Robert Avila is a structural engineer and avid reader of biology regeneration, with emphasis on quality research.
1. Lizards Regrow their Tails
Ever try to catch a lizard as a kid? I did. He promptly dropped his tail and sped to the underside of a log pile. The tail's inside on the open end was pink in the center and radiated outward to white and then to radiant blues and greens. I thought I must have grabbed something made of plastic. Then, I thought I must have ripped it off.
My sisters, crying, took the incriminating evidence to our grandmother and aunt. Looking up from their sandwiches and tea, they explained very carefully that lizards "let go" of their tails so they can escape from animals that want to eat them.
Some time later, we saw it again. It was sunning on the top of the split logs. And, right behind him was a small new tail growing out!
So, what other animals can lose a tail? What about a leg, an arm, or even a head? As curious as it sounds, some animals can lose their head, and regrow it. Some of these are described on this page.
Does a Lizard Regrow an Exact Replica Tail?
Mexican Salamander, the Axolotl
2. The Axolotl
Okay, it is also called the Mexican Salamander. But, Axolotl sounds cooler. Plus, doesn't it sound a like a name from the Mayan pantheon?
The Mexican Salamander can regrow a tail, similar to the lizard. However, the Axolotl outperforms the common American lizard. It can also regrow any of its four legs, or even it's lower jaw.
It is believed that axolotls are now extinct in the wild. However, these are very popular as pets. And, some university research departments have colonies. One population at Indiana University has selectively bred albino Axolotls.
The tunicate is also called a Sea Squirt in the common parlance. Scientists say Botrylloides leachi. Tunicates live in colonies. Each individual member can produce an entire new colony all by itself.
Tunicates are connected to the other members of their colony by a network of blood vessels called ampullae. Some scientists took 95 samples of ampullae and put them into the appropriate environment. Of these, 80 regrew into full adult Sea Squirts.
If you want to read more about tunicate life cycles and research, see the links section at the bottom of this page about animals that regrow limbs.
Sharks Regrow Unlimited Teeth
4. Shark Teeth
Most humans grow two sets of teeth. We discard one set in early youth. Then, we grow our "adult teeth." These you will keep for the remainder of your life, barring accidents. But, some people have hyperdontia, more than two sets. One such woman lived in my childhood neighborhood. In her thirties, she lost all her teeth, and regrew a third set! She told us it was not uncommon in her family. She said this happened to some people on her mother's side.
But, sharks have far more than two, or even three sets. Shark jaws continue to produce new teeth over and over again. That is how human jaws produce teeth, too. A young child has adult teeth inset into his jawbone. When the body reaches the right conditions, the first set begin falling out. And, the second set comes in.
In an average shark lifetime, one of these carnivorous fish can go through 40 sets of teeth.
Does Everything Regenerate?
All life can recreate its own kind of life. Every animal has the ability to regenerate. Plants produce fruit. Each year, year after year, following the first harvest of fruits, trees produce a new crop. Apple trees, orange trees, and others are able to produce fruit, cast it off, and then regrow new fruits the following year.
Even more interesting, in each fruit, seeds are carefully nestled inside. Those seeds contain the ability to regenerate an entire tree from just one seed. All the seed requires is the right set of conditions. Once the proper environmental triggers are present, the seed produces roots and pushes a stem up toward the sun.
So, while this article discusses animals which can regenerate a lost part, all living things are able to replicate new generations. The process is locked inside each animal.
Hydras live in the sea. They stick to rocks and reefs and other things on the sea floor. Once in a while, an animal passes by and nibbles off a tentacle. The hydra does not worry about this loss. It just regrows a new tentacle!
Even more curious, a hydra can be cut in half, and grow a new bottom half. If that impresses you, ponder this:
The hydra can regrow its head. Yes, if it loses its head (it has only one), it will regrow a new head.
Don't be jealous of the hydra just yet. Sure, it can regenerate no matter what is lost. But, when you get to feeling envious, remember this caveat: the hydra has just one orifice which fulfills the functions of both mouth and anus.
How a hydra makes baby hydras:
Deer live on all continents except Antarctica (where they only have Rudolph and other flying deer.) Every year, male deer grow a new set of horns. They use these to intimidate other males, and if necessary, duel. At the end of the season, the horns simply drop off.
