Will Crabs Ever Rule The World?
Updated: Dec 30, 2020
Yes, they just might... because this is peculiar. It is truly bizarre.
Apparently, crustaceans keep evolving into crabs.
Yes, you read that right.
Crustaceans. Keep. Evolving. Into. Crabs.
The evolution even has a name. It's called 'Carcinization', which defined in Wikipedia. The first time I came across this word (while reading up about decorator crabs) I wondered if I had read and understood it right. But the term is legitimate.
The word was introduced by the evolutionary biologist L. A. Borradaile, who described this form of evolution, where a crustacean evolves from a non-crab like form to a crab-like form, as - "one of the many attempts of Nature to evolve a crab".
This is what Wikipedia says -
Carcinisation is believed to have occurred independently in at least five groups of decapod crustaceans:
King crabs, which most scientists believe evolved from hermit crab ancestors.
Porcelain crabs, which are closely related to squat lobsters.
The hairy stone crab (Lomis hirta).
Hermit crabs.
True crabs (Brachyura).
Five groups of crustaceans!
Apparently, nature has settled on a favored body, form, and shape and it is crab.
This extremely well-written article in Popular Mechanics by Caroline Delbert says -
"We knew the long quarantine was making us all crabby, but this is extreme: People now feel fully betrayed by the long history of crabification (technically, “carcinization”) of different species over time. That means groups of crustaceans have evolved into crabs in five completely different contexts, giving rise to a meme that the long arc of history truly bends toward the crab."
"... Groups of crustaceans have evolved into crabs in five completely different contexts..."
The pithy summary - which she writes so well - is in the last sentence -
"The long arc of history bends towards the crab."
Another article (Why everything eventually becomes a crab?) is in Popular Science, which is longer and more explanatory than the Popular Mechanic article and says -
The joke—that everything will eventually look like a crab—comes from an actual truth. The crab shape has evolved so many times that scientists had to come up with a special term for it: carcinization.
Furthermore, the same article explains -
Not only is there a question of how many times a creature has gone to the crabby side, but also why they would do so in the first place. Wolfe and Bracken-Grissom are trying to figure that out now with the help of an NSF grant.
“There has to be some kind of evolutionary advantage to be this crablike shape,” Bracken-Grissom says. And while right now the gains from a crab shape are a mystery, biologists think it could have something to do with the ability to colonize new habitats or diversify into new species. After all, there are over six thousand unique species of Brachyurans scampering around the world, compared to only a handful of lobster species.
Like I said, nature has found a shape and form it likes and so many crustaceans evolve into crabs. The crab-like form may not (and will not) be their final evolutionary resting state, but this has happened enough times that scientists have a name for it.
I feel crabby more often that I like to admit and I know many others who say the same thing, but humans are not evolving into crabs any time in the future, but crustaceans are. So, next time we are crabby, we shouldn't feel badly about it. We might not molt or grow a hard shell or walk sideways, but we're feeling the evolutionary tendencies of our fellow crustaceans.
Of course, this question... as to what happened and why... is still being studied.
With NSF grants, no less.
Here is a hermit crab. Hermit crabs don't have an exoskeleton, i.e., a hard outer shell, which is the reason they carry another form of shelter (like a conch shell) with them, as below.
So, that widely given example of carcinization?
Well, King crabs evolved from hermit crabs. King crabs are huge - weighing 20 - 25 pounds. Found in Alaskan waters, they come in different varieties and are prized for their meat. For a crab meat lover, I imagine this was a good evolution. For the King crabs, not so much.
Back to what I wanted to write about - decorator crabs and their evolutionary tendencies.
One of the most interesting videos on Youtube is of decorator crabs modeling themselves. These crabs use algae, kelp, and anemones to fool their predators and hide themselves.
This decorator crab is using anemones - in a rather fetching way - to decorate itself and hide.
It's fascinating that a crab's shell doesn't grow although it does. So while the crab grows big, its shell doesn't, which means, it must discard its shell (molt) and grow a newer, bigger one.
Clearly during the time the crab doesn't have its shell - (or what is called the exoskeleton) it's unprotected and in danger from predators. So while the crab is growing a new shell, it hides.
It must.
Else it's crab cake.
Once the crab's new shell is grown, it decorates it again - with all the old decor and lots of new ones. The fascinating thing is that these crabs are really attached to what they used to decorate. So, if the crab uses ten different kinds of algae, kelp, or anemones, it removes all of that from its old shell and uses that and more to redecorate the new, bigger shell.
Mind you - a crab doesn't have a mirror. Neither does it have friends to tell it if it has missed a key spot. It uses its claws to cut and trim, then attach each of the kelp, algae, or anemone on its shell. It arranges this on its back without the benefit of any feedback - with the danger being that if it doesn't hide itself well, it will be eaten.
So, in a nutshell: it chooses, it clips, it decides on a design and decorates. Then when it must molt, it takes the decorations down, grows a new shell, then attaches everything back again.
Modeling... without mirrors, designers, helpers, or assistants... and if they mess up, they DIE.
Pretty nifty, huh?
Final question of the Day: Do Decorator Crabs get 'Decorator Crab' Envy?
Brown Crab to Green Crab: "Red is not her color - is it?"
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