For the most part, your organs and limbs serve a purpose, so it stands to reason that losing one of these can interfere with your body’s normal, everyday function.

On the other hand, it’s well-known that certain organs, such as the appendix, can be removed without much consequence. That’s because, while many body structures are useful in an obvious way, some structures have lost their original functions over the course of time.

Human vestigiality refers to parts of the body that seem to no longer serve a purpose. It’s believed that our ancestors, at some point, needed these body parts. Yet, many of these structures have lost most of their original function, essentially becoming what some label as “junk organs.”

Some believe that these structures are examples of human evolution. Others believe that so-called vestigial organs do have a purpose, although these purposes aren’t yet understood.

To illustrate, some doctors and scientists once considered tonsils a human vestigiality. But scientists later discovered that the tonsils play a role in immunity, helping the body fight infections.

A few examples of vestigiality include:

Some people also have a vestigial tail. Although a rare entity, humans with apparent tails have been noted in literature throughout history.

While tails are very rare in humans, temporary tail-like structures are found in the human embryo. These tails develop around the fifth or sixth week of gestation, and contain about 10 to 12 vertebrae.

Most people aren’t born with a tail because the structure disappears or absorbs into the body during fetal development, forming the tailbone or coccyx. The tailbone is a triangular bone located at the lower part of the spine below the sacrum.

Disappearance of the tail in the embryo takes place around the eighth week of gestation.

Although a vestigial tail disappears for most people, sometimes the tail remains due to a defect during the developmental stage. In the case of a “true” vestigial tail, the exact cause of this defect is unknown.

It’s important to note that some people are also born with a pseudotail, which isn’t the same as a “true” vestigial tail. A pseudotail can look like a vestigial tail, but it’s typically caused by an elongated coccyx or linked to spina bifida.

In two case studies of newborns with a congenital pseudotail, MRIs showed evidence of spina bifida — a birth defect where the spine and spinal cord don’t form properly.

When a vestigial tail doesn’t fuse with the coccyx and remains after birth, what’s left is skin that contain no bones. Although the tail lacks bones, it does contain nerves, blood, adipose tissue, connective tissue, and muscles.

Interestingly, the tail is also movable (in some people) like other parts of the body, although it doesn’t provide a useful function. Therefore, the tail isn’t used to grasp or grip objects.

The decision to seek treatment for a vestigial tail depends on the severity of the abnormality. Some tails are small and don’t cause any problems. But longer tails can eventually interfere with sitting. These tails can be up to 5 inches.

Since vestigial tails contain no bone, these tails don’t typically cause pain or discomfort. Pain might occur with a pseudotail because they do contain bone or vertebrae.

Babies born with a vestigial tail will need to undergo an imaging test such as an MRI or an ultrasound. This is necessary to classify the tail and make sure it isn’t associated with a medical condition like spina bifida.

Surgery is the treatment for a vestigial tail. Because a “true” vestigial tail is composed of adipose and muscular tissue, doctors can quickly remove these types of tails with a simple excision. This procedure doesn’t cause any residual side effects.

Keep in mind that removal isn’t medically necessary, although some parents prefer surgery for cosmetic reasons. They may opt to have the structure removed from their child soon after birth. When a vestigial tail is small and looks like a nub, parents may forgo surgery.

If you or your child has a vestigial tail, you can have it removed through a simple procedure, or keep the tail if it’s small.

Living with a vestigial tail doesn’t lead to complications or cause long-term problems. But if you choose to remove the tail, the prognosis is good and losing the structure doesn’t have any adverse effects.

The decision to remove or keep primarily depends on how the tail impacts your life. If it’s something that upsets you or prevents intimate relationships, getting rid of the structure could improve the quality of your life and increase your self-confidence.