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Humans, by nature, lack remarkable regenerative capabilities. If you lose a finger, you can't just grow it back unless a highly skilled medical team is involved. And even with the best care, full recovery may not happen. But imagine if we could regenerate body parts like some animals do.
While humans can heal from injuries to some extent, our healing abilities are nothing compared to the impressive regeneration skills of some animals. Here’s a look at ten animals that possess the extraordinary ability to regenerate parts of their bodies, leaving human regeneration abilities in the dust.
10. Sea Slug
Sea slugs might not sound exciting, but they are far more fascinating than their name implies. Not only do these slugs live in the sea, but they also have a surprising set of abilities. Some sea slugs defend themselves by stealing stinging cells from jellyfish, using them as weapons. Others eject ink or slime to fend off predators. And some even have the ability to sever their own head to escape danger.
Elysia marginata, a type of sea slug, doesn't think twice about shedding its head—or even its whole body. This slug feeds on algae, but instead of merely absorbing nutrients, it cleverly incorporates chloroplasts from the algae into its body. By doing so, the slug can directly harness energy from the sun. However, as slugs, they are vulnerable to many other creatures, including parasites.
When a sea slug faces parasite damage to its body, it has a remarkable defense mechanism—it can decapitate itself. After severing its own head, the head continues to move around and feed. Meanwhile, the body regenerates an entirely new form. The discarded body remains alive for a time, with its heart still beating, but it is incapable of regrowing a new head.
9. Sea Cucumbers
Though sea cucumbers may resemble slugs and live in the ocean, they are actually quite distinct from sea slugs. These creatures spend their time scavenging the ocean floor, feeding on organic matter that sinks down. Despite their soft, tubular form, sea cucumbers possess one of nature's most incredible defense mechanisms. When threatened, they can expel their internal organs, creating a sticky mess that deters predators, a process known as evisceration.
However, the process of evisceration comes with a catch. Once a sea cucumber ejects its organs, it can't simply retrieve them. To survive, it must regenerate a whole new set of organs. Amazingly, sea cucumbers can accomplish this feat in just one to five weeks.
Whether a sea cucumber expels its organs through its mouth or posterior, it begins the process of regenerating an entirely new digestive tract from both ends. Over time, the two parts meet in the middle. However, if the cucumber faces further threats, it may have to undergo this process again, ejecting its insides once more.
8. Planarians
For most animals, being cut in half would be a major disaster. But not for planarian worms—they take it in stride, especially if the head is the half that remains. If you cut a planarian in two, you'll end up with two genetically identical worms, both fully capable of regenerating in just a week.
Planarians are simple flatworms that inhabit water, and their simplicity may be the key to their remarkable regenerative abilities. It doesn’t matter whether they are sliced across the middle or lengthwise; they will still regenerate successfully. In fact, they can be cut multiple times, and as little as 1/279th of a worm can regenerate into a whole new one. The secret lies in the adult stem cells, which make up 20% of their body and retain the ability to form new tissues throughout their lives, even replacing lost parts like the brain.
Researchers are particularly fascinated by the ability of planarians to regenerate their brains. It's possible to train these worms to respond to certain stimuli, and intriguingly, they appear to retain that training even after their brain has been severed.
7. Spiny Mice Skin
Mammals aren't known for their regenerative abilities. When injured, they tend to heal slowly, often leaving behind unsightly scar tissue. However, a unique species of mice from Africa seems to have found a way around this common problem.
Spiny mice are small and delicate creatures, and while their stiff hairs may offer some protection from predators, they aren’t foolproof. When grabbed by a predator, these mice showcase a remarkable ability—they can shed their skin instantly. As the predator is left holding a clump of fur and skin, the mouse escapes unscathed, continuing to live another day.
Though the mouse may be missing a significant portion of its skin, it doesn't take long for it to regenerate. The mouse grows back its skin, including hair follicles, sweat glands, and other important tissues that would typically be lost to scarring. Scientists are hopeful that the same genetic pathways used by spiny mice for regeneration could one day be activated in humans.
6. Sponges
Few animals would welcome being shoved through a sieve or thrown into a blender, but for sponges, it's just another routine in the lab. Sea sponges are among the simplest animals on Earth, lacking circulatory, nervous, or digestive systems. Their cells are mostly undifferentiated and can transform into various types throughout their lifetime. Despite their simplicity, sponges possess one remarkable ability that helps them thrive.
If sponges are broken into individual cells, those cells will naturally begin to reassemble. When the right combination of cell types is present, the cells will regenerate into a fully functioning sponge. Remarkably, if cells from two different sponges are mixed, each group of cells can recognize its own, and they will separate and reassemble into distinct sponges.