New horns grow during "rut season." The new horns have a dermal layer which the deer rubs off after the horns complete their growth. Near the base of the horns, deer have glands that secret a scent. As the deer rubs the trees, the scent is left. This signals females he is ready for courting. And, it warns other males that the territory is claimed.
One interesting facet of the horns is that the horns regrow a little longer each rut season. But, the length equal to the previous year is exactly the same.
Here are two videos showing the deer seasonal cycle of horns. In the first, at the end of the season, a mule deer takes running leaps to jar the left tines off. In the second video, a deer exfoliates his velvet using a tree.
A Mule Deer Loses his Horns
A Deer Rubs the Velvet off his Horns and Marks his Territory
Two Legs Regenerated
7. Spiders can Regenerate Legs
This is not true if you've crushed one under boot. There is no need to fear zombie spiders growing new legs and seeking revenge. Spiders cannot reanimate themselves. But, their innate capacity to regrow a lost leg is still impressive.
If a predator captures a spider by one of its eight legs, the spider will self-amputate the leg. Then, it will slowly regrow the lost appendage. Spiders must molt in order to grow (similar to snakes.) When a Wolf Spider loses a leg, that molting cycle is delayed by an average 3.7 days. But, the spider body corrects for this delay in growth by accelerating the subsequent molt cycle.
A Must Read
What can humans regrow? Well, let's start the discussion with a reminder that humans, like all other animals, plants, and insects, can produce future generations.
Aside from that, humans regenerate a second set of teeth. We can also regrow hair. And, if a fingernail is ripped out, it will regrow. But, there is something more interesting than this. young humans can regrow the tips of their fingers if they are accidentally cut off.
For the finger to regrow, the child must be younger than about 12. This is the age where this benefit seems to wane. And, at least the lower part of the base of the finger nail must remain in place.
Liver: Humans can also regenerate a portion of the liver. If up to twenty-five percent is lost, it can regenerate.
The research into human regeneration capabilities, and the electrical activity associated with healing, repair,and regeneration has been largely spearheaded by Robert O. Becker. He published a book written for the general public, "The Body Electric." It is an amazing book. Everyone should read it. Every medical researcher and practicing physician should read it, too.
A fascinating photo series of a regrowing finger on an adult male.
Plants Growing from a Part
Yep. Many of the common vegetables you make into stews can regrow from a just a part. Carrot tops, even without any stems or leaves, can regrow (new greens sprout first.) A potato can grow out from just a chunk with one eye on it. Green onion can regrow from just the tiny stump at the bottom, the part with the roots. Lemongrass also regrows into a full plant from just the roots. Basil can grow from a cutting. Bury a piece of ginger, and it will grow a full plant and many more ginger roots.
See the link at the bottom for an interesting and fun article. You can try to regrow full plants from just parts of them. Some fruits can also regrow from just the top. Pineapple is one such regenerating fruit.
The first living thing to ever be cloned was a carrot. That was in 1958. A carrot was fully cloned from a single stem cell taken from a root.
Main Parts of a Sea Cucumber
10. Sea Cucumber (Shoots out its Innards & Regrows them)
The Sea Cucumber looks a bit like a Hydra. It has a long, cylindrical body and tentacles surrounding it's main orifice (where it eats.) But, the Sea Cucumber is not sedentary. It is not attached to rocks at it's base, as are Hydra. So, the Sea Cucumber has an exit for consumed food, same as most other mobile creatures.
It is categorized in the same sub-phylum as the Sea Star. Like Sea Stars, Sea Cucumbers have no brain.
What makes the Sea Cucumber interesting is the ability to expel some or most of its own internal organs. There are many reasons it does this. See bottom links on this page for a great piece on how and why they do this.
What parts can it regenerate? Some types, cut in half, will fully regrow into two adults. In all of them, whatever organs they expel, they can replace. So, this animal can regenerate everything from suction feet to nerves to tentacles.
Most Interesting Regenerative Power so Far?
11. The "Immortal" Jellyfish (humorous/informative version)
12. Sea Star
The creature formerly known as starfish is today cruising the coral reefs and beaches under a new nom de mar: Sea Star. These multi-legged crawlers of the sea bottom can be cut into several pieces of just one leg each, and each leg (also called a ray) will mature into a full sea star. It will have legs equal in number to the original host.
Sea Stars are related to the Sea Cucumber family. Like their cousins, they have no brain as do vertebrate animals on land. Instead, they have clusters of nerves which seem to control life, personality, sense of humor, and of course, regeneration.
