The Origins of Regeneration

Meera Singhal
6 min readDec 5, 2020


From ancient stories and tales to animals and humans, regeneration has turned from a myth to reality. Keep reading to see the storyline behind it!

Looking at ancient ideas and the research they inspired

The remarkable animal (and human) ability to grow body parts back has baffled and inspired curiosity in humans for such a long time. From the ancient Greek myths and gods to proven regenerative genes in animals, the line between what’s possible and what isn’t often gets blurred by society (and movies). Before the science was proven, or the facts were discovered, the ancient Greeks used their belief in gods and myths to portray the concept of regeneration.

Through all of Greek mythology, two myths stand out in the relevance of stem cell research and the idea of regeneration or the idea of using stem cells to grow (regenerate) new body parts; the story of Prometheus’s eternally regenerating liver, and the tale of the many-headed Hydra.

The tale of Prometheus originates long back to the creation of humans. When God had created humans and placed them on earth, he didn’t realize how his creations would become so greedy so soon. As time went on and this cycle of greed continued, Zeus' anger towards humans started to increase at a massive rate. Finally, he blew up at them and took fire away. Without fire, they started to freeze to death. Prometheus, as a kind-hearted god, decided to face Zeus' wrath, steal fire from Zeus, and gift it to the humans. Instead of punishing the humans again, he decided to punish Prometheus for stealing from him. Zeus tied him to the Caucasus Mountains, and he sentenced him to a lifetime of torture; every day a vulture could come, pick out his liver, leave him to regenerate his liver, and repeat the process. Besides this being a fascinating (and disturbing), myth, it actually inspired quite a few scientists to explore the liver and its properties. The scientist made a discovery that you can cut out a piece of a human's liver, and they can grow it back within a month! Even though humans can replace their liver every single day, the idea of regenerating a portion of their liver is well within scientists' grasp of understanding.

This next story involves regrowing heads; something that the Greeks couldn’t prove without committing murder. However, Greeks could have observed something similar in other animals like how some lizards can regrow their tale. Regardless, this spectacular idea somehow made its way into a story about Hercules.

As a punishment for killing his children after being manipulated by a furious god, Hercules had to perform a series of near to impossible tasks known as the Labors of Hercules. The first task was the slay a sea creature with poisonous breath and regenerating heads. This fearsome, many-headed beast was named Hydra. Hercules eventually destroyed the creature by cauterizing the Hydra’s necks so that new heads couldn’t grow back.

No one really knows where the idea of the many-headed beast came from, but researchers have known for centuries that some creatures can regenerate body parts and even whole new bodies. This idea however has been passed through myths and stories (like Harry Potter and the 3 headed dogs), Other animals that can regenerate include certain types of worms, frogs, lizards, and crustaceans. Early Greek storytellers may have observed regeneration among certain animals and used it as the basis for the tale of the Hydra.

Regenerative Animals

In 1700, the father of Zoology, Abraham Trembley of Switzerland, discovered a small creature that attaches itself to plants in fresh water and uses its tentacles to capture and eat prey. He spent countless hours conducting countless experiments to decided whether it was a plant or an animal. The experiment that led to his success was when he split this creature halfway down the center. The result of this? It grew two heads. In one of his experiments, Trembley induced one of these creatures to regenerate seven heads. Thinking he had discovered a new species; he called the creatures polyps. Today however they are called hydra because of the Latin root water and the fearsome beast in Greek Mythology.

Over hundreds of years, curious scientists (and even children!), have discovered many animals that have regenerative body parts such as:

· Crayfish: When crayfish lose a claw or leg, they grow new ones. In fact, crayfish have special break-away joints so that when a predator grabs a claw or leg, the appendage breaks at the base, allowing the crayfish to escape.

· Earthworms: If you cut an earthworm in half, the head end will grow a new tail. Interestingly, in some earthworm species, the tail end, if it survives, also grows another tail, so it eventually starves to death.

· Frogs: Adult frogs don’t generate new legs, but the hind legs in frog tadpoles can grow back. Since the tadpole is still in developing stages, it can have its legs cut off, grow them back, and live a healthy life, with healthy legs.

· Newts and starfish: When newts or starfish lose a leg, they grow new ones. This is one of the more “famous: facts about regenerative animals.

· Planaria (a half-inch long flatworm): You can cut Planarian worms into as many as 32 pieces, and each piece will grow into a complete worm with head, tail, mouth, eyes, and all internal organs. Scientists now know that these types of worms have huge numbers of stem cells all over their bodies, and those stem cells seem to be able to grow into any type of cell the worm needs at any time during its life.

Human Regeneration

All animals, including humans, have at least limited regeneration powers of regeneration. Even if it's something as simple as healing from a wound (a small cut or graze), all animals can use their skin cells' regenerative properties to heal.

Humans do not have the same regeneration capabilities as starfish and crayfish; if you chop an arm off a human, it doesn’t grow back. But your body does regenerate some things. If you lose a fingernail, for example, your body grows a new one. If you break a bone, your body creates new bone tissue to mend the fracture. Other human tissues that regenerate include blood (generated by bone marrow), liver, and skin.

Red and white blood cells eventually wear out and die off, so stem cells in your bone marrow create new supplies of these cells. This may seem like it’s a part of the cell cycle, but scientists have also classified it as a regenerative property.

Stem cells in the skin generate new skin to replace the cells you lose every day and to cover minor wounds, such as a scrape or shallow cut. However, if you keep picking at a scab or wound, the skin cells won't regenerate forever so you may be left with a scar. This is the primary reason doctors tell you not to pick your wounds (also because they don’t want to see you get hurt). In more serious wounds, your body creates scar tissue in addition to new skin. In severe burns, the skin stem cells are destroyed, leaving the body’s skin regeneration system crippled. The loss of skin stem cells explains why treating and healing burns is so challenging — and the presence of skin stem cells in other parts of the body explains why skin grafts are sometimes successful in repairing burned areas. This is why you may use neurosporene for some deeper cuts, it simply helps the skin grow healthier and faster.

Remember, no one has yet figured out the biological mechanisms that allow some human tissues to regenerate and not others. Whether it’s the extra nutrients and factors that your body contains or another scientific reason, scientists simply haven’t figured out why some animals can regenerate some body parts and not others. Clearly, humans and the various animals who do grow new body parts have significant biological differences. Even more puzzling, though, is why your liver can regenerate itself, but your kidneys and heart (among other organs) don’t seem to have that ability. Stem cells may hold the answer to creating new tissues that the body doesn’t regenerate if scientists can figure out how to activate the proper mechanisms to grow those tissues in the lab.



Meera Singhal

Biotech Enthusiast at TKS | Stem Cells | Gene Editing