How are octopi, salamanders, etc. able to regrow limbs, and why can’t all animals do it?
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Someone smarter than me will be able to explain the mechanics of it, but basically our DNA does not include instructions for ‘regrow lost limb’. Hell we can barely regrow lost skin.
The exact mechanism that allow animals to regrow parts of their bodies are something scientist study to figure out how to help humans. It seems very complicated and not immediately transferable, but it might give us clues as to how to help people.
The reason why humans and other similar animals can’t regrow limbs when animals like Lizards can usually comes down to evolution and costs and benefits.
Keeping or evolving such a trait if it was easily done, would be more of a cost on the average individual than a benefit (especially if the individual is highly likely to die anyway after an injury like that).
Unrelated fun fact:
The plural of octopus is not octopi. Most of the words that end in -us and have an -i plural are from Latin. Octopus is Greek and Greek grammar is different. The correct Greek-derived plural is octopodes. The normal English-based plural of octopuses is the least wrong plural though.
Our DNA has a blueprint of where every cell must be and what they must do in every stage of development. In early stages, most cells are pluripotent (stem cells), meaning that they can become any type of specific cell . As development goes on, the cells lose that ability, and can only duplicate to make cells of the same type.
So, losing a limb should not be a problem, you just keep duplicating the cells of the same type until the limb is complete again, right? Well, If you have joints and multiple, different bones, you need something that can start duplicating into that joint and bone tissue. But the cells on what remained of the limb know only to build that specific part of the limb, not the other parts.
Lizards, contrary to most people think, cannot really regrow limbs. Some of them can only replace the tail, and that tail can only be replaced a finite number of times. They have special system with defined places of breakage, which allow them to significantly reduce the loss of blood associated with losing a body part. Those breaking points are situated along the tail so if they break it too close to the body, they lose the other breaking points closer to the tail, reducing the number chances to replace it.
Salamanders can regrow whole limbs, but it seems they have a way of creating new stem cells for that situation.
Even in humans, scar tissue is not a regrowth of skin, but rather a replacement, as the new tissue does not have the same characteristics as the original skin (cannot grow hair, sweat glands, etc).
Actually they’re working on gene therapies for similar stuff, one would be a shot you take whenever you get a cavity and then your tooth will regrow instead of you getting a filling.
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