Why Don’t Humans Have Tails?
How We Lost Our Tails:
A major evolutionary change cannot be explained
by Jerry Bergman, PhD
The tail of primates may not appear to present a pressing issue in evolutionary biology, but it is central to the study of human evolution. A new study presented the central implications of the loss of the tail in the great ape primates. The importance of the primate tail was described by Xia et al. who wrote the
loss of the tail is one of the main anatomical evolutionary changes to have occurred along the lineage leading to humans and to the “anthropomorphous apes.” This morphological reprogramming in the ancestral hominoids has been long considered to have accommodated a characteristic style of locomotion and contributed to the evolution of bipedalism in humans.[1]
Tail loss may have contributed to the evolution of bipedalism in humans, they say, but none of the other so-called great apes are bipedal, so how did it help them? In spite of its importance, Xia et al. admit that “the precise genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown.”[2]
Vestiges of the Vestigial Organs Myth
They then incorrectly defined the coccyx as a “small bit of bone at the base of the spine that is a vestige of mammalian tails.”[3] This mistake was then added to other mistakes in the paper. The fact is, the coccyx is the terminal portion of the backbone which has to end somewhere.[4] It is not a vestigial tail but is a critical structure in humans and probably in all of the anthropomorphous apes. The major function of the coccyx is to serve as an attachment site for the interconnected muscle fibers and tissues that support the bladder neck, urethra, uterus, rectum, and the set of structures that form the bowl-shaped muscular floor of the abdomen, collectively called the pelvic diaphragm.[5]
The muscles and ligaments that insert into the coccyx include the coccygeus muscle ventrally, and the gluteus maximus muscle dorsally. The coccygeus muscle is a strong, yet flexible, muscle, often described as a “hammock,” that adds support to the pelvic floor against abdominal pressure.[6] The coccygeus muscle, which is inserted by its base into the margin of the coccyx and into the side of the last section of the sacrum, also helps to support the posterior organs of the pelvic floor. The levator ani muscles constrict the lower end of both the rectum and, in women, the vagina, drawing the rectum both forward and upward.[7] The coccyx muscle system expands and contracts during urination and bowel movements, and also distends to help enlarge the birth canal during childbirth.[8]
Another structure connected to the coccyx is the anococcygeal raphe, a narrow fibrous band that extends from the coccyx to the margin of the anus.[9] Without the coccyx and its attached muscle system, humans would require a very different support system for their internal organs necessitating numerous major design changes in humans.[10] The coccyx bone is not vestigial in any sense of the word.
The Findings of the 2021 Xia et al. Study
Ernst Haeckel, a Darwin disciple, contributed to evolutionary racism with his drawings portraying humans as mere apes, usually with dark skin.
Xia et al. compared ape and monkey versions of the 31 genes they determined are involved in tail development. They could not find evidence of differences between tailed and non-tailed primates in the genes controlling the protein-coding regions. Next, they researched introns (noncoding regions inside a gene) which are normally removed from mRNA before proteins are made. They detected an Alu element in the middle of an intron in the tail of gene TBXT. Alu elements have been assumed by evolutionists to be genetic parasites that copy and paste themselves everywhere in the genome. They are actually transposable elements or “jumping genes” that can move around the genome. Alu elements are common in human and other genomes. An estimated 1 million Alu elements are in the human genome, making up about ten percent of our DNA.
Normally, a 300-base-pair-long Alu located in an intron would be edited out of the gene with the intron. In this case, an another Alu element was located nearby and this other Alu sequence was in inverse order. Because the two sequences are complementary, they bind together, forming a loop in the mRNA which effectively glues several DNA transcripts together. When the extra sections are excised out, some of the instructions are lost.
The result is that a key piece of the TBXT protein is missing. Mice with this mutation ended up with a mixture of full-length and missing-bit TBXT proteins which usually results in the complete loss of the tail. Thus it was lost in one step, not requiring the need to “posit millions of years of successive tiny changes accumulating gradually.”[11] University of Missouri evolutionist Carol Ward noted, “It may tell us why all of a sudden when we see the apes [emerge from evolution] they have no tails.” While “there’s no evidence of a slow reduction in tail length in the fossil record… we have too few fossils to rule it out.”[12] This effect was first noted in 1923 when a Russian geneticist exposed male mice to X-rays. The researcher then observed that some of their offspring developed shortened or kinked tails. We now know that the cause of the malformation was TBXT mutations.[13]
Tail Loss in Great Apes
Enlightened apes have their own narrative of evolution.
Another problem is that all of our supposed nearest ‘relatives,’ including chimpanzees, gorillas, orangutans, bonobos, gibbons, and some of the lesser apes, such as siamangs, lack tails. This could be true only if all of these primates had one single common ancestor which lost its tail due to the TBXT mutation, or the common ancestors of all of these primates had the same mutation, both of which would be very unrealistic events. If the findings of Xia et al. are true, we would expect that the descendants of the chimp with the TBXT mutation would be tailless and the descendants of the chimp without the mutation would all have tails unless the mutation occurred again. The result would be two lines would lack tails and one line would have them. Only a few of the over 100 types of monkeys and apes, such as spider monkeys, have tails. This mutation would therefore be common, assuming that the mutation was actually the cause of the tail loss.
The primates that have tails tend to be small cat-like lemurs, tarsiers, lorises, and pottos. The distinction of tailed versus tailless is too clean; all of one monkey type either having a tail or being tailless. The evolutionist’s explanation was that the tailless primates were evolutionary more fit, thus the tailed great-ape primates all became extinct. The problem with this theory is all of the many primates that have tails are doing well. Tails are very useful for small primates to swing in the trees but, for the larger, great-ape primates, even though tails are less useful, they would not seem to make them significantly less fit.
