Animals continue to evolve into crabs. Are humans next?

Coconut crabs are massive. Up to three feet in diameter, they roam remote tropical islands in the western Indo-Pacific Ocean, cracking open coconuts like they’re made of butter, eating anything edible and hiding in burrows. Last spring, Harvard University evolutionary biologist Joanna Wolfe, Ph.D., was in Okinawa, Japan, gathering information for her research on carcinization, or the study of how animals acquire carcinization-like characteristics. crabs, when he approached these monsters. Despite their name and their intimidating bulk, they don’t have a grumpy personality at all — they’re slow and “super calm,” he says.

The fact is that coconut crabs are not crabs; they are just posers. Over millions of years, evolution has “crabified” five different types of animals, including the coconut crab, the largest “land crab,” to adapt to marine or sea-adjacent environments. True crabs have been around for about 300 million years, since before the dinosaurs, and other crustaceans have been followers of evolution for nearly as long.

For carcinization to occur, an animal must lose its functional tail. It should develop a flat and rounded body, with a bent and segmented abdomen and multiple legs. So could humans ever suffer the same kind of carcinization? Will your great-great-great-grandchild or whatever look like a crab?

UNFORTUNATELY FOR THE SOUTH PARK FANS AMONG US who have dreamed of transforming into a humanoid crab, there is no way to become a crab. At the very least, you first need to be some kind of arthropod, a group that includes crustaceans, spiders and insects, Wolfe says. She is the lead author of a March 2021 article that discusses several cases and characteristics of carcinization. Although scientists have known that carcinization has existed as an evolutionary advantage in crustacean environments for nearly 150 years, the paper was widely covered in mainstream publications, which excited people.

In several interviews, Wolfe has raised the question, “Could humans ever become crabs?” It makes her laugh, but it’s also a disconcerting thought.

“Our body is not articulated and segmented like that. So we can’t do that, because you have to articulate to fold like a crab does,” explains Wolfe. “So from the earliest time of animal evolution, we’re on a different path than them”.

The most recent common ancestor of humans and true crabs, genus Decapoda (meaning “ten-legged”), was probably a worm-like animal, called a bilaterian, that lived hundreds of millions of years ago. Vertebrates and invertebrates took very different evolutionary paths up the tree of life. Mammals do not have the developmental and genomic flexibility to become carcinized, just as crabs do not have the ability to become mammals. The problem is that groups of genes in living things act collectively to perform biological functions, so “it’s increasingly difficult to make a change in one place without harmful effects in another,” says Matthew Wills, Ph.D. ., an evolutionary paleobiologist at the University of Bath in England. Compare long necks in birds and mammals. While birds retained the plasticity to develop different numbers of neck vertebrae, all mammals have seven neck vertebrae, including you and the giraffe. With very few exceptions, we’re stuck with that number, Wills says.

🦀 Did you know? The quickest way to identify a true crab, a decapod, is to count its legs. A real crab has four pairs of legs plus a pair of claws in front. Those suitors, just trying to reap the full benefits of being crabified, have three or fewer pairs of legs, plus pincers.

We see groups of significantly different animals that sometimes evolve with the same characteristics, a phenomenon called convergent evolution. The most striking example of this may be in the development of the eye, says Wills. “The convergence becomes more noticeable the longer the separation between lineages,” he says.

You, a land mammal with a complete internal skeleton and backbone, have eyes. But so does a squid, a spongy boneless sea animal. Somewhere in your ancestry, you both evolved independently to see the world through camera eyes, a complex mechanism with striking similarities. These include the structure of the eyeball itself, the way the surrounding muscles move the eyeball, the pupil that controls the penetration of light, and the lens that focuses light. Other animals from very different parts of the tree of life also developed eyes. Snails, fish, and even box jellyfish developed visual organs that share similarities with human eyes, long after their predecessors had branched off from any common ancestor with us.

The eye of a Bigfin reef squid (Sepioteuthis lessoniana), photographed near the Philippines, is remarkably like a human eye and an example of a convergent evolutionary trait.

“Crabification” is another ideal model of convergent evolution, and it has great advantages. It involves becoming fairly flat and wider than you are long. Because you can fold your abdomen under your body, you can protect it. This form is ideal for crawling under rocks to escape predators and for protecting your vulnerable soft body under a layer of thick chitin and calcium carbonate. But getting those traits comes with a trade-off: You lose the ability to escape quickly, Wills says. For example, lobsters and shrimps can fold almost in half and open quickly to shoot away from danger. So the king crab you love to eat might actually have been able to escape the net if it hadn’t been carcinized into its previous, lobster-like form. (Sorry, the delicious real crab is not real crab).

The coconut crab is a type of carcinized hermit crab, a “land crab” that roams the remote tropical islands of the western Indo-Pacific Ocean. It eats not only coconuts, but birds and small animals.

WHAT CAUSES INCORPORATION IS THE CENTRAL MYSTERY Wolfe and his colleagues are trying to solve. He is now investigating the gene pathways involved in carcinization and hopes to learn which groups of genes are common among carcinized animals, including true crabs.

While she thinks crabs are cool, Wolfe sure wouldn’t want to be crabified herself. “Do you know how arthropods grow? They molt their entire outer exoskeleton. Part of its exoskeleton includes the outside of its eyes and the first inner half or so of its gut. Do you want to do this?”

humans they are still evolving though. In one case, modern descendants of people who settled on the Tibetan Plateau more than 10,000 years ago can do what most cannot: live their lives more than 11,480 feet above sea level but not experience hypoxia, which is the starvation of oxygen in the body. fabrics That’s because they’ve developed traits that help their blood deliver oxygen more efficiently throughout the body, according to a recently published study of Tibetan women. Blood flows to your lungs at a greater rate, and your hemoglobin, the protein in red blood cells responsible for delivering oxygen to your tissues, can carry supersaturated levels of oxygen. Their hearts are also larger than most people’s, with a wider-than-average left ventricle, the heart chamber responsible for pumping oxygenated blood around the body.

Given enough time, humans can and do evolve. Just not to crabs.

Before joining Popular MechanicsManasee Wagh worked as a newspaper reporter, science journalist, technology writer and computer engineer. He is always looking for ways to combine the three greatest joys in his life: science, travel and food.