Answering Scientific Questions on Neanderthal-Human Interbreeding

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By Fazale Rana – August 5, 2020

So don’t ask me no questions
And I won’t tell you no lies
And don’t ask me about my business
And I won’t tell you good-bye

“Don’t Ask Me No Questions”

—Ronnie Van Zandt and Gary Robert Rossington

One of my favorite rock bands of all time is Lynyrd Skynyrd. (That’s right…Skynyrd, baby!) I know their musical catalog forward and backwards. I don’t know if it is a good thing or not, but I am conversant with the history of most of the songs recorded by the band’s original lineup.

“Don’t Ask Me No Questions” was the first single released from their second studio album, Second Helping. The album also included “Sweet Home Alabama.” When juxtaposed with the success of “Sweet Home Alabama,” it’s ironic that “Don’t Ask Me No Questions” never even broke the charts.

An admonition to family and friends not to pry into their personal affairs, this song describes the exhaustion the band members felt after spending months on tour. All they want is peace and respite when they return home. Instead, they find themselves continuously confronted by unrelenting and inappropriate questions about the rock ‘n’ roll lifestyle.

As a Christian apologist, people ask me questions all the time. Yet, rarely do I find the questions annoying and inappropriate. I am happy to do my best to answer most of the questions asked of me—even the snarky ones posed by internet trolls. As of late, one topic that comes up often is interbreeding between modern humans and Neanderthals:

  • Is it true that modern humans and Neanderthals interbred?
  • If interbreeding took place, what does that mean for the credibility of the biblical account of human origins?
  • Did the children resulting from these interbreeding events have a soul? Did they bear the image of God?

Recently, an international team of investigators looking to catalog Neanderthal genetic contributions, surveyed a large sampling of Icelander genomes. This work generated new and unexpected insights about interbreeding between hominins and modern humans.1

No lie.

It came as little surprise to me when the headlines announcing this discovery triggered another round of questions about interbreeding between modern humans and Neanderthals. I will address the first two questions above in this article and the third one in a future post.

RTB’s Human Origins Model in 2005

To tell the truth, for a number of years I resisted the idea that modern humans interbred with Neanderthals and Denisovans. When Hugh Ross and I published the first edition of our book, Who Was Adam? (2005), there was no real evidence that modern humans and Neanderthals interbred. We took this absence of evidence as support for the RTB human origins model.

According to our model, Neanderthals have no evolutionary connection to modern humans. The RTB model posits that the hominins, such as Neanderthals and Denisovans, were creatures made by God that existed for a time and went extinct. These creatures had intelligence and emotional capacity (like most mammals), which enabled them to establish a culture. However, unlike modern humans, these creatures lacked the image of God. Accordingly, they were cognitively inferior to modern humans. In this sense, the RTB human origins model regards the hominins in the same vein as the great apes: intelligent, fascinating creatures in their own right that share some biological and behavioral attributes with modern humans (reflecting common design). Yet, no one would confuse a great ape and a modern human because of key biological distinctions and, more importantly, because of profound cognitive and behavioral differences.

When we initially proposed our model, we predicted that the biological differences between modern humans and Neanderthals would have made interbreeding unlikely. And if they did interbreed, then these differences would have prohibited the production of viable, fertile offspring.

Did Humans and Neanderthals Interbreed?

In 2010, researchers produced a rough draft sequence of the Neanderthal genome and compared it to modern human genomes. They discovered a closer statistical association of the Neanderthal genome with those from European and Asian people groups than with genomes from African people groups.2 The researchers maintained that this effect could be readily explained if a limited number of interbreeding events took place between humans and Neanderthals in the eastern portion of the Middle East, roughly 45,000 to 80,000 years ago, just as humans began to migrate around the world. This would explain why non-African populations display what appears to be a 1 to 4 percent genetic contribution from Neanderthals while African people groups have no contribution whatsoever.

At that time, I wasn’t entirely convinced that modern humans and Neanderthals interbred because there were other ways to explain the statistical association. Additionally, studies of Neanderthal genomes indicate that these hominins lived in small insular groups. At that time, I argued that the low population densities of Neanderthals would have greatly reduced the likelihood of encounters with modern humans migrating in small populations. It seemed to me that it was unlikely that interbreeding occurred.

Other studies demonstrated that Neanderthals most likely were extinct before modern humans made their way into Europe. Once again, I argued that the earlier extinction of Neanderthals makes it impossible for them to have interbred with humans in Europe. Extinction also raises questions about whether the two species interbred at all.

The Case for Interbreeding

Despite these concerns, in the last few years I have become largely convinced that modern humans and Neanderthals interbred. Studies such as the one cataloging the Neanderthal contribution to the genomes of Icelanders leave me little choice in the matter.

Thanks to the deCODE project, the genome sequences for nearly half the Icelandic population have been determined. An international team of collaborators made use of this data set, analyzing over 27,500 Icelander genomes for Neanderthal contribution using a newly developed algorithm. They detected over 14.4 million fragments of Neanderthal DNA in their data set. Of these, 112,709 were unique sequences that collectively constituted 48 percent of the Neanderthal genome.

This finding has important implications. Even though individual Icelanders have about a 1 to 4 percent Neanderthal contribution to their genomes, the precise contribution differs from person to person. And when these individual contributions are combined it yields Neanderthal DNA sequences that cover nearly 50 percent of the Neanderthal genome. This finding aligns with previous studies which demonstrate that, collectively, across the human population Neanderthal sequences are distributed throughout 20 percent of the human genome. And 40 percent of the Neanderthal genome can be reconstructed from Neanderthal sequences found in a sampling of Eurasian genomes.3

Adding to this evidence for interbreeding are studies that characterized ancient DNA recovered from several modern human fossil remains unearthed in Europe, dating between about 35,000 and 45,000 years in age. The genomes of these ancient modern humans contain much longer stretches of Neanderthal DNA than what’s found in contemporary modern humans, which is exactly what would be expected if modern humans interbred with these hominins.4

As I see it, interbreeding is the only way to make sense of these results.

