This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
The Story of Evolution, Spring 2005
First Web Papers
Let me tell you a story. At age twelve I became horribly ill, crying for hours from a most painful "stomachache". My parents, being the frugal people they are, kept me from the doctor for a full day—I would get better; I always did. By the next morning, however, my stomach still throbbed and by now I was puking blackish bile. Realizing that a catastrophe could prevail, I was rushed to the emergency room. Sure enough, something was wrong. I had appendicitis.
Due to advanced medical practices and the proximity of a skilled doctor, my appendix was quickly removed from my body via my belly button. (Yes, belly button!) My doctor told me that I was lucky because never again would I have to worry about my appendix erupting. Ernst Mayr confirmed my doctor's opinion that the human appendix is only an impediment on the species. In What Evolution Is, Mayr claims that
Every shift into a new adaptive zone leaves a residue of no longer needed morphological features that then become an impediment. One only needs to think of the many weaknesses in humans that are remnants of our quadrupedal and more vegetarian past, for instance... the caecal appendix. (143)
Why, though, did I—or any other human—have an appendix in the first place? Does the appendix have a use that I am now deprived of? If not, why is the human body wasting energy to produce the nine-centimeter long organ? This paper is my quest for an answer.
The appendix has long been considered a vestigial structure. That is, "a deconstructed, nonfunctional characteristic that has been fully functional in a species' ancestor."(Mayr, 291) Humans seem to have a fair number of other vestigial organs such as male nipples, wisdom teeth, tailbones (coccyx), and ear muscles. (1)(txtwriter.com) Each ignites its own debate, so I will focus primarily on the role of the appendix in the human body.
The appendix is present in many primates, and primarily (pun intended) used to aid in the digestion of cellulose. Located between the small and large intestines, the appendix and neighboring caecum slows down the body's digestive process. (For drawings of the structure in various mammals click (2)here.) The human appendix (commonly referred to as the vermiform appendix, although Mayr calls it the caecal appendix) has lost this cellulose-digesting ability. Dr. Douglas Theobald argues that while humans do consume some cellulose, the ability of the caecum and appendix to digest it is insignificant. Consequently, plants like grass cannot be digested by humans. (And that's why my cousin always yelled at me for eating grass!)
So, while the human appendix has lost its aptitude for digesting cellulose, recent studies have shown that it may play a different, but still trivial, role in the gastrointestinal immune system. Dr. Theobald suggests that the percentage of immune system cells produced by the appendix is not critical when compared with the overall number of lymphoid in the gut. Thus, the positive effects from the human appendix seem to be non-existent. Adverse effects, however, are familiar.
A full seven percent of the U.S. population is at risk of acute appendicitis. Risk is notably higher for children ages 11-20 and during the colder months of the year, a statistic my case retold. (3)(kidshealth.org) Although most cases of acute appendicitis can now be treated, appendectomy is a surgery that works against natural selection. Consequently, I am likely to pass on a propensity to develop appendicitis to my children. Since the majority of acute appendicitis cases pre-20th century did result in fatality, why hasn't the appendix died out as well? It is arguably maladaptive. It seems natural selection would have discarded it from the human body thousands of years ago.
As an evolutionist, it is difficult not to produce possible reasons for the prevalence of appendixes in humans. My theory is three-fold. Firstly, it must be noted that recent laparoscopies have shown that many people do lack any appendix at all. Evolution happens over time—long periods of it. It is likely that the process of natural selection has been going on all along and that it has not yet finished. Because the odds of dying from a clogged appendix are merely seven percent, it is likely that this number is just not large enough to kill off all of the carriers. Potential benefits of appendixes in hunter-and-gatherer times are also possible. If 30,000 years ago the appendix produced cellulose-digesting bacteria, humans may have been able to digest grass and other plants which would have been particularly useful in times of famine. Lastly, the energy "wasted" in building the appendix in modern men may also be trivial. Perhaps the energy required is so insignificant that it could not have been better spent elsewhere.
Vestigial structures like the appendix are often referred to as evidence of evolution. Yet while showing organisms' link to past species, they fail to show the adaptiveness of organisms to their current environments. If evolution's concept of time is not critically analyzed, this situation may feel like a catch-22. If vestigial structures are investigated over a long enough time frame, however, the loss of vestigial structures should prevail. As for humans, owing to their new technologies, this may happen in a very artificial way.
Mayr, Ernst. What Evolution Is. Basic Books; New York, NY: 2001.
2)The Vestigiality of the Human Vermiform Appendix
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