Eli5: Why do we not regrow teeth and limbs?
In: Biology
It makes little sense for an animal to evolve an ability that would never be used. Regrowing a human limb (maybe 10-20kg worth of complicated bone, flesh, muscle, nerve, connective tissue, blood vessels etc) is too energy and time consuming. Say that an adult limb takes 3 months to grow. During that period the person is vulnerable. Also, there will not be enough energy and material to regrow the limb stored in the body so it will require a LOT of excess foods during this period. Basically (before modern times) most humans will die before the limbs can regrow. So the ability is useless for our ancestors of 20-30 thousand years ago.
Our body doesn’t evolve to survive to our imagination (ie we’re not evolved to live hundreds of years, fight off all diseases, regrow limbs). Rather it evolves to survive well enough to be able to reproduce. While any one individual benefits from these capabilities, the species would not be better off.
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