Eli5: if our bodies are able to form entire human beings from scratch, why can’t it grow back organs that have been amputated?
In: Biology
1. The body is not designed to survive *everything.* It is designed to survive the most common problems that are easiest to fix. It would be nice for animals (thinking of mammals) to be able to regrow a limb that was torn off. But 99% of the time, they would die from the initial wound, or not survive the regrowth process (they would starve or be eaten first). So evolution could not select for a regrowing feature.
2. People describe DNA as a “blueprint” for the body, but that isn’t true. DNA is closer to the literal, detailed, step-by-step instructions on how to build the body from scratch. So if you lose a body part, your DNA does not “know” what to do.
3. Many things are easier to replace than repair. Think about a fan. If a blade in the fan breaks, we could replace the fan blades or even build a custom blade piece and solder it on. But it is much easier, if more wasteful, to buy a whole new fan and junk the old one. In a way, this is our genes’ approach to our bodies. If something big breaks, give up on that body and let someone else take its place.
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