The koala population crash, long blamed on early human settlers, has been rewritten in history. A new study reveals that the decline began around 100,000 years ago, driven by a drying climate and shrinking forests, not human activity. This finding challenges the long-held belief that early Australians were the culprits. Toby Kovacs, a PhD candidate at the University of Sydney, led the study, which analyzed the DNA of 457 koalas across Australia. The research dates the decline to roughly 100,000 years ago, with a critical bottleneck around 60,000 years ago, well before any human contact. This timeline coincides with the late Pleistocene, a period of intense upheaval due to repeated glacial cycles, resulting in a colder, drier, and more fire-prone Australia. The Nullarbor Plain's expansion split the koala range, leading to the extinction of the western population and the survival of a small eastern group. As the climate warmed, the surviving eastern koalas expanded and diversified into five genetic populations between 16,500 and 6,000 years ago. This discovery shifts the blame from early humans, who arrived around 60,000 years ago, to the natural forces of climate change and environmental shifts. The study's mutation rate, calculated for the first time in koalas, provides a tool to track living populations and test the decline of other Australian species before human arrival. The koala's resilience is remarkable, as every koala alive today descends from a single group that endured harsh conditions. However, the current threats to koalas, such as land clearing, bushfires, vehicle strikes, and disease, are very different from the past. The species is now listed as endangered in several Australian states, highlighting the ongoing challenges they face. This research not only rewrites the timeline of koala history but also offers valuable insights into the species' resilience and the impact of climate change on Australian wildlife.
