The human appendix is not really vestigial. It has an immunological
function as part of the lymphatic system. Its lymphoid follicles produce
antibodies.
Vestigial does not mean functionless. The
appendix appears as
part of the tissues of the digestive system; it is homologous to the
end of the mammalian caecum. Since it does not
function as part of the digestive system, it is a vestigial part of
that system, no matter what other functions it may have.
The human appendix may not be functional. Its absence causes no known
harmful effects (other than surgical complications from removing it).
When it is present, there is a 7 percent lifetime risk of acute
appendicitis, which is usually fatal without modern surgical techniques
(Hardin 1999).
Co-opting a part for an entirely different function, such as turning
part of the intestines into part of the lymphatic system, is entirely
compatible with, and even expected from, evolution. However, it argues
against design because
