What stops humans from growing back fingers or arms or legs?
In: Biology
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.
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