Vestigial Structures in Humans

Vestigial structures — or vestigial organs — are body parts that either no longer have a function or don’t have the same function they did for our ancestors. In other words, you could remove the body part, and it wouldn’t make much difference in how your body works.

We have vestigial structures because our ancestors originally had a use for them. Over time, we’ve evolved to not need them, but the structures still exist in our bodies. “Evolving” means changing over a long period of time to adapt to the environment, food sources and other factors.

Examples

Examples of vestigial structures in humans include your:

• Appendix, a small pouch that’s attached to your colon
• Coccyx (tailbone)
• Plica semilunaris, a small fold of tissue near the inside corner of your eye
• Wisdom teeth (third molars)

Many areas of tissue and muscles in your body are also vestigial. For example, ear muscles don’t allow your ears to move. (But it’s possible they used to, to help locate sounds and listen for danger.)

There are also body parts that are useful to a developing fetus that don’t have a function after birth — like your belly button. Or body parts that develop in everyone but might only serve a purpose in certain circumstances (like nipples).

What’s the purpose of vestigial structures?

It’s common to think that vestigial structures serve no purpose. But many still function in some way. Scientists can study fossils and existing similar species to understand what functions these body parts might’ve served in the past.

Here are some examples of the functions your vestigial structures once served and what they do now:

• Appendix: Experts think your appendix once helped in digestion. Now, it contains immune system cells and good bacteria to help fight off germs in your digestive tract.
• Coccyx: Your coccyx once supported a tail. Our ancestors no longer needed a tail when they began walking on land (instead of climbing trees). But many muscles and nerves still connect to your tailbone, and it helps keep you stable while sitting.
• Plica semilunaris: This piece of tissue might’ve once been part of a third eyelid, or nictitating membrane. Other species use this thin covering to protect their eyes while still being able to see. In humans, it helps our eyes move.
• Wisdom teeth: Your wisdom teeth were once useful in grinding tough meats, nuts and plants. Modern cooking and diet mean we don’t need them as much anymore. And we’ve since evolved to have a smaller jaw, so these extra teeth often can’t grow in correctly.

What conditions affect vestigial structures?

While they might not perform a major function for our bodies anymore, some issues can still affect your vestigial structures. Some conditions include:

• Appendicitis: Inflammation in your appendix from a blockage or infection. Appendicitis can be life-threatening. You’ll likely have your appendix removed to treat it.
• Coccydynia: Tailbone pain from trauma, infection or tumors. Treatment depends on the cause.
• Impacted wisdom teeth: Wisdom teeth that don’t grow in properly can lead to infections and other complications. Healthcare providers treat impacted wisdom teeth by removing them.

Cancer and infections can also affect many vestigial structures.

Are toenails vestigial?

No. Toenails protect the ends of your toes. If you’ve ever lost a toenail, you probably realize how important they are!