Answer: Liver

When it comes to amazing regenerative abilities, human beings sort of got the short end of the stick in the animal kingdom—we can’t regrow lost limbs and cutting us in half definitely won’t trigger regeneration that results in two identical and functional people.

We do, however, have remarkably hardy livers. Unlike every other internal organ, the liver is capable of a type of natural regeneration. In the case of every other internal organ, the organ can potentially, under the right conditions, heal itself, but regeneration is a whole different story. If part of your lungs are severely damaged or removed, your body can’t grow new lung tissue. The liver, however, can fully regenerate itself with as little as 51 percent healthy liver remaining.

The regenerative ability of the liver in both humans and other mammalian species is a natural outgrowth—if you’ll pardon the pun—of its function: detoxification. Because the liver is the primary site in the body for drug/chemical detoxification, the cells take a particularly strong beating compared to other organs, and the ability to regenerate ensures the liver doesn’t fail while performing its primary function day in and day out.