For millennia — since at least the time of Aristotle — medical thinkers have pondered why certain animals like salamanders are able to regrow entire lost limbs, while mammals like us humans have to make due without any appendages we’ve lost.

Now, researchers at the Texas A&M College of Veterinary Medicine and Biomedical Sciences say they may have cracked the code. In a new study published in the journal Nature Communications, they detail a process they say causes bones, joints, and ligaments to regenerate in mammals which otherwise would not be able to regrow tissue.

Basically, the researchers used a two-step process that mimics the way regenerative animals such as salamanders regrow lost tissue after amputation. They pull it off via a process known as epimorphic regeneration, in which lost limbs are first covered by a layer of skin cells. Local cells then rearrange themselves into a blastema, a temporary structure that forms the base-layer for the rest of the limb.

By controlling this limb-loss process with a specially-engineered serum that sends signals to cells, researchers found they can encourage the growth of a blastema in mammals: lab mice, in this case.

“This is really a two-step process,” Ken Muneoka, one of the authors of the study, said in a press release. “You first shift the cells away from scarring, and then you provide the signals that tell them what to build.”

Unlike typical regenerative approaches which use external stem cells, this newly-uncovered process uses the cells that are locally available. As Muneoka put it: “they’re already there — you just need to learn how to get them to behave the way you want.”

While the process isn’t perfect, scientists hope it can help reduce scarring and encourage tissue regeneration after traumatic injuries. Either way, study co-author Larry Suva said the findings change our understanding of mammalian healing, which has particularly fascinating implications for humans.

“The cells that we thought to be unprogrammable, in fact are,” Suva said. “The capacity is not absent — it’s just obscured.”

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