A fascinating new study has potentially discovered a huge interbreeding zone for Neanderthals and Homo sapiens from the late Pleistocene (c.129,000 and c.11,700 years ago) who lived in parts of Southeast Europe and Southwest Asia. Narrowing down the list of potential places for this, the researchers zeroed in on the Zagros Mountains on the Persian Plateau, which stretches from Iran to northern parts of Iraq and into southeastern Turkey in modern geographical terms.
Ecological Niche Modelling: Where the Science is At
While scientists have long known of this interbreeding, the precise locations for these encounters had remained elusive. This is because fossil evidence is sparse, and the availability of ancient DNA is limited. In response, a team of researchers led by Saman Guran from the University of Cologne in Germany turned to an innovative approach: ecological niche modelling, and have published their finds in the latest edition of the journal Scientific Reports.
This method assesses habitat suitability by examining environmental factors such as temperature and precipitation. By integrating this model with geographic information systems (GIS), the team reconstructed the potential ranges of both species during a crucial window of time—between 120,000 and 80,000 years ago—referred to as Marine Isotope Stage 5 (MIS 5).
The results of their work are striking: during MIS 5, the Zagros Mountains, with their dramatic cliffs and fertile valleys, likely served as a key crossroads. Neanderthals from the Palearctic region and modern humans migrating out of Africa may have encountered one another in this very landscape. The region’s rich biodiversity and varied topography would have provided the ideal conditions for both species to thrive. It was, perhaps, also the perfect setting for them to meet, and potentially interbreed.
Howraman Valley in Zagros Mountain. Kurdistan Province, Iran. (Elena Odareeva/Adobe Stock)
In the Zagros: Favorable Climate, Favorable Geography
This hypothesis situates the Zagros Mountains at the heart of a significant chapter in human evolution. According to the researchers, shifts in climate during this period would have made the environmental conditions of the Zagros especially hospitable. This created what scientists term a “niche overlap,” where the habitats of Neanderthals and modern humans intersected, according to a press release.
The researchers wrote in their study.
“Our study identified the Persian Plateau, particularly the Zagros Mountains, as a potential interbreeding area for AMHs and Neanderthals. The possibility of attracting different hominin groups in the Zagros Mountains is justified by the geographical conditions of this region, since it is located in two different biogeographical zones, namely, the Palearctic and Afrotropical realms.”
Neanderthals, long accustomed to the cold, rugged environments of Europe, found in the Zagros a landscape that mirrored their native habitats. Meanwhile, modern humans, adept at navigating new and challenging terrains, would have been well-prepared to traverse this mountainous region. This overlap of habitats increased the likelihood of contact between the two species, and consequently, the possibility of interbreeding.
While modeling can offer valuable insights, physical evidence is essential to support such theories. Fortunately, the Zagros Mountains are not merely a theoretical meeting point on a map.
“The border areas of two realms are important in biology since they operate as refugia for species from glacial environments. Consequently, some parts of the Zagros Mountains could have been visited repeatedly by people living in the border areas of the Palearctic and Afrotropical realms during Pleistocene climatic shifts. Therefore, the possibility of interaction between different hominins, including AMHs and Neanderthals, was greater in these areas,” wrote the authors.
Neanderthal Rising: Further Evidence of their Presence
This region has already yielded some of the most significant fossil and archaeological discoveries related to Neanderthals.
In the northern Zagros, Shanidar Cave has provided a wealth of evidence. Excavations there have uncovered the remains of ten Neanderthals, offering an intimate glimpse into their lives—and perhaps, their deaths. Several of these individuals are thought to have been buried with flowers, (although there are some other theories) a practice that hints at rituals and customs previously thought to be unique to Homo sapiens, reports ZME Science.
Further south, in the Kermanshah region of Iran, additional Neanderthal fossils have been discovered in caves such as Wezmeh and Bisetun, bolstering the notion that this mountainous region was a long-term home for Neanderthals. However, it is the discovery of a single Neanderthal tooth at the Bawa Yawan rock shelter, dated to around 65,000 years ago, that has captured the most attention.
Found alongside Mousterian stone tools, this tooth provides critical evidence that Neanderthals were present in the Zagros during the timeframe when interbreeding with modern humans likely occurred.
The implications of Neanderthal-AMH interbreeding are profound. Today, Neanderthal DNA constitutes a small, but significant, portion of the genomes of most people of non-African descent (1-4%), influencing everything from immune responses to skin pigmentation. By uncovering the locations and times where this interbreeding took place, researchers are piecing together a more complete and complex narrative of human evolution.
Top image: Habitat suitability models of the two Homo species and their potential contact and interbreeding zones in Southwest Asia and Southeast Europe. Source: Guran et al./Scientific Reports
By Sahir Pandey
