It is hard to overestimate how much of a game-changer this information is.

A month ago, I wrote on the search for the historical Adam. Shortly after I turned that article in came the news out of Europe that 9% of the genes that are carried by non-African modern humans can be specifically, unequivocally described as Neandertal genes. As the story notes:

Dr. [Damien] Labuda and his team almost a decade ago had identified a piece of DNA (called a haplotype) in the human X chromosome that seemed different and whose origins they questioned. When the Neanderthal genome was sequenced in 2010, they quickly compared 6000 chromosomes from all parts of the world to the Neanderthal haplotype. The Neanderthal sequence was present in peoples across all continents, except for sub-Saharan Africa, and including Australia.

In the study of modern human origins, it is hard to overestimate how much of a game-changer this information is. Within the last thirty years, the predominance of opinion among the palaeoanthropological community has been that modern humans originated in sub-Saharan Africa and quickly replaced the Neandertals and their contemporaries in other places in the Old World (everywhere except the Americas). This has come about largely through work on the human genome that was carried out in the late 1980s and early 1990s involving mitochondrial DNA (mtDNA). 

The competing hypothesis of modern human origins, called the multi-regional evolution model proposes that, while there was selection for the traits that make up modern humans, this selection took place in regional contexts with abundant gene flow between regions and that the archaic humans in each area of the Old World contributed genetically to the modern humans in each area (Frayer, Wolpoff, Thorne, Smith, & Pope, 1993). 

As everyone learns in school, the reason you don’t look exactly like either one of your parents is that when your parents decided to have you, there was a recombination of each of their DNA to produce the variation present in you and your siblings. This is one of the many ways in which variation in a species is maximized. This is nuclear DNA.

Mitochrondrial DNA is kept in the mitochondria of the cell, the area in which energy production and respiration occurs. Unlike nuclear DNA, this kind of DNA does not recombine but is passed entirely through the maternal line of the family. If a woman has a particular strain of mitochondrial DNA, her daughters will have it and they will pass it on to their daughters as well.

What the genetic work in the late 1980s and early 1990s revealed is that, when individuals of different populations all over the world were studied, the modern human genome was found to have a strikingly small amount of mtDNA variants—exactly 138. Further, it was found that the greatest amount of variability was found in Africans. This led to the “out of Africa” or “Eve” hypothesis of modern humans origins in which all of modern humanity was traced to one human being with that strain of mtDNA (Cann, Stoneking, & Wilson, 1987).

This new information, however, strongly suggests two things: 1) That the replacement model of modern human origins is no longer tenable and that some model of assimilation of anatomically modern Homo sapiens and archaic Homo sapiens is the best way to approach the data (Smith, Jankovic, & Karavanic, 2005), and 2) That modern humans are not a separate species from Neandertals and their contemporaries and did not arise as such. Consequently, while there may have been a major influx of modern humans between 60 and 50 thousand years ago, very little uniqueness can be placed on these incoming moderns. 

It is difficult to discern how this information could not be interpreted in an evolutionary context.  Were modern humans a separate creation, why would there be any specifically Neandertal genes at all? Like the arguments involving shared mistakes and retroviral segments, the data best indicates shared ancestry and genetic continuity from archaic Homo sapiens to modern Homo sapiens. 

Cann, R. L., Stoneking, M., & Wilson, A. (1987). Mitochondrial DNA and human evolution. Nature, 325, 1200.

Frayer, D. W., Wolpoff, M. H., Thorne, A. G., Smith, F. H., & Pope, G. G. (1993). Theories of Modern Human Origins: The Paleontological Test. American Anthropologist, 95(1), 14-50.

Smith, F. H., Jankovic, I., & Karavanic, I. (2005). The assimilation model, modern human origins in Europe, and the extinction of Neandertals. Quaternary International, 137(1), 7-19.