The appendix is a "worm-looking" organ which is attached to the cecum in the lower right of the "quandrant". It was Darwin's theory that the appendix was a left over, no longer valuable organ, which had dangled since evolution. Darwin theorized that man was once a leaf muncher and required the appendix for digestive purposes. He reasoned that as man's diet evolved to less complex digestive needs, the appendix became a useless organ. However, it has been learned that the appendix is rich in immunity cells important to the body and drains lymphatics into the ileocolic lymph nodes.
Dr. William Parker, a professor of surgery at Duke University, having found "good" bacteria around the appendix has reasoned that perhaps the appendix is a type of "hang-out" for cells of immunity during tragedies such as diarhea, when the body is busy expelling anything not attached. The type of "good" bacteria discovered around the appendix actually aid in digestion throughout the gut.
Think of the appendix as sort of the tonsil. It is there to guard against infection, between the "almost sterile" ileum and the horribly bacterial colon.
So, rather than vestigial (involution through evolution), doctors are beginning to think of the appendix as a "highly specialized organ".
In terms of evolutionary cause and effect, the monkey does not have an appendix. However the Anthropoid Apes do. Anthropoid Apes are Gibbons, Baboons, Chimpanzees and Gorillas.
Most usually when inflammation of the appendix occurs, it is due to a blockage of the opening between the cecum and the appendix. The bacteria take over and invade the lining of the organ. This can cause a rupture of the appendix and bacteria to invade the immediate area. The body can heal an episode of appendicitis itself.
The inflammation of the appendix is the reaction of the bodies immune system, not the result of bacteria.
There are two very dangerous conditions which can evolve if the appendicitis is not cured or the appendix is not removed. First, a very serious blockage of the intestine can occur, because during appendicitis the muscle of the intestine can stop working. This can cause nausea, vomiting and contents of the intestine to come out of the nose. Also, Sepsis can occur. Sepsis is a condition of the bacteria which caused the appendicitis traveling throughout and infecting the body. It can be life threatening in either circumstance.
Symptoms of appendicitis are, abdominal pain which is difficult to pinpoint. Later stages of course can include nausea and vomiting. Fever is not unusual and there will be an elevated white blood content.