In the late third millenium BC, society in south-eastern Arabia began to change.

The environment grew extremely arid and trade with Mesopotamia was in decline.

People began to abandon settlements, leave palm gardens and, supposedly, return to a mobile lifestyle.

The Bronze Age transition from the Umm An Nar (2700 to 2000 BC) to the Wadi Suq (2000 to 1300 BC) period is hotly debated by archaeologists.

The popular view is that external forces – such as acute climate change and the breakdown of trade between regions – caused people to leave Umm An Nar centres and form smaller, more mobile communities in the early second millennium.

Dramatic changes in the archaeological record suggest people adjusted to climate change with a sudden shift.

The Wadi Suq period is portrayed as one of social collapse and cultural isolation.

But teeth from Ras Al Khaimah’s prehistoric tombs tell a different story.

A recent study of mandibular, or jawbone, first molars by the bioarchaeologist Lesley Gregoricka shows a more gradual change, suggesting that dispersal was a deliberate decision.

Prof Gregoricka’s analysis of strontium, carbon and oxygen isotope ratios show homogeneity in mobility and diet, indicating continuity instead of collapse between the late third to early second millennium BC.

Societal changes, she said, may have been an “equal or even more powerful” motivator for dispersal than climate change during this period.

Her study, Human Response to Climate Change during the Umm an-Nar/Wadi Suq Transition in the United Arab Emirates, was published online in the International Journal of Osteoarchaeology this month.

“I think the idea that Bronze Age peoples were capable of successfully adapting to their changing surroundings is one that is gaining traction among archaeologists working in this region,” said Prof Gregoricka, of the University of South Alabama.

“Rather than viewing these ancient communities as passive players whose behaviour was dictated solely by external forces like climate, we instead see them actively reacting to and coping with both environmental and social stress.”

Prof Gregoricka deciphers history with stable isotopes, biogeochemical signatures embedded in bones and teeth.

Stable strontium, oxygen and carbon isotopes from human and animal skeletal remains hold important clues about residential mobility, migration, trade networks and diet.

For this study, she examined teeth from 32 people from the Shimal necropolis, 8 kilometres north-east of Ras Al Khaimah city, near the modern-day village of Shimal.

The tombs, part of the protected Shimal Archaeological Park, are one of the most significant Middle Bronze Age centres in Arabia.

The population may have left Umm An Nar centres because of a food or water shortage. Extreme regional aridity started around 2200BC.

Equally, it may have been to prevent violence or to avoid developing hierarchies like those of Mesopotamia and the Indus Valley.

Hierarchies had already started developing in the early Umm An Nar period, as shown by enormous tombs that required extensive effort and organised labour to build and maintain.

“This kind of organisation is typically not possible without a developed social hierarchy, where [in a most basic sense] we have managers of large, communal projects and labourers,” said Prof Gregoricka.

A possible conflict between a growing elite and traditional kin-based organisation was likely worsened by fewer available resources.

“These groups were engaged in interregional trade networks with the city-states of Mesopotamia and the Indus Valley Civilisation, both of which exhibited urban development and social hierarchies on a scale far beyond what we see in the UAE,” she said.

“The inhabitants of the UAE during the third and second millennia BC would have been familiar with these places but, rather than emulating them and continuing to develop hierarchies as had taken place in Mesopotamia and the Indus Valley, they seem to have chosen a different path.”

Prof Gregoricka’s findings support a growing body of work by prominent and respected Arabian archaeologists.

“Decades of research in Arabia have highlighted the fact that many of the communities that lived there did not embark on the march towards state-level complexity, but rather maintained a society based upon cohesion,” said Peter Magee, a professor of archaeology and director of Middle East studies at Philadelphia’s Bryn Mawr College.

The research by Prof Gregoricka and her colleagues is of “immense importance” and supports a boarder emerging pattern indicating gradual change in the transition.

“This is important because it highlights the fact that local people exercised agency and flexibility in the manner in which they interacted with the environment,” said Prof Magee. “Their economy and social structures were not just reliant on external trade, which around 2000 BC seem to have been truncated in some way, but rather had developed in a robust fashion since the Neolithic 5,000 years earlier.”

The social structure, he says, was resilient.

Mark Beech, head of the coastal heritage and palaeontology section at Abu Dhabi Tourism and Culture Authority, stressed that several factors would have influenced the transition.

“My impression is that often the transitions between different chronological periods are more subtle and gradual than previously believed,” he said.

“We have many gaps in the archaeological evidence which we are still trying to fill with new discoveries. The whole question of cultural continuity between the Umm An Nar and Wadi Suq period is very much a topic for debate.”

The Bronze Age population left little behind to tell us about their lives. But what they did leave were monumental tombs.

Some mass graves were used for generations.

Umm An Nar tombs such as those at Shimal were typically used for 200 years and contain hundreds of bodies, making traditional analysis on fragmented and co-mingled skeletal remains difficult.

It is certain that Umm An Nar and Wadi Suq periods had very different subsistence strategies, social organisation, exchange systems and mortuary practices.

The transition saw a shift from sedentary date palm horticulture to mobile pastoralism and coastal foraging. The question is, how mobile did they become?

Evidence indicates that south-eastern Arabia, once a major provider of copper to Mesopotamia, lost its trade importance to Dilmun, in the western Arabian Gulf, about 2000 BC. Copper mining declined.

Mortuary practices also changed. Circular, above-ground tombs with hundreds of individuals of the Umm An Nar period were replaced in the Wadi Suq period with cairns of different shapes and sizes, used for shorter periods.

Some communities, like those at Tell Abraq, maintained the Umm An Nar lifestyle for next 200 years, perhaps because of ample marine resources.

But by about 2000 BC, previously settled areas were no longer able to sustain large populations because of a lack of fresh water. Settlements dispersed, decreasing in size and number.

The new study corresponds to earlier findings by Prof Gregoricka on strontium and oxygen isotope analyses that show limited changes in mobility for Bronze Age communities during the transition in the same area.

In a paper on residential mobility, she found people from six tombs had little isotopic variability, indicating that most people stayed where they were.

Teeth from three immigrants, indicated by different strontium values, show the area was not as isolated as previously thought and trade continued, though it had significantly decreased.

“Instead of viewing this period as one of ‘collapse’, we should frame these changes as an active response by human populations to cope with environmental stress through adaptive innovation,” the study says.

azacharias@thenational.ae