Are there truly useless parts in the human body. How do scientists’ views on organ functionality evolve over time. Which body parts were once considered vestigial but are now known to be essential. What is the current understanding of supposedly unnecessary anatomical features.

The Enigma of Male Nipples: Evolutionary Remnant or Hidden Purpose?

Male nipples have long been considered a prime example of vestigial structures in the human body. Their apparent lack of function raises intriguing questions about human evolution and embryonic development. Why do males retain these seemingly purposeless anatomical features?

The answer lies in our early fetal development. All human embryos, regardless of sex, initially develop the same basic anatomical structures. It’s only around the seventh week of gestation that sexual differentiation begins to occur. This process is triggered by the SRY gene on the Y chromosome in male embryos, which initiates the development of male reproductive organs and suppresses the formation of female ones.

Interestingly, nipples begin to form before this sexual differentiation takes place. As a result, all humans end up with nipples, regardless of their eventual sex. This phenomenon highlights the complex interplay between genetics and embryonic development in shaping human anatomy.

Potential Functions of Male Nipples

• Sensory role in sexual stimulation
• Possible evolutionary advantage in nurturing behavior
• Indicator of overall health and hormonal balance

While male nipples may not serve a direct reproductive function, some researchers argue that they may still play subtle roles in human physiology and behavior. Their sensitivity could contribute to sexual pleasure, and their presence might have evolutionary implications for paternal care instincts. Additionally, changes in male nipples can sometimes indicate underlying health issues, making them potentially useful diagnostic markers.

The Appendix: From Vestigial Organ to Immune System Ally

For decades, the appendix was dismissed as a useless evolutionary leftover. However, recent research has dramatically shifted our understanding of this small, finger-shaped organ located in the lower right abdomen. Far from being vestigial, the appendix may play a crucial role in maintaining gut health and supporting the immune system.

Key Functions of the Appendix

1. Acts as a safe house for beneficial gut bacteria
2. Supports the immune system by producing and training immune cells
3. Helps in the production of certain hormones
4. May play a role in fetal development and early childhood

The appendix appears to serve as a reservoir for beneficial gut bacteria, helping to repopulate the digestive system after illnesses that deplete these crucial microorganisms. This function could be particularly important in maintaining a healthy gut microbiome, which is increasingly recognized as essential for overall health.

Moreover, the appendix contains a high concentration of lymphoid tissue, suggesting an important role in the body’s immune defenses. It produces and trains immune cells, contributing to the body’s ability to fight off infections and maintain immunological balance.

Wisdom Teeth: Evolutionary Relic or Functional Molars?

Wisdom teeth, also known as third molars, often cause problems when they emerge in modern humans. Their tendency to become impacted or cause dental crowding has led many to consider them unnecessary. However, the story of wisdom teeth is more complex than it might initially appear.

Historical Context of Wisdom Teeth

• Evolved to help our ancestors process tough, fibrous foods
• Useful for replacing worn-out molars in prehistoric diets
• Became problematic as human jaws evolved to be smaller

In our evolutionary past, wisdom teeth served a clear purpose. They provided additional chewing power for our ancestors, who consumed diets rich in tough plants and raw meats. These teeth also acted as replacements for other molars that wore down due to the abrasive nature of prehistoric diets.

As human diets changed and cooking became prevalent, our jaws gradually evolved to be smaller. This reduction in jaw size has led to the common problems associated with wisdom teeth in modern humans, such as overcrowding and impaction.

Current Perspectives on Wisdom Teeth

Despite the problems they often cause, some researchers argue that wisdom teeth should not be automatically classified as vestigial. In individuals with sufficient jaw space, these teeth can still serve their original purpose as functional molars. Additionally, the roots of wisdom teeth contain valuable stem cells that could potentially be used in regenerative medicine.

The Mysterious World of Body Hair: Remnants of Our Evolutionary Past?

Human body hair, particularly the fine vellus hair covering most of our skin, often seems to serve little purpose in modern life. Unlike our primate relatives, humans lack a thick, insulating coat of fur. This has led many to question the role of our remaining body hair.

Potential Functions of Human Body Hair

1. Enhances tactile sensitivity
2. Regulates body temperature through sweat evaporation
3. Provides a barrier against environmental irritants
4. May play a role in pheromone dispersion

While our body hair may seem vestigial, it continues to serve several subtle but important functions. The hair follicles are connected to nerve endings, enhancing our sense of touch and allowing us to detect even slight changes in our environment. This heightened tactile sensitivity could have been crucial for our ancestors’ survival.

Body hair also plays a role in thermoregulation. By trapping a thin layer of air near the skin, it can help insulate the body. More importantly, it aids in the evaporation of sweat, which is critical for cooling the body during physical exertion or in hot environments.

The Coccyx: Tailbone or Essential Anchor?

The coccyx, commonly known as the tailbone, is often cited as a vestigial structure – a remnant of the tails our distant ancestors possessed. However, this small collection of fused vertebrae at the base of the spine serves several important functions in the human body.