The Sea Sponge is perhaps the most amazing of all. Put one in a blender, and every tiny bit can reassemble to the others and grow into new sponges. Even a single cell can generate an entire sponge.
Sponges can reproduce either sexually, or asexually. Perhaps because they are so hearty, they exist in every sea of the world. Sponges are widely harvested and used for common tasks. Some sponges make excellent cleaning aids because of their super power in absorbing and holding liquids. Others are used by proponents of natural products to exfoliate skin in the shower. Some are even used by menstruating women.
The most famous sponge of all is Sponge Bob Square Pants. Curiously, his best buddy is Patrick the Sea Star, who can also regenerate. They live in pineapple. The pineapple can regrow from just the top portion. And, Sponge Bob works at the Krusty Krabb, for Eugene Krabs. Crabs can regenerate a claw, if one is lost. Another character, Squidword Tentacles, is another animal with regenerative abilities; the squid can regenerate tentacles.
Wounded Crab Detaches Claw (go to 1:10 of video)
The crab can regrow claws if lost. Regeneration is not as rapid as it is for the spider. It takes three molt cycles. And, each molting cycle is a full year in length. After three years, the crab will have replaced the lost claw with one about 95% of the one it lost in size.
And, like spiders, crabs regenerate lost legs.
A Tadpole Tail Influenced to Regenerate in a Late Life Cycle
If a tadpole loses a tail, no problem. A new tail will be fully regrown after just a week. At the University of Manchester, England, experimenters were able to observe that H2O2 increases after a tail is amputated. And, during the entire regrowth process, H2O2 levels remain elevated.
A fresh water Planaria worm can be cut up into 279 pieces, and all will regrow into a full worm. The video below is an excellent overview of the life of flat worms.
Flatworms have only one opening to both eat and to discharge waste. It is similar to the Hydra in this regard. They can also reproduce asexually. This is another similarity to the Hydra.
Flat Worm Life
- How tadpoles re-grow their tails: Implications for human healing -- ScienceDaily
Scientists have made a surprising finding after studying how tadpoles re-grow their tails which could have big implications for research into human healing and regeneration. * New thinking on the role of oxidants.
- sea squirt | chordate | Encyclopedia Britannica
Any member of the invertebrate class Ascidiacea (subphylum Urochordata, also called Tunicata), marine animals with some primitive vertebrate features. Sea squirts are primarily... (a very serious brief on Sea Squirts.)
- The Echinoblog: Sea Cucumber Evisceration! Defense! Regeneration! Why? GROSS!
A somewhat flippant, yet informed discussion of Sea Cucumber evisceration and regeneration of organs.
- Dual leg regeneration in a Mexican red knee tarantula (Brachypelma smithi) | Things Biological
The opportunity to watch and record leg regeneration in this individual has been really enjoyable. It was obtained in a batch of six siblings on January 11, 2013 and voluntarily automized one of its front legs on January 21, 2013. You can access deta
- 13 Vegetables That Magically Regrow Themselves
Some plants can fully regrow from a top portion. Others can regrow from any part at all.
- Missing Legs? Not Much of a Problem for Spiders | EvoEcoLab, Scientific American Blog Network
This interesting, brief article overviews a study of Wolf Spiders regenerating legs. After just two molting cycles, the spiders had made up for any setbacks in growth rate and size. This anecdotal evidence suggests the cells know the appropriate size
- From One to Many and Back Again: A Systemic Signal Triggers Tunicate Regeneration
A brief overview of tunicate life cycles and colony process.
Robert A. Avila, PE, MCE (author) from Kiev, Ukraine on July 22, 2015:
Yes, sea sponges can regenerate a lost portion. Sponge Bob Square Pants has been killed, and returned for the next show. So, I'm assuming he's immortal.
peachy from Home Sweet Home on July 22, 2015:
spongebob can regrow? I thought sponge don't
Robert A. Avila, PE, MCE (author) from Kiev, Ukraine on April 18, 2015:
Thank you, Sharp Points, for the generous comment. And, thank you anonymous up-voters! Much appreciated.
Sharp Points from Big Bear Lake, California on April 17, 2015:
Very interesting and awesome article. That Mexican Salamander is wild. I can tell you put quite a bit of work into this hub, Two thumbs up!