Then a strange thing began to happen. The mirror carp began growing scales again. According to a paper published in Proceedings of the Royal Society B, it took just forty generations for the carp to re-evolve — or devolve — their scales. The pressures of natural selection, the authors write, allowed the so called "wild type" trait of scales to return to the species. Research findings came by way of analyzing both the DNA and scales of about 700 captured carp specimens.