Evolution Requires Gain of Structures, not Loss of Structures
Tails perform many useful functions for monkeys and lemurs.
Loss of a structure such as a tail is not what evolution requires in the long term. What is required is the gain of structures and functions. Because a putative lesser-evolved animal has a structure that humans don’t, evolutionists assume that it must have been lost in evolution.
The genetic difference between humans and our claimed closest ancestors, the chimpanzees, is 15 percent (85 percent similarity) in 3 billion base pairs. That equals a difference of 450 million base-pairs – close to a billion bases difference when considering both halves the DNA strand. Evolutionists know that 99.9 percent of all mutations are slightly deleterious, and a small percent are lethal. Consequently, to claim a bridge between chimps and humans requiring close to a billion-base beneficial mutations is irrational. Evolutionists deny the logically obvious alternative explanation: that chimpanzees and humans were originally created with the differences we find today.
The Mutation Explanation Problematic
The researchers also found that humans and apes both produce longer and shorter versions of the transcript. In contrast, mice only make the longer version, and when the “researchers used CRISPR to introduce the two-Alu version of TXBT into mice, they found that having both copies of the mutant gene was lethal, but having one longer copy and one shorter copy resulted in a range of tail lengths, including no tail at all.[14] Thus, many of the genetically modified mice that produced alterations in the TBXT gene developed neural tube problems similar to the birth defects that cause spina bifida or anencephaly (a lethal congenital condition in which a large part of the skull is absent along with the cerebral hemispheres of the brain). Annie Melchor waffled on tail fitness in The Scientist this year, saying that humans “apparently paid a cost for the loss of the tail, and we still feel the echoes …. We must have had a clear benefit for losing the tail, whether it was improved locomotion or something else.”[15]
Evolutionary Diagram of Primate Relationships. The fact that all primates classified as hominoids lack a tail and all those classified as non-hominoids have a tail, at the least, implies to evolutionists that all the hominoids have a single common ancestor which has never been determined. The dates given here in this chart are also problematic. Old World monkeys were claimed to have originated 25 million years ago. Other sources dated the first primates at 50-55 million years ago based on “very fragmentary fossil evidence.”[16] Gibbons were claimed as having evolved 16 million years ago and gorillas as evolving a comparatively short 10 million years ago.[17] Furthermore, according to new genetic research, when compared with known fossils, the lineage that led to humans, chimps, and gorillas evolved from a common ancestor about ten million years ago. Thus, according to evolution, their single common ancestor must have had the mutation causing the loss of their tails.[18] See text for problems with this narrative.
Summary
The attempt to explain the cause and advantages of tails (or the lack of them) by evolution is problematic except in humans. In humans, a tail would get in the way of upright walking, sitting, and other distinctively human activities. A more logical explanation for the tail-versus-tailless differences is that they are part of the original design of primates. More research in this area will likely support this position. This new study did not support the evolutionary narrative. It has actually highlighted another difference between humans and chimps and other primates, posing a new challenge for the mutation/selection mechanism.
References
[1] Xia, Bo, et al. 2021. The genetic basis of tail-loss evolution in humans and apes. bioRxiv doi: https://doi.org/10.1101/2021.09.14.460388.
[2] Xia, Bo, et al., 2021.
[3] Le Page, Michael. 2021. How our ape ancestors suddenly lost their tails 25 million years ago.
https://www.newscientist.com/article/2291130-how-our-ape-ancestors-suddenly-lost-their-tails-25-million-years-ago/
[4] Reno, Cora A. 1970. Evolution on Trial. Chicago, IL: Moody Press, p. 81.
[5] Newman, Diane K. 1997. The Urinary Incontinence Sourcebook. Los Angeles, CA: Lowell House, p. 13.
[6] Walker, Warren F. 1987. Functional Anatomy of the Vertebrates: An Evolutionary Perspective. Philadelphia, PA: Saunders, p. 253.
[7] Anthony, Catherine Parker. 1963. Textbook of Anatomy and Physiology. Sixth edition. St. Louis, MO: C.V. Mosby Company, p. 411.
[8] Smith, Anthony. 1986. The Body. New York, NY: Viking-Penguin Books, p. 134.
[9] Gray, Henry. 1966. Gray’s Anatomy. Philadelphia, PA: Lea Febiger, p. 130.
[10] Allford, Dorothy. 1978. Instant Creation—Not Evolution. New York, NY: Stein and Day, p. 42; Weischnitzer, Saul. 1978. Outline of Human Anatomy. Baltimore, MD: University Park Press, p. 285.
[11] LePage, 2021.
[12] LePage, 2021.
[13] Melchor, Annie. 2021. Alu leap may explain why apes don’t have tails. The Scientist, September 13. https://www.the-scientist.com/news-opinion/alu-leap-may-explain-why-apes-don-t-have-tails-69215.
[14] Xia, Bo, et al., 2021.
[15] Melchor, 2021.
[16] Palomar education. 2021. Early Primate Evolution: The First Primates. https://www2.palomar.edu/anthro/earlyprimates/early_2.htm.
[17] Mosher, Dave. 2012. Gorillas more related to people than thought, genome says surprising differences include gene that aids knuckle walking. National Geographic News, March 8.
[18]Carbone, Lucia, et al. 2014. Gibbon genome and the fast karyotype evolution of small apes. Nature 513:195-201, September 11.
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,500 college libraries in 27 countries. So far over 80,000 copies of the 40 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.