To some extent the answer to the question of whether some humans are born with tails and how prevalent it is depends on your definition of “tail.” For instance, a variety of things may protrude from the tailbone of a newborn, including cysts, tumors and even a parasitic twin. But very rarely a human is born with an actual extra appendage that is generally considered a vestigial tail.

During fetal development, the human embryo at about the 5th week has a tail that usually disappears by the 8th week, being absorbed by the growing embryo. However, for a rare few, the tail is not absorbed and persists through birth.

Typically (for those exceptionally few born with tails), the appendage in question is comprised of adipose and connective tissue, bundles of striated muscle and even nerves and blood vessels. Noticeably absent from even a vestigial tail, however, are any sign of vertebrae or controlled movement.

As for specific examples, in 2012, the paper, Spectrum of human tails: A report of six cases, detailing the experience of a handful of patients with vestigial tails, ranging in age from 3 days to 2 years. Of the six, four of the tails were situated in the lumbar area, and, perhaps not surprisingly, three of the patients had spina bifida (a congenital defect where the lower part of the spinal cord is exposed through a hole in the spine). One child had a tail protruding from his buttock, while the last had a protrusion from the sacral region.

Five of the six had no connection between their tails and spines, and they underwent successful surgeries to remove the unwanted appendages. The sixth’s parents refused to give consent, although it is not clear why, and the doctors in question were not able to follow up with that child. Notably, in one of the children, her tail unusually included bone, as well as cartilage, fat and neural tissue.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

• How Do Other Animals Deal with the Umbilical Cord and Placenta When the Baby is Born?
• Where Birthmarks Come From
• The Many Myths Surrounding Charles Darwin
• The Woman Who Carried a Fetus in Her Body for 60 Years
• The Surprisingly Recent Time Period When Boys Wore Pink, Girls Wore Blue, and Both Wore Dresses

Bonus Facts:

• For many years the appendix was considered a vestigial organ, although more recent scholarship has demonstrated that it stores useful bacteria that help with digestion, and which are used to repopulate the intestines with beneficial bacteria after a bought with diarrheal disease.
• Likewise, a strange nasal structure called the vomeronasal organ (or Jacobson’s organ) was also thought to be vestigial and of no use, until recent scholarship revealed that it likely plays a role in human sensory functions, perhaps related to the perception of pheromones.
• Parasitic twins are uncommon, but occur when a single egg that splits during fertilization fails to fully separate and one twin “absorbs” the other in the womb. In 2014, a baby boy was born in eastern Uganda with the legs, arms and torso of his twin attached (and his heart and liver were on the wrong sides of his body). After three hours of surgery, the parasitic twin was removed, and within three weeks, the host twin was thriving and set to make a full recovery.
• If you’re curious, the longest human tail on record is generally credited to Chandre Oram, whose extra appendage, which many argue doesn’t constitute a true tail, rings in at about 13 inches long. If you guessed his refusal to have his very hairy appendage removed has interfered with his love-life, you’d be correct.  He did finally get married in 2007, but his wife is less than pleased with it. To quote, “He doesn’t look good. My mother and my father passed away when I was young. My brothers wanted me to get married, so I had to compromise and marry him.” Ouch…