Vestigial organs are the organs which are now “useless” or “non-functional”. Some biologists say that these vestigial organs are proof of our evolution. It was first mentioned by Charles Darwin in his book – “The Descent of Man (1890)”. However, many biologists now say that there are no vestigial organs in human body and those so-called vestigial organs functions are not yet known to humans. So, unless scientists actually come up with a proper explanation of the actual functions of these organs, we will consider them as vestigial. Let us take a look at 15 such vestigial organs and functions in human body that have no real use.
Human Vestigial Organs and Functions: 1-5
1. Appendix – The Vermiform Appendix is a vestigial organ in our digestive system which was functional in our ancestors and had some digestive functions. It is present in some mammals like rodents, primates (superorder: eurachontoglires) and help in digesting cellulose and other such indigestible components of plants. It is also seen that the appendix supplies the good bacteria to large intestine when needed (when the colon is infected, or the animal is ill and good bacteria is washed out). But it is not seen in carnivorous animals and even if it is seen, it remains a vestigial organ in them too.
2. The Coccyx – It is also known as tail bone. The tail is present in all mammals at some stage of the development. For humans, it is present during the embryonic stage when the embryo is 31-35 days old. Its main function is to maintain balance and mobility. However, these functions are lost but the secondary functions remain active till date. Its secondary function is to attach the tendons, ligaments etc. and for insertion for some muscles in the pelvic joint.
3. Wisdom Teeth – These are the third molars which were present in our ancestors. Even now wisdom teeth are seen in most of the people. Ancient humans had bigger and stronger jaws to chew on plants and somewhat raw meat but as the humans developed, smaller jaws were naturally chosen over bigger jaws because there is no need to chew the food that hard! Now the wisdom teeth are completely useless and in some cases, they must be surgically removed.
4. External Ear – Orangutan, human and other primate species have ears which are externally identifiable but they serve no biological function whereas animals like deer, cats, macaque monkey have externally identifiable ears which help them to hear better and they move too. The inability to move our ears is compensated with the head moving in a horizontal plane.
5. Nictitating Membrane – Many animals have a third eyelid called as nictitating membrane. Its function is to protect and keep the eyes moist and at the same time aid in vision. In humans’ plica semilunaris replaces the nictitating membrane. This plica semilunaris is a small fold of tissue which is present inside corner of the eye. All primates except for Calabar angwantibo have plica semilunaris. Calabar angwantibo has nictitating membrane.
Human Vestigial Organs and Functions: 6-10
6. Hymen – Hymen is a layer of tissue which either partially or fully covers the vaginal orifice. According to some scientists the hymen present in young girls protects the vagina and reproductive system from infection starting from embryonic stage till the time when they first mate. Hymen has no other vital function in women’s body. However, hymen present in horses, elephants, chimps etc. exists even after they mate and prevents the leaking of semen from vagina.
7. Hirsuties Coronae Glandis – These are small outgrowths which protrude from the ridge of glans of the penis. They are sometimes mistaken with HPV infection. They are also called as hirustoid papillomas or pearly penile papules. They are remnants of penile spines which are present in the males of other species of animals. The penile spines which are completely functional help in sexual stimulation and it also aids in quicker orgasms.
8. Extra Nipples or Breasts – Some women (very rare) have extra nipples and/or extra breasts. This is unusual occurrence is because our mammal ancestors and the present mammal relatives have more than two breasts and this feature sometimes occur in humans too.
9. Palmaris Longus Muscle – This muscle runs from wrist to elbow. It functioned in grip especially for hanging. The muscle is absent in 10% of the human population and in the rest 90% too, it serves no purpose.
10. Tonsils – Tonsils are said to be in the first line of defence organs where they protect the body from the harmful microorganisms which are either inhaled or ingested. However, these tonsils have become a cause of concern lately because they get infected and inflamed and in some cases to such an extent that they have to be surgically removed. They remain as vestigial organs in human body.
Human Vestigial Organs and Functions: 11-15
11. Male Nipples – Males or females start their journey of life as females in the womb. The nipples are formed in the fetus by the time the Y chromosome starts its action. When the Y chromosome produces and releases testosterone and other male hormones, the nipples on male fetus are completely formed and remain so for the entire life. They serve no function. This one vestigial organ is the result of a developmental or embryological event but not evolutionary one.
12. Arrector Pili – These are smooth muscles (smooth muscles are the muscles which act involuntarily) which are present under our skin and these muscles are responsible for the goose bumps we get when we feel cold or stressed. It is a vestigial behavioral reflex. This reflex had a couple of very important functions in our ancestors. Our ancestors had their body covered with hair. In case of a predatory threat, the hair used to stand erect, making them look bigger than usual and thereby warding off predators. Also, erect hair helped to trap body heat from escaping and thereby helped them to stay warm. But now, the hair on human body is scanty and the goose bumps are of no real function now.
13. The Palmar Grasp Reflex – The Palmar Grasp Reflex is shown by infants. The ability of babies to hold onto any object is Palmar Grasp Reflex. It is seen in hands and feet. For the animal babies, they can hold onto to their mothers’ body hair and the mother can run away from the predator. However, with no to minimal hair present on the human body, this reflex’s main purpose is lost in humans.
14. Hiccups – Hiccups are remnant of amphibian respiration. Tadpoles take in air and water through their gills by a motor reflex which is similar to the reflex seen when we get a hiccup. The motor pathways of hiccupping during fetal development later transform to the motor pathways which help in respiration through lungs.
15. L- Gulonolactone Oxidase – It is a gene which was responsible for production of an enzyme which synthesizes vitamin C. It is present in most of the animals and some mammals too. But in animals of the suborder Haplorrhini (which includes human species too), this gene is disabled because of a mutation. Now this gene is non-functional and remains as a pseudogene in human DNA.