Climate change may have played an important role in the extinction of Neanderthals, say scientists who found that a complete absence of archaeological artefacts from the species during cold periods.
Researchers including those from the Northumbria University in the UK produced detailed new natural records from stalagmites that highlight changes in the European climate more than 40,000 years ago.
The study, published in the journal Proceedings of the Natural Academy of Sciences, found several cold periods that coincide with the timings of a near complete absence of archaeological artefacts from the Neanderthals, suggesting the impact that changes in climate had on the long-term survival of Neanderthal man.
Stalagmites grow in thin layers each year and any change in temperature alters their chemical composition. The layers therefore preserve a natural archive of climate change over many thousands of years.
The researchers examined stalagmites in two Romanian caves, which revealed more detailed records of climate change in continental Europe than had previously been available.
The layers of the stalagmites showed a series of prolonged extreme cold and excessively dry conditions in Europe between 44,000 and 40,000 years ago. They highlight a cycle of temperatures gradually cooling, staying very cold for centuries to millennia and then warming again very abruptly.
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The researchers compared these palaeoclimate records with archaeological records of Neanderthal artefacts and found a correlation between the cold periods -- known as stadials -- and an absence of Neanderthal tools.
This indicates the Neanderthal population greatly reduced during the cold periods, suggesting that climate change played a role in their decline.
"The Neanderthals were the human species closest to ours and lived in Eurasia for some 350,000 years," said Vasile Ersek, senior lecturer at Northumbria University.
"However, around 40,000 years ago -- during the last Ice Age and shortly after the arrival of anatomically modern humans in Europe -- they became extinct," said Ersek.
For many years scientists have wondered what could have caused their demise.
"Our study suggests that climate change may have had an important role in the Neanderthal extinction," he said.
The researchers believe that modern humans survived these cold stadial periods because they were better adapted to their environment than the Neanderthals.
Neanderthals were skilled hunters and had learned how to control fire, but they had a less diverse diet than modern humans, living largely on meat from the animals they had successfully pursued.
These food sources would naturally become scarce during colder periods, making the Neanderthals more vulnerable to rapid environmental change.
In comparison, modern humans had incorporated fish and plants into their diet alongside meat, which supplemented their food intake and potentially enabled their survival.
The findings had indicated that this cycle of "hostile climate intervals" over thousands of years, in which the climate varied abruptly and was characterised by extreme cold temperatures, was responsible for the future demographic character of Europe.