is it about the crab's form that makes it so evolutionarily successful that non-crabs are apparently jealous of it?" (Metafilter).
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Evolution is a proven fact!
Inferring patterns in the chaos (e.g. evolution) that arises when systems and processes are incompletely or insufficiently characterized or computationally unwieldy. Back filling, infilling the missing links with dark... brown matter. Science is, with cause, a philosophy and practice in the near-domain.
Mess with crabbo you get a stabbo.
...while crabs are evolving to look like humans.
I have some educated guesses on the reasons...
We could say the same thing about worms. Worms or things that look a lot like worms have independently evolved many times.
We could say the same thing about eyes. I can't remember the correct number but I think it's something like 20. That is there are about twenty different times that we know of that eyes have evolved. Now the details of these different eyes are often different.
For instance, in our eyes, and the eyes of all vertebrates, the wiring of the retina is backwards. That is the neural fibers which connect the light sensing cells in the retina to our brain emerge outwards inside the eyeball and go across the surface of the retina before diving down at near to the center of the retina and then connecting to the optical nerve that runs to the brain. That creates a blind spot in our vision, and I don't think any of the other 19 independently evolved eye designs duplicate that flaw.
But I like the crab video. It is astonishing that such a complicated body plan has evolved multiple times and they look almost the same.
PBS Eons: Why do things keep evolving into crabs?
Good comments over there.
I should have been a pair of ragged claws scuttling across the floors of silent seas
Ah, my favorite poem, Mccoullough.
It is an excellent survival design, selective pressure will produce it repeatedly. You may as well wonder why so many animals run fast, have horns, or big scary teeth.
Crabs have evolved many times? Is that before or after butter evolved?
When you're a crab, it's easy to pull others down.
Hello wonderful person.
Anton Petrov made a video of this 6 days ago.
Link
"Anton Petrov made a video of this 6 days ago."
Yes, he did. But then I viewed it and I saw the mistakes he made.
He compares placental mammals with marsupials and talks about the similarities, but doesn't realize that both placental mammals and marsupial mammals are mammals and that all of the features that he describes as convergent already existed in the common ancestor to both groups.
For instance both placentals and marsupials have hair. This is not an example of convergence since the common ancestor of placentals and marsupials had hair. Or for another example, in both placentals and marsupials mothers secrete milk. This is not an example of convergence, since the original species from which both of these groups are descended also had mothers that secreted milk.
Actually if I want to get critical, this whole crab thing is kind of silly. It really isn't a good example of convergent evolution. What we are actually talking about is crabs versus lobsters. Most of us would agree that crabs and lobsters are already pretty similar and in most respects are basically the same thing.
What is really going on is that things that look like lobsters have evolved at least five times to look like crabs, and things that look like crabs have evolved almost as many times to look like lobsters.
This is not a good example of convergence since there are so many shared features of lobsters, crabs, pseudo-lobsters and pseudo-crabs that are the way they are not because of convergence but because they all have the same common shared ancestor.
So what is actually interesting about all of this -- this business of animals changing through time and then reversing direction to go back to something that they were earlier -- is poorly explained. And also it's not unique to crabs and lobsters for we can find many other species where a kind of wandering through time, a kind of vacillation about the preferred form, has occurred.
I last studied biology in the 10th Grade, so I don't mean to argue with someone who seems to understand this stuff. I don't have a dog in the "covergance" fight, if there is one. I thought the video made it pretty clear that there's no reason to think that we all will evolve into crabs, and that those non-crab creatures that evolved into crab-like ones did so for good reasons (or, I guess, the reasons seemed good to them). Just as, I understand, the tree-dwelling ancestors of humans came down to the ground for good reasons.
"What is it about the crab's form that makes it so evolutionarily successful that non-crabs are apparently jealous of it?
Ladies and gentlemen, the Party of Science!
I'm mostly kidding. But there are a shocking number of "I effing love science!" types who "believe in" evolution in the same way that I (who find the Theory of Evolution compelling based on the evidence) "believe in" the One who called me, the particular and specific me, into being.
Perhaps God has a sense of humor.
Chuck looks like a crab.
Is that why I'm getting crabbier the older I get?
When it comes to super stardom, natural selection disfavors bad hair and bad guitar riffs.
Ladies and gentlemen...
Crabby Appleton!
So, the biped is an anomaly? A missing link in the evolutionary saga?
"Far away up the desolate slope I heard a harsh scream, and saw a thing like a huge white butterfly go slanting and fluttering up into the sky and, circling, disappear over some low hillocks beyond. The sound of its voice was so dismal that I shivered and seated myself more firmly upon the machine. Looking round me again, I saw that, quite near, what I had taken to be a reddish mass of rock was moving slowly towards me.
Then I saw the thing was really a monstrous crab-like creature. Can you imagine a crab as large as yonder table, with its many legs moving slowly and uncertainly, its big claws swaying, its long antennæ, like carters’ whips, waving and feeling, and its stalked eyes gleaming at you on either side of its metallic front? Its back was corrugated and ornamented with ungainly bosses, and a greenish incrustation blotched
it here and there. I could see the many palps of its complicated mouth flickering and feeling as it moved."
"So, the biped is an anomaly? A missing link in the evolutionary saga?"
Yes, sort of. Except we know step by step how it happened. The only other bipeds like ourselves, and I assume you are talking about us, are species related to us. And none of these related species, of the ones that are still alive, are full-time bipeds.
Many of the dinosaurs were bipeds but big and massive tails were essential to their balance.
The birds are bipeds but again need relatively big and massive tails to balance themselves. Plus I think bird and dinosaur legs bend oppositely to our own.
Kangaroos are bipeds but the big and massive tail they need to balance themselves spends most of time on the ground propping them up.
Nothing else has convergently evolved to walk like we do.
Or then again maybe the ostrich and the rheas aren't that far off from what we do. So yes, that is an example of almost convergent evolution of bipedal locomotion.
I once went home with a woman I shouldn't have. Little critters hitched a ride in my nether region. Later, in the shower, I pulled one and took a good close look at it and thought, "I'll be damned....they really DO look like crabs".
There is a school of thought that the last common ancestor of chimps and humans was bipedal (that it walked on branches like gibbons) but that the chimp lost bipedality. Bipedality seems to be a somewhat specialized adaptation.
(And, yes, the legs of birds and dinosaurs bend opposite to our's.)
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