Great question. Obviously, it would be wonderful if we could regenerate body parts too. To understand this issue, we need to go all the way back to when each of us was just a fertilized egg. At first that egg divides to make 2 identical, smaller cells. This keeps up until we’re a solid ball of cells. At first, a cell could turn into any kind of cell: a liver cell, a muscle cell, a hair cell, or a brain cell. If the ball of cells splits at this point, the halves grow into identical twins.

Then the cells start to specialize. Imagine that a bunch of squirrels started at the base of a tree, then started climbing. Soon they would be off on a bunch of different branches. If the squirrels can only climb in one direction, they could never change to a different small branch. Something like that happens with cells when they specialize.

The embryo goes from being a solid ball to a hollow ball. Then the tube that will be our digestive system starts to form. At that point the cells get more specialized. Some will become cells that form the lining of things like our gut or lungs. Other cells could become things like bones, muscles, or blood. A third set will become part of things like our outer skin or nervous system. Once a cell has branched into one of these three types, it usually can’t go back.

As development continues, cells get more and more specialized. Each cell still has the entire set of our DNA, but any particular cell will only use a small part of the many “recipes” in the DNA. A skin cell uses different genes than a brain cell. The cells also send signals to each other so that they can work together to form things like our limbs. As the cells divide on the bud that will become our arm, they have to signal each other so that the arm gets to be the right size and shape and so cells “know” whether they are forming an elbow or a fingertip.

Unfortunately, when we lose a finger, for example, the cells in our hands can’t seem to “turn back time” and send cells out to make a new finger.

Many reptiles cannot regenerate body parts either, but some lizards and their close kin can grow a replacement tail. The cells in the stump seem to get a signal that they need to start dividing to make a new tail. The new tail is not the same as the old one. It has cartilage instead of bones and does not have all the nerves of the old one, but it works okay. Some lizards can go through this regeneration multiple times. Others will only regenerate once. Others never regenerate.

If the lizard has low stress and plenty of food, regeneration happens faster. I found a reference that said 60 days for one type of lizard. I recommend the article for learning about how regeneration is different in reptiles and amphibians and how they might help researchers learn to help humans. please lean more here .

Why do you think it helps lizards to have break-away tails?

The ability of reptiles to regenerate limbs stems from their genetics and DNA. Scientists recently found 326 genes in specific spots along a lizard’s tail that “turned on” during regeneration. After a reptile is wounded, the surrounding cells become active and start to remodel tissues and vital organs back to their pre-existing state. And not just skin cells, but cells specifically for muscle, cartilage, and spinal cord too. For reptiles like lizards, it’s usually just the tail. Lizards escape predators by losing their tail and growing it back later, which is called autonomy. It takes them more than 60 days to regenerate a functional tail. There are many other species that participate in regeneration such as sea stars, salamanders, zebra fish, and cockroaches. Most of them can do it over and over again, if needed.

Sea stars are special because their detached or wounded limbs are capable of regenerating a whole new body! Now that researchers understand the genetics behind regeneration, they are beginning to look into research on limb regeneration in humans!

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