Were the Neanderthals Human?

(a continuation of "Who was Mitochondrial Eve")

 

All Europeans have some small measure of Neanderthal DNA within the mix received from both parents.  Even so, no one alive today has been found to have a Neanderthal mitochondrial DNA signature or Y-chromosome DNA signature.  However, the mixed autosomal DNA within each of us proves that at some point in our ancestral past, people with European descent connect to Neanderthals. Many scientists classify Neanderthals as Homo sapiens neanderthalensis, a subset of the human branch, rather than a parallel branch. If we include the Neanderthals, our common maternal ancestor is further back in our ancestry than Mitochondrial Eve.  Neanderthals lived in Europe for about 350,000 years—and in the Middle East even longer.  Neanderthals’ ancestors lived in Africa 600,000 years ago—nearly three times older than the “Mitochondrial Eve” of the currently living human population.



This Neanderthal reconstruction is from the
Neanderthal Museum in Mettmann, Germany

My 23andMe DNA test and National Geographic DNA test both confirm that 3.2% of my uniquely human DNA markers are specifically Neanderthal.  That’s a small percent, but it says something special about my ancestry 25,000 years ago. Archeological evidence reveals Neanderthals to have lived in southern Europe up to about 25,000 years ago.  Their extinction was not exactly a genetic extinction, but rather, an assimilation.  My anatomically modern human ancestors moved from Africa through the Middle East and began to arrive in Europe about 43,000 years ago.  For nearly 20,000 years there existed an admixture of these populations—Neanderthals who resided in Europe, and the more sender, agile, anatomically modern humans, who arrived in Europe from the Levant.  Modern humans overtook the Neanderthals, yet they remained strong enough to leave their mark on 3.2% of my DNA.

Approximately a thousand human generations elapsed within the last 25,000 years.  That’s a lot of ancestors to document.  Of course many of our ancestral lineages converge together much more recently than 25,000 years ago.  My DNA suggests that 3.2% of those ancestors were Neanderthal, having distinctive mitochondrial DNA as found in my DNA comparison report. While Neanderthal autosomal DNA survives in the present human population, Neanderthal mitochondrial DNA at some point became extinct.  We don’t know when that extinction occurred, except to say that it is certainly more recent than our most recent archaeological samples of Neanderthal—more recent than 25,000 years ago.

If we bundle these Neanderthal ancestors into the category of what it means to be human, we push the convergence point of all humans back much further in time. The African ancestors of Neanderthals and anatomically modern humans converged between 600,000 and 800,000 years ago.  Personally, I classify Neanderthals as human.  They are certainly closer to anatomically modern humans than any other primate alive today, even with their own distinctive features included.

Anthropologists who study human evolution categorize these earlier ancestors as “archaic humans.”  If we look back 600,000 or more years, there are clear physiological differences between us and our ancestors in the archeological record.  There are also clear intellectual differences.  Should we consider these ancestors human?   It depends on our definition of human.  We have archaeological evidence that archaic humans utilized fire as early as a million years ago.  Our means of successfully controlling fire (at least some of the time) sets us apart from the rest of nature.  This mastery of fire included a complex level of imagination, discernment of risk, and very likely was combined with a sense of spirituality—all distinctive characteristics of humans. 

I’ll defend that the definition of human should be pushed back even further than our mastery of fire.  At some point in our ancestry there was a first person to imagine where the sun went after it set on the horizon at night.  This person, of course, had no idea where the sun escaped only to return on the opposite horizon the next morning. But somehow this early ancestor was able to imagine the question, and convey that message to others.  After the first human raises the question, of course there were others who pretended to know the answer.  This is a new level of socialization, again, as far as we know, distinct among humans.

The sun always returned on the other end of the sky the next morning.  These repeating cycles, built into nature itself, gave our ancestors the necessary level of order combined with mystery to begin a voyage of discovery.  That voyage led to the mastery of fire and to deeper questions.  Fire is here with us, but also in the sky. We need fire for warmth and light, yet fire can also destroy us.  Water destroys fire. We need water for life, yet water can also destroy us.  All the basic questions of life emerge out of our relationship with nature.

At what time in prehistory do we begin to ask questions of our experiences?

