Does the human body contain truly useless parts? Arguably so, but they may not be the ones you assume.
It could be said that some parts of the body, such as the male nipple, do not serve any useful function. But others, like the appendix, remain up for debate, as recent research suggests they may serve a purpose that scientists don’t yet fully understand.
Scientists have a history of classifying the importance of organs before knowing their true functions. But the more we learn, the more we realize that many of those “useless” parts are really essential.
For example, in the 1890s, anatomist Robert Wiedersheim published a list of 86 human “remnants,” or body parts that had “lost their original physiological significance” for humans. The list, published in his book “The structure of man: an index of his past history (opens in a new tab)it included essential anatomy, such as key valves in veins that help direct blood flow; the thymus gland, which produces disease-fighting white blood cells; and the hormone-producing pituitary and pineal glands.
Scientists continue to discover new things about the human body to this day. With that in mind, here are 10 of the seemingly useless parts of the human body, some of which remain controversial.
Related: How many organs are in the human body?
1. male nipples
In the womb, all human embryos initially develop all the same parts, and then, at around seven weeks, the sexes begin to diverge, michelle moscow (opens in a new tab)leader of the Healthcare Innovations research team at the University of New South Wales in Sydney, wrote in The conversation (opens in a new tab). That’s when a gene called SRY on the Y chromosome kicks in and initiates the development of the male reproductive organs and the disappearance of the female ones. Nipples start to form before SRY kicks in, so all humans end up with nipples, regardless of gender. Although generally not capable of nursing, male nipples are often still responsive to sexual stimulation, so some may disagree with the idea that they are totally “useless.”
2. wisdom teeth
Human third molars, better known as wisdom teeth, can be used to chew food, but are often considered unnecessary. In about 22% (opens in a new tab) of people worldwide, at least one in four wisdom teeth do not grow. When they grow up, the molars are the most likely (opens in a new tab) become impacted, which means they do not break through the gums correctly. That’s because human jaws are often too small to accommodate teeth. Some scientists have attributed this to humans developing smaller jaws over time, but now, there’s evidence to suggest our childhood diets are more to blame. Eating hard-to-chew foods like raw vegetables and nuts can stimulate jaw growth, while eating soft and processed foods somehow stunts jaw growth, leaving little room for the back teeth. judgment. discover reports (opens in a new tab).
Related: Why do wisdom teeth come in so late?
3. The vomeronasal organ
In some humans, scientists aren’t sure how many, remnants of a tube-shaped pheromone-sensing organ can be found poking through the roof of the nasal cavity. This structure, called the vomeronasal organ or Jacobson’s organ, is present and functional in many animals, including reptiles, amphibians, and mammals. There is anatomical and genetic evidence to suggest that the organ is not functional in humans who carry it, but this issue “is still widely debated,” according to a 2018 review in the journal. cure (opens in a new tab).
4. Palmaris longus muscle
The palmaris longus muscle runs from the bottom of the upper arm bone, or humerus, to the thick connective tissue, or fascia, in the palm of the hand. Functionally, it is one of the muscles involved in hand flexion at the wrist and palm tension, but not all humans have the muscle, and those who do not can still execute these movements without issue. Some scientists theorize that muscle is stronger and more functionally relevant in tree-climbing primates than in terrestrial primates such as humans, according to a 2014 report in the journal Medical Hypotheses (opens in a new tab).
5. Piriformis muscles
The two pyramidal muscles originate at the joint between the two pubic bones, the pubic symphysis, and run on either side of the linea alba, a line of connective tissue that runs down the center of the abdomen. These muscles vary in size, with a percentage of humans missing one or both muscles and suffering no ill effects from their absence, according to a 2017 report in the Journal of Clinical and Diagnostic Research (opens in a new tab). Estimates suggest that 10-20% of people lack at least one piriformis muscle, but these estimates vary depending on the population of people studied.
6. Darwin’s Point
Darwin’s point, or Darwin’s tubercle, is a bump that sometimes appears on the edge of the outer ear. Considered a harmless malformation of the ear, the structure is believed to be a remnant of a joint that once allowed the top of the ear to bend over the ear canal, New scientific reports (opens in a new tab).
7. Auricular muscles
The pinna, or pinna, is the visible part of the ear on the outside of the head; the muscles attached to the auricle are considered vestigial in humans, meaning they have lost all or most of their original function over evolutionary time. (“Vestigial” is widely thought to mean “completely non-functional”, but this is a misconception.) While many animals can turn their ears in response to sounds, humans have lost this ability and some cannot even move their ears, according to The New York Times (opens in a new tab).
8. The “Tailbone”
The human coccyx, or coccyx, is also considered vestigial, meaning it lost its original function over evolutionary time. Once part of an actual tail, the human tailbone now consists of three to five rudimentary vertebrae fused together to form a single bone; it serves as the anchor point for many muscles, ligaments and tendons, New Scientist reported. So while it’s far from useless, it’s not a queue anymore.
9. The appendix? (Maybe not.)
Charles Darwin was the first to propose that the appendix, a pouch-like structure that extends from the large intestine, might be a vestigial organ that once helped our herbivorous ancestors digest abundant plants. The fact that some people are born without an appendix and that many have the organ surgically removed without any obvious consequence seems to support this idea. But more recently, research has revealed possible functions of the appendix in a wide range of mammals, including humans. The organ can be a reservoir of helpful gut bacteria, for example, and also a site where disease-fighting immune cells are born. So it’s useless? Maybe not, but have it removed if you have appendicitis.
10. “Third eyelid”
Birds, reptiles, and some mammals, including cats, have a third eyelid that blinks across the eye, from the lower inner corner to the upper outer corner. This wiper-like structure, called the nictitating membrane, does not exist in humans, but humans do carry a remnant of the third eyelid in the inner corner of each eye, according to american scientist (opens in a new tab).
This remnant, called the plica semilunaris, looks like a small fleshy bump. Although it is sometimes thought to be useless because it does not work like an eyelid, in reality supports rotation (opens in a new tab) of the eyeball and helps with tear drainage. That being said, the fabric can be removed in patients (opens in a new tab) requiring surgery for narrowing or obstruction of the lacrimal duct.