A genomic study published in June 2026 found that koalas suffered a severe population decline roughly 100,000 years ago — long before humans arrived in Australia. Led by PhD student Toby Kovacs at the University of Sydney, working with researchers at Texas A&M University, and announced in the journal Molecular Biology and Evolution, the research overturns earlier studies suggesting koala populations declined only after humans reached the continent. The ancient crash was driven by climate upheaval, not by people.
Koalas' Ancient Past: A Climate-Driven Crash 100,000 Years Ago
The study reshapes the koala's evolutionary timeline. According to the University of Sydney's announcement, the species experienced a severe population decline around 100,000 years ago, before the arrival of humans on the continent. All modern koalas, the researchers report, descend from a single ancestral population that survived harsh climate upheavals — severe glacial periods and fluctuating cold and dry conditions as the Australian tectonic plate drifted.
That single-population origin matters. It means the koalas alive today carry the genetic legacy of one small, struggling group that endured repeated climate shocks. "The study rewrites the timeline for the koala's genetic history in Australia," Kovacs said in the university's announcement. The finding directly contradicts previous accounts that placed the species' decline after human arrival, reframing the deep past as a story of survival through natural climate extremes.