This regenerative ability is especially useful in the ocean, where pieces of a sponge can be torn away by the force of waves. These small fragments can then travel to new areas, where they can settle and grow into new sponge colonies.
5. Lizard Tails
Autotomy is the process by which an animal deliberately sheds part of its body, often as a means of escaping a predator. One of the most well-known—and somewhat grisly—examples of this behavior is the lizard's ability to sever its own tail.
Lizards are predators, which means they must venture out to hunt for food, but this also puts them at risk of being caught by other animals. If a predator grabs hold of a lizard's head or body, escape is difficult. However, if the predator targets the lizard’s tail, the lizard may have a chance to break free. Many lizards have weak spots in their tails that can be further weakened by muscle contractions, causing the tail to separate at the vertebrae. This allows the tail to fall off, giving the lizard a chance to flee. Some lizard tails continue to wriggle even after being detached, helping distract the predator.
The lizard that escapes by losing its tail can grow a new one over several months. However, this new tail often differs from the original in that it lacks the bones of the original. Instead, cartilage replaces the bones that were lost.
4. Antlers
Several species of mammals, such as deer and moose, grow striking pairs of antlers, which serve multiple functions. Male deer, for example, use their antlers to fight other males for mating rights, defend themselves against predators, and even scrape through snow to find food. Moose might also use their large antlers to help detect sounds. What many people don't realize is that most antlers regrow every year, and the process is a messy one.
In the spring, male deer shed their old antlers, and new ones begin to grow. These new antlers sprout from bony ridges on the skull and grow rapidly. The developing antlers are covered with soft fur, known as velvet, which contains blood vessels that supply the growing antlers with nutrients. Once the antlers are fully grown, the cartilage turns to bone, and the velvet falls off in a bloody mass.
It appears that the remarkable ability of antlers to completely regenerate after being shed is linked to a specific type of adult stem cell, a cell type not typically found in mammals.
3. Axolotls
Regeneration is a skill common to many small creatures, but it's much rarer in vertebrates. However, the axolotl, a type of amphibian, has perfected it. These remarkable animals can regrow entire limbs, heal their spinal cords, regenerate their tails, and even parts of their hearts and eyes. Their extraordinary regenerative powers have made them a key subject of study for scientists.
When many organisms regenerate a lost body part, the replacement tissue is often inferior to the original. But in axolotls, the regenerated tissue is identical to the original. They achieve this by converting mature tissues like blood and muscle at the site of injury back into undifferentiated cells, similar to stem cells. These stem cells then grow as if they were in a newborn axolotl. This process can continue indefinitely—if a researcher were cruel enough, they could keep cutting off an axolotl’s leg and it would keep regenerating.
One thing that axolotls cannot regenerate, however, is their natural environment. Today, they are only found in a few locations near Mexico City.
2. Hydra
Hydra are tiny aquatic creatures with a simple anatomy. They have a head with stinging tentacles and a foot that allows them to attach to surfaces. They survive by capturing prey with their tentacles and pulling it into their stomachs. After digestion, the remains are expelled through their mouth, as they lack an anus. While their life may sound basic, hydras make the most of it—they could actually be immortal.
If you cut a hydra in half, each half will regenerate into a smaller hydra. If you fragment it into many pieces, each piece may turn into a separate hydra. This happens because much of a hydra is made up of stem cells, each capable of forming a new hydra. As long as parts of the hydra's protein skeleton remain intact after being cut, the organism can regenerate perfectly.
The stem cells in hydras also account for their apparent immortality. Their stem cells continually regenerate throughout their lives. As long as a hydra is kept in a suitable and secure environment, it will never age.
1. Starfish
Starfish are intricate creatures with a relatively simple body structure. They usually feature a central disc with five or more arms extending outward. Beneath these arms are rows of tube feet that help the starfish move and hunt for food. However, the arms of a starfish are quite delicate and prone to injury or detachment. When this happens, the starfish can grow a new arm—or the severed arm may regenerate into a whole new starfish.
If a detached arm includes part of the central disc, it has a good chance of regenerating into a complete starfish. Typically, a starfish loses an arm due to an attack, or it may even intentionally sever its own limb to escape. If the arm is torn off by a predator, it’s more likely to retain part of the central disc. If the arm isn’t consumed, it may crawl off to start a new life as a separate starfish.
In certain situations, a young starfish may choose to reproduce asexually by splitting in two. Each resulting half regenerates its missing limbs, and the two halves then move on as independent organisms.
