Human Vestigiality

In Evolution, vestigiality is where components of a body that have evolved to suit a certain purpose remain after its purpose is no longer needed. This could be genetic or psychological in nature.

For example, let's say humans evolve the ability to sense infrared light using our skin. Our eyes could become useless. If we still have eyes and they don't have a purpose any more, they are considered vestigial. Lets say our toes become webbed for better swimming abilities but we still have toenails. The toenails may not have a purpose any more and would become vestigial. The second of these examples you can actually see in Manatees

Humans have a number of vestigial elements that you may or may not be aware of, so I'm gonna talk about some of them here.

The Variable Muscle

Here's a little experiment you can do now. Place your pinkie finger and your thumb together. Bend your wrist inwards (like the image). If you can see a muscle popping out, you have have some vestigial DNA.

The muscle is called Palmaris Longus. It serves basically no purpose in the movement and coordination of your wrist. The effect it has on strength and capability is very minimal. The muscle is so useless, in fact, it is often the first to be cannibalised when undergoing surgery to correct ligament/ muscular damage. They just take it out and put it somewhere else.

The purpose of the muscle is that it likely had some benefit to our tree-dwelling ape-like ancestors. Over time it has become useless, but because not having one bears very little benefit, it has just stuck around. Scientists argue that there may potentially be offshoot issues to evolving it out that affects other aspects of our DNA, but there's very little evidence.

Human Tails

Tails have many benefits to many animals, they help balance and stabilise in species like Spider monkeys. They help to manoeuvre when running at speed by swiftly shifting directions in predators like Cheetahs.

As our species left the trees and stood upright, the need for a tail declined. As such, the bones that used to form a tail are stagnated (whilst we grow in the womb) and we're left with the butts that we have today. We actually still have a tail bone, it's just insignificantly small and does nothing.

In fairly rare instances, a person can be born with an extended tailbone. This leads to what is, essentially, a human tail. These vestigial limbs are usually surgically removed. They impede the day to day of the people who have them, demonstrating that what was once a useful trait can actually become a hindrance in modern life.

The Baby Gripping Reflex

In newborn babies, you've probably experienced the baby death grip. Hold out a finger and they will latch on, even if they currently have no advanced coordination of their hands. This is called the Palmar Grasp Reflex, and it's a vestigial primitive reflex.

When we were tree-animals, we had to spend a lot of time in our mothers arms. It was high up, not a lot of room to step out and explore. Eventually though, momma ape would get tired of carrying us and have to put us somewhere; a dangerous prospect. She would have to put us on a branch so we could stay safe from predators. Once there we would grip hold of that branch tightly and just stay there until she picked us up again. We would also need that strong grip to cling onto her fur both when suckling milk or if we had siblings to compete with.

Even in Human babies, the grasp is still theoretically strong enough to suspend the child, but obviously has lost its effectiveness and usefulness over time. It's also not recommended that you try to suspend your newborn, so please don't.

Wisdom Teeth

The third molars in your mouth, the 'wisdom' teeth are throwbacks to when humans had to eat more solid whole foods. The reason that Wisdom Teeth are so painful and fail to come through for us is very simple. Wisdom teeth are vestigial. Our mouths are no longer built to house them.

As we evolved, our brains got bigger at the expense of the size of our jaws. Basically, the smarter we got, the less we needed the extra teeth. We learned to break up our food with our hands before chewing and to prepare meals so that food was easier to eat. It meant we needed less biting power to survive. Our jaws eventually shrank so much that the wisdom teeth no longer had room to come through.

Evidence of its vestigial nature can easily be seen in how late it takes for wisdom teeth to actually emerge, appearing much much later than any of the other teeth.

The Third Eyelid

Did you know you have a third eyelid. It's vestigial. See that pink area on the innermost edge of your eye? That is what remains of our third eyelids. It is our 'Nictitating Membrane' or more specifically the 'Plica Semilunaris' of the eye.

This extra eyelid is transparent/ translucent and is a common, fully functional, aspect of much of the animal kingdom. Crocodiles utilise their Nictating Membrane eyelid to cover their eyes underwater. It provides a transparent protection that allows them to better see when submerged. Notable birds like Owls use them to moisten the eye without impacting their vision (useful if you're normally prey).

Humans still also retain the vestigial muscles that were once used to control this third eyelid's movement.

The Plantaris Muscle

Just like the Palmaris Longus in our wrists, we can find another tendon with sporadic presence in human beings. This one, the Plantaris, is absent in around 12% of humans (and it's lack-of appears to be quite regionally specific). When present it is the longest single tendon in the human body.

The original purpose of this vestigial muscle was lost when our ancestors left the trees and began walking on two legs.

Hiccups

It has been postulated that the presence of hiccups are a vestigial remnant of very ancient, pre-mammalian, DNA. This is because the action of a hiccup is extremely similar to the respiratory processes of frogs and other amphibians. Frogs hiccup to gulp in air and water.

Likely evidence for this can come from the frequency of hiccups in new-borns and the very young. Those with lungs that have not yet fully developed. In this, the theory goes that their bodies are instinctually trying to gulp the air.