Key Roles of the Coccyx

• Provides attachment points for important muscles and ligaments
• Supports and stabilizes the pelvis when sitting
• Plays a role in weight-bearing and distribution of body forces

Far from being useless, the coccyx is an integral part of our musculoskeletal system. It serves as an attachment point for several muscles, including those of the pelvic floor, which are crucial for continence and sexual function. The coccyx also provides anchor points for ligaments that support the anus and help maintain pelvic stability.

When sitting, the coccyx acts as a weight-bearing structure, helping to distribute the body’s forces and provide stability. Its slight mobility also aids in shock absorption during activities like walking and running.

The Plica Semilunaris: Vestigial Third Eyelid or Protective Feature?

The plica semilunaris, a small fold of tissue in the inner corner of the eye, is often described as a vestigial remnant of a third eyelid found in some animals. While it’s true that this structure is much reduced in humans compared to species with fully functional nictitating membranes, the plica semilunaris may still serve important purposes.

Functions of the Plica Semilunaris

1. Aids in tear drainage and distribution
2. Provides some protection against foreign particles
3. Allows for greater eye movement

Although not as prominent as in other animals, the human plica semilunaris contributes to eye health and function. It helps guide tears towards the tear ducts, ensuring proper lubrication and cleaning of the eye surface. The structure also offers a degree of protection against dust and other small particles that might enter the eye.

Moreover, the plica semilunaris allows for a greater range of eye movement by providing a small amount of slack in the conjunctiva (the membrane covering the eye). This flexibility is particularly useful when looking in extreme directions.

Erector Pili Muscles: More Than Just Goosebumps

Erector pili muscles, responsible for causing goosebumps, are often considered vestigial in humans. These tiny muscles attached to hair follicles contract in response to cold or strong emotions, causing hair to stand on end. While this response doesn’t provide significant warmth or intimidation in humans as it does in other mammals, these muscles may serve other purposes.

Potential Roles of Erector Pili Muscles

• Assist in regulating body temperature
• Aid in sebum production and skin health
• Contribute to tactile sensitivity
• May have psychological or social signaling functions

The contraction of erector pili muscles, while not providing significant insulation, can help expel cold air trapped near the skin, potentially aiding in temperature regulation. This action also squeezes the sebaceous glands associated with hair follicles, promoting the release of sebum, which helps keep skin moisturized and protected.

Furthermore, the sensation of goosebumps may serve as a form of emotional expression or social signaling. The shared experience of getting goosebumps in response to music or other stimuli could potentially enhance group bonding and empathy.

Palmaris Longus: The Variable Muscle

The palmaris longus is a slender muscle in the forearm that is absent in about 10-15% of the population. This high degree of variability has led some to classify it as a vestigial structure. However, its presence in the majority of humans suggests it may still serve a purpose, even if not an essential one.

Functions and Significance of the Palmaris Longus

1. Assists in wrist flexion
2. Provides additional strength for gripping actions
3. Serves as a useful tendon graft in reconstructive surgery

While not crucial for hand function, the palmaris longus does contribute to the strength and dexterity of the hand. It aids in flexing the wrist and tensing the palmar fascia, which can enhance grip strength. These functions, while subtle, could have provided our ancestors with a slight advantage in tasks requiring manual dexterity.

Interestingly, the palmaris longus has found a new purpose in modern medicine. Its long, slender tendon makes it an ideal candidate for tendon grafts in various surgical procedures, particularly in hand reconstruction. This medical utility has given new value to this supposedly vestigial structure.

The story of the palmaris longus highlights an important principle in evolutionary biology: structures that are not strictly necessary for survival can still persist if they provide even a small benefit or if there’s no significant disadvantage to retaining them.

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10 body parts that are useless in humans (or maybe not)

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(Image credit: SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY via Getty Images)

Does the human body contain any truly useless parts? Arguably, yes — but they might not be the ones you assume.

Some body parts, like the male nipple, arguably serve no useful function. But others, like the appendix, remain a matter of debate, as recent research suggests that they may serve a purpose scientists don’t yet fully understand. 

Scientists have a track record of rating organs’ importance before learning their true functions. But the more we learn, the more we realize many of those “useless” parts are actually essential. 

For example, in the 1890s, anatomist Robert Wiedersheim published a list of 86 human “vestiges,” or body parts that had “lost their original physiological significance” to humans. The list, published in his book “The Structure of Man: An Index to His Past History,” included essential anatomy, such as key valves in veins that help direct blood flow; the thymus gland, which makes 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 human body’s seemingly useless parts, some of which remain controversial.  

Related: How many organs are in the human body? 

