Genetics are a curious thing. Don’t get me wrong, on paper and in theory, the study and science behind our inheritance completely checks out. However, in practice, it can still be a bit disconcerting to look in the mirror one day and recognize your father’s nose and eyebrows in your own face, or to realize you gesticulate in the same animated fashion as your mother, and sometimes hear her laugh come bubbling out of your own mouth.
More curious still are the structures and behaviors that have been carried throughout evolution to the modern era of humanity, though we are considerably distinguishable from our more primitive ancestors.
And perhaps most curious of all, are the structures we continue to pack along with us, as that have little to no known useful function in the contemporary human body. These features are better known as vestigial structures, and are classically defined as features and behaviors that no longer serve the function and purpose they were designed to perform (in comparison to other creatures with the same parts).
Currently, as I recover from the aftermath of a painful encounter with one of my own vestigial organs, I find myself considering if my late appendix ever did anything much for me, or if it’s only purpose was to lie in wait as a metaphorical ticking time-bomb. Prior to my surprise appendectomy, I hadn’t spared much thought for my appendix, and decided I wanted to honor it’s memory by learning more about it, in addition to several of our other human evolutionary leftovers. Man, I wish I would’ve asked the doctors to hang on to that bad boy for me!
The Evolutionary Junk in Our Trunk
The appendix is perhaps the most widely known vestigial organ in the human body of today. If you’ve never seen one, the appendix is a small, pouch-like tube of tissue that juts off the large intestine where the small and large intestines connect. By comparison, in herbivorous vertebrates the appendix is much larger, and functions primarily to aid in the breakdown of cellulose in consumed plants. Today, the appendix is considered a small leftover from one of our plant-eating ancestors. As our diets have changed over time, the role our appendix plays in digestion has declined, leaving plenty of room for speculation regarding what purpose it serves now.
Recent studies have shown it might function as a production hub of antibodies and white blood cells or potentially serve as a warehouse for beneficial bacteria that can be ushered back into the intestines after undergoing illnesses such as dysentery or bouts of diarrhea.
In spite of these potentially beneficial functions, there is no denying that when the appendix gets infected, it’s got to come out. Appendicitis is a medical emergency, escalates at a shocking rate, and speaking from experience, the pain is no joke. As appendicitis progresses, the appendix can perforate, or burst, resulting in infection of the abdominal cavity, that can be fatal if not treated quickly.
The good news is, if caught early, appendectomies are fairly easy and low-risk surgeries, and fortunately for the 1 in 20 of us who do have to get them removed in our lifetime, the potential benefits of having an appendix are not necessary to our survival.
Wisdom teeth are another vestigial structure, widely acknowledged to be more of a hindrance than a help to the modern human. This third and final set of molars, originating from our hominid ancestors, often make their grand debut later in life, crowding your other teeth, causing misalignment and damage to your jawbone and surrounding nerves, usually packing along a whole lot of pain.
Despite being surgically removed in nearly 85% of adults, these decidedly unfun structures have continued to stick with us as we’ve evolved. But what was their original intended purpose and why aren’t they useful now?
Good question, friend! There are two main possibilities that have been most discussed as to why these extra teeth have become vestigial. The first theory involves the size of our jaws and noggins. As human beings have evolved, our heads and jaws have become smaller than those of our ancestors. This means that now the teeth are trying to force their way into a mouth that is simply not large enough to accommodate them, hence the pain and discomfort.
The second school of thought is that dental hygiene is a thing now. In the past, it was not uncommon for our ancestors to have lost most of their teeth by the time they reached early adulthood. The appearance of those additional teeth at that point in their lives was definitely useful back then, and due to the absence of all the other teeth, there was actually somewhere for the wisdom teeth to go. Now that humans have the knowledge and desire to take care of their teeth, it’s possible to keep them all for a lifetime, rendering the need for supplemental teeth effectively useless.
The tonsils are another vestigial organ that have been the subject of debate in terms of necessity. It has been argued that the tonsils play an important role as the front defensive lines against harmful pathogens that may be ingested or inhaled. However, similar to the appendix, the tonsils are notorious for turning against the body they’re supposed to be defending, and more severe health complications can arise if infected tonsils are left untreated.
It is this penchant to became dangerously infected that has led experts to believe that if immune response was their actual purpose, the benefits of that response have been certainly—and easily—outweighed by the need to have them removed.
Auricular Muscles and Darwin’s Tubercle
Are you able to wiggle your ears? If so, you are in the minority (It’s estimated that only 10-20% of the human population can), and you can say thanks to your auricular muscles for that, uh, let’s go with…amusing, ability. These muscles are responsible for the movement of the visible parts of the ear, and are much more useful to other mammals, including our feline, canine, and larger farm animal friends. These muscles are what you’re observing when your pet’s ears perk up and swivel in response to sounds. As humans evolved and moved up the food chain, the need to prick our ears for sound detection decreased, and our neck flexibility increased, allowing us to more easily turn our heads to observe the source of sounds.
If you take closer look at your ears, you may potentially find another trace of our ancestral past, known as Darwin’s tubercle. It most often presents as a tenuous thickening in the mid- to upper region of the ear’s outer rim, and similar to the auricular muscles, they no longer serve any real purpose in this day and age, but are rather simply a nod to all the pointier and more mobile ears that came before us.
