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Ancient DNA Indicates Modern Humans Are One-of-a-Kind

By Fazale Rana - February 19, 2020
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The wonderful thing about tiggers
Is tiggers are wonderful things!
Their tops are made out of rubber
Their bottoms are made out of springs!
They’re bouncy, trouncy, flouncy, pouncy
Fun, fun, fun, fun, fun!
But the most wonderful thing about tiggers is
I’m the only one!1

With eight grandchildren and counting (number nine will be born toward the end of February), I have become reacquainted with children’s stories. Some of the stories my grandchildren want to hear are new, but many of them are classics. It is fun to see my grandchildren experiencing the same stories and characters I enjoyed as a little kid.

Perhaps my favorite children’s book of all time is A. A. Milne’s (1882–1956) Winnie-the-Pooh. And of all the characters that populated Pooh Corner, my favorite character is the ineffable Tigger—the self-declared one-of-a-kind.

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A. A. Milne. Credit: Wikipedia

For many people (such as me), human beings are like Tigger. We are one-of-a-kind among creation. As a Christian, I take the view that we are unique and exceptional because we alone have been created in God’s image.

For many others, the Christian perspective on human nature is unpopular and offensive. Who are we to claim some type of special status? They insist that humans aren’t truly unique and exceptional. We are not fundamentally different from other creatures. If anything, we differ only in degree, not kind. Naturalists and others assert that there is no evidence that human beings bear God’s image. In fact, some would go so far as to claim that creatures such as Neanderthals were quite a bit like us. They maintain that these hominins were “exceptional,” just like us. Accordingly, if we are one-of-a-kind it is because, like Tigger, we have arrogantly declared ourselves to be so, when in reality we are no different from any of the other characters who make their home at Pooh Corner.

Despite this pervasive and popular challenge to human exceptionalism (and the image-of-God concept), there is mounting evidence that human beings stand apart from all extant creatures (such as the great apes) and extinct creatures (such as Neanderthals). This growing evidence can be marshaled to make a scientific case that as human beings we, indeed, are image bearers.

As a case in point, many archeological studies affirm human uniqueness and exceptionalism. (See the Resources section for a sampling of some of this work.) These studies indicate that human beings alone possess a suite of characteristics that distinguish us from all other hominins. I regard these qualities as scientific descriptors of the image of God:

  • Capacity for symbolism
  • Ability for open-ended manipulation of symbols
  • Theory of mind
  • Capacity to form complex, hierarchical social structures

Other studies have identified key differences between the brains of modern humans and Neanderthals. (For a sample of this evidence see the Resources section.) One key difference relates to skull shape. Neanderthals (and other hominins) possessed an elongated skull. In contradistinction, our skull shape is globular. The globularity allows for the expansion of the parietal lobe. This is significant because an expanded parietal lobe explains a number of unique human characteristics:

  • Perception of stimuli
  • Sensorimotor transformation (which plays a role in planning)
  • Visuospatial integration (which provides hand-eye coordination)
  • Imagery
  • Self-awareness
  • Working and long-term memory

Again, I connect these scientific qualities to the image of God.

Now, two recent studies add to the case for human exceptionalism. They involve genetic comparisons of modern humans with both Neanderthals and Denisovans. Through the recovery and sequencing of ancient DNA, we have high quality genomes for these hominins that we can analyze and compare to the genomes of modern humans.

While the DNA sequences of protein-coding genes in modern human genomes and the genomes of these two extant hominins is quite similar, both studies demonstrate that the gene expression is dramatically different. That difference accounts for anatomical differences between humans and these two hominins and suggests that significant cognitive differences exist as well.

Differences in Gene Regulation

To characterize gene expression patterns in Neanderthals and Denisovans and compare them to modern humans, researchers from Vanderbilt University (VU) used statistical methods to develop a mathematical model that would predict gene expression profiles from the DNA sequences of genomes.2 They built their model using DNA sequences and gene expression data (measured from RNA produced by transcription) for a set of human genomes. To ensure that their model could be used to assess gene expression for Neanderthals and Denisovans, the researchers paid close attention to the gene expression pattern for genes in the human genome that were introduced when modern humans and Neanderthals presumably interbred and compared their expression to human genes that were not of Neanderthal origin.

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The Process of Gene Expression. Credit: Shutterstock

With their model in hand, the researchers analyzed the expression profile for nearly 17,000 genes from the Altai Neanderthal. Their model predicts that 766 genes in the Neanderthal genome had a different expression profile than the corresponding genes in modern humans. As it turns out, the differentially expressed genes in the Neanderthal genomes failed to be incorporated into the human genome after interbreeding took place, suggesting to the researchers that these genes are responsible for key anatomical and physiological differences between modern humans and Neanderthals.

The VU investigators determined that these 766 differentially expressed genes play roles in reproduction, forming skeletal structures, and the functioning of cardiovascular and immune systems.

Then, the researchers expanded their analysis to include two other Neanderthal genomes (from the Vindija and Croatian specimens) and the Denisovan genome. The researchers learned that the gene expression profiles of the three Neanderthal genomes were more similar to one another than they were to either the gene expression patterns of modern human and Denisovan genomes.

