Everyone’s seen Rudolph Zallinger’s “The March of Progress” illustration showcasing the evolution of humans: from early primate ape ancestor, Dryopithecus, and progressing toward modern man, Homo sapiens. Evolution is a fascinating phenomenon, but it doesn’t necessarily always follow a straight path as portrayed by Zallinger.

The idea that evolution marches from simple to complex forms, building irreversibly on each prior form has been around for a long time. Paleontologist Louis Dollo’s law states that once an organism progresses with a specialized structure, it does not revert to the previous state.

But now, a new study published in the journal Evolution is challenging the prevailing belief that life progresses unidirectionally. The findings suggest some plants can evolve backward, i.e., specialized species can revert to their more primitive forms.