Why do vestigial structures persist in modern organisms?
It takes some time for a structure to completely lose its function, and then considerable amount of time after than for it to disappear completely. For example, the appendix is a vestigial structure. It still has some *traces* of its ancestral function. In herbivores, the cecum is the breeding ground for bacteria used for digesting cellulose. In purely carnivorous animals the cecum is reduced. In the omnivorous primates (humans, apes, and Old World monkeys of Asia and Africa), the cecum is mostly replaced with the appendix, which still has traces of its ancestral function, in that it may have some function in harboring good bacteria used in digestion, during disease. However, this is a *trace* of the function that plays a much more important role in herbivores. It is such a minor function that the appendix can be removed without harm to the individual, and in fact, many humans are born without an appendix at all. So the appendix is an example of a structure whose original function is a
