Which animals can regenerate like Doctor Who? | BBC Earth Explore

Wouldn't it be amazing if like our favourite Time Lord, or Time Lady for that matter, we could regenerate our bodies when we need it? Our friends over at the Doctor Who channel are experts at all things Who, and I'll leave a link in the description for you to check out all of the Doctor's regeneration so far. Sadly though, for those of us that aren't Time Lords, there's no chance of a full body overhaul in just a few minutes. But you might be surprised by how much regeneration does go on in the natural world. Because in fact, every animal has the ability to regenerate some part of itself, even humans. I bet you're doing it right now. Every second, we regenerate 2 million blood cells to replace those at the end of their life. And when we cut ourselves, skin cells can regenerate to close the wound. It's not just individual cells either. Our livers are remarkably resilient, and the whole organ can regrow from just a fragment, a quarter of its original size. But there is a limit to our Time Lord-like abilities, and there's a lot of crucial stuff we can't regrow. Lose a hand or a leg, and a replacement won't appear, however long you leave it. But for lots of animals, that's not the case. Take deer for instance. Male deer have impressive antlers made of bone, blood vessels, and a layer of skin called velvet. They're structures, but the deer will actually shed them every summer. Regrowing the antlers can take up to four months every summer, but by the end, they will have a glorious new set of prongs ready for the mating season. While deer use regeneration to keep them looking fresh for the ladies, for other creatures, it can be a matter of life and death. When threatened by a predator, certain types of lizards are able to completely detach and drop their own tails. Once severed, the tail will wriggle around on the ground, distracting the attacker while the lizard makes its escape. And then, over the next few weeks, the new tail will regrow. It won't be an exact copy, but it will help it stay balanced, and of course, help them to avoid being caught again. Similarly, sea cucumbers also opt to eject body parts as a defence mechanism, only they go a step further. When threatened, they can violently contract their muscles and eject some of their internal organs through their anus. Lovely. Obviously, it's hard to get by without your innards on the inside, so regeneration for these guys is crucial, and therefore, very quick. It doesn't end there either. Some animals have almost limitless potential to regrow parts they lose. Axolotls can make a perfect copy of almost any part of their bodies. Sea stars can replace all five of their arms as long as their central ring of nerves is intact. And certain flatworms can rebuild their entire bodies, including their head, from just a single fragment. The trick for these animals lies in embryonic stem cells, which have the potential to become any kind of cell, to build different body parts when in the woo. In humans, our embryonic stem cells are basically switched off after we're born, but it works differently for these miraculously regenerating animals. They still have a reserve of stem cells, and when a new body part is needed, they migrate to the injury site to begin dividing and differentiating, following a blueprint provided by some newly activated genes. So whether it's a tail, leg, intestine, or even a head, stem cells are the all-purpose tools for the job. And in fact, medical researchers are investigating both the stem cells and the blueprint genes in the hope that we might be able to put them to use in our own bodies. Meaning that maybe our dreams of real-life Time Lords aren't too far away. If you enjoyed this romp through regeneration, be sure to give us a like and subscribe, and don't forget to check out the Doctor Who channel for more about the real Time Lords. I'll see you next time.