Koala genomes reveal that populations once deemed genetically doomed are actually recovering

Science, 2026. DOI: 10.1126/science.adz1430

For decades, conservation genetics has operated on a simple assumption: when a population crashes, its genetic diversity drops, harmful mutations accumulate, and extinction risk climbs. This is the extinction vortex, and it has shaped how biologists assess which populations are most endangered.

A new study published in Science complicates that picture considerably. Researchers who sequenced 418 whole koala genomes from 27 populations across Australia found that the populations with the most severe historical bottlenecks are not, in fact, spiraling toward genetic collapse. They are recovering.

A natural experiment in population genetics

Koalas offer an unusually clear test case. Different regional populations have experienced dramatically different management histories. Northern populations have been in serious decline. Southern populations, particularly in Victoria, were nearly wiped out in the late 19th and early 20th centuries through hunting and habitat loss, then rebuilt from very small founding groups.

These Victorian populations have long been viewed as genetically compromised. They carry the signature of their bottleneck: low overall genetic diversity. But the new analysis reveals something the raw diversity numbers miss.

The bottlenecked populations are expanding. That growth is generating new mutations, and recombination, the natural reshuffling of genetic material during reproduction, is creating new genetic combinations. Harmful mutations are being reduced and adaptive potential is increasing.

More diversity does not always mean less risk

Here is the counterintuitive finding: populations with higher genetic diversity, such as those in northern Australia, actually carried more harmful genetic mutations and showed declines in effective population size. The standard conservation metric, overall genetic diversity, would flag the Victorian populations as more endangered. But the genomic data tells a different story.

Collin Ahrens, principal research scientist at Cesar Australia and lead author, put it directly: conservation decisions cannot rely on static measures of genetic diversity. What matters is the direction populations are evolving, not just a snapshot of how much variation they currently hold.

Andrew Weeks, director of Cesar Australia, framed the broader implication: for decades, genetic diversity has been treated as a simple scorecard of extinction risk. But evolution is dynamic. Understanding whether a population is expanding, stabilizing, or declining over time may be just as important as measuring how much diversity it holds today.

Implications beyond koalas

Many threatened species worldwide have experienced bottlenecks, habitat loss, and rapid environmental change. The research suggests that judging extinction risk based solely on static genetic measures risks misclassifying both danger and recovery. A population that looks genetically impoverished by conventional metrics may actually be on a trajectory of regeneration.

This has direct consequences for conservation management. Translocation, the practice of moving individuals between populations to boost genetic diversity, has been widely used for koalas in the past. It is now considered high-risk, complex, and expensive. If bottlenecked populations are recovering on their own, the calculus around intervention changes.

What the study does not resolve

The sequencing effort was catalyzed by the 2019-20 Black Summer bushfires, which intensified concern for the species' future. Luke Silver, a postdoctoral researcher at the University of Sydney, described the 418 genomes as a critical baseline for understanding how koala populations are evolving over time.

But a baseline is just that. The study captures a moment in time. Whether the recovery trends observed in Victorian populations will continue, stall, or reverse under future pressures, including climate change, disease, and habitat fragmentation, is unknown.

Northern populations remain in serious decline. The study does not suggest that all bottlenecked populations will recover; it demonstrates that some can, under the right conditions. Rapid population growth appears to be a key factor, and not all species or populations will have that opportunity.