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Friday, April 25, 2014

No, It’s Not a Tail!

Posted by jlwile on May 21, 2012

A human embryo after about 7 weeks of development
(public domain image)

I have written a lot about the evolutionary myth of vestigial organs (here, here, here, here, and here), showing how several biological structures evolutionists once thought were vestigial are, in fact, quite necessary. The concept of vestigial organs is very popular among many evolutionists, but it usually boils down to ignorance. If evolutionists don’t know the use for a biological structure, they assume that it must be vestigial. As is often the case, however, further research generally shows that this evolutionary assumption is quite wrong, due to our ignorance of the structure being considered.


This concept is often employed when studying the development of embryos. Because of the fraudulent work of Ernst Haeckel, evolutionists have long promoted the myth that an embryo will produce vestiges of its evolutionary history as it develops. Once again, this is mostly the result of ignorance. Embryonic development is rather difficult to study, so we often observe things that we don’t understand. When these things superficially resemble something that supposedly developed in the evolutionary history of the organism that is being studied, it is often pointed to as some vestige of evolution.

For example, in Why Evolution is True, Dr. Jerry Coyne tries to make the case that the human embryo is covered in a fine coat of lanugo hair simply because it is a part of the evolutionary heritage of humans. He says that there is no reason for a human embryo to be covered with hair, but it happens because humans evolved from an ape-like ancestor that was covered in hair. The coat of hair is simply a leftover vestige from that part of the human evolutionary lineage. As I have already pointed out, this is utterly false. In fact, the fine coat of hair that human embryos have is incredibly important to their development, and the idea that it is a leftover vestige of evolution is just a result of ignorance when it comes to human embryonic development.

Well, in a Facebook group discussion I recently had, the conversation turned to the supposed “tail” that human embryos have early in their development. This is a popular myth, but it is utterly false, and I thought I would post this so that others would benefit from a modern scientific analysis of this important embryonic structure. As you can see in the photograph of a human embryo above, there is a structure (pointed out in the figure) that resembles a tail. The structure eventually goes away, but it is a rather striking part of the embryo while it is present. Evolutionists have long taught that this is a leftover vestige of when our ancestors had tails,1 but we now know that such an idea is simply 100% false.

As noted in the photo, the structure that evolutionists have labeled a vestigial tail is, in fact, the caudaul eminence, and it has nothing to do with a tail. In 2004, an important study was published in the journal Cells Tissues Organs. It studied 52 different human embryos at different stages of development, and it reassessed our knowledge of human embryonic development. In that study, the authors note:2

The eminence produces the caudal part of the notochord and, after closure of the caudal neuropore, all caudal structures, but it does not produce even a temporary ‘tail’ in the human.

In case you are not aware, the term caudal is a directional term in anatomy, referring to the posterior of the organism being studied. In the end, then, this study showed that the caudal eminence really has nothing to do with a tail.

So what is the caudal eminence? It is a neurological structure that is necessary for the development of the spinal cord and many other caudal structures. John Alan Kiernan and Murray Llewellyn Barr probably say it best in their text, Barr’s The Human Nervous System: An Anatomical Viewpoint. When discussing the development of the spinal cord, they say:3

Further caudally, the spinal cord is formed by ‘secondary neurulation,’ which is the coalescence of chain vesicles that becomes continuous with the lumen of the neural tube about three weeks after the closure of the caudal neuropore. The vesicles are derived from the caudal eminence, a mass of pluripotent cells located dorsal to the developing coccyx.

As you may already know, the term pluripotent refers to cells that can develop into many different kinds of cells, depending on the instructions they receive.

So we see that far from being some remnant of a tail, the caudal eminence is the source of cells that are used to produce vesicles that are integral to the development of the spinal cord. As detailed in the 2004 study I quoted previously, it also produces other caudal structures. That’s why it is a mass of pluripotent cells – it is the source of cells that develop into several structures. It eventually goes away, of course, because the spinal cord and the other caudal structures are eventually completed, and the embryo no longer has a need for those pluripotent cells. In some cases of abnormal development, the caudal eminence does not go away, and the child is born with a mass of tissue extending from the posterior. While this resembles a stubby tail, it is simply a mass of flesh that can be easily snipped off.

As you can see, then, the idea that human embryos have temporary tails during their embryonic development has been thoroughly debunked in the scientific literature. The only question that remains is how long evolutionists will continue to use this myth to promote their failing hypothesis.

REFERENCES

1. David Krogh, Biology: a Guide to the Natural World, Pearson Education, 2005, p. 467
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2. Müller F and O’Rahilly R., “The primitive streak, the caudal eminence and related structures in staged human embryos,” Cells Tissues Organs. 177(1):2-20, 2004
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3. John Alan Kiernan and Murray Llewellyn Barr, Barr’s The Human Nervous System: An Anatomical Viewpoint, Ninth Edition, Lippincott Williams & Wilkins, 2008, p. 5
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Comments

5 Responses to “No, It’s Not a Tail!”
  1. shevrae says:

    So evolutionists have their own version of the “God of the gaps?”

  2. jlwile says:

    That’s an interesting parallel, Shevrae. If they don’t know what a structure does, that’s a gap in their knowledge, and they fill it with the idea that the structure is vestigial.

  3. josiah says:

    Hypothetically, could such a mass of flesh provide an alternative source for stem cell research/therapy that doesn’t involve killing human embryos?

  4. jlwile says:

    If you mean the mass of flesh that some children are born with, Josiah, then the answer is no. If the neurological development is complete and the caudal eminence does not get “turned off,” the pluripotent cells end up getting signals that turn them into fat and skin cells. This is a consequence of where they are on the body. As a result, by the time the child is born, the caudal eminence doesn’t have pluripotent cells. It has skin and fat cells. On the other hand, if you tried somehow to harvest the pluripotent cells during development, I would think that there would be serious consequences to the embryo.

  5. josiah says:

    I did mean the former. Oh well.

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