Stephen Jay Gould, a paleontologist, proposed a thought experiment in 1989. He said that he didn't think anything like Homo sapiens would evolve again. It's possible that maybe not. Crabs could.
Crabs can continue to be created by evolution. The flat-and-wide body plan has evolved many times. The process is referred to as carcinization, and it is inspired by a lot of different things.
Biologists don't know why crabs evolve. Figuring it out would satisfy the online crowd, but it would also help solve other important scientific mysteries. Some species share evolutionary paths while others don't.
Crabs are part of a group called meiurans and include brachyurans and anomurans. The biggest difference between the two groups is that brachyurans walk on four pairs of legs while anomurans walk on three. They are separated by hundreds of million of years of evolution. Each has different crabby body plans.
The earliest meiurans may have looked like squat lobsters. They widened, flattened and hardened their bodies. Their abdomens were tucked under their shells.
The transition can be dramatic. When you look at them, you wonder what the hell is going on. The girts and king crabs are vastly different. It's jaw-dropping that there have been at least four instances of this happening.
It's not clear why crustaceans keep doing this, but it could be related to mobility and predation. Extending the body makes their stance more stable. The group is famous for their sideways walking and could use that to their advantage.
The crustaceans can squeeze their discs into narrow cracks if they are crabbiness. It seems like the reverse is also true. Some species, such as co-opting snail shells or burrowing, will lose their crab-like body plans in the first place.
There isn't a one-way street for carcinization. At least seven times, crabs decarcinized, leading to weird crustaceans like frog crabs and porcelain crabs. The extinct crustacean Callichimaera perplexa might be the poster child of decarcinized misfits. According to Luque, the 90-million-year-old creature is stuck in puberty.
When crustaceans are young, they are called zoea. The newborns have long tails. Once they are mature, they settle to the ocean and form crab-like forms. Even though it's an adult, C. perplexa still has its juvenile qualities.
Luque calls it the platypus of the crab world. It's an important key for crab evolution. Crabs gain and lose their form frequently because they can change their form at will.
To find out, Wolfe and Luque are shoring up the fragmented fossil record and refining evolutionary trees. Modern tools include X-rays and genetics. Wolfe said it was a complicated story. That's alright because that's evolution.
The meme portrays crabs as the optimal body form, but it might not be. It could reflect constraints such as deep-rooted genes and developmental patterns that funnel meiurans into a small set of body plans. Jonathan Losos, an evolutionary Biologist at Washington University in St. Louis, thinks that something else has driven the evolution.
Evolutionary integration is a phenomenon that Wolfe and Luque theorize about. The shell could have been flattened if natural selection favored hidden abdomens.
Evolution is a person who tinkers. It can jury-rig different inventions with a single Lego set but it is limited by the pieces in the box. It is possible that one component is beneficial while the others are evolutionarily integrated and forced to tag along.
One example of convergent evolution is carcinization. Losos studies lizards that are commonly known as anoles and they show that convergence can cause whole bodies to align. It can be more nuanced, as shown by crabs. Crabs are not the same. They can be larger than a human and live on land or sea.
Losos believes that there must be a benefit to unifying this amazing diversity. He wants to know why convergent evolution produces facsimiles in some cases while allowing diversity in others.
When people learn of convergent evolution, they are amazed, but crabs take that to a new level. They are in cartoons, astrology, and even a dancing crab rave video that has over 200 million views.
They are different from us. We can see ourselves in there. Luque said it. They are so strange. Carcinization is so shocking to most people because they think they know what a crab is.
All Rights Reserved © 2024
