In 2002, archaeologists made an extraordinary discovery in Romania when they unearthed a jawbone in a cave called Pe?tera cu Oase. This bone, estimated to be between 37,000 and 42,000 years old, quickly became a focal point of scientific investigation. Initial observations indicated that the bone belonged to a human, though its physical characteristics exhibited some Neanderthal-like traits, prompting the researchers to propose that it could have been the remains of a person with Neanderthal ancestry. What followed was a groundbreaking genetic study that provided the first concrete evidence that modern humans and Neanderthals interbred in Europe, a discovery that changed our understanding of human evolution and our shared history with Neanderthals.
Neanderthals had once been the dominant human species in Europe until their disappearance around 35,000 years ago, roughly at the same time modern humans began migrating across the continent. While archaeological evidence suggests that modern humans and Neanderthals coexisted for thousands of years, the interaction between these two groups had been largely speculative, with cultural exchanges—such as similarities in tool-making techniques, burial rituals, and body decoration—suggesting some form of contact. However, direct evidence of interbreeding had been sparse, leaving many questions unanswered about how, or even if, these two groups had mixed.
The research team that eventually analyzed the jawbone was led by two prominent figures in genetics: David Reich, an investigator at the Howard Hughes Medical Institute and a professor at Harvard Medical School, and Svante Pääbo, a director at the Max Planck Institute for Evolutionary Anthropology in Germany. Their combined expertise in ancient DNA analysis would lead to the revelation of the first genetic evidence of interbreeding between modern humans and Neanderthals in Europe, marking a significant milestone in the field of human evolutionary genetics. Their findings were published in the Nature journal in June 2015.
Before diving into the genetic analysis, it is important to understand the context of the discovery. By 45,000 years ago, Neanderthals were the only human species inhabiting Europe. Their extinction, around 35,000 years ago, coincided with the arrival of modern humans, making it a dramatic and pivotal transition in the history of the continent. The archaeological evidence from the period of Neanderthal disappearance points to increasing interaction between Neanderthals and modern humans, but the lack of skeletal remains from this time made it difficult to confirm the extent of this interaction.
The jawbone, however, offered a rare and valuable glimpse into this transitional period. The bone was found alongside a skull of another individual, but no artifacts were recovered from the site. This lack of cultural evidence left archaeologists with little to go on regarding the lives or behaviors of the individuals. Still, the physical features of the jawbone were predominantly human, with only a few Neanderthal-like traits. The uniqueness of this bone was evident, and it quickly became the subject of intense scientific inquiry, especially when researchers noticed the potential for genetic analysis to reveal more about its origins.
One of the primary challenges of analyzing ancient DNA is the contamination from microbes, soil particles, and human handling, which can overwhelm the minute traces of ancient genetic material that remain. Despite these obstacles, Qiaomei Fu, a graduate student in Pääbo’s lab, succeeded in extracting DNA from the bone. The initial DNA sample was largely contaminated with microbes, including bacteria from the soil in which the jawbone was found, and DNA from people who had handled the bone after its discovery. Fu’s next step was to separate the ancient human DNA from the contaminating DNA, a process that was made more difficult by the age and degradation of the sample.
Using methods developed by Pääbo’s lab, Fu enriched the DNA sample to increase the proportion of human DNA, focusing on the most useful regions of the genome—those areas known to be valuable for evaluating genetic variation between human populations. After sifting through the contaminating DNA, Fu was able to isolate and analyze the human genetic material that was likely to have come from the ancient individual.
The results were both astonishing and unexpected. The genome of the individual from the Oase jawbone showed that this person was more closely related to Neanderthals than to any modern human population. In fact, the team estimated that six to nine percent of the individual’s genome came from Neanderthals. This was a much higher percentage than what is seen in the genomes of present-day Europeans or East Asians, who typically have around two percent Neanderthal DNA in their genomes. This indicated that the Oase individual’s Neanderthal ancestry was recent, likely within just a few generations.
Through careful analysis of the DNA, Reich’s team determined that the individual had a Neanderthal ancestor within four to six generations before their death. This was an extraordinary finding, as it indicated that the Oase individual’s ancestors had interbred with Neanderthals just a few generations prior to this person’s life. Such a discovery gave clear evidence that modern humans who migrated into Europe after their arrival had interbred with Neanderthals, blending their genetic material with that of the local Neanderthal populations. This was the first genetic evidence that modern humans did not entirely replace Neanderthals but instead mixed with them in Europe.
Reich’s team, however, clarified that the Oase individual was not directly responsible for passing on Neanderthal genes to present-day Europeans. The genetic material present in the Oase individual’s genome did not appear to have contributed to the modern European gene pool. Instead, it is possible that the individual was part of an early group of modern humans who arrived in Europe but was later replaced by other populations of modern humans, whose genetic legacy is present in today’s European populations. This implies that there may have been several waves of human migration into Europe, and that early human groups were sometimes replaced by later groups, even though there was some interbreeding between these populations.
The implications of this discovery are far-reaching, providing new insights into the complex interactions between Neanderthals and modern humans. It suggests that the genetic mixing between the two species occurred more recently than previously thought, with some modern humans inheriting a significant amount of Neanderthal DNA from their direct ancestors. These findings reinforce the growing evidence that Neanderthals and modern humans were not two entirely separate species but rather shared a history of interbreeding and coexistence in Europe for thousands of years.
The research also contributes to our understanding of human migration patterns, suggesting that early modern humans who left Africa and moved into Europe encountered and interbred with Neanderthal populations already established in the region. This mixing of genes may have had important implications for the survival and adaptation of modern humans as they adapted to the harsh climates of Ice Age Europe.
More information: An early modern human from Romania with a recent Neanderthal ancestor, Nature; 22 June, 2015. DOI: 10.1038/nature14558