Salivary Protein: Evolution or Just Adaptation?

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Whether discussing neo-Darwinian evolution, emergent evolution, or extended synthesis, these versions of evolution are all typically defined as simply change over time. Yet this vague definition leaves many unanswered questions. What types of change? What length of time? What causes these changes?

Each of these evolution versions is offered as an explanation for the origin and diversity of all life on earth, but examples of mere change offer little insight into the genetic events involved. Only specific types of changes will provide the evolutionary mechanism necessary to account for all of life’s complexity and diversity.

Within this broad definition, the evolutionary literature has tended to refer to virtually any documented biological change as a demonstration of evolution. An excellent example of this is provided by evolutionists’ interpretation of variations in a salivary gene. Variation of salivary proteins is associated with changes in diet and exposure to different pathogens.1 For example, different salivary proteins help in digestion of starch and even affect the textural feel of starch-containing foods.

A recent study of the salivary mucin-7 gene (MUC7) demonstrated there was genetic variation of this gene among different primate species.2 This gene codes for a protein found in saliva secretions of placental mammals.3 While this protein may contribute to the lubrication function of saliva, it likely has a more significant role as part of the saliva’s antimicrobial properties.4

MUC7 was found to vary in the number of tandem repeats5 among different primates.6 African green monkeys had the most tandem repeats (11–12 repeats), while gorillas had the fewest (4–5 repeats). Humans were in the middle range with 5–6 repeats. Presumably, these variations reflect adaptation to the differing pathogens to which each species is exposed.

The difference in tandem repeats is claimed as another example of evolution. More specifically, the difference is offered as an example of rapid evolution. Alteration of the number of tandem repeats in various genes is suggested to have a possible role in the evolution of different organisms.7 The assumption in this recent study is that an original version of MUC7 began to vary in its number of tandem repeats as mammals evolved and were exposed to different pathogens. Thus, the tandem-repeat difference of MUC7 in gorillas, chimpanzees, and humans is presumed to illustrate how these repeats were involved in primate/human evolution.8 Although the exact effect and role of the differing repeats is still uncertain.

This recent MUC7 study appears to be another example where evolution is included in the interpretation (and article title), but the data is really just about variation. Nothing has evolved, in the sense of something new or innovating being formed. The MUC7 gene is already present in humans and in each primate that was studied. The report is simply appealing to evolution in the form of mere change.

Notice a Pattern?

Other studies follow a similar pattern. Demonstration of gene duplication, transposition, deletions, and recombination are frequently offered as examples of evolutionary change. Yet, none of these genetic events account for the origin of genes or other genetic systems.

Vanilla definitions of evolution do little to distinguish the predictions of an evolution model from that of a biblical creation model. Both predict that biological changes will occur over time, but they differ on the types of changes that can naturally occur. All versions of evolution predict nearly unlimited levels of change resulting in universal common descent—the concept that all life has arisen and diversified from a shared common ancestor deep in earth history. In contrast, the biblical creation model predicts only limited changes will occur within the created kinds. Humans have always been humans, and do not share a common ancestry with chimpanzees, dogs, fish, or rose bushes.

Physical changes consistently occur in many animals. Documenting the genetics behind such changes can provide useful information. But, when such variations are consistently referred to as “evolution,” these references present a misleading concept in both the scientific community and the general public. Peppering the word evolution in innumerable journal articles and textbooks does not make universal common descent more scientifically viable.

Instead, universal common descent requires the formation of new genes and new genetic systems. Only with such genetic developments can invertebrates become vertebrates and reptiles become mammals. It is at this level of genetic evidence that the evolutionary literature becomes vague and nondescript. This is exemplified by the current salivary gene study. Differences in tandem repeats of a gene do not offer insight into the origin of that gene (or any gene). In fact, difference of repeat sequences requires the pre-existence of those repeated sequences.

