To investigate the stability of ancient cave bear populations over time, the researchers obtained DNA samples from 29 cave bear teeth from three geographically close caves in the Ach Valley, near the Danube River in modern-day southern Germany. Twenty of the teeth ultimately provided useful mitochondrial DNA sequence (mitochondrial DNA is especially useful for tracking population changes). The findings indicated that while four sequence types (known as haplotypes) corresponded to bears 28,000 to 38,000 years old, a fifth DNA haplotype was found only in bears that were 28,000 years old or younger. These data suggested that what had been a stable, long-established cave bear population became disrupted around 28,000 years ago and was replaced by a new, genetically distinct cave bear group.
The timing of the disruption appears to roughly coincide with the arrival of modern humans in the Ach Valley, thought to have occurred by 32,000 years ago. The researchers suggest that human influence in the form of hunting and competition for sheltering caves may represent a plausible explanation for the disruption in the cave bear population, creating an opportunity for the infiltration by a neighboring cave bear group. The authors note that though the new bears successfully colonized the Ach Va lley for a time, they endured only another 2,000 years before becoming extinct in the region.