In Charles Darwin’s book On the Origin of Species, he referred to a number of “vestiges” in human anatomy that he posited are remnants left over from the course of our species’ development over time. Darwin suggested that these vestigial organs are evidence of evolution and represent functions that were once necessary for our survival, but have since had their role drastically diminished or even eliminated altogether. This concept formed the basis for the idea of common descent which predicts that organisms should retain these vestigial organs as structural remnants of lost functions. The following are 10 examples of vestigial organs that have shed some light on where we came from and where we’re heading on the evolutionary road.
10. The Appendix
In plant-eating vertebrates, the appendix is much larger and has a much more pronounced function in helping the animal digest a predominantly herbivorous diet. In humans, the appendix is a tiny pouch located at the junction between the large and small intestine and, while it might have helped our primate ancestors breakdown a diet rich in cellulose, today it doesn’t aid in digestion directly. Interestingly, in a text called The Vertebrate Body, paleontologist Alfred Sherwood Romer noted that the major importance of the appendix “would appear to be financial support of the surgical profession”, referring, of course, to the large number of appendectomies performed annually. In the United States alone there are nearly 300,000 appendectomies performed each year, and more than 350 annual deaths resulting from appendicitis. So any secondary function that the appendix might still perform is surely not important enough keep it around in the event that it might rupture.
9. Arrector Pili and Body Hair
The arrector pili are smooth muscle fibers that involuntarily contract to give you “goose bumps.” When the arrector pili are triggered, the hairs that come out of the nearby follicles stand up, giving the animal a thicker, warmer coat and also a larger appearance that might scare off potential predators. But humans don’t have thick fur anymore because our strategy for the past several thousand years has been to steal the fur from other warm looking animals to help stave off the cold. Of course, some body hair is still useful to humans. Eyebrows in particular are great at keeping sweat and dust out of our eyes and facial hair can actually be the decisive factor in influencing a woman’s choice of sexual partner these days. But all the rest of that body hair is more or less useless.
Tonsils are supposedly our body’s first line of defense against ingested or inhaled pathogens, but, much like the appendix, they tend to get easily infected and inflamed and require removing from the body. This has led many scientists to the conclusion that the supposedly beneficial effects of having tonsils is greatly overshadowed by the need to have them removed so often.
7. Paranasal Sinuses
Our sinuses are essentially just pockets of air nested inside our face. The nasal sinuses of our early ancestors were likely lined with specific odor receptors that gave them a heightened sense of smell and aided in survival. Today, our sinuses are usually only associated with headaches or infections and scientists aren’t really sure why we retain them except perhaps to make our heads lighter and warm the air we breathe.
6. The Plica Semilunaris / Nictitating Membrane
The plica semilunaris is a mucous membrane located at the inner corner of the human eye. It bears a strong likeness to the nictitating membrane, or third eyelid, found in other animals and has led to the idea that it might be the vestige of such a structure. It’s an especially interesting hypothesis when you consider that a functional third eyelid is still part of the eye in some primates such as gorillas. However, in chimpanzees, one of our species closest relatives, the plica semilunaris also appears to be vestigial. The purpose of the nictitating membrane in many animals is protective and helps keep the eye clean and moist or conceals the shiny iris from predators. Although the reason for the loss of the nictitating membrane in humans is still relatively unknown, it could be that changes in our habitat and eye physiology have resulted in the tissue becoming unnecessary.
5. The Palmer Grasp Reflex
The palmar grasp reflex is a behavior characteristic of human babies that develops as early as 16 weeks after conception when the fetus begins to grasp the umbilical cord in the womb. Now, research has found that newborn babies, relying on their grasp reflex, can hold their own bodyweight for at least 10 seconds when hanging by their hands from a horizontal rod. By comparison, newborn monkeys, which possess a similar involuntary grasping behavior, are able to hang from one hand for over half an hour. The research demonstrated that this reflex is essential for monkey infants because it enables them to cling to the mother’s body fur. Since humans have evolved away from a life in the harsh wilderness, we’re now losing the covering of fur over the body and, as a result, no longer need that powerful grasp early on in life. But despite its weakened strength, some researchers believe that the reflex may still play an important role in humans.
4. Parts of the Ear
The extrinsic muscles of the human ear include the anterior auricular muscle, the superior auricular muscle, and the posterior auricular muscle. Together, they control, the entire visible portion of the ear. A lot of mammals are able to move their ears and utilize the auricular muscles in sound localization and the expression of emotion. In humans, however, the muscles are now believed to be largely ineffectual. Darwin proposed that humans now effectively capture sounds by simply positioning the head to receive them, thereby eliminating the need to use auricular muscles. Although there are still people who seem to have the capacity to wiggle their ears, this ability really doesn’t have much use except to impress elementary school classmates.
3. Male Nipples and Breast Tissue
Male nipples are a sensitive issue. Although the odd case of a lactating man does arise now and again, the biological function of male nipples still remains a mystery. Both men and women have nipples because in early stages of fetal development, an unborn child is essentially sexless. It’s only in a later stage of fetal development, when testosterone is added to the mix, that sex differentiation takes place. But all mammals, both male and female, have mammary glands, but, at least on males, nipples are vestigial. Sure, one could make the argument that they still have a role in sexual stimulation, however, they most certainly are not functional and, since cancer can still grow in male breast tissue, its continued presence could actually be deemed a hindrance.
2. The Tailbone
The coccyx, or tailbone, is a series of fused vertebrae that are the only remnant left of the tail that earlier species in the history of our evolution used to have and use primarily for balance. As our ancestors learned to walk upright, their tail became less and less important and, slowly, it began to disappear. Some biologists have proposed that the coccyx helps to anchor small muscles and might help support pelvic organs, however, there have been numerous well documented cases of medical procedures where the tailbone has been surgically removed with little or no adverse effects to the subject. In addition, there have been cases of babies born with tails that are an extended version of the tailbone composed of extra vertebrae. Again there are no adverse physical health effects associated with the presence of such tails.
1. Wisdom Teeth
When the human species migrated beyond the continent of Africa, it was introduced to a variety of new habitats and, eventually, a civilization was born. With new habitats came new edibles which marked a shift in the human diet towards the consumption of softer cooked foods. This change in diet gradually eliminated the need for large, powerful jaws with big teeth to rip apart and grind up tougher foodstuffs. And this, in turn, led to a reduction in human jaw size. But the presence of those larger teeth still remain to this day. Now, because of our smaller jaws, our third molars, also known as wisdom teeth, are highly prone to becoming impacted and often need to be removed as an adult less they become unbearably painful. The good news is that wisdom teeth are actually becoming increasingly absent in populations so that’s one less surgery current and future generations can look forward to not having.