Why Salamanders Can Regrow Limbs, but Humans Can’t

Introduction

Salamanders, especially the axolotl, have an amazing power that has puzzled scientists for hundreds of years they can regrow lost body parts. If an axolotl loses a leg, it doesn’t stay gone forever. Within just a few weeks, the animal can grow it back, complete with bones, muscles, nerves, and skin. What’s even more surprising is that this ability isn’t limited to legs; axolotls can also repair parts of their heart, lungs, and even brain.

Humans, on the other hand, don’t have this kind of superpower. We can heal small injuries, like cuts and scrapes, and our livers can regrow to some extent, but we cannot replace something as complex as an entire arm or leg. Instead, our bodies often form scar tissue. While scars close wounds and protect us from infection, they block the chance of rebuilding the original structure. This big difference between humans and salamanders leads to fascinating questions: Why did evolution give some creatures this ability but not us? What’s happening inside the cells of salamanders that makes this possible?

How Salamanders Regrow Limbs

The process starts the moment a salamander loses a limb. Cells near the injury change back into a more flexible, “youthful” state similar to stem cells and gather into a small lump called a blastema. This blastema is like a construction site where new tissues will form.

From there, the blastema grows quickly, guided by special signals from other cells. Nerves play a huge role by sending growth signals; without nerves, the regeneration process doesn’t work. Another key player is the immune system. In salamanders, certain immune cells called macrophages calm down inflammation and prevent scar tissue from forming. That’s why healing is smooth and functional instead of scarred and stiff.

Chemicals like retinoic acid also direct the rebuilding, deciding what part of the limb grows back and how it’s shaped. For example, depending on the concentration of this chemical, a foot might form instead of a longer leg. Salamanders also keep certain “youthful” genes switched on throughout their lives, which helps them repeat the regeneration process without developing cancer, something that rapid cell division might otherwise trigger.

Why Humans Lost This Power

Long ago, the ancestors of both salamanders and humans probably had the ability to regrow body parts. Fossil evidence and genetic studies suggest that amphibians living about 350 million years ago could repair themselves after injury. But over time, humans and other mammals appear to have lost this gift.

Why? Scientists believe it was a trade-off. For salamanders living in dangerous waters, losing a leg to predators or rivals was common, so regrowing it was essential for survival. But as humans evolved in different environments, the focus shifted to quick wound closure to avoid infections and blood loss. Our bodies became very good at forming scars, but this came at the cost of regeneration.

Interestingly, humans still carry many of the same genes used in regeneration we just don’t “activate” them after birth. Our macrophages, instead of preventing scars, trigger inflammation that leads to scarring. Even our nerves show some attempt at regrowth, forming tangles called neuromas in amputees. These signs suggest that the ability to regenerate is still hidden inside us, just not fully switched on.

What This Means for Medicine

Studying salamanders could completely change the future of human medicine. By decoding the axolotl genome, researchers are identifying genes that might be reactivated in humans. Tools like CRISPR could one day “turn back on” the regenerative programs in our bodies. Scientists are also testing ways to control macrophages and chemical signals like retinoic acid to reduce scarring and encourage healthy tissue repair.

While we are still far from regrowing a full human arm or leg, these discoveries offer hope. They could lead to new treatments for amputations, spinal injuries, or organ damage. Salamanders show us that the blueprint for regeneration exists in nature the challenge is learning how to unlock it for ourselves.