Vestigial Structures

Vestigial Structures

By Pranav Angadi

Edited by Sophia Zhu, Arnesh Kumar, and Sidarth Raman

Through the process of evolution, organisms develop parts of their bodies that are necessary to survive under certain circumstances. However, if those circumstances go away, those parts of the body have no use. These parts remain in the body as vestiges of a once circumstantially necessary organ. These are vestigial structures. The concept of a vestigial structure is listed in the Origin of the Species by Charles Darwin. He claims there that although vestigial structures have lost their primary function, they still have their secondary anatomical function. They retain their existence as a structure in the body regardless of losing their primary purpose. There are many important examples of these structures that have been covered in the book, The Descent of Man, by Charles Darwin. Here are a few vestigial structures.

Auricular Muscles

The auricular muscles of the human ear include the anterior auricular muscle, the superior auricular muscle, and the posterior auricular muscle. Together, these muscles control the visible part of the ear called the pinna. Many other mammals use the auricular muscles for purposes such as a way to express emotion. However, humans do not use the auricular muscles to function. Humans can receive sounds and perform the functions of the auricular muscles without needing them; hence, they are vestigial. Figure 1 below diagrams the auricular muscles in the ear.

Figure 1

Wisdom Teeth

All humans are said to have originated from Africa to different locations around the world. As humans started to evolve and the human civilization developed, people were more involved in agriculture. As this was increasingly happening, human consumption of soft foods increased. Thus, the need for wisdom teeth was eliminated for much of the population. Now, wisdom teeth have become vestigial structures as they overly crowd the mouth and have little to no purpose. Wisdom teeth in the human mouth are depicted in Figure 2.

Figure 2

Palmar Grasp Reflex

Another characteristic of human infants that disappears after roughly 3 months of birth is the palmar grasp reflex. When human infants are born, they grasp the umbilical cords of their mothers. This strong grasping reflex is also present in monkeys. Monkey infants need this reflex in order to cling onto the fur of their mothers, and so this is a functional characteristic of their bodies. However, since humans have evolved out of an arboreal existence (existence in tree habitats), this reflex is rather unnecessary for them. Thus, it is considered a vestigial property for humans. The Palmar Grasp Reflex in infants is shown in Figure 3.

Figure 3

Although vestigial structures lose their purposes in organisms, they can potentially regain function in new forms. This is all determined by the beauty of evolution.