How is it that some animals like salamanders and lizards are able to regrow lost limbs, while humans are not able to do the same thing?
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We can regenerate fingertips. And it’s possible that we can regrow larger limbs. There’s research into limb regeneration that focuses on the idea that if you induce the right conditions, the human body will actually do the hard work for you. Obviously we *do* have the ability to grow a limb, or we wouldn’t have limbs. But growth is dangerous if it doesn’t happen *exactly* how you want it. We’re not like plants where we can just keep growing in a rough pattern and things will work out. We need to be a specific size and shape and literally *any* uncontrolled growth in our body is a potential death sentence without intervention.
So, why do some animals regrow limbs? Because the risk of the downsides when regrowth goes wrong were outweighed by the benefits of regrowing their limbs. Maybe they lose them more often than others, or losing one is more of a disadvantage, or they just happened to evolve a solution that works well enough that it mitigated the downsides. Or they have some behavior that is particularly beneficial to them that often results in lost limbs. And when there is some selective pressure pushing them either towards limb regrowth, or away from a “lack of limb regrowth”, that gives them time to actually evolve incrementally better solutions for the downsides of regrowth rather than just evolving to avoid the process entirely to mitigate risk.
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