The amphibians' immune systems are the key to the trait, which allows them to regrow limbs as well as regenerate spinal cords, brain tissue and even parts of their heart.

Now scientists say immune cells called macrophages could be vital for regeneration - and could help scientists control the process and even use it in humans.

Researchers at Australia's Monash University found that when the macrophages were systemically removed, salamanders lost their ability to regenerate a limb and instead formed scar tissue

Dr James Godwin said the findings, published in the Proceedings of the National Academy of Sciences, brought researchers a step closer to understanding what conditions were needed for regeneration.

Dr Godwin said: 'Previously, we thought that macrophages were negative for regeneration, and this research shows that that's not the case - if the macrophages are not present in the early phases of healing, regeneration does not occur.'

'Now, we need to find out exactly how these macrophages are contributing to regeneration. Down the road, this could lead to therapies that tweak the human immune system down a more regenerative pathway.'

The tissue regenerated by salamanders is scar free and almost perfectly replicates the injury site before damage occurred.

'We can look to salamanders as a template of what perfect regeneration looks like,' Dr Godwin said.

Aside from 'holy grail' applications, such as healing spinal cord and brain injuries, Dr Godwin believes that studying the healing processes of salamanders could lead to new treatments for a number of common conditions, such as heart and liver diseases, which are linked to fibrosis or scarring.

Promotion of scar-free healing would also dramatically improve patients' recovery following surgery.

There are indications that there is the capacity for regeneration in a range of animal species, but it has, in most cases been turned off by evolution.

'Some of these regenerative pathways may still be open to us. We may be able to turn up the volume on some of these processes,' Dr Godwin said.

'We need to know exactly what salamanders do and how they do it well, so we can reverse-engineer that into human therapies.'