If it weren’t for humans, things might have turned out differently for the European cave bear.
Before their extinction some 24,000 years ago, they lived across much of Europe, from northern Spain in the west all the way to Siberia in the east.
When they finally died out the last glacial maximum, or ice age, was in full swing. But questions have lingered about whether humans also played a role in their demise.
Now new work led by Verena Schünemann from the University of Tübingen in Germany suggests they did.
Charting the decline in cave bears – or any of the now-extinct megafauna – using the fossil record alone is fraught. Fossils are rare and don’t give a good indication about how many bears padded about at any given time.
That’s where ancient DNA comes in. By extracting precious shards of DNA that have survived thousands of years in the ground, scientists can discover how genetically diverse cave bears were, and from that work out approximate population sizes.
Schünemann’s team extracted ancient DNA from 59 cave bear fossils from 14 sites across Europe and sequenced the mitochondrial genome – a small portion of the bears’ genetic blueprint that is inherited through the female line.
Combining these with 64 published sequences, they could model the population dynamics of cave bears prior to extinction.
The team found that 200,000 to 50,000 years ago cave bear populations were quite stable. That’s despite this period spanning two much colder periods, as well as two periods of warming.
Cave bear numbers started falling gradually about 50,000 years ago, the modelling shows.
Then, at around 40,000 years ago, population size fell precipitously. That’s more than 10,000 years before the ice age hit, and it coincides with when anatomically modern humans moved into Europe, says Schünemann.
The curvaceous female “Venus figurines” of the Aurignacian culture are evidence of these early European settlers.
But cave bear fossils also bear the signs of human arrival. Cave bear fossils with human-made spearheads still embedded in them are clear signs of hunting.
Humans would also have competed with the cave bears for habitat – both used caves – and other resources.
But while humans put them on the precipice, the ice age probably finished them off.
“If they would have stayed in the same population size as before this dramatic drop, they might’ve survived that cooling period,” says Schünemann.
“It’s an interesting piece of the puzzle,” says palaeoecologist Corey Bradshaw from Australia’s Flinders University, who wasn’t involved in the study. But the story might not be the same for all cave bear populations.
“It really depends on where you are in the landscape,” he says. Ultimately, more ancient-DNA-yielding fossils are needed to find out what happened to individual populations.