Back in 2014 I wrote a series of articles at Evolution News (posted as a single piece here) about whether the human “tail” was an atavism — an evolutionary throwback — that provides evidence for evolution. The debate started after scientist and theistic evolutionist Karl Giberson used an image of a human baby with a photoshopped tail that looked completely real — as if it were evidence for evolution. This then led to a deep dive into the literature wherein I learned a lot about the human tail. It’s all documented at the link above, but at the end of the series, I offered the following findings based upon my literature review:

• No babies are born with perfectly formed, fully functional tails.
• Babies that do have tails typically have serious associated neurological defects.
• The exact causes of tails are debated, but because of their persistent association with neurological defects, the most plausible view is that they result from abnormalities and deviations in development.

What the Medical Evidence Shows

Now a very nice new article at ScienceAlert has completely vindicated my arguments about human tails. Titled “Some Babies Are Born With ‘Tails’, But Not For The Reason You Might Think,” the article by Carly Cassella basically comes to the same conclusions I did. She starts by noting that many people still believe that human “tails” are evolutionary throwbacks — but this is not what the medical evidence shows:

[T]he rare case studies tend to generate “an unusual amount of interest, excitement and anxiety”, according to researchers. Often, this is because the ‘tails’ are considered to be benign, evolutionary remnants of a long lost ancestor. 

As it turns out, that’s based on an outdated theory that has been contentious for decades now. The reality for these children may be much darker, and they deserve medical attention, not our morbid fascination.

The appendages some babies are born with have historically been deemed ‘true’ or ‘vestigial’ tails. But that’s a bit of a misnomer, as they aren’t really like any other tail known in nature. They typically don’t contain bones, cartilage, or a spinal cord. They just kind of hang there without a clear function.

Still, that doesn’t mean these appendages are as harmless as scientists used to think.

This is precisely what I found in my literature review, as I explained:

Human tails are extremely rare, with perhaps only a few hundred cases documented worldwide over the past half-century. Medical researchers who have had the lucky opportunity to study a human tail have divided them into two general categories: “true tails,” which extend from the coccyx (tailbone) where one might expect a so-called “vestigial tail,” and “pseudotails” which are often found in other locations on the lower back, and seem to be obvious aberrations since they are often associated with anomalies.

This distinction is based upon evolutionary assumptions, and in recent years it has become quite controversial as researchers have learned more about the phenomenon. I’ll say more later about why even the “true tails” in humans don’t deserve that name. For now, here’s a crucial fact: even such so-called “tails” aren’t anything like those found in tailed mammals. That is for the simple reason that “true tails” in humans entirely lack vertebrae — or any kind of bone, cartilage, notochord, or spinal cord. As the aforementioned paper in the Journal of Neurosurgery explains:

“In all reported cases, the vestigial human tail lacks bone, cartilage, notochord, and spinal cord. It is unique in this feature.” (Roberto Spiegelmann, Edgardo Schinder, Mordejai Mintz, and Alexander Blakstein, “The human tail: a benign stigma,” Journal of Neurosurgery, 63: 461-462 (1985).)

Other prominent medical research journals agree…

It All Started with Darwin

Now it turns out that the 1985 paper cited above was actually largely responsible for spreading the myth that human tails are an evolutionary throwback, as the ScienceAlert article explains:

The misunderstanding over the tail’s origin starts with Charles Darwin himself. Over a century ago, Darwin proposed that human vestigial tails are evolutionary accidents, or rudimentary leftovers from a primate ancestor that was once tailed itself.

In the 1980s, scientists took this theory and ran with it. They argued that a genetic mutation, evolved by humans to erase our tails, could sometimes revert back to its ancestral state.

In 1985, a seminal paper defined two different types of ‘tails’ that human babies can be born with. The first, as mentioned before, is a vestigial or true tail, originally thought to be inherited from our ancestors.

But, the article reports that even these supposedly “true tails” are often associated with birth defects, showing that they are not a benign evolutionary atavism that can be ignored but rather a birth defect that ought to be taken very seriously:

As it turns out, both rare appendages probably represent an incomplete fusion of the spinal column, or what’s known as a spinal dysraphism. This suggests their formation is not a harmless ‘regression’ in the evolutionary process but a concerning disturbance in an embryo’s growth most likely resulting from a mix of genetic and environmental factors.

[…]

Roughly half of the cases reviewed were associated with either meningocele or spina bifida occulta.

This suggests babies born with tails need greater medical attention than a simple surgery. And it strongly disagrees with the 1985 paper that argued “the true human tail is a benign condition not associated with any underlying [spinal] cord malformation.”

“Not a Harmless Vestigial Trait”

The article goes on to draw a very similar conclusion to the one I did:

Regardless of where a baby’s tail came from, however, evidence strongly suggests it is the result of a congenital issue and is not a harmless vestigial trait.

For the life and health of these children, that’s an important message that needs to be cleared up once and for all.

I agree, and wrote the following in my article:

Thankfully, most doctors today take their view on this not from Darwinian evolution, but from the evidence, the accumulated experience of clinical researchers as represented in the medical literature. Researchers warn that seeing tails as benign structures can lead doctors to miss serious developmental problems.

It’s a good thing, not least for patients, that the Darwinian doctrine, little more than an urban legend, is fast on its way to being abandoned.

The ScienceAlert article cites new literature that has appeared since I published my own review nine years ago. It’s encouraging to see that my findings about the human tail have stood the test of time.