A global team analyzed 457 koala genomes and directly measured mutation rates from four parent-offspring trios, finding koalas mutate at about half the rate of humans and using this to build a genetic timeline back roughly 100,000 years.

Despite ancient declines tied to climate, today’s koalas face human-caused threats—habitat loss, bushfires, vehicle collisions, and disease—making genomic insights critical to predicting inbreeding risk and prioritizing at-risk populations.

Modern pressures from humans continue to drive declines, underscoring the need for targeted conservation actions.

The timeline reveals a major population bottleneck between 60,000 and 100,000 years ago, indicating koalas nearly went extinct long before humans reached Australia.

This mutation-rate–driven timeline enhances understanding of recent population changes and can guide conservation, including monitoring genetic diversity and directing interventions in Queensland, New South Wales, and Victoria.

The eastern koala population persisted and expanded after climate improvement, giving rise to current eastern lineages, while the western population disappeared amid habitat fragmentation from the Nullarbor Plain’s expansion about 70,000 years ago.

The late-Pleistocene bottleneck around 60,000 years ago aligns with environmental shifts, signaling a climate-driven decline rather than a recent event.

Genomic analyses provide a clearer timeline of population changes than sparse fossil records, offering a more precise view of ancient koala diversity.

Some earlier population collapses were climate-driven (ice ages), challenging views that koala declines began primarily with human arrival around 65,000 years ago.

The researchers plan to apply the same genomic approach to other native Australian animals to determine whether pre-human declines occurred and to improve conservation planning for koalas and related species.