Vestigial Structures

The Appendix:

The appendix is one of the most commonly known vestigial structures found in humans. Most of the time it does not require removal unless it is inflamed or swollen. This is known as appendicitis and instead of treating the appendix itself, we remove it because it does not serve a purpose in our digestive system. The use of the appendix was to digest leaves in our diet. As our food preferences shifted away from rougher plants such as leaves and roots, the use of the appendix became minimal (Oxford Science, 2015).

Palmar Grasp Reflex:

The palmar grasp reflex is a motor function that is apparent in newborn children and exists up to 6 months in age. If said child is touched in the palm or something is placed in their palm, an unconscious reflex will make them grab or attempt to grab what touched their hand. This function was used in our ancestors before us who had more fur on their backs such as Ardipithecus Ramidus. The palmar grasp reflex would allow newborns to grab onto their parents furry backs allowing for easy transport since the child could not yet walk, see, hear, or communicate properly. This is vestigial today because we no longer transport our children on our backs because of the major loss of body hair over time as a species (Rogers, 2018).

Auricular Muscles:

The auricular muscles within humans are located in the outer ear. They consist of the superior auricular muscle, the anterior auricular muscle, and the posterior auricular muscle. They are used in other species such as horses and dogs to move the ear adjusting to where a sound came from. This was useful to locate danger quickly. Primates could not turn their heads on the horizontal plane so these muscles were necessary for survival. Since we have adapted to be able to move our necks and head, the use for the auricular muscles has become vestigial (Rogers, 2018).

Palmaris Longus Muscle:

The palmaris longus muscle is a muscle that starts in the wrist and goes up to our elbows. It is inferred that this muscle’s primary function was for hanging from tree limbs or other elevated surfaces. This function no longer serves a purpose for us since we do not hang from branches any more. Even though this muscle helps grip strength when hanging, it does not add any additional strength to our normal grips. The muscle also improves strength when pinching something with our fingers. It is known that up to 10% of people are born without this muscle. This is because evolutionarily, the need for this muscle had become vestigial so the trait of not having the muscle is getting carried on throughout new generations of humans. Within the medical field, this muscle is harvested and used in reconstructive surgery since it does not serve a purpose in our lives (Rogers 2018).

Plica Semilunaris:

Conjunctiva is the mucous membrane that layers over our eyes. It lubricates the inner surfaces of the eye and protects from dust, debris, and infection-causing microorganisms (Heiting, 2021). The plica semilunaris is a fold of conjunctiva in the corner of our eyes. The use of this membrane was to protect the eye and in some cases conceal the iris from predators. The membrane would also help with vision underground or underwater. With the change in environment for humans, the use of this membrane has become vestigial (Rogers, 2018).