Are Humans and Neanderthals the Same Species?

Because the biological species concept (BSC) defines a species as an interbreeding population, some people argue that modern humans and Neanderthals must belong to the same species. This perspective is common among young-earth creationists who see Neanderthals as a subset of humanity.

This argument fails to take into account the limitations of the BSC, one being the phenomenon of hybridization. Mammals that belong to separate species have been known to interbreed and produce viable—even fertile—offspring called hybrids. For example, lions and tigers in captivity have interbred successfully—yet both parent animals remain considered separate species. I would argue that the concept of hybridization applies to the interbreeding that took place between modern humans and Neanderthals.

Even though it appears that modern humans and Neanderthals interbred, other lines of evidence indicate that these two hominins were distinct species. Significant anatomical differences exist between the two. The most profound difference is skull anatomy and, consequently, brain structure

blog__inline--answering-scientific-questions-on-neanderthal-human-interbreeding-part-1Anatomical Differences between Human and
Neanderthal Skulls. Image credit: Wikipedia.

Additionally, Neanderthals possessed a hyper-polar body design, consisting of a stout, barrel-shaped body with shortened limbs to help with heat retention. Neanderthals and modern humans display significant developmental differences as well. Neanderthals, for example, spent a minimal time in adolescence compared to modern humans. The two hominins also exhibit significant genetic differences (which includes differences in gene expression patterns), most notably for genes that play a role in cognition and cognitive development. Most critically, modern humans and Neanderthals display significant behavioral differences that stem from substantial differences in cognitive capacity.

Along these lines, it is important to note that researchers believe that the resulting human-Neanderthal hybrids lacked fecundity.5 As geneticist David Reich notes, “Modern humans and Neanderthals were at the edge of biological compatibility.”6

In other words, even though modern humans and Neanderthals interbred, they displayed sufficient biological differences that are extensive enough to justify classing the two as distinct species, just as the RTB model predicts. The extensive behavioral differences also validate the view that modern humans are exceptional and unique in ways that align with the image of God—again, in accord with RTB model predictions.

Is the RTB Human Origins Model Invalid?

It is safe to say that most paleoanthropologists view modern humans and Neanderthals as distinct species (or at least distinct populations that were isolated from one another for over 500,000 to 600,000 years). From an evolutionary perspective, modern humans and Neanderthals share a common evolutionary ancestor, perhaps Homo heidelbergensis, and arose as separate species as the two lineages diverged from this ancestral population. In the evolutionary framework, the capacity of Neanderthals and modern humans to interbreed reflects their shared evolutionary heritage. For this reason, some critics have pointed to the interbreeding between modern humans and other hominins as a devastating blow to the RTB model and as clear-cut evidence for human evolution.

In light of this concern, it is important to recognize that the RTB human origins model readily accommodates the evidence for interbreeding between modern humans and Neanderthals. Instead of reflecting a shared evolutionary ancestry, within a creation model framework, the capacity for interbreeding is a consequence of the biological designs shared by modern humans and Neanderthals.

The RTB model’s stance that shared biological features represent common design taps into a rich tradition within the history of biology. Prior to Charles Darwin, life scientists such as the preeminent biologist Sir Richard Owen, routinely viewed homologous systems as manifestations of archetypal designs that resided in the Mind of the First Cause. The RTB human origins model co-opts Owen’s ideas and applies them to the biological features modern humans share with other creatures, including the hominins.

Without question, the discovery that modern humans interbred with other hominins, stands as a failed prediction of the initial version of the RTB human origins model. However, this discovery can be accommodated by revising the model–as is often done in science. Of course, this leads to the next set of questions.

  • Is there biblical warrant to think that modern humans interbred with other creatures?
  • Did the modern human-Neanderthal hybrid have a soul? Did it bear God’s image?

I will take on these questions in the next article. And I am telling you no lie.

Resources

Biological Differences between Humans and Neanderthals

Archetype Biology

Endnotes
  1. Laurits Skov et al., “The Nature of Neanderthal Introgression Revealed by 27,566 Icelandic Genomes,” Nature (published online April 22, 2020), doi:10.1038/s49586-020-2225-9.
  2. Fazale Rana with Hugh Ross, Who Was Adam? A Creation Model Approach to the Origin of Humanity, 10-Year Update (Covina, CA: RTB Press, 2015), 301–12.
  3. Sriram Sankararaman et al., “The Genomic Landscape of Neanderthal Ancestry in Present-Day Humans,” Nature 507 (2014): 354–57, doi:10.1038/nature12961; Benjamin Vernot and Joshua M. Akey, “Resurrecting Surviving Neandertal Lineages from Modern Human Genomes,” Science 343 (2014): 1017–21, doi: 10.1126/science.1245938.
  4. Rana with Ross, Who Was Adam?, 304–5.
  5. Sankararaman et al., “Genomic Landscape,” 354–57, Vernot and Akey, “Resurrecting Surviving Neandertal Lineages,” 1017–21.
  6. Ewen Callaway, “Modern Human Genomes Reveal Our Inner Neanderthal,” Nature News (January 29, 2014), https://www.nature.com/news/modern-human-genomes-reveal-our-inner-neanderthal-1.14615.

Reprinted with permission by the author

Original article at:
https://reasons.org/explore/blogs/the-cells-design

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