The Myth of Evolutionary Homology

How evolution’s greatest strength shows its ultimate weakness

   

         It is almost certain that the majority of people educated in America have seen it: the image in their biology or anatomy classes that compares the structural anatomy of a human hand with a bat’s wing, a horse’s leg, and a cat’s paw. Mapped out clearly before everyone is this similarity that is held up as one of the defining evidences of Darwinian evolution. Because these similarities seem to be built using common parts, a successive relationship is inferred. To the evolutionist, these similarities are undeniable proof for common ancestry, the core dogma of Darwinian evolution. Is this field of comparative biology as impregnable as it is touted to be? Is this pillar of evolution upholding Darwin’s argument nearly one hundred and fifty years later?

I. Homology

            Before we can delve into the arguments for and against comparative biology, we must clarify what it is. Evolutionary theory predicts that all living organisms will share some similarities due to their common ancestry. Yet common functional structures do not automatically confirm relationship. There is a key difference between structures that are considered truly homologous and those considered analogous. Homologous structures, like the forelimbs of the organisms commonly pictured in the biology class poster, have not only common functions, but common structures as well. The bones in our forearm, while different sizes, closely resemble the organizational structures within other vertebrates like the bat wing, whale fin, etc.  The homology goes beyond simple structure these days, spilling into the study of genetics and embryology.

            On the other hand, analogous structures are ones that are similar in function, but have arisen via different origins. The wings of an insect and the wings of a bat have a common use, but their structures are clearly different. Insect wings have membranous wings stiffened by harden veins that dried soon after they morph into the adult stages. Bat wings, while seemingly membranous, are actually bone with layers of skin growing between the digits and the creature’s sides. They are both functionally used for flight, but neither works the same way, nor are they in any way related.

            This line between homologous and analogous structures is a fine one in many situations. Similarities are sometimes very close in both structure and function and the organisms in question could be uncannily similar, yet at the same time, they could have very different structures that cannot be related. Convergent evolution comes into play in situations like these. Sharks and dolphins have very similar external appearances and structural functions, but the fish to mammal difference confirm that they are not close evolutionary relatives. The same could be said about sugar gliders and flying squirrels, both incredibly alike in structure, function, and behavior with one drastic difference: their reproductive systems. Any evolutionary relationship between these two species would have to be found all the way back at the divergence of mammalian reproduction between placental mammals and marsupials. Because of this, no evolutionary relationship is implied, but the homologous definition is blurred. It is incredibly difficult to assume evolution could produce nearly identical structures and creatures more than once.

II. Vestigial Structures

            Within this argument for homology lies the evolutionary presupposition that there exists many structures that are nothing but evolutionary leftovers. Some might have adapted to serve some minor purpose, but many are considered worthless leftovers from previous evolutionary stages. As well known biology textbook writers Kenneth Miller and Joseph Levine wrote,

Vestigial structures are inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendant… [Why] retain structures with little or no function? One possibility is that the presence of the structure does not affect an organism’s fitness, and, therefore, natural selection does not act to eliminate it.[1]

Popular layman sources for science education like livescience.com lay out this argument in simplified slideshow format.[2] The story is very similar to many other sources, including some textbooks. Examples include the human appendix, the human tailbone, and even the whale pelvic bones. These few structures, as well as a dwindling list of others, are claimed to have no functions and are worthless leftovers.

            The appendix is found in many animals. It is significantly larger in herbivorous mammals and much tinier in our bodies. In the herbivores, it assists the digestion of plant materials, but in omnivores and carnivores, it is much reduced. To some people, it is considered not just a useless leftover, but a liability as well, with its frequently capacity to become infected, inflamed and eventually burst, which could cause drastic damage, if not deadly results. But is this organ as worthless as implied? Is it just an evolutionary leftover? Apparently it is not. The growing scientific consensus suggests that the appendix is indeed quite important, especially in embryonic development, though it remains functional in different ways into adulthood.[3]

            Another very common structure deemed vestigial is the so-called “tailbone” in humans. This curved structure at the end of the spine is said to be the remnants of a tail from when our proto-monkey ancestors still had them, presumably for balance during their arboreal lifestyle. It is not at all uncommon for many to deem it as worthless leftovers[4] without thinking twice. These claims, if true, would leave us in a very uncomfortable situation, quite literally.

