Vestigial structures are body parts that we've evolved to no longer need. The natural selection process dictates that we keep the traits that continue to serve a purpose while the others become functionless or degenerate. Here are five vestigial body parts.
In humans, this organ dates back almost 80 million years and helped our ancestors to digest tough plants and vegetables. Located in the lower right part of the intestine, the appendix is approximately 3.5 inches long and less than .5 inches wide — with its shape reflected in its Latin name, "vermiform," which means "worm-shaped."
Although the appendix is considered vestigial in terms of its original usefulness, modern researchers believe it has evolved to play a role in supporting the immune system, thanks to its abundance of lymphoid cells. Other scientists think we will evolve to the point that the appendix will no longer be a part of the human body.
Read More: What Is the Function of the Appendix?
2. Ear Muscles
Our ancient ancestors could move their ears — which they did in response to different sounds. This allowed for more accurate identification of the source of the sound. Eventually, human ancestors began walking upright, and vision became more important than sound.
More than 30 million years ago, the dry-nosed primates evolved; along with their evolution, their ear size and muscles decreased. A 2015 study found that the vestigial muscles of the ear may still be activated with certain intense or exciting sounds. This led researchers to believe that further studying the vestigial auditory system could lead to meaningful insights. These include the potential for developing tests for hearing deficits in infants and measuring emotions in adults.
Paranasal sinuses are air pockets in our skull and facial bones. Humans have four sets of them:
Frontal: Located above the eyes — near the forehead.
Ethmoid: Located on each side of the nose bridge, near the eyes.
Sphenoid: Located behind the nose.
Maxillary: Located beneath the cheekbones.
Researchers believe that early ancestors relied on sinuses for a more pronounced sense of smell that aided survival. In modern times, aside from moistening and warming the air we breathe, they do not seem to serve a meaningful function. However, these open spaces are prone to infection, either through congestion or illness. They appear to have evolved to possibly aid in producing nitric oxide, which could boost nasal cavity defenses. But there is currently no definitive need for sinuses, and people can live without them.
Many primates have tails that help them with balance when swinging through trees. However, when apes evolved about 25 million years ago — they did so without tails. This evolution eventually led to humans. Human embryos still develop tails during the beginning of gestation, though it is absorbed back into the body. The remnant that remains is the tailbone, also called the coccyx.
Although most babies are born without a tail, there are extremely rare cases where a tail is present. When this happens, surgical removal is usually the treatment, mostly for aesthetic purposes. When a tail does exist, it can reach 5 inches long and consists of connective tissue, blood vessels and muscles — but no bone or cartilage.
5. Wisdom Teeth
The diet of early humans consisted of dense food such as raw meat, leaves, roots, plants, nuts, and bark. Wisdom teeth (or the third set of molars) were once needed to grind down these foods for proper digestion. The discovery of fire, cooking and eventually eating utensils led to the consumption of softer foods.
Softer foods meant the need for wisdom teeth was eliminated. During the time of the hunter-gatherer lifestyle, human jaws were adapted for stronger, larger teeth and muscles. When humans shifted to a more modern diet, it led to the development of smaller jaws. Smaller jaws do not easily accommodate wisdom teeth, so they often cause dental issues.
Read More: How Did Humans Evolve?