Are Human Tails Mere "Vestigial" or "Benign" Structures Born to "Otherwise Healthy" Babies? - Evolution News & Views

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Are Human Tails Mere "Vestigial" or "Benign" Structures Born to "Otherwise Healthy" Babies?

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In a debate with Stephen Meyer, Karl Giberson brandished the phenomenon of human "tails" as evidence of our descent from tailed forebears. I have been analyzing this view, shared by many Darwin advocates, in a series of posts (see here, here, and here).

For years, proponents of Darwin's notion that human tails are mere vestiges of our ancestry have also promoted the idea that these tails are benign structures that can be removed with little thought or concern about other potential problems. Dr. Giberson, a physicist, thus states without qualification that human tails are born to "otherwise healthy" humans. Not true. This false belief follows from the evolutionary paradigm, and it has led to some dangerous medical practices. Because human tails are so rare, and because techniques like magnetic resonance imaging (MRI) have only been around for a few decades, biologists have been slow to accumulate and interpret data about what so-called "tails" actually are, what's going on when they fail to regress, and what else is likely going wrong when a baby is born with a tail.

Prominent medical researchers on the "human tail" now see it as "a disturbance in the development of the embryo but not a regression in the evolutionary process."21 Why do they say this? Because, as a paper I noted from Pediatric Neurology by Lu et al. (1998) explains, the human tail is often associated with other deformations and developmental problems:

The high incidence of human tail combined with spinal dysraphism noted recently may throw light on the problem. A high association with skin lesions such as subcutaneous tumors, skin dimples or sinuses, hemangiomas, hypertrichosis, and hyperpigmentation was observed in the patients with spinal dysraphism. These associations give a hint to the relationship between human tail and spinal dysraphism.

Focal premature dysjunction of the neural tube may thus be an important factor in the disturbance of human tail development and regression. The unfused neural tube exposes the paraxial mesoderm to the dorsal aspect of the neural ectoderm and induces formation of fatty elements and lipoma. This event can be supported by the high incidence of lipoma (27.12%) in the authors' series. The formation of fatty elements and lipoma may prevent the fusion of the neural tube thus tethering the cord because of attachment of the fatty elements with neural structures, resulting in tethered spinal cord syndrome. The different extents of the fusing tube may develop different features of the lumbosacrococcygeal area that may result in human tail.22

The human tail isn't as an evolutionary regression yielding a benign structure left over from our ancestors. It is a developmental aberration, the result of improper forming of the neural tube. In support of their thesis, Lu et al. present data showing a high level of concurrence of the human tail with other "anomalies." In 59 examples of human tails examined between 1960 and 1997 they found:23

Associated AnomalyIncidence (%)
Spinal dysraphism29/59 (49.15)
Meningocele8/29 (27.59)
Spina bifida only21/29 (72.41)
Lipoma16/59 (27.12)
Tethered spinal cord12/59 (20.34)
Coccygeal vertebrae7/59 (11.86)
Syndactyly2/59 (3.39)
Hemangioma1/59 (1.69)
Cleft palate1/59 (1.69)
Crouzon syndrome1/59 (1.69)
Congenital tracheal stenosis1/59 (1.69)
Clubfoot1/59 (1.69)
Von Recklinghausen disease1/59 (1.69)
Omphalocele1/59 (1.69)
Hypoplasia of digits1/59 (1.69)
Tetralogy of Fallot1/59 (1.69)

This data strongly contradicts the view that the human tail is a "benign" structure found in "otherwise healthy" babies. In fact, Lu et al. probably significantly underestimated the incidence of disease and abnormalities associated with the human tail, because MRI technologies -- which in many cases are the only way to detect some of these defects -- were not available at the time many of these tails were examined. They write:

After 1980 the incidence of associated anomalies, such as spinal dysraphism, became higher because CT or MRI began to be performed as part of examination. The incidence is probably underestimated because some reports did not perform any detailed image studies.24
Indeed, a later paper commenting on the study observed, "Of the 16 cases imaged with MR or CT myelography, 81% had a tethered spinal cord"25 -- a defect also called an occult spinal dysraphism, which typically leads to serious neurological problems if untreated. This is an extremely significant finding. It means Karl Giberson is simply wrong to claim that tails are normally found in "otherwise healthy" humans.

Other papers concur. A paper in the Journal of Pediatric Surgery finds that human tails are "often associated with occult spinal dysraphism."26 A paper in British Journal of Plastic Surgery notes the tail "is potentially a site of peculiar tumours."27 A paper in Journal of Perinatology states: "Caudal appendages also occur as typical or frequent manifestations of certain syndromes."28 A paper in the Journal of the Indian Association of Pediatric Surgery states, "Tails are usually associated with occult spinal dysraphism."29 A paper in Pediatric Neurosurgery found:

Children born with a tail-like appendage have a rare malformation that is frequently associated with abnormalities of the spine and spinal cord. ... many [cases of tails] simply represented a form of spina bifida, rather than a "true" tail. ... Children born with a tail appendage have a high rate of associated spinal dysraphism and tethered cord.30
In fact, another paper in Pediatric Neurosurgery finds the reason the tail is "important" isn't because it reveals something about our ancestry, but because it can indicate something is wrong with the nervous system:
The human tail is a rare congenital anomaly and is important primarily because it sometimes accompanies central nervous system anomalies, such as spinal dysraphism, lipoma and spinal cord tethering.31
While considering the strong evidence that the human tail is associated with developmental defects, various papers have found, the view of the "tail" as a regression is just as wrong as old superstitions that it represented some supernatural omen:
Many authors saw this curious and rare condition to be evidence of man's descent from or relation to other animals, while others made it the subject of superstition. Advanced imaging technology in recent decades has allowed a more thorough investigation of these patients and better defined their association with spinal dysraphism and tethered spinal cord.32
Still another paper in Advances in Orthopedics finds that the "so-called human tail...is often considered to be a cutaneous marker of underlying occult dysraphism."33 Or, as a paper in Pediatric Neurosurgery states, "The human tail or caudal appendage is usually associated with occult spinal dysraphism."34 And on and on. In other words, the human tail is typically the sign of an underlying developmental abnormality, and according to Lu et al., "This fact plays an important role in understanding the disturbance of development and regression of human tails."35 It's unfortunate that the evolutionary viewpoint at first led doctors to think of the tail as a benign structure that, without further trouble or careful examination, could simply be surgically excised. In a subsequent post I'll examine the medical harms that have resulted from this now thoroughly outdated idea -- a legacy of Charles Darwin, still being advanced today by Darwin-advocates like Karl Giberson.