“For instance, the coccyx is one part of a three-part support for a person in the seated position. Weight is distributed between the bottom portions of the two hip bones (or ischium) and the tailbone, providing balance and stability when a person is seated…The tailbone is the connecting point for many pelvic floor muscles. These muscles help support the anus and aid in defecation, support the vagina in females, and assist in walking, running, and moving the legs.[5]

Even with these admissions of important purpose of this bone, properly called the coccyx, these authors still dogmatically define it as vestigial, apparently ignorant to the words they wrote directly opposite to that conclusion. If the coccyx bone is an important location for the attachments of ligaments and tendons, then how could it truly be considered vestigial? This is a clear example of the weakness of the homological argument: it may look similar to a tiny tail to the imaginative eye, but that in no way proves that it actually is a tail. Similarity does not equal relationship.

            In a similar instance, though outside the human body, it is commonly argued that the little pelvic bones in cetaceans are the remnants of legs from their evolutionary ancestors that walked the land. Over time, with the fading need to return to land and the further adaptation into a fully aquatic environment, the early proto-whales were suggested to have slowly lost functional legs. The legs didn’t simply disappear, but rather shrank in size and complexity until all that are left are the current pelvic bones. Like the coccyx bone in humans, it had, for many years, been deemed an evolutionary leftover with no function. Yet again, however, we see that this assumption of vestigiality is incorrect. 

            Evolutionary biologists from none other than the respectable Harvard University have tackled this false vestigiality, even if they themselves do not even realize it.[6] While still assuming the whale pelvic bones are the remnants of legs, they turn around and preach how useful they actually are.  Their research has found that these pelvic bones are actually important attachment sites of muscles important for sexual reproduction. These bones are apparently able to help guide the male whale genitalia during mating, a difficult task for such a large, water-bound mammal. Without these pelvic bones, whale copulation would be quite a bit more hit and miss, resulting in lower chances of producing offspring, and possibly limiting the population of cetaceans altogether, which could easily end in an evolutionary dead end.  Again, because of their positioning, homologous relationships are presumed, but not proven.

            Overall, this argument for vestigiality ends up being too shallow to be as clear a proof for evolutionary relationships as is typically claimed. This is mainly because the argument for vestigial organs is not a scientific one, but rather a theological one. Dr. Paul Nelson wrote on this very concept in Biology and Philosophy. He noted, “Evolutionists have long contended that the organic world falls short of what one might expect from an omnipotent and benevolent creator. “[7]

When people try to explain how or why a creator might have created, they are well beyond the boundaries of the modern applications of science. To make such claims, you have to imply knowledge of the creator and what their goals were. When an evolutionist implies “God would not build an organ that way,” they are building their case as a negative case against their understanding of who God is and how they perceive him to work, not on scientific suppositions. This use of theology undermines the purpose of the argument for vestigial organs.

III. Ontogeny

            Another common argument from homology is found in the study of embryology. Stemming from as early as Darwin’s lifetime, some biologists claimed to see the actual evolutionary stages played out in the development of an organism’s embryo. As Darwin himself wrote, “…the embryo is the animal in its less modified state; and in so far it reveals the structure of it progenitor… community in embryonic structure reveals community of descent.”[8] Many of the shapes and structures that early embryologists discovered seemed very similar to each other, leading to these claims of homologous relationship. Embryologists like Karl Ernst von Baer suggested that the early stages of embryonic growth, be it in birds, mammals or reptiles, all looked incredibly alike. German biologist Ernst Haeckel took this concept to the extreme with his famous phrase “ontogeny recapitulates phylogeny.” This biogenetic law of his, also known as recapitulation, was influential in shaping evolutionary thought during his day. His artistic representations of the embryonic stages of multiple different species spread like wildfire because the similarities were uncannily similar. Haeckel claimed that organisms, humans for example, undergo the major evolutionary stages during development, going from single cellular, to multicellular, and all the way up to chordates and finally to their final modern stage on the evolutionary ladder.

            Sadly, Haeckel was overly attached to his biogenetic law and its boon for evolutionary theory. In his drive to prove Darwinian evolution, he took short cuts by literally altering the artistic representations in manners that forced the similarity beyond what was actually seen. His ruse was eventually discovered and he was forced to retract the claims he made, but by then it was too late. His concept had already taken root in the mind of the public. For decades, his infamous depictions of embryonic homologies remained for all to see in educational textbooks. Some college professors admit that the biogenetic law in its full form was false, but that the basic concepts are still sound science.

