When a piece of skin, muscle, bone, nails, or hair gets removed or damaged, those usually grow back like nothing happened. So, why isn’t it possible for hands, or even something smaller like a finger to regrow? Or would a piece of meat just regrow there instead of something useful?
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The way I understand it, and I’m not a biologist, is that we essentially have little templates all around our body. When our nails need a model to make themselves from, they get it from our nail bed, when our bones need that tissue it’s in the marrow for example.
However, all of those are generic structures. You have many bones, many nails, etc. For your entire body like macro structures, it’s much much more expensive to template that and more importantly to keep that specific template alive for your entire lifespan. YES, THAT TEMPLATE, THE BLUEPRINT IS LIVING TOO. YOU NEED TO KEEP IT ALIVE. Remember that. There’s a cost to each part.
Lizards do it over just their tail, but they don’t live long. And every time they do it, its very very energy intensive and takes up crucial nutrients. Things that can regrow limbs like octopi/octopodes (for funsies) are pretty simple structurally compared to us — on a large scale, yes they have very complex inner workings, but the simplicity and redundancy are key here. Same with things like starfish, it’s literally a blob with a shape and organs mixed in.
When we’re first conceived, we’re just a blob too. Our template cells are all there. But as we grow out and get more complex it’s just not worth it for our body to keep those templates alive, it’s pretty much keeping another copy of yourself alive in the background just in case you need it. So our bodies ditch those templates until we’re down to those generic ones I mentioned. The odds of you needing those over time lessen more and more, for example, your bones add density and you build muscle mass.
A child might sustain an injury in ways adults can’t and when they have those template cells they can heal from it and are more likely to survive and procreate. Our bodies toughen up drastically over time. Side note but children are ridiculously durable. That’s a hilarious thing to say but… parents will know lmao
Evolution has a way of trimming down fat. At what point is it more efficient and gives the highest probability of passing on genes vs to just have the individual die but have a healthier more robust offspring by taking out that extra burden of keeping those templates alive.
Why build extra armor or padding if you don’t plan to get hit? If I build a nice fortress and no one will break it, why would I invest in the materials, keep them in storage, and keep those plans. Better to just keep the recipe for a generic brick that you can use to replace the broken ones. And the pestle and mortar to patch it. That’s like your bones. If you lose one, in nature, you’re probably screwed anyway. The odds of you escaping are pretty low at that point. Easier to focus on avoiding that scenario with other means like stronger muscles to fight off or stronger bones. You can see where I’m going.
Now picture those templates as stem cells. Our body tends to really focus on keeping the most generic ones (in the sense of widely used across the body) over the specific yet unlikely to be needed outside of crazy circumstances. That’s why our body doesn’t really keep a lot of heart stem cells, if you get to that point that it’s needed to grow another, you’re probably fucked for some other reason. Like totalling a car… at what point is it more expensive to buy a new one than to add a new engine and in evolutions case… to build that engine and keep it around until you need it. Multiply that for every organ you want to regrow. Zoinks.
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