why our skin and liver, the largest organs in our body, regenerate but other organs can’t?
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Most organs regenerate to some degree, some more than others. Still the regeneration isn’t perfect. Scarring usually occurs or the regenerated tissue is not exactly like the damaged one. Sure livers regenerate and they become as big as they were but that doesn’t mean their functional capacity is the same. Bones heal too, and muscles and ligaments but often injury to those means chronic complications and their full capacity may never be regained. It’s the same with skin. Sure a paper cut heals pretty well but serious injury to skin leaves scars and often nerve damage and partial or complete loss of sensation.
Imagine your body as a wall of a building. Then something or someone makes a big hole in it. When body tries to repair it, it looks around the hole and tries to make something similar from the same bricks. Liver is big for sure, and skin is also, but they are not very “detailed”. It takes time to repair them, for sure, but it is possible. Imagine that your eye is a window in the wall. Or that’s a part of the wall with the graffiti on it. If it is destroyed, body will look around and repair the hole .. But it has no idea this part of the wall had a window. It will repair it with the same bricks. That’s why eye can’t regenerate. Or why we can’t grow finger again: imagine that half of the wall was destroyed. Body doesn’t know how large the wall was. All it sees is some broken in half bricks. It will restore them, but won’t go further.
Also it is much harder to live without the liver or heart than without finger or eye. Eye damage is rare. Statistically the mutation that helps liver/skin regenerate will be much more helpful for reproducing than mutation that helps an eye regenerate. Also – even a small mutation that helps regenerate liver will help you. For an eye regeneration mutation to have any evolutionary benefits it must be a huge (HUGE) mutation that almost can’t happen in such complex creatures as humans are.
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