People Are Sometimes Born With a Tail — A Rare Genetic Change May Explain Why Humans Lost Them

Key Points to Remember About People Born With Tails

• People born with a tail either have a real tail or a pseudo-tail. A true tail is a vestigial body part that serves no function, while a pseudo-tail is the result of a medical problem.
• People born with a tail often have it surgically done as children, and they usually have no adverse effects.
• Although our primate relatives have tails, humans do not, probably because of something inserted into our genes.

As human embryos develop, a small tail is present during weeks four to six. Around the sixth or seventh week, the tail regresses through tissue remodeling and about 30 to 32 weeks later, the baby is born without a tail.

In rare cases, the tail does not regress and the child is born with a small appendage in the lower back. This “human tail” is medically rare and has long fascinated scientists.

Healthcare professionals can now use imaging to visualize the cause of the tail and safely remove it. Scientists understand more and more why these tails form. They also wonder why these tails don’t form.

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What are the different types of human tail?

Clinicians generally define human tails as true tails or pseudo-tails. A true tail is vestigial, meaning it is an evolutionary remnant of a body part that our ancestors needed but which serves no important function today. Pseudotails can result from other conditions, such as damage or neural tube defects.

A real tail contains fatty and connective tissues as well as blood vessels, muscles and nerves, according to a study published in Advances in orthopedics. It appears under the skin, but it does not contain bone, cartilage, or any part of the spinal cord. A pseudo-tail can be the result of several deformations. It could be an enlarged tailbone, the result of a tumor, or even the remains of a twin that stopped developing and attached itself to the surviving twin.

Both types of human tails are extremely rare, and a 2024 study International Surgical Neurology found that only 60 cases had been documented in the medical literature in 2020.

In a 2023 article in Case reports from the Journal of Pediatric Surgery, for example, researchers described a six-month-old girl who had a nearly three-inch-long pseudo-tail extending from her lower back. They determined the tail was due to spina bifida and were able to surgically remove it. At the time of article submission, the patient was 3 years old and had no complications related to tail removal.

Why don’t humans have tails?

Scientists understand why both types of tails form, but why don’t do it Do humans have tails like other primates?

A 2024 study in Nature presented evidence that tail loss during human evolution could be due to the insertion of an Alu element into an intron of the TBXT embarrassed.

“It’s a very fascinating gene. It was originally called ‘Brachyury,’ which derives from Greek and means ‘short tail,'” says Bo Xia, lead author of the study and assistant professor of pathology at Harvard Medical School and Massachusetts General Hospital, as well as an associate member of the Broad Institute of MIT and Harvard.

Within the TBXT gene, the research team discovered a type of protein mutation that could be responsible for humans not growing tails. The research team is currently testing their hypothesis on mice genetically manipulated to be able to express the protein. So far, mice carrying this mutation do not have tails.

“Each experiment is very clear and consistent with our hypothesis,” says Xia.

Future research on human tails

Future research could help scientists better understand which genes contribute to the development of diseases such as spina bifida, which in extremely rare cases can be responsible for the development of a pseudotail.

However, Xia warns that scientists may find that many genes are responsible, not just one. In the case of other diseases, researchers have found that dozens or even hundreds of genes are involved.

“For example, in the case of schizophrenia, more than 100 genes can contribute to this disease,” explains Xia.

This article does not offer medical advice and should be used for informational purposes only.

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