Snail shells reveal change in climate when hunters turned to farming in Northwest Africa

Yurena Yanes from the University of Cincinnati unearths ancient snail shells (gastropods) from beneath a paleontological site.

Yurena Yanes from the University of Cincinnati unearths ancient snail shells (gastropods) from beneath a palaeontological site.

Existing research tells us that during the last 11,500 years most of us transformed from hunter gatherers into agriculturalists. Why we did this remains largely unanswered. New findings from University of Cincinnati geologist Yurena Yanes suggest that natural climate change occurring seven to six thousand years ago in Northwest Africa warmed the environment and enhanced the conditions for growing enough crops to help sustain the growing human population.

Significant natural climate change

As part of a new project looking at snail shells from Northeastern Morocco, Yanes, assistant professor of geology in UC’s McMicken College of Arts and Sciences, analysed oxygen isotope samples from ancient shells. What she has observed is clear evidence for significant climate change that accounts for the introduction of early agricultural development in Northwest Africa.

Yanes research findings were presented at the 2015 Geology Society of America Annual Meeting in Baltimore, titled “Holocene Environmental and Cultural Transition in IFRI Oudadane, NE Morocco, Inferred from Oxygen Stable Isotopes of the Topshell Phorcus Turbinatus,”.

In a multi-collaborative effort with two researchers in Germany – Rainer Hutterer from Zoologisches Forschungsmuseum and Jorg Linstadter from the Institute of Prehistoric Archaeology, University of Cologne – Yanes looked at shells collected from an archaeological site and dated from 10,800 to 6,700 years old. They analysed the oxygen isotope values of archaeological shells and were able to calculate the sea surface temperatures from when the original human occupants living in the region began to shift their cultural practices.

Even though previous research has not observed major climate change at that temporal transition at the study site, with the oxygen isotope analysis of these shells, we have evidence for a significant natural climate change,” says Yanes.

Because the isotopes of snail shells are only influenced by temperature and water conditions and not by humans, we have natural archives at the time of prehistoric occupation.”

New ways to feed a rising population

Yanes postulates that some groups of humans may have migrated there, but even the occupants living there initially may have shifted their substantive cultural strategies. She adds that at a time before there was any food production, people likely did not feel the need to produce food because they were able to sustain themselves by hunting and collecting.

But there was evidence for a change and something triggered that transition from hunting to farming and agriculture.”

Yanes says scientists continue to hypothesize that increasing human population density during this transition necessitated finding new ways to feed the population. Moreover, with the changing climate from cooler to warmer, the conditions were ripe, so to speak, for growing optimal crops.