What stops humans from growing back fingers or arms or legs?
In: Biology
For the same reason we don’t grow wings. There simply isn’t a mechanism for it in place. Now we could at some point maybe engineer that mechinism in the future but it isn’t in our bodies at the moment.
What stops my car from walking? Just not the right equipment lol
Your genes aren’t a blueprint, they’re a long list of instructions. To make you a new arm, you can’t just grow a new adult finger. Your body doesn’t know how to do that, and your cells don’t really know where they are, either.
The way your body was built the first time was just following an insanely long list of instructions. Your cells coordinate chemically (ok, the concentration of this hormone is 3%, so I start reading the DNA here…. ok, divide six times and then emit hormone B, and wait for hormone C to reach….).
So to grow back a finger, you’d need to essentially designate a cell in the stump, and chemically tell it “OK, you’re in a fetus, and you’re the cell that’s located where a finger’s going to be… start reading at step 12B”. And that’s how species that *can* regrow limbs do it. You basically grow a fetus finger that grows up to match the rest of you, sorta. Regrown parts don’t turn out as good as the original.
The human body doesn’t have a mechanism to see that something is missing. After we’ve developed we have instructions to continue growth for a while. We do have mechanisms for sensing and repairing damage but it is highly localized and more along the lines of ‘SEAL THE BREACH’ than ‘restore to factory spec’.
In homo sapiens (and quite a bit down our branch of the tree of life) there wasn’t really an evolutionary pressure to have this ability and I suspect that somewhere on the tree, some of the ‘tools’ needed to fulfill such a function (like keeping stem cells active for our whole lives) may have even proved to be a liability. It may have carried increase risk of cancers, it may have raised the ‘cost’ of our metabolism.
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