Vestigial organs

Have you ever wondered why our bodies have organs that are seemingly pointless? The appendix doesn’t appear to do anything except cause trouble, why can some people wiggle their ears and why do we have to go through the pain of wisdom teeth!?

These ‘useless’ body-parts, otherwise known as vestigial organs, are remnants of lost functions that our ancestors possessed. They once represented a function that evolved out of a necessity for survival, but over time that function became non-existent. They provide some intriguing insight into the evolutionary history of our species.

 

Image courtesy of Blausen.com

Image courtesy of Blausen.com

The Appendix:

The appendix looks like a narrow tube that joins to the end of the colon. It’s thought to have come from our herbivorous ancestors where it played a role in digesting tough plant-based food. Thousands of years ago human hunter-gatherers ate a wide variety of vegetation, the appendix also helped them to digest complex plant materials.

As our diet changed the digestive role of the appendix became useless. However, natural selection prevented the human appendix from shrinking and leaving the body; appendixes that are smaller are more likely to become infected. This means people with larger appendixes were the ones that survived and contributed to our gene pool.

Interestingly, recent research actually suggests this organ may not be so pointless after all. A group of researchers from Duke University Medical Centre found that the appendix might have a role in storing beneficial bacteria that is vital for repopulating intestines after an illness.

 

Plica Semilunaris:

The Plica Semilunaris, or your third eyelid, is a small fold of tissue located in your inner eye. It sits just by your tear duct (see image below). It is thought to be a remnant of nictitating membranes found in birds, reptiles and amphibians. These membranes keep their eyes moist and offer protection enabling them to maintain visibility while their eyes are still open. Unlike our upper and lower eyelids, these move horizontally rather than vertically across the eyeball, hence the position of this vestigial remnant in the human eye. Plica Semilunaris

 

Wisdom Teeth:

In the past these molars were useful for grinding down plant tissue, especially as other teeth were worn down more quickly from tough vegetation and grit. Larger jaws were needed to help chew down foliage and compensate for the ineffective digestion of cellulose. When we began cooking our food chewing became much easier, our jaws became smaller and our teeth remained in better shape. Today, when wisdom teeth finally decide to come through, long after we stop receiving change from the tooth fairy, they force themselves into a jaw that is too small, often causing a lot of pain.

 

Image courtesy of Henry Vandyke Carter, via Wikimedia Commons

Extrinsic Ear muscles:

The auricle muscle helps to perk up ears in animals when they are alerted to danger or in search of prey. Only some humans are able to still use these muscles. This function was particularly useful in primates that weren’t able to move their head on a horizontal plane. As Darwin proposed, since humans are able to capture sound effectively by moving their head, the need for these muscles has been eliminated. Apart from having comedy value, wiggling our ears has no functional use.

 

Palmar Grasp Reflex:

The palmar grasp reflex is more of a vestigial behaviour rather than organ. This primitive reflex can appear as early as 16 weeks in utero and remains until a child reaches six months old. When a baby’s palm is stroked and an object is placed in its hand the baby’s fingers spontaneously curl around the object. They will hold on so tightly that they are even able to support their own body weight. When you stroke the back of the baby’s hand they will release their grip.This reflex would have been essential in our distant monkey ancestors; enabling infants to cling on to their mother’s fur while travelling.

Palmar reflex

 

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