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Another Icon of Evolution: The Darwinian Myth of Human "Tails"

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Writing for The Daily Beast about his recent debate with Stephen Meyer, theistic evolutionist Karl Giberson commented:

I showed pictures of otherwise healthy humans who had been born with webbed feet and tails. I asked the challenging question: "Why does the human genome contain instructions for the production of features we don't use?" The scientific explanation is that we inherited these instructions from our tailed ancestors but the instructions for producing them have been shut off in our genomes, which is why Shallow Hal is the only person most people know who has a tail. Sometimes the "ignore these genes" message gets lost in fetal development, however, and babies are born with perfectly formed, even functional tails.
Dr. Giberson, a physicist, has done a fine job of stating the often-heard Darwinian evolutionary view of human "tails." But is any of it true?
  • Are humans ever born with "perfectly formed, even functional tails"?
  • Is the "scientific explanation" of the human tail that really they're simply an accidental turning on of the "complete instructions for the production" of tails retained from our "tailed ancestors," that is, the failure to "ignore" our vestigial "genes" for tails?
  • Are humans born with tails typically "otherwise healthy" -- i.e., are human "tails" simply benign structures that indicate nothing more than our descent from tailed ancestors?
The answer, unequivocally, is no, no and no. Because this point comes up periodically in the Darwin debate, achieving the status of what Jonathan Wells has called (in his book of the same name) an "icon of evolution," these questions are worth considering in detail. I plan to do just that in coming days here at ENV, examining the peer-reviewed scientific and medical literature on human tails.

In brief, what are called human "tails" lack bone (i.e., vertebrae normally found in tails), cartilage, notochord, and spinal cord. This makes them totally unlike any tail found anywhere among other mammals or for that matter, any other animals. As one paper found, there is "no zoological precedent" for the so-called "tails" found in humans. In fact, Giberson's statement notwithstanding, no human baby has ever been documented as possessing a "perfectly formed, even functional tail."

Moreover, the most current medical thinking about human tails views them as a type of developmental defect, not an evolutionary regression. They are an abnormality almost always associated with other neurodevelopmental defects. They are not the result of the accidental "turning on" of "vestigial genes." Specifically, they are the result of the failure of a developmental structure, one that grows during normal human development, to regress into the embryo. Though the causes of this are still not entirely clear, what is clear is that the failure to regress is caused by underlying developmental abnormalities that cause a variety of other birth defects as well. As a general rule, tails are not found in "otherwise healthy" babies.

Moreover, we'll see that the classical evolutionary view of human tails has caused some doctors to wrongly view them as nothing more than a mere benign evolutionary relict -- a diagnosis that multiple experts have warned is potentially dangerous. Why? Because it could lead to treatments that ignore other defects commonly associated with tails. In other words, the evolutionary myth of human tails is not only mistaken. It is also medically harmful.

Photo credit: Josef Vybíral/Flickr.