Today’s Wonder of the Day was inspired by Aiden from , . Aiden Wonders, “How close are we to regenerating limbs?” Thanks for WONDERing with us, Aiden!

Do you know the pain of a scraped knee? If you've ever been skateboarding or bicycling, then you might have experienced an unfortunate accident that caused your skin to come into contact with the hard pavement. Ouch!

When you scrape or cut your skin, the pain can be intense. Fortunately, you can clean the wound, apply some bandages and ointment, and your skin will heal itself over the next week or so.

But what happens if you're in a serious accident, such as a car wreck, and you lose a hand, foot, arm, or leg? Such tragic wounds can leave people with permanent disabilities. While some people are able to use prosthetic limbs, others must simply learn to live life in new ways. If only human beings could regrow missing limbs…

Although human beings aren't able to regrow missing limbs, there are several creatures who can accomplish this amazing feat. For example, newts and salamanders can regrow missing limbs, such as arms and legs. Lizards, such as skinks, can regrow missing tails. Starfish can regenerate missing arms. Flatworms can rebuild an entire body from a single cell!

Scientists have studied these creatures to figure out how it is that they're able to regrow limbs. They hope to apply their findings to humans one day. Based upon the limitations of the human body and modern science, however, it's not likely that humans will be able to regenerate missing limbs anytime soon.

When salamanders lose a limb, nearby skin cells seal the wound, forming a structure scientists call the wound epidermis. The cells in the wound epidermis send chemical instructions to the cells below. In response, nerves start to grow again while other mature cell types revert to form a mass of immature cells called a blastema.

Eventually, the cells in the blastema multiply and become new bones, skin, nerves, and muscles. Incredibly, these cells somehow know exactly what is missing and only regenerate what is needed. Despite years of study, scientists still don't know much about how these amazing processes work.

In addition to trying to learn how salamanders and other animals regenerate limbs, scientists have also studied why humans cannot. Although scientists don't yet fully understand why humans can't regrow limbs, they do have several ideas.

One hypothesis involves how the human body works to stop cancers from forming and growing. Some scientists believe the processes that keep cells from growing uncontrollably into tumors might also prevent a structure similar to a blastema from forming in humans.

Other scientists believe our warm blood might be a factor. Unlike amphibians, humans have high metabolic rates that require regular feeding. One result is that the human body must heal itself quickly. Human bodies simply don't have time for a limb to regrow slowly over the course of a month or more.

The secrets of limb regeneration might also lie within DNA. Compared with humans, salamanders have 10 times more DNA. Does all that extra genetic information help them to regenerate limbs like they do? If you grow up to be a genetic scientist one day, maybe you can study salamander DNA to unlock the secret!

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