Duke University Medical Center biologists have discovered a molecular switch that controls a zebrafish’s ability to regenerate organs and tissues, including hearts, eye parts and fins.

In zebrafish, one or more microRNAs appear to keep regeneration on hold until the fish needs new tissue. In response to an injury, the fish reduce levels of these microRNAs to aid regrowth.

The researchers believe that mammals may have the same tissue regeneration capability, but that it is locked away somewhere in our genome, silenced in the course of evolution.