This study clearly demonstrates that significant differences existed in the regulation of gene expression in modern humans, Neanderthals, and Denisovans and that these differences account for biological distinctives between the three hominin species.

Differences in DNA Methylation

In another study, researchers from Israel compared gene expression profiles in modern human genomes with those from and Neanderthals and Denisovans using a different technique. This method assesses DNA methylation.3 (Methylation of DNA downregulates gene expression, turning genes off.)

Methylation of DNA influences the degradation process for this biomolecule. Because of this influence, researchers can determine the DNA methylation pattern in ancient DNA by characterizing the damage to the DNA fragments isolated from fossil remains.

Using this technique, the researchers measured the methylation pattern for genomes of two Neanderthals (Altai and Vindija) and a Denisovan and compared these patterns with genomes recovered from the remains of three modern humans, dating to 45,000 years in age, 8,000 years in age, and 7,000 years in age, respectively. They discovered 588 genes in modern human genomes with a unique DNA methylation pattern, indicating that these genes are expressed differently in modern humans than in Neanderthals and Denisovans. Among the 588 genes, researchers discovered some that influence the structure of the pelvis, facial morphology, and the larynx.

The researchers think that differences in gene expression may explain the anatomical differences between modern humans and Neanderthals. They also think that this result indicates that Neanderthals lacked the capacity for speech.

What Is the Relationship between Modern Humans and Neanderthals?

These two genetic studies add to the extensive body of evidence from the fossil record, which indicates that Neanderthals are biologically distinct from modern humans. For a variety of reasons, some Christian apologists and Intelligent Design proponents classify Neanderthals and modern humans into a single group, arguing that the two are equivalent. But these two studies comparing gene regulation profiles make it difficult to maintain that perspective.

Modern Humans, Neanderthals, and the RTB Human Origins Model

RTB’s human origins model regards Neanderthals (and other hominins) as creatures made by God, without any evolutionary connection to modern humans. These extraordinary creatures walked erect and possessed some level of intelligence, which allowed them to cobble together tools and even adopt some level of “culture.” However, our model maintains that the hominins were not spiritual beings made in God’s image. RTB’s model reserves this status exclusively for modern humans.

Based on our view, we predict that biological similarities will exist among the hominins and modern humans to varying degrees. In this regard, we consider the biological similarities to reflect shared designs, not a shared evolutionary ancestry. We also expect biological differences because, according to our model, the hominins would belong to different biological groups from modern humans.

We also predict that significant cognitive differences would exist between modern humans and the other hominins. These differences would be reflected in brain anatomy and behavior (inferred from the archeological record). According to our model, these differences reflect the absence of God’s image in the hominins.

The results of these two studies affirm both sets of predictions that flow from the RTB human origins model. The differences in gene regulation between modern human and Neanderthals is precisely what our model predicts. These differences seem to account for the observed anatomical differences between Neanderthals and modern humans observed from fossil remains.

The difference in the regulation of genes affecting the larynx is also significant for our model and the idea of human exceptionalism. One of the controversies surrounding Neanderthals relates to their capacity for speech and language. Yet, it is difficult to ascertain from fossil remains if Neanderthals had the anatomical structures needed for the vocalization range required for speech. The differences in the expression profiles for genes that control the development and structure of the larynx in modern humans and Neanderthals suggests that Neanderthals lacked the capacity for speech. This result dovetails nicely with the differences in modern human and Neanderthal brain structure, which suggest that Neanderthals also lacked the neural capacity for language and speech. And, of course, it is significant that there is no conclusive evidence for Neanderthal symbolism in the archeological record.

With these two innovative genetic studies, the scientific support for human exceptionalism continues to mount. And the wonderful thing about this insight is that it supports the notion that as human beings we are the only ones who bear God’s image and can form a relationship with our Creator.

Resources

Behavioral Differences between Humans and Neanderthals

Biological Differences between Humans and Neanderthals

Endnotes
  1. Richard M. Sherman and Robert B. Sherman, composers, “The Wonderful Thing about Tiggers” (song), released December 1968.
  2. Laura L. Colbran et al., “Inferred Divergent Gene Regulation in Archaic Hominins Reveals Potential Phenotypic Differences,” Nature Evolution and Ecology 3 (November 2019): 1598-606, doi:10.1038/s41559-019-0996-x.
  3. David Gokhman et al., “Reconstructing the DNA Methylation Maps of the Neandertal and the Denisovan,” Science 344, no. 6183 (May 2, 2014): 523–27, doi:1126/science.1250368; David Gokhman et al., “Extensive Regulatory Changes in Genes Affecting Vocal and Facial Anatomy Separate Modern from Archaic Humans,” bioRxiv, preprint (October 2017), doi:10.1101/106955.

Category
  • Image of God
  • Neanderthals/Hominids
  • Human Uniqueness
  • Human Origins
Tags
  • speech
  • language
  • gene regulation
  • gene expression
  • Ancient DNA
  • Blogs

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