A modern day embryologist realized that the similarities claimed by people like Haeckel had not been accurately tested. He built a team of researchers and tackled the question himself. His published findings in the journal Anatomy and Embryology[9] reviewed the similarities of an even larger sample size than Haeckel had reviewed. His findings were conclusive. Needless to say, there were very obvious differences that any competent embryologist could see that show the differences between the organisms in the earlier stages, undermining the original assumptions of homology.

IV. DNA Homologies

            Darwinian evolution is founded on the concept of common ancestry. Darwin made a convincing case to his contemporaries, but the generations that followed him have had to morph the argument based on the ever-growing knowledge of DNA and genetics. If you ask an evolutionist, the transition into the growing field of genetics was one of the best things for evolution. Textbook authors like Kenneth Miller and Joseph Levine state categorically

At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent…All cells use information coded in DNA and RNA to carry information from one generation to the next and direct protein synthesis. This genetic code is nearly identical in almost all organisms, including bacteria, yeasts, plants, fungi, and animals. This is powerful evidence that all organisms evolved from common ancestors that shared this code.[10]

The realization that all life on Earth has DNA was gobbled up like candy to further the Darwinian gospel, but do these homologies truly support Darwinian evolution?

            A first shortcoming of this common evolutionary assumption is a clear upset of universal ancestry by none other than what could be compared to a universal familial DNA test. Unlike what Miller and Levine boldly claim, we are now finding many different genetic codes in different organisms. They may use the same basic DNA materials, but their codes are far too different to show a united ancestry of all living things. In fact, they have found twenty-four different codes,[11] and, due to the fragility of the encoded information, such drastic variations could not be sustained between the generations. This could be compared to a child knowing fluent Spanish after being raised in an exclusively English home. Where did that child learn its language? There is no feasible way to tweak one or two words from English to arrive at fluent Spanish, yet these codes would have to make such sudden (but still functional) changes to be related, which is not feasible. Each of these is more likely to have its own unique origins. A cohesive, universal, homologous genetic code for all life has major disconnects.

            It goes beyond just those twenty four codes too. Some of the codes that are different than what was deemed standard are found in the mitochondria’s own set of DNA. Multiple mDNA’s have been discovered that use unique codes. If we find eukaryotic cells that have similar nuclear DNA, yet their mDNA is different, we are forced away from the conclusion of close relationship, since all mDNA should have originated early on in the evolution of eukaryotes. For example, invertebrates and vertebrates cannot share a common ancestor since their mDNA is not even based upon the same code. These codes cannot change overnight. Even slight changes can be catastrophic.

            Even if we focus on what is often considered a great example of close homology, we find the evidence coming up short. In the instance of our relationship with the higher apes, such as the bonobos or chimpanzees, it is very often claimed that we have a 96% similarity between our DNAs.[12] Frans de Waal, a primate scientist at Emory University in Atlanta, Georgia boldly asserted, “We are apes in every way, from our long arms and tailless bodies to our habits and temperament.” Again, as with other examples of homologies, once we look past the outer layers of the arguments, the illusion drops away.

            This 96-98% similarity figure is based upon comparison of small sections of the human and chimp genomes. When one does a more thorough comparison of larger portions of the chromosomes, we get much lower percentages.

Genome-wide, only 70% of the chimpanzee DNA was similar to human under the most optimal alignment conditions. While, chimpanzees and humans share many localized protein-coding regions of high similarity, the overall extreme discontinuity between the two genomes defies evolutionary time-scales and dogmatic presuppositions about a common ancestor.[13]

That 70% similarity is a drastic reversal for homology claims. These higher claims of similarity are borderline deceptive, but have been very effective in duping many people for decades. Homologies like this are nothing more than conclusions based upon incomplete research.

