"In the course of evolution there is a fairly precise interval of time in which sensitivity to light in the animal kingdom may have developed for the first time: about 600 million years ago." This is what David Plachetzki of the University says of California of Santa Barbara (Ucsb), author of a study on the hydra, an aquatic animal of the class (or, more properly, "phylum") of coelenterates, to which also corals, jellyfish and sea anemones belong. The research allowed to discover in the hydra a photosensitive gene, opsin, absent in other aquatic animals that boast more distant origins, such as sponges, and the precision of dating is a consequence of the fact that it is known that the precursors of the hydra actually hesitated about 600 million years ago. Todd Oakley, co-author of the study, thus explains another important aspect of the discovery: "It is rare to be able to document the specific mutation that gives rise to a new evolutionary characteristic. This mutation has allowed the opsin gene to interact in a completely new way with different proteins, and over time the process has translated into the genetic machine of vision ". The discovery, according to Oakley, is also in open contradiction with the theories of anti-evolutionists, for whom mutations can only lead to the elimination of traits and do not produce new features. The hydra is a predator, and researchers believe it used light sensitivity to find its prey. (Photo © David Plachetzki / Ucsb: in blue, the opsin genes of the hydra. In this coelenterate the opsins are distributed throughout the body: it has no "eyes", but is genetically sensitive to light.)