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Why Do Animals Keep Evolving into Crab-like Forms?
The crab-like body plan has emerged many times among very closely related animals. This phenomenon is called carcinization. Crustaceans have repeatedly gone from having a cylindrical body plan with a big tail to a flatter, rounder, crabbier look, with a much less prominent tail. However, many crustaceans that resemble crabs, like the king crab that’s coveted as a seafood delicacy, aren’t even technically true crabs. They’ve adopted a crab-like body plan but belong to a closely related group of crustaceans called false crabs.
Convergent evolution is the reason why both bats and birds have wings. Carcinization is an example of convergent evolution where different groups independently evolved the same traits. Evolution is flexible and dynamic, which is evident in the fine scale at which the crab-like body plan has emerged so many times.
The Benefit of the Crab-like Body Plan
The diverse sizes and habitats in which crabs and crab-like organisms thrive make it challenging to pinpoint a single common benefit for their body plan. Some hypotheses suggest that crabs’ tucked-in tail could reduce the amount of vulnerable flesh accessible to predators. In contrast, the flat, rounded shell could help a crab scuttle sideways more efficiently than a cylindrical lobster body would allow. However, more research is needed to test these hypotheses.
There’s also the possibility that the crab-like body plan isn’t necessarily advantageous and is a consequence of something else in the organism. For instance, the crab body plan might be so successful because it opens up possibilities for other parts of the body. Some crabs have adapted their legs for digging under sediment or paddling through water, which the crab-like body plan allows them to do easily.
Why Has the Crab-like Body Plan Emerged So Many Times?
The versatility and flexibility that the crab-like body plan offers have led to it emerging so many times over evolutionary time. As a result, crabs have been able to go places that no other crustaceans have been able to go. The crab-like body plan also allows animals to evolve specialized roles for their legs beyond walking.
Crabs and other crustaceans are like Lego creations. They have many different components that can be swapped out, without dramatically changing other features. The crab body plan might leave more flexibility for animals to evolve specialized roles for their legs beyond walking, thus allowing them to easily adapt to new habitats.
Decarcinization and Why Humans Won’t Be Turning Into Crabs Anytime Soon
The crab-like body plan has been lost multiple times over evolutionary time, a process known as decarcinization. While crabs and other crustaceans can evolve the crab-like body plan in multiple ways, humans can’t. Crustaceans already have the right building blocks.
Conclusion
The crab-like body plan has evolved many times among closely related animals, with many crustaceans that resemble crabs, such as the king crab, not being true crabs. Carcinization is an example of convergent evolution where different groups independently evolve the same traits. The crab-like body plan is versatile, allowing animals to evolve specialized roles for their legs beyond walking. While hypotheses suggest various benefits of the crab-like body plan, more research is needed to confirm this.
FAQs
1) What is carcinization?
Carcinization is when the crab-like body plan has evolved multiple times among closely related animals.
2) Why have animals evolved the crab-like body plan so many times?
The crab-like body plan offers versatility and flexibility, allowing animals such as crabs to adapt to new habitats.
3) Are all organisms that look like crabs true crabs?
No, many organisms that look like crabs, such as the king crab, aren’t technically true crabs. They belong to a closely related group of crustaceans called false crabs.
4) Why haven’t humans evolved the crab-like body plan?
Crabs and other crustaceans are like Lego creations, and their body plan has many different components that can be swapped out without dramatically changing other features, which is not the case with human anatomy.
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