            The human-chimpanzee relationship is an even deeper problem for evolution than just the genome comparisons. It also gets down to finding the actual genetic links that could prove the possibility of the physical changes we see. Dr. Paul Nelson, in a presentation at Biola University, described a short list of traits that set chimpanzees apart from humans physically. The list includes a baculum, a lack of pharyngeal air sacs, no chin, pigmented sclera, no eyebrows, and many others. If we hypothetically agreed with the 96-98% similarity in the two genomes, we still have an uphill battle to show that it is even possible to create all of these changes with only that 2-4% DNA change. If all those changes could occur with so little DNA variation, then we should be able to identify where the “switches” are that control them. The pigmentation in the eye in a chimp is black while in humans it is white. Shouldn’t that color change be a simple switch of a gene or two? But such things have been evading evolutionists. Could they possibly find one or two possible changes? Sure, but the list is incredibly long and varied for such a small DNA difference to account for. To lose a full bone (like the baculum), we are likely to see a much larger variation. Even if the DNA matched as much as they claimed, the homologies have very little strength behind their claims of common ancestry.

V. Conclusion

            Evolutionary homologies seem so conclusive, but as in the Wizard of Oz, once we peer behind the curtain, we find that the whole thing was a charade. The comparative anatomy posters in biology textbooks are deceptively used to push the Darwinian concept in dogmatic fashion, yet they lack the strength to stand on their own merits. If anyone dares to move the curtain of evolutionary dogmatism, they will find a theory that is crumbling under its own insinuations. Modern scientific investigation does not support homologous relationships; rather, it reveals it for what it really is: a modern myth.

Works Cited

  • Darwin, Charles. On the Origin of Species, Cambridge: Harvard University Press. (1964) 449.
  • Miller & Levine, Biology,  (New Jersey: Pearson Education Inc., 2014), 469-470.
  • Nelson, Paul. “The Role of Theology in Current Evolutionary Reasoning,” Biology & Philosophy. (October 1996), Volume 11, Issue 4, pp 493–517

[1] Miller & Levine, Biology,  (New Jersey: Pearson Education Inc., 2014), 469.

[2] Miller, Brandon. “Top 10 Useless Limbs (and Other Vestigial Organs),” Live Science (February 2005) https://www.livescience.com/11317-top-10-useless-limbs-vestigial-organs.html (accessed Oct. 10th, 2016).

[3] Martin, Loren G. “What is the function of the human appendix? Did it once have a purpose that has since been lost?” Scientific American (2017). https://www.scientificamerican.com/article/what-is-the-function-of-the-human-appendix-did-it-once-have-a-purpose-that-has-since-been-lost/ (accessed Oct. 11th, 2017)

[4] Caba, Justin. “10 Useless Human Body Parts: What You Do And Don’t Need.” Medical Daily (2017). http://www.medicaldaily.com/10-useless-human-body-parts-what-you-do-and-dont-need-297264

[5] Staehler, Richard A. “Anatomy of the Coccyx (Tailbone).” Spine Health (January 2017). https://www.spine-health.com/conditions/spine-anatomy/anatomy-coccyx-tailbone (accessed Oct. 11th, 2017)

[6] Reuell, Peter. “Status Shift for Whale Pelvic Bones,” Harvard Gazette (October 2014). https://news.harvard.edu/gazette/story/2014/10/status-shift-for-whale-pelvic-bones/ (accessed Oct. 11th, 2017).

[7] Nelson, Paul. “The Role of Theology in Current Evolutionary Reasoning,” Biology & Philosophy. (October 1996), Volume 11, Issue 4, pp 493–517

[8] Darwin, Charles. On the Origin of Species, Cambridge: Harvard University Press. (1964) 449.

[9] Richardson, M., Hanken, J., Gooneratne, M. et al. Anatomy & Embryology (1997) 196: 91. https://doi.org/10.1007/s004290050082

[10] Miller & Levine, Biology,  (New Jersey: Pearson Education Inc., 2014), 470.

[11]Koonin, Eugene V. and Wolf, Yuri, I. “The Common Ancestry of Life,” NCBI (2010). https://www.ncbi.nlm.nih.gov/Taxonomy/taxonomyhome.html/index.cgi?chapter=cgencodes (accessed Oct. 12th, 2017).

[12] Lovgren, Stefan “Chimps, Humans 96 Percent the Same, Gene Study Finds,”

 National Geographic News (August 2005). http://news.nationalgeographic.com/news/2005/08/0831_050831_chimp_genes.html (accessed Oct. 10th, 2017).

[13] Tomkins, Jeffrey P. “New Research Evaluationg Similarities Between Human and Chimpanzee DNA,” Institute of Creation Research (2013). http://www.icr.org/article/new-research-evaluating-similarities (accessed Oct. 12th, 2017).

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