Palmaris Longis is a long muscle that runs the inner length of the forearm from wrist to elbow. In the days where the primary route of transport for our ancestors was through the treetops, the muscle is believed to have played a significant role in their grips. Once we began walking upright, the necessity for a powerful grip to hang on so tightly became abysmal. Today, approximately 16% of the human population no longer has this muscle (myself included), and those who do, don’t possess any additional or extraordinary strength because of it. However, even though the muscle no longer serves its original intended purpose, it has potential to be repurposed in the medical field. The muscle functions well for folks who need tendon grafts, as it can be completely cut out and relocated elsewhere in the body, without affecting function and movement of the hand and wrist.
Think you might have it? To check, turn your palm up and touch your thumb and pinky together. If you see a long, skinny band pop up in the middle of your wrist when you perform this movement, then congratulations, you’re the lucky owner of a Palmaris Longis! Be sure to use it wisely.
Another lingering hint at our evolutionary past, the coccyx is all that remains of our ancestral tails. In many creatures, tails can serve several beneficial functions by way of balance, communication, and in the case of some primates, are even prehensile. As humans gradually evolved to walk upright, our tails became unnecessary for our balance, and began to disappear altogether, leaving our tailbone as the only evidence of their previous existence.
If you’ve ever taken an unlucky spill and landed on your tailbone, you’ve probably found yourself shouting something along the lines of “LITERALLY WHY DO I EVEN HAVE THIS?”, in addition to some other choice words. And really, that’s a great question. It’s been argued that the fused vertebrae that comprise the coccyx serves to help anchor some minor muscles, and possibly aid in the support of the pelvic organs. However, there are many well-documented cases involving the surgical removal of the tailbone, which all resulted in little to no side effects for the patient, which suggests this evolutionary leftover may be totally unnecessary.
So if you’re someone who often finds yourself at the mercy of banana peels or having footballs pulled out from under you at the last minute, maybe a preemptive removal of the tailbone would be to your benefit. 😉
A lesser known vestigial feature, known as the fabella, has actually shocked scientists by making a surprising comeback, after being considered a feature that was initially lost to evolution. The fabella is a teeny, tiny bone that sits inside the tendon behind the knee, and was found to be present in a mere 11.2% of people in 1918. In a recent study, it was discovered that those numbers have more than tripled in the last century, with up to 39% of the population now in possession of the bone.
It’s believed that the modern human diet has made us taller and heavier than our ancestors, which results in additional strain on our knees, and the appearance of the fabella was in response to the additional stress. The bone provides a smooth surface for the tendon in the back of the knee to slide on, reducing the amount of friction and stress our larger calf muscles and longer shin bones put on our knees.
Unfortunately, it’s a bit of a Catch-22, as experts also believe the existence of the fabella contributes to uneven force on the knee, leading to cartilage damage that may result in osteoarthritis. Either way, it remains up for debate if the bone presence is truly necessary.
Fun Fact: The word fabella is latin for “little bean”, which is the cutest thing I’ve ever heard, and should probably be the name of the next fuzzy creature I adopt.
Ever wish you had self-cleaning eyes? Unfortunately for us, we’ve evolved beyond possession of a nictitating membrane, or third eyelid, which serves to clear away debris and moisten the eyes of most reptiles, amphibians, and birds. All that remains of the feature in humans is the small fold of tissue in the innermost corner of the eyes, called the Plica Semilunaris, which doesn’t seem to have any useful purpose to speak of.
Another Fun Fact: Not all vestigial features are necessarily bodily organs or structures! They can also present as behaviors, reflexes, and even biochemical processes! Let’s take a quick look at a few.
Palmar Grasp Reflex
Ever notice that if you press a finger or an object into an infant’s palm, their tiny baby fingers immediately grasp onto it? This is due to the primitive reflex known as the palmar grasp reflex. For our primate ancestors, this reflex was necessary for babies to cling onto the body fur of their mothers, freeing up the mother’s hands to forage for food and escape predators. As we evolved, we’ve lost the vast majority of our body hair, and due to accessibility of resources and general lack of impending threats, it’s no longer necessary for our babies to cling onto us.
In my research for this article, I stumbled across this not-exactly-scientific, though undoubtedly amusing dispute of the vestigiality of this reflex, made by a parent. They argued that this endearing behavior, along with the inherent cuteness of babies, isn’t vestigial but is rather extremely necessary for their survival, similar to the way the inherent cuteness of puppies and kittens enables them to survive, as it compensates for their total helplessness and, to be frank, annoying and frustrating behavior at times.
If you are a living, breathing human person, you’ve most likely experienced the irritation and, sometimes discomfort, brought on by hiccups. Hiccups occur when the muscles we use to inhale undergo sudden contractions—though it’s still up in the air as to why it happens and if they actually serve any sort of purpose. It has been proposed that the hiccups might be attributed to an ancient amphibian ancestor. The motor reflex that allows tadpoles to take in air and water through their gills is apparently quite comparable to the reflexes observed when we hiccup. In terms of purpose, one theory suggests that the contractions help to prepare the respiratory muscles of a developing fetus for breathing after they are born, and another postulates that hiccups may serve to keep amniotic fluid from entering into an unborn baby’s lungs. However, there currently isn’t sufficient evidence to support either of these theories.