Not only 'man's nipples' 10 useless body parts at first glance

Robert Wiederheim, a German anatomist active in the late 19th century, announced in his book '

The Structure of Man ' that humans have 86 vestigial organs . Since then, scientists have continued to make new discoveries in various parts of the human body, and some of them are considered unnecessary for the human body, and debates continue among experts about their usefulness. Live Science, a scientific news site, has selected 10 of them and explained them.

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

◆ 01: male nipple
The human embryo developed in the mother's womb initially develops all parts in the same way, but the male and female divergence begins around the 7th week after birth. Specifically, the ' SRY ' gene on the Y chromosome, which is a sex chromosome, works to initiate the development of male reproductive organs and the disappearance of female reproductive organs.

However, nipples are formed before the SRY gene is activated, so even men who never had the opportunity to breastfeed their children are born with nipples. ``However, some may disagree that male nipples often respond to sexual stimulation, so they are completely useless,'' Live Science commented.

◆ 02: Wisdom teeth
Human third molars are known as 'wisdom teeth' in Japan, and are called 'wisdom teeth' in the English-speaking world because they grow when they are sensible. It is said that 22% of people in the world have at least one out of four wisdom teeth that do not grow, and even if they do, most of them do not grow properly from the

gums .

In the past, it was said that wisdom teeth do not grow properly because human faces have become smaller and there is no more space, but recent research has shown that eating habits during childhood are also closely related. I understand. For example, eating crunchy foods such as raw vegetables and nuts may encourage jaw development, while eating soft processed foods may impede jaw growth and leave room for wisdom teeth to erupt. It is almost gone.

◆ 03: vomeronasal device

The vomeronasal organ, sometimes called the 'Jacobson's organ,' is an organ found in many animals, including amphibians, reptiles, and mammals, and is actually used for pheromones and for smelling. On the other hand, humans do not have this organ, or even if they do, it is not useful. However, some researchers say the function of the human vomeronasal organ 'is still widely debated.'

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4: palmaris longus

The palmaris longus muscle is a muscle that runs from the elbow part of the humerus, which is the upper arm, through the wrist and connects to the aponeurosis of the palm, but some people do not have the palmaris longus muscle. However, there is no problem even if it can be substituted with other muscles. According to a paper published in 2014, this muscle strength is stronger in tree-climbing primates than in land-based primates, including humans, and is functionally important.

◆ 05: Pyramidal muscle
The pyramidal muscle is a muscle that begins at the symphysis pubis, where the left and right pubic bones connect, and extends on either side of the linea alba, the connective tissue that runs down the center of the abdomen. According to a 2017 paper , it is estimated that 10-20% of people lack at least one of the two pyramidal muscles, but there is no particular problem without it.


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◆ 06: Darwin's nodule
Darwin's nodules , also called 'auricular nodules', are often found on the edge of the ear. This structure is believed to be a remnant of the joint that was once necessary to fold the top of the ear, and is considered a benign and harmless malformation.

◆ 07: auricular muscle
Many animals can move their ears in response to sound, but humans have lost all or most of this function in the course of evolution. However,

some people can move their ears .

◆ 08: Coccyx
The human coccyx was once part of the tail, but today it is fused together into a single bone of 3 to 5 immature vertebrae. It is considered one of the lost relics. It still serves as a fixation point for many muscles, ligaments, etc., so it's not entirely unnecessary, but at least it's useless as a tail.

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◆ 09: appendix
Charles Darwin, an advocate of evolutionary theory, advocated that ``

the appendix , which is a bag-like protrusion extending from the large intestine, is a remnant of the organ that our herbivore ancestors used to digest plants.'' This theory has been supported by the fact that some people are born without an appendix and that surgical removal has no particular effect, but recent research has shown that the appendix plays a role as a 'repository of intestinal bacteria'. I found out that there is However, it is better to remove it if it becomes acute appendicitis (cecum).

◆ 10: The third eyelid
Some mammals, such as reptiles, birds, and cats, have

a nictitating membrane that moves horizontally across the eye from the inner corner to the outer corner of the eye. I'm here. Humans do not have a nictitating membrane.

The meniscal fold does not function as an eyelid, so it may seem useless, but in fact, it has the role of assisting the rotation of the eyeball and helping the discharge of tears. Also, if the lacrimal duct, which is the passage of tears, is narrowed or clogged, surgery may be performed to remove the meniscal fold.

in Science,   Creature, Posted by log1l_ks