1. Male nipples

(Image credit: PeopleImages via Getty Images)

In the womb, all human embryos initially develop all the same parts, and then about seven weeks in, the sexes begin to diverge, Michelle Moscova, leader of the Healthcare Innovations research team at the University of New South Wales Sydney, wrote in The Conversation. That’s when a gene called SRY on the Y chromosome kicks in and jump-starts the development of male reproductive organs and the disappearance of female ones. Nipples start to form before SRY activates, so all humans end up with nipples, regardless of their sex. Although usually not capable of lactation, male nipples often still respond to sexual stimulation, so some may disagree with the idea that they’re totally “useless. ” 

2. Wisdom teeth

(Image credit: BSIP / Contributor via Getty Images)

Humans’ third molars, better known as wisdom teeth, can be used to chew food but are often considered unnecessary. In about 22% of people worldwide, at least one out of four wisdom teeth fails to grow in. When they do grow, the teeth are the most likely to become impacted, meaning they don’t properly emerge through the gums. That’s because humans’ jaws are often too small to accommodate the teeth. Some scientists have chalked this up to humans evolving smaller jaws over time, but now, there’s evidence to suggest that our childhood diets are more to blame. Consuming hard-to-chew foods, like raw vegetables and nuts, may stimulate jaw growth, while eating soft, processed foods somewhat stunts jaw growth, leaving little room for wisdom teeth, Discover reported.

Related: Why do wisdom teeth come in so late? 

3. The vomeronasal organ

(Image credit: Henry Vandyke Carter, Public domain, via Wikimedia Commons)

In some humans — scientists aren’t sure how many — remnants of a tube-shaped, pheromone-detecting 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’s anatomical and genetic evidence to suggest that the organ is nonfunctional in the humans who carry it, but this matter is “still widely debated,” per a 2018 review in the journal Cureus. 

4. Palmaris longus muscle

(Image credit: SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY via Getty Images)

The palmaris longus muscle extends from the bottom of the upper arm bone, or humerus, to thick connective tissue, or fascia, in the palm of the hand. Functionally, it’s one of the muscles involved in flexing the hand at the wrist and in tensing the palm — but not all humans carry the muscle, and those without it can still execute these motions without issue. Some scientists theorize that the muscle is stronger and more functionally relevant in tree-climbing primates than in land-bound primates, like humans, according to a 2014 report in the journal Medical Hypotheses.  

5. Pyramidalis muscles

One of the two pyramidalis muscles is labeled in the bottom left corner of the drawing. (Image credit: Image from page 421 of “Anatomy, descriptive and surgical” (1887) via Flickr)

The two pyramidalis muscles originate at the joint between the two pubic bones — the pubic symphysis — and extend to each side of the linea alba, a line of connective tissue that runs down the center of the abdomen. These muscles vary in size, and a percentage of humans are missing one or both of the muscles and suffer no ill effects from their absence, according to a 2017 report in the Journal of Clinical and Diagnostic Research. Estimates suggest that between 10% and 20% of people are missing at least one pyramidalis muscle, but these estimates vary depending on the population of people studied.

6. Darwin’s point

The individual pictured has a small “Darwin’s point” on her ear; the feature can sometimes be more pronounced. (Image credit: Alona Siniehina via Getty Images)

Darwin’s point, or Darwin’s tubercle, is a bump that sometimes appears on the rim of the outer ear. Considered a harmless malformation of the ear, the structure is thought to be a remnant of a joint that once allowed the top of the ear to fold down over the ear canal, New Scientist reported. 

7. Auricular muscles

(Image credit: Sms1371, CC BY-SA 3.0 , via Wikimedia Commons)

The auricle, or pinna, is the visible portion of the ear on the outside of the head; the muscles attached to the auricle are considered vestigial in humans, meaning they’ve lost all or most of their original function over evolutionary time. (“Vestigial” is widely thought to mean “completely nonfunctional,” but this is a misconception.) While many animals can pivot their ears in response to sounds, humans have lost this ability and some can’t even wiggle their ears, according to The New York Times. 

8. The “tailbone”

(Image credit: SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY via Getty Images)

The human tailbone, or coccyx, is also considered vestigial, meaning it’s 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 an anchoring point for many muscles, ligaments and tendons, New Scientist reported. So while it’s far from useless, it’s no longer a tail.

9. The appendix? (Maybe not.)

(Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)

Charles Darwin first proposed that the appendix, a pouch-like structure that extends off the large intestine, might be a vestigial organ that once helped our herbivorous ancestors digest hearty plants. The fact that some people are born without an appendix and many have the organ surgically removed without any obvious consequence seemed 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 may be a reservoir for helpful gut bacteria, for example, and also a site where disease-fighting immune cells are born. So is it useless? Maybe not, but get it removed if you have appendicitis. 

10. “Third eyelid”

(Image credit: Jonathan Storey via Getty Images)

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 windshield wiper-like structure, called the nictitating membrane, doesn’t exist in humans, but humans do carry a remnant of the third eyelid in the inner corner of each eye, according to Scientific American. 

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This remnant, called the plica semilunaris, looks like a small, fleshy bump. Although sometimes thought to be useless because it doesn’t function as an eyelid, it actually supports the rotation of the eyeball and helps with tear drainage. That said, the tissue may be removed in patients who require surgery for narrowing or blockage of the tear duct.

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Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers’ work.

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