Cave bears wiped out by humans: study confirms

During the last Ice Age, humans may have played a key role in driving cave bears to extinction in Europe. This is the conclusion of an international study involving the University of Zurich, which analysed genetic material from several caves.

In which regions of Europe did cave bears live, and what migratory movements did they undertake during the Late Pleistocene? This question was investigated by researchers led by Verena Schünemann from the Institute of Evolutionary Medicine at the University of Zurich. They reconstructed the mitochondrial genome from bone samples taken from 59 cave bears at fourteen sites in Poland, France, Spain, Germany, Italy, and Serbia. Bones were also found in Switzerland, in the cave known as «Bärenloch» near Charmey in the Fribourg Pre-Alps. These demonstrate that cave bears wintered there and gave birth to their young. The researchers compared the genomes from these fourteen sites with 64 previously published mitochondrial DNA sequences.

Both present-day and ancient brown bears carry between 0.9 and 2.4 percent cave bear DNA in their genome. Conversely, genetic material from brown bears can also be found in cave bears, albeit to a lesser extent. The scientists conclude from this that cave bears and brown bears must have interbred before one species ultimately went extinct. Researchers had previously reported that this was the first time DNA from an extinct Ice Age animal species had been detected in a living animal population.

Family tree of Europe's cave bears

«Our data revealed that the distribution of cave bears during the last Ice Age was far more complex than previously assumed», explains last author Verena Schünemann from UZH. Using the mitochondrial genomes, a kind of family tree of the cave bears was created: the researchers identified five major DNA lineages scattered across Europe, all tracing back to a common ancestor. This ancestor lived approximately 451’000 years ago.

Cave bear populations appear to have remained relatively stable until around 40’000 years ago, even through two cold periods and several cooler episodes. The intense cooling of the last ice age only set in around 30’000 years ago, by which time cave bear populations had already been severely decimated. This suggests that other factors had a major influence on the extinction of the cave bears.

Humans decimate the bears

«The drastic decline of the cave bear population began around 40’000 years ago. This is also the point at which modern humans spread across Europe and increasingly became competitors of the bears. In certain areas, humans claimed the same habitat as the bears — namely caves — and hunted the animals», explains Schünemann. Archaeological finds confirm that the bears were killed and used as a resource.

The increasingly cool climate and the resulting reduced availability of plants as food placed additional strain on the herbivores. As a result, the entire bear population may have been fragmented into separate sub-populations inhabiting more moderate climate zones and habitats with abundant plant life. Through bear hunting and the existence of small, isolated populations, humans may have played a decisive role in the extinction of the bears, according to the researchers.