Why are so few species able to regenerate damaged or missing body parts, even though regeneration might seem an obvious survival advantage? Researchers at the Max Planck Institute (MPI) for Multidisciplinary Sciences in Göttingen, Germany, and colleagues have now found a possible explanation in planarian flatworms. Analyzing head regeneration abilities in a large collection of planarian species, they found that these capacities vary greatly and depend on how the different species reproduce.