[Reading Science] My Tailbone That Has Now Disappeared?

The human tailbone is a representative vestigial organ.
[Photo by YouTube screen capture]

[Asia Economy Reporter Kim Jong-hwa] There is a phrase people use called 'kkorireul chinda' (literally "wagging the tail"). According to the dictionary, it is defined as "(colloquially) a woman acting coquettishly to please a man." The origin of this phrase is intriguing. Did humans have tails long ago?

If humans had tails, how would they use them? Cows swat flies off their backs with their tails, and small monkeys use their tails to hang from trees. Humans might have used tails to scratch their backs or dust off their clothes in various ways.

Humans do not have tails, but they do have a remnant called the coccyx. Similar primates like chimpanzees, orangutans, and gorillas also lack tails but retain traces of the coccyx. Such organs that have become reduced or degenerated through evolution because they are no longer necessary for survival, leaving only traces of their original function, are called vestigial organs.

Whales living in the sea have no legs or feet, but their fins and internal bodies contain remnants of leg bones. This suggests that ancient ancestors of whales once lived on land. Like whales, snakes also have remnants of legs, and animals living in dark caves or deep-sea fish that receive no light have degenerated eyes, leaving only traces.

These vestigial organs are evidence of evolution. Humans also have several vestigial organs. The coccyx, the auricular muscles that move the ears, the appendix of the cecum, and wisdom teeth are representative examples. In the late 19th century, an anatomist claimed that humans had as many as 86 vestigial organs. However, today only about 10 are generally recognized as vestigial organs.

The human coccyx, mentioned earlier, is attached to the end of the spine. During fetal development, nearly 10 coccygeal vertebrae may appear but gradually disappear as growth proceeds, with only some fused to form the coccyx. The human coccyx serves as an attachment point for important muscles of the pelvis, playing a significant role in upright posture, and helps support the body and maintain balance when sitting along with other pelvic bones. This means it is not completely degenerated but still performs some functions.

Just as cats can move their ears, humans once could move their ears as well. As humans adopted upright walking, their field of vision widened, and they became relatively less sensitive to sound, reducing the need to move their ears. Consequently, the auricular muscles degenerated and remain as vestigial organs.

Before humans cooked their food, they had to gnaw on plant cell walls like cows or horses. At that time, having many molars was advantageous, and humans had eight more teeth than they do now. The jaw joint was also much larger than today. After discovering fire, the role of molars gradually diminished, starting with the inner molars disappearing, and now wisdom teeth are next in line to disappear.

The appendix of the cecum is also one of the vestigial organs. The cecum is an organ present in higher animals above reptiles, but some mammals lack a cecum. Herbivores generally have a long and well-developed cecum, while omnivores like humans or carnivores tend to have a shorter cecum.

The appendix attached below the cecum is a vestigial organ, but there are quite a few claims that it is an essential organ for the human body. [Image=YouTube screenshot]

The appendix is a small, thin tube about 6 to 7 cm long attached to the lower end of the cecum, found only in humans and apes. People can live without an appendix, and about 6% of the population has had their appendix removed due to appendicitis.

However, some scientists argue that the appendix is an essential organ. They claim that the appendix acts as a factory and storage site for beneficial bacteria in the body. While it may be a vestigial organ in terms of digestion, it plays a very important role as an immune organ. Nevertheless, the evidence is not clear enough to overturn its classification as a vestigial organ, so it is still considered one.

Monkeys have much more body hair than humans. Although humans have body hair, it is not enough to cover the entire body like monkeys. Goosebumps when cold are also thought to be a remnant from when humans had more body hair.

Other vestigial organs include the eustachian tube near the ear, which is said to be a degenerated gill slit, the Jacobson's organ between the palate and nose, the thyroid gland, tonsils, pituitary gland, and nipples in male mammals, all of which bear traces of evolution.