In the late 19th and early 20th centuries, koalas in the Australian state of Victoria were hunted almost to extinction for the fur trade. By the early 1900s, fewer than 1,000 animals remained in the region. To save the species, conservationists moved fewer than ten koalas to nearby offshore islands. Those island populations later formed the foundation for restoring koalas to mainland Victoria.
The recovery was dramatic in terms of numbers. But geneticists had long worried that what came back was genetically damaged — a population carrying the consequences of a severe bottleneck, the term used when a species is reduced to so few individuals that much of its genetic diversity is permanently lost. Low genetic diversity makes a species more vulnerable to disease, less able to adapt to environmental change, and at greater long-term risk of extinction.
A new study published in the journal Science in March 2026 has challenged that assumption in a profound way. Led by Dr Collin Ahrens, Principal Research Scientist at Cesar Australia — an independent environmental research company in Brunswick, Victoria — the team analysed the complete genome sequences of 418 koalas drawn from 27 populations across Australia. What they found in Victoria surprised them.
Despite the population's devastatingly low starting point, the koalas there are showing early signs of genuine genetic recovery. As their numbers have expanded rapidly, a natural process called recombination — in which existing genetic material is reshuffled into new combinations during reproduction — has been rebuilding functional genetic diversity. Harmful mutations are decreasing. New genetic variants are appearing. The effective breeding population has grown substantially over recent decades.
The findings do not mean koalas are out of danger. Northern populations remain in serious decline. But the research provides what Dr Ahrens describes as world-first evidence that rapid population growth can sometimes allow a species to escape the genetic trap that many scientists assumed was permanent — a message of hope, he says, that extends well beyond koalas.