“Evolution doesn’t invent new cells or organs very often. In the same sense, once organ systems have been established by natural selection, they don’t go extinct (though some organs lose their function—for instance the human appendix, which was originally larger in our ancestors, as seen in other mammals, and used to digest cellulose at an earlier stage of mammalian evolution). Through the long course of evolution, organs have retained their physiological functions, even if sometimes they get used in new ways. It’s not at all uncommon to find ancient organs co-opted, or perhaps “improved upon” by more recent taxa, while at the same time retaining their basic functions under new environmental circumstances.”