For countless generations, our ancestors went into the river to bathe, to cool down, to play, to drink.  For countless generations, our ancestors felt the flow of that water.  Yet at some point there was a first person who began to raise new questions.  Looking upstream, she pondered, “Where does this water begin?”  Looking downstream, she pondered, “Where does this water lead?”  These are human questions.  These questions are our own way to engage the mystery that surrounds us, the mystery that is in us. 

I think it’s these questions, ones that occurred very early in our ancestry, that make us human.

 

Who is "Mitochondrial Eve?"

In the Biblical account, after the first humans were banished from Eden, Adam named his wife “Eve,” a name symbolizing she would become “mother of all the living” (Gen. 3:20).  Our mitochondrial DNA also reveals that we descend from a common female ancestor, and hence we colloquially call this ancestor “Mitochondrial Eve.”  Who are we talking about when we use the term “Mitochondrial Eve?” 

A 1988 article by Newsweek is among the
first popular articles to discuss
Mitochondrial Eve. 

Mitochondrial Eve is defined by geneticists as the most recent matrilineal ancestor of all humans alive today.  Since mitochondrial DNA is inherited directly from one’s mother, uncombined with any DNA of a male ancestor, it can only change due to mutations.  Those mutations are traceable, through maternal ancestry.  The mutations are nested, in that a certain mutation, let’s name it “B” always occurs when “A” is also present.  However, the opposite is not true: “A” can be present without “B.” Therefore one can determine which mutations occurred more recently and which ones are more ancient.   In this example “A” is older than “B.”  This nesting pattern is the scientific basis behind the study of cladistics.

As we trace mtDNA haplotypes back through time we encounter less and less human genetic variation, and ultimately converge to a single, common matriarchal ancestor.  My haplotype T2b2, descends in an unbroken chain from T2b > T2 > T > JT > R2’JT > R > N > L3, and then  through several steps in haplogroup L back to Mitochondrial Eve.  Every person’s tree will lead back to Mitochondrial Eve. Although we cannot pinpoint an exact generation or date in which the maternal convergence of all humans occurred, it was sometime around 10,000 generations ago, approximately 200,000 years ago.  However, don’t get caught up on this convergence as a specific “event” in its own time. This convergence only has meaning from the perspective of our modern time (in this generation). Here’s why:

Think of it this way.  The set of humans presently alive is approximately 7.3 billion. This large number is only a subset of the number of humans who have ever existed.  If, say 500 years ago, we were able to take DNA samples from across the ethnic groups of humans alive, we would find lineages that have since become extinct, particularly among indigenous peoples whose lineages have been exterminated by the impact of colonialism.  Some of those extinct lineages, particularly in Africa, would descend from the basal branches of our current tree. Therefore the “Mitochondrial Eve” of 500 years ago was an earlier ancestor of the “Mitochondrial Eve” we have today.  The trunk of the tree would need to be extended back further to take into account the lineages that went extinct.  The female ancestor that unites all people living 500 years ago would have herself lived earlier than Mitochondrial Eve, as defined today.

We should also note that basal lineages are no closer to our ancestors than ourselves.  We are all the same distance, both in generations and time, from our early ancestors, whether we are African, Asian, European or Native American.  There is more human genetic diversity in Africa, so it is clear that continent is our origin, however it is a misrepresentation to believe that basal branches have a closer connection to our ancestors.

Typical male response to the bigger questions of life?

In no case is Mitochondrial Eve the sole human female in existence. On the East African prairie 200,000 years ago, there were many interrelated tribes of humans.  Eve is simply the one female from whom we all descend via an unbroken maternal lineage.  Everyone descends from mitochondrial Eve the same way, through their mother.  While many of her contemporary friends and enemies were also our ancestors, we descend from the others in a complexity of paths via fathers and mothers.

Scientifically, the maternal ancestor of all humans alive today is not the first female human that ever existed, so the name “Mitochondrial Eve” is a bit of a misnomer.  The “first human” is not easy to define because DNA mutations proceed back through time eventually to converge with a similar progression arising from the chimpanzee branch of the tree of life. At what time and at what place along this branch can we define the first human?  That depends on our definition of human. But first, where do the Neanderthals fit in?  That's the subject of the next blog.