What a great question! There are actually multiple levels of regenerative abilities in animals, and this is a huge area of research for scientists. Some animals have remarkable regenerative abilities, like one called botryllus, can regenerate entirely from a single tiny piece of blood vessel. The worm planarian can be cut in half and both halves will regenerate to create two whole new animals! The better-known starfish can regenerate from a single limb!

Geckos can regenerate their limbs and tails (but we humans cannot!). However, geckos cannot regenerate everything. Regeneration in geckos follows a similar pattern to how geckos grow and develop – how the limbs and tails are created when a baby gecko is forming!

If a gecko didn’t regenerate its limbs it would probably still survive. Before the limb is regenerated, the wound is already sealed. Therefore, the limb is regenerated for future survival, since it will be easier for it to find food and escape from predators if it regenerates lost limbs. The lost limbs are regenerated using a similar process to how the limb was generated in the first place when the gecko was an embryo.

Internal bleeding is when blood vessels rupture, spilling blood into the internal cavities. Unlike the loss of limb, this poses an immediate danger and the slow process of limb regeneration won’t help.

Additionally, the blood vessels are present throughout the entire body which makes it way more complicated than re-growing an appendage in one place. The loss of blood alone can kill the gecko, or pressure of the blood can compress its organs. Think about it this way, if you lose a finger or even an arm you can survive, but if your organs are severely damaged, you often can’t survive.

It's a question of how much damage you inflict. If you cut a gecko in half, it will die, because you will have done too much damage to its important organs. Limbs and tails are important for moving around, but aren't so important for just living, so the gecko can regenerate them.

Everything that is alive will die. It makes sense that geckos and some other reptiles can lose a tail or limb, and there's not too much blood loss; and they can regrow the tail or limb. Once I was digging in my garden, and I cut the tail off a little lizard and the tail wiggled and wiggled in my hand for maybe 15 seconds. I think that's how long it took for all the chemical energy in the tail to be used up.

But there's more blood in the internal organs, and so if those start bleeding, the gecko dies, just like all living things die when they are too badly injured.

Geckos are able to regenerate their limbs and tails because those processes are governed differently than internal bleeding. Check out this video of a leopard gecko tail regeneration! DO NOT FORGET TO SKIP THE AD IN ORDER TO WATCH THE VIDEO!
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Great question. The ability to regenerate limbs and tails is pretty awesome. Scientists are very interested in this because allowing people to regrow even a finger is currently not possible. The answer to this mystery probably has to do with turning on certain genes in the stump of the limb or tail.

Every cell in our bodies (except mature red blood cells and sex cells) has a complete set of DNA, but only certain genes are switched on at certain times, depending on the age of the cell and where it ends up. Our cells get locked into certain “jobs” pretty early, so the cells in our wrists won’t turn into cells that will make a new hand.

But why do geckos bleed to death from internal injuries? Well, that’s a different process from limb growth. Limb regeneration takes a really long time. It can take weeks or months, depending on things like the amount of damage, nutrition, and temperature. Bleeding has to stop pretty quickly, in seconds or minutes. We have clotting factors in our blood that get activated when our tissues are damaged. The tissue sends out a chemical signal. If all goes well, a plug of tiny fibers and platelets (pieces of a special kind of blood cell) forms in the tear, making a sort of patch until new cells can replace the damaged ones. If the damage is too bad, the plug can’t form or can’t form soon enough. The process is probably similar in geckos. Why do you think the ability to regenerate limbs is pretty common in reptiles and amphibians, but not possible in mammals?

Blood serves a number of functions that are necessary for an organism to live, including transporting oxygen around the body and bringing white blood cells which are involved in fighting infections/diseases. If an organism loses enough blood, these functions cannot be properly executed, and the organism will lose its life. Hope this helps!