Environment influenced hominin dispersals across ancient Iran

The waxing and waning of the environment influenced hominin dispersals across ancient Iran, according to new research

A world-first model of paleoclimate and hydrology in Iran has highlighted favourable routes for Neanderthals and modern human expansions eastwards into Asia.

The findings reveal for the first time that multiple humid periods in ancient Iran led to the expansions of human populations, opening dispersal routes across the region, and the possible interactions of species such as Neanderthals and our own Homo sapiens.

Professor Michael Petraglia, a key researcher in the study, said historic humid periods resulted in massive environmental changes to ecosystems and led the team to identify large lakes in areas that were formerly ancient deserts.

Petraglia, who is the director of Griffith University’s Australian Research Centre for Human Evolution, said: “Conversely, during glacial periods this increased aridity would have led to the expansion of deserts, [leading] to contractions, and the isolation of hominin populations.

“This cycle of wetting and drying is shown for the first time in Iran.”

Out of Africa

The research team, led by PhD candidate Mohammad Javad Shoaee from the Max Planck Institute for Geoanthropology in Germany, found that during Marine Isotope Stage (MIS) 5, a warm, humid period beginning roughly 130,000 years ago, lakes and rivers enabled two pathways for human groups.

One was a northern route through the Alborz and Kopet Dagh Mountains and north of the Dasht-I Kavir desert. The other route, first identified here, ran south along the Zagros Mountains before extending eastwards towards modern-day Pakistan and Afghanistan.

The researchers also found evidence for a potential northern route during MIS 3, beginning about 57,000 years ago, which, given artifacts attributed to multiple tool-making groups, could have permitted interactions between modern humans and Neanderthals.

Petraglia said: “These findings highlight the importance of Iran for our species’ dispersals out of Africa and ultimately around the globe.

“As in other regions long considered too arid for early human occupations, such as the Arabian Peninsula, recent palaeoclimatic research is changing how we understand the human story and the role that changing climates have played.”

Shoaee said: “We recognised a new southern route along the Zagros Mountains and extending eastwards towards Pakistan and Afghanistan. We found evidence for a potential northern route during MIS 3, which would have permitted hominin movements and species interactions in Southwest Asia.”

Clear relationship

To find out how human groups made their way into Iran, the team developed the first spatially comprehensive, high-resolution palaeohydrological model for Iran.

They then compared their model, which showed when and where water was available, to the distribution of previously documented archaeological sites.

The result was a clear relationship between the availability of water and the evidence of human presence.

Not only does the current study help to explain the presence of previously documented sites, it also serves as a guide for future archaeological surveys in the region.

Shoaee said: “Our palaeohydrological analyses identified 145,354km of rivers and 115 paleolakes calculated from 6380 paleolake deposits. Only a handful of these paleolakes have so far been studied.”

By focusing on regions where water once made human occupations possible, Petraglia said “researchers could maximise the potential of finding archaeological sites”.

The findings are published in PLOS ONE.

Image 1: Upland terrain in the Zagros Mountains during Spring demonstrating the ‘greening’ of environmental landscapes.

Image 2: Stone tools recovered during a recent survey of the Central Zagros Mountains, indicating that this zone would have been a favourable habitat for human occupations in humid periods.