Neanderthals declined rapidly and to extinction just a few thousand years after reaching their peak. Why? It's a mystery we're still piecing together. Now, an article recently published in Proceedings of the Natural Academy of Sciences provides yet more evidence that climate change is (at least partly) to blame.
"The Neanderthals were the human species closest to ours and lived in Eurasia for some 350,000 years," co-author Vasile Ersek, a senior lecturer in physical geography in Northumbria University's Department of Geography and Environmental Sciences, explained in a statement.
"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... Our study suggests that climate change may have had an important role in the Neanderthal extinction."
A team of international researchers reached this conclusion after examining stalagmites, a type of rock formation found in caves. They grow extraordinarily slowly – roughly equivalent to a width of paper every year – trapping within their many layers a scrupulous record of the changing climate over the millennia. This is because even a small drop (or rise) in temperature can change their chemical composition.
The study includes two stalagmite-containing caves in Romania, which offer the most extensive and detailed records of climate change in continental Europe.
Importantly, the composition of these stalagmites reveal a period of recurring spells of cold, dry weather between 44,000 and 40,000 years ago, ie exactly when the Neanderthal population plummeted (according to current archaeological evidence). During this time, weather would remain icy for centuries or millennia before rising rapidly.
While this is correlational rather than causal, it seems to suggest that changing temperatures could, at least in part, be responsible for the Neanderthal's grisly fate.
Then again, Neanderthals were a robust species. They had existed for more than 350,000 years and withstood previous ice ages. What made this particular weather pattern so different and how were our ancestors Homo sapiens, who had only very recently arrived on the scene, able to survive when the Neanderthals were not?
The study authors believe it may come down to the food supply. They say the Neanderthals may have been successful hunters but their diet was less diverse than those of H. Sapiens. In particular, their reliance on meat could have left them vulnerable to food scarcity as animal-derived food sources would have dropped off during the colder weather. In contrast, H. Sapiens were supplementing their diet with fish and plants, helping them to weather the storm.
Not everyone has been persuaded. Physical anthropologist Israel Hershkovitz from at Tel Aviv University told Ariel David at Haraatz that this still doesn't sufficiently explain why this particular batch of cold weather events was so different from earlier ones. Neither can it prove the stalagmites in Romania represent the weather patterns in the rest of Europe. (In fact, he added, there is some evidence that other parts of Europe were relatively mild during this period.)
Still, the authors say this is the most concrete evidence to link Neanderthal decline to climate change so far.
"Before now, we did not have climate records from the region where Neanderthals lived which had the necessary age accuracy and resolution to establish a link between when Neanderthals died out and the timing of these extreme cold periods," Ersek added.
"When temperatures warmed again, their smaller populations could not expand as their habitat was also being occupied by modern humans and this facilitated a staggered expansion of modern humans into Europe."