Star-Crossed Lovers: Resolving the Neanderthal-Human Love Affair Debate

Chances are you believe you have met a Neanderthal at least once in your lifetime.  I met my first "Neanderthal" my junior year of college.  He was a young man who identified himself as a Neanderthal based on an exaggerated nuchal crest (bony ridge at the back of the skull) that he identified as an occipital bun, a characteristic that is diagnostic of Neanderthals.  He believed that he was a Neanderthal as a girlfriend of his had just taken an anthropology course and said that he had several features that were reminiscent of Neanderthals.  At the time I laughed and didn't think too much of it because there was no evidence to support his assertions, but recent investigations over the last few years have changed that viewpoint and provide support for this young man's assertions.  Today's blog post is dedicated to discussing the now resolved debate about sexual relations and the production of viable offspring between Neanderthal and Archaic Homo. sapiens couplings.

Neanderthals have had one of the most colorful histories in regards to how they have been interpreted in the paleoanthropological community.  They were originally depicted as brutish, hunched over, dim-witted members of the human lineage, and some of the times they were depicted as the slightly funny looking cousins of modern Homo. sapiens.  Both are inaccurate depictions of Neanderthals that still resonate today.  

These inaccurate depictions may have led to several scholars reluctance to acknowledge the possible relations and viable offspring between Neanderthals and Archaic Homo. sapiens.  Both species coexisted for a period of time, meaning that couplings between them was possible.  Whether or not said unions occurred and successfully produced offspring was hotly debated by many paleoanthropologists.  Paleoanthropologists who did not believe such unions occurred cited morphological and growth and development differences between the two species as sufficient evidence as evidence against successful Neanderthal and Archaic Homo. sapiens couplings.  Other scholars who believed such unions did occur and produced viable offspring cited small similarities in DNA between the two species.  These genetic studies, however, were not without criticisms, particularly as paleo-DNA analyses were new and delicate and prone to inaccuracies as a result.  

This debate, however, was resolved in 2010 when scholars at the Max Plank Institute successfully sequenced the entire Neanderthal genome.  Scholars at the Max Plank Institute compared Neanderthal DNA to human DNA and noted that several populations around the globe had Neanderthal DNA present in their modern Homo. sapiens DNA (Figure 1).  The modern populations that have Neanderthal DNA present in their own DNA correspond to the geographical expanse of Neanderthal populations in the past or, in the case of East Asia, Polynesia, and Australia, are derived from populations that came from these areas.  This pattern makes sense as Neanderthals would have had greater access to Archaic Homo. sapiens mating partners that existed in their same geographical areas, which is similar to modern Homo. sapiens mating preferences where we find mating partners within a small geographical ranges.  

Figure 1: Map Demonstrating % of Neanderthal DNA in Modern Human Populations (Source: Live Science)

But why did Archaic Homo. sapiens elect to breed with Neanderthals?  It appears that there were some genetic reasons that may have led Archaic Homo. sapiens women to choose Neanderthal males as their sexual partners and the fathers of their offspring.  Neanderthals had a suite of immunity genes known as HLA genes that may have provided them a longer life span* or a more healthy appearance* that was seen as attractive in some way to Archaic Homo. sapiens females who bore their children.  These HLA genes were passed on to their offspring and continue to exist in modern Homo. sapiens populations.  But these were not the only genes that came from Neanderthals and continue to exist in modern Homo. sapiens populations.  Neanderthals also provided genes that increased Homo. sapiens jaw size; allowed us to have rosy cheeks; and thicker skin, thick, straight hair.  Neanderthals may have also provided alleles for pale skin and red hair, but this information is highly contentious and not fully explored by scholars.

All was not well in regards to the gene flow from Neanderthals to Archaic Homo. sapiens.  Modern Homo. sapiens also received several not-so-great genes from Neanderthals.  From Neanderthals modern Homo. sapiens became more susceptible to several diseases and conditions, including Lupus, an autoimmune disease; Type II Diabetes, an insulin deficiency; Chrone's Disease, a gastro-intestinal disease; and Biliary Cirrhosis, a liver disease.  Also, while Neanderthals never consumed tobacco or possibly nicotine based plants something in their genetics that they passed on to modern Homo. sapiens provided us with a predisposition toward nicotine addiction.  

Ultimately, this evidence supports the position that Neanderthals and Archaic Homo. sapiens did breed and were successfully producing offspring.  This evidence, however, goes beyond resolving this debate.  It provides scholars with insights into what it means to be human and where hominid ancestors exist within the definition of human.  The next few years should be exciting as scholars evaluate and redefine human evolution based on this new evidence, but on a lighter note the lay public can confidently say that we all know at least one (or more) Neanderthals because they-or at least parts of them-still exist today.  

*Author's Note: Neither I nor any scholars have definitive proof of what led Archaic Homo. sapiens females to choose Neanderthal males as their mating partners.  This information is my personal conjecture based on the principles of natural selection.  In order for genes to be passed on individuals must live long enough to successfully breed and pass on those genes to offspring.  The HLA genes in Neanderthals may have allowed them to live longer than Archaic Homo. sapiens males and therefore provided more opportunities to breed with Archaic Homo. sapiens females.  Alternatively, the offspring of these unions may have been more successful than offspring of solely Archaic Homo. sapiens unions and therefore those hybrid offspring were more reproductively successful due to their HLA gene suite.