As I became a Believer in the spring of 2003, I remember hearing of the concept of “vestigial structures.” Vestigial structures are body parts that once had a purpose but somewhere along the way, due to evolution, they lost their functionality. Over the years, I had heard refutation of this concept in popular literature so imagine my surprise when I recently heard vestigial structures, once again, proffered as a proof of evolution and an argument against theism.
The appendix is a tube-shaped sac that’s attached to the large intestine. Seemingly without function, Charles Darwin proposed that it was once used by primates to digest leaves and has long been used by atheists to argue for evolution. Recent research from the Duke University Medical Center, however, suggests that the appendix serves as a “reservoir” for beneficial gut flora. When illness reduces good bacteria from the intestines, the appendix may store some of that good bacteria for back up  It’s also been shown that individuals without an appendix may be four times more likely to suffer from recurrent Clostridium difficile colitis, an irritation of the large intestine by spore-forming bacteria. 
Evolutionary biologists suggest that the coccyx would be where the tail was attached to the skeleton. Since tails on humans have been selected against in nature, the coccyx is unnecessary in modern day humans. Yet, it is still a part of the human skeleton. But, the coccyx serves as an attachment site for tendons, ligaments, and muscles. It also functions as an insertion point of some of the muscles of the pelvic floor. The coccyx also functions to support and stabilize a person while he or she is in a sitting position. 
It has been suggested that since wisdom teeth give a great many people a lot of trouble, and that chewing is not impaired when they are surgically removed, this third and final set of molars have no modern function. Anthropologists have said that the human jaw is smaller now than it was just 300 years ago, because we chew less. The bones we use more get more developed. But this would not be an evolutionary change. In evolutionary theory, the genes change. It is now understood that the problem was seldom seen in pre-industrial societies. It has been discovered that the way in which soft foodstuffs have come to be preferred to harder ones, over the last few hundred years in particular, has negatively affected the way the human jaw develops. It has thus been realized that most wisdom tooth troubles emerge as a result of jaw development problems relating to dietary habits. 
It is suggested that nipples in male mammals illustrate a constrained evolutionary result. In a now-famous paper, Stephen Jay Gould and Richard C. Lewontin emphasize that we should not immediately assume that every trait has an adaptive explanation. Just as the spandrels of St. Mark’s domed cathedral in Venice are simply an architectural consequence of the meeting of a vaulted ceiling with its supporting pillars, the presence of nipples in male mammals is a genetic architectural by-product of nipples in females. So, why do men have nipples? Because females do.
 R. Randal Bollinger, Andrew S. Barbas, Errol L. Bush, Shu S. Lin, William Parker. Biofilms in the large bowel suggest an apparent function of the human vermiform appendix. Journal of Theoretical Biology. Volume 249, Issue 4, 21 December 2007, Pages 826-831.
 Rob Dunn. Your Appendix Could Save Your Life. Scientific American.