References Cited:

[21.] Frank L. Lu, Pen-Jung Wang, Ru-Jeng Teng, and Kuo-Inn Tsou Yau, "The Human Tail," Pediatric Neurology, 19 No. 3 (1998) (emphases added). See also Chunquan Cai, Ouyan Shi, and Changhong Shen, "Surgical Treatment of a Patient with Human Tail and Multiple Abnormalities of the Spinal Cord and Column," Advances in Orthopedics, 2011: 153797.

[22.] Frank L. Lu, Pen-Jung Wang, Ru-Jeng Teng, and Kuo-Inn Tsou Yau, "The Human Tail," Pediatric Neurology, 19 No. 3 (1998) (emphasis added). See also Chunquan Cai, Ouyan Shi, and Changhong Shen, "Surgical Treatment of a Patient with Human Tail and Multiple Abnormalities of the Spinal Cord and Column," Advances in Orthopedics, 2011: 153797.

[23.] "Associated anomalies in human tail" table reprinted from Lu et al. (1998): Frank L. Lu, Pen-Jung Wang, Ru-Jeng Teng, and Kuo-Inn Tsou Yau, "The Human Tail," Pediatric Neurology, 19 No. 3 (1998).

[24.] Frank L. Lu, Pen-Jung Wang, Ru-Jeng Teng, and Kuo-Inn Tsou Yau, "The Human Tail," Pediatric Neurology, 19 No. 3 (1998) (emphasis added). See also Chunquan Cai, Ouyan Shi, and Changhong Shen, "Surgical Treatment of a Patient with Human Tail and Multiple Abnormalities of the Spinal Cord and Column," Advances in Orthopedics, 2011: 153797.

[25.] Daniel J. Donovan Robert C. Pedersen, "Human Tail with Noncontiguous Intraspinal Lipoma and Spinal Cord Tethering: Case Report and Embryologic Discussion," Pediatric Neurosurgery, 41:35-40 (2005) (emphasis added).

[26.] Deepak Kumar Singha, Basant Kumarb, V.D. Sinhaa, and H.R. Bagariaa, "The human tail: rare lesion with occult spinal dysraphism--a case report," Journal of Pediatric Surgery, 43: E41-E43 (2008).

[27.] Abraham M. Baruchin, Dan Mahler, Dan J. Hauben, and Lior Rosenberg, "The human caudal appendage (human tail)," British Journal of Plastic Surgery, 36: 120-123 (1983).

[28.] T.E. Herman and M.J. Siegel, "Human tail-caudal appendage: tethered cord," Journal of Perinatology, 28: 518-519 (2008).

[29.] Biswanath Mukhopadhyay, Ram M. Shukla, Madhumita Mukhopadhyay, Kartik C. Mandal, Pankaj Haldar, and Abhijit Benare, "Spectrum of human tails: A report of six cases," Journal of the Indian Association of Pediatric Surgery, 17(1): 23-25 (Jan-Mar, 2012).

[30.] Daniel J. Donovan Robert C. Pedersen, "Human Tail with Noncontiguous Intraspinal Lipoma and Spinal Cord Tethering: Case Report and Embryologic Discussion," Pediatric Neurosurgery, 41:35-40 (2005).

[31.] Se-Hyuck Park, Jee Soon Huh, Ki Hong Cho, Yong Sam Shin, Se Hyck Kim, Young Hwan Ahn, Kyung Gi Cho, Soo Han Yoon, "Teratoma in Human Tail Lipoma," Pediatric Neurosurgery, 41:158-161 (2005).

[32.] Daniel J. Donovan Robert C. Pedersen, "Human Tail with Noncontiguous Intraspinal Lipoma and Spinal Cord Tethering: Case Report and Embryologic Discussion," Pediatric Neurosurgery, 41:35-40 (2005); Chunquan Cai, Ouyan Shi, and Changhong Shen, "Human born with a tail: A case report," SA Journal of Child Health, 7(1): 38-39 (2013); Chunquan Cai, Ouyan Shi, and Changhong Shen, "Surgical Treatment of a Patient with Human Tail and Multiple Abnormalities of the Spinal Cord and Column," Advances in Orthopedics, 2011: 153797.

[33.] Chunquan Cai, Ouyan Shi, and Changhong Shen, "Surgical Treatment of a Patient with Human Tail and Multiple Abnormalities of the Spinal Cord and Column," Advances in Orthopedics, 2011: 153797 (emphasis added).

[34.] Pei-Jung Lin, Yu-Tang Chang, Hsing-I Tseng, Jan-You Lin, Yu-Sheng Huang," Human Tail and Myelomeningocele," Pediatric Neurosurgery, 43:334-337 (2007) (emphasis added).

[35.] Frank L. Lu, Pen-Jung Wang, Ru-Jeng Teng, and Kuo-Inn Tsou Yau, "The Human Tail," Pediatric Neurology, 19 No. 3 (1998).

Photo source: Drew McLellan/Flickr.


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