Speculations have been offered of the evolutionary origin of MUC7,9 but no clear evolutionary pathway is known. One proposal is that perhaps the gene originated from the mutation of a duplicated copy of the SCCP gene.10 However, mutations have not been shown to actually convert a gene to a different gene.11 Also, such historical reconstructions are simply speculation and are not evidence of an evolutionary origin or lineage since an evolutionary lineage is assumed as part of the reconstruction.

The biblical creation model proposes that the creator pre-programmed the capacity for change (even rapid change) within organisms. As suggested by this recent study, tandem repeats within different species may even enable them to adapt to a changing array of pathogens. Thus, variation of tandem repeats of segments within pre-existing genes fits within a biblical creation model. In contrast, this variation of repeats offers no insight into an evolutionary origin of any salivary gene and is simply an example of adaptive variation.

Footnotes

  1. Rebecca C. Iskow, Omer Gokcumen, and Charles Lee, “Exploring the Role of Copy Number Variants in Human Adaptation,” Trends in Genetics 28, no. 6 (2012): 245–257.
  2. Duo Xu et. al, “Recent evolution of the salivary mucin MUC7,” Scientific Reports 6 (2016): doi:10.1038/srep31791.
  3. Stefan Ruhl, “The Scientific Exploration of Saliva in the Post-proteomic Era: From Database Back to Basic Function,” Expert Review of Oroteomics 9, no. 1 (2012): 85–96.
  4. Libuse A. Bobek and Hongsa Situ, “MUC7 20-Mer: Investigation of Antimicrobial Activity, Secondary Structure, and Possible Mechanism of Antifungal Action,” Antimicrobial Agents and Chemotherapy 47, no. 2 (2003): 643–652.
  5. Tandem repeats occur when one or more directly adjacent nucleotides of DNA are repeated. Most tandem repeats are short (2–5 nucleotides) and repeated at least five times (e.g., GAGAGAGAGA), although larger repeats of 10–60 nucleotides sometimes occur.
  6. Xu et al., “Recent Evolution of the Salivary Mucin MUC7.”
  7. John W. Fondon and Harold R. Garner, “Molecular Origins of Rapid and Continuous Morphological Evolution,” Proceedings of the National Academy of Sciences 101, no. 52 (2004): 18058–18063; Rita Gemayel, Marcelo D. Vinces, Matthieu Legendre, and Kevin J. Verstrepen, “Variable Tandem Repeats Accelerate Evolution of Coding and Regulatory Sequences,” Annual Review of Genetics 44 (2010): 445–477; Rita Gemayel, Janice Cho, Steven Boeynaems, and Kevin J. Verstrepen, “Beyond Junk-variable Tandem Repeats as Facilitators of Rapid Evolution of Regulatory and Coding Sequences,” Genes 3, no. 3 (2012): 461–480; and Yechezkel Kashi and David G. King, “Simple Sequence Repeats as Advantageous Mutators in Evolution,” Trends in Genetics 22, no. 5 (2006): 253–259.
  8. Iskow et al., “Exploring the Role of Copy Number Variants in Human Adaptation.”
  9. Sekhar Duraisamy, Selvi Ramasamy, Surender Kharbanda, and Donald Kufe, “Distinct Evolution of the Human Carcinoma-associated Transmembrane Mucins, MUC1, MUC4 AND MUC16,” Gene 373 (2006): 28–34; and Tiange Lang, Gunnar C. Hansson, and Tore Samuelsson, “Gel-forming Mucins Appeared Early in Metazoan Evolution,” Proceedings of the National Academy of Sciences 104, no. 41 (2007): 16209–16214.
  10. Kazuhiko Kawasaki and Kenneth M. Weiss, “Mineralized Tissue and Vertebrate Evolution: The Secretory Calcium-binding Phosphoprotein Gene Cluster,” Proceedings of the National Academy of Sciences 100, no. 7 (2003): 4060–4065.
  11. Kevin Anderson and Jean Lightner, “The Challenge of Mount Improbable,” Creation Research Society Quarterly 52, no. 4 (2016): 244–248; and Kevin Anderson, “How Are New Genes Made?” Answers in Depth 11, (2016): https://answersingenesis.org/genetics/how-are-new-genes-made/.

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