Erik Veland / Wikimedia
New research has found that koalas were at risk of extinction due to climate change around 100,000 years ago, long before the first humans arrived in Australia.
A major genomic study has reshaped scientists’ understanding of koala evolution, revealing that the species suffered a drastic population collapse about 100 thousand years ago.
The research, led by scientists at the University of Sydney and Texas A&M University and published in the journal Molecular Biology and Evolution, challenges previous theories that linked the most significant decline of the species to human colonization approximately 65 thousand years ago.
When analyzing the genomes of 457 koalasresearchers discovered that all modern koalas descend from a small ancestral population that survived severe climate change during the late Pleistocene. The findings suggest that natural environmental changes, rather than human activity, were responsible for the species’ first and most severe population bottleneck.
“The study rewrites the chronology of the koala’s genetic history in Australia,” said principal investigator Toby Kovacs, a PhD student involved in the project. According to Kovacs, genomic data offers a unique window into the past, allowing scientists to reconstruct population trends from periods when fossil evidence is scarce.
To unravel the evolutionary history of the species, the research team carried out the first direct measurement of mutation rates in koalas and any member of the marsupial order Diprotodontia, which includes kangaroos, wombats and opossums. By sequencing the genomes of four groups of parents and children, they calculated a mutation rate approximately half that observed in humans.
Using this new genetic parameter, scientists tracked population changes over thousands of generations. Their analysis revealed that koala numbers began to decline around 100,000 years ago and reached a critical point around 60,000 years ago. coinciding with a period of intense environmental changes to Australia.
During this period, repeated glacial cycles brought cooler, drier conditionswhile the expansion of the Nullarbor Plain has reduced suitable habitat and fragmented koala populations. Researchers believe that western koala populations eventually disappeared, with only a small eastern population remaining.
As climate conditions improved during the current interglacial period, surviving koalas expanded across eastern Australia. Between 16,500 and 6,000 years ago, diversified into five genetic populations that form the basis of modern koala groups, explains .
While the study highlights the role of ancient climate change in shaping koala history, the researchers stress that modern threats are largely caused by human action. Habitat destruction, hunting, disease and increasingly severe bushfires continue to threaten the species, which has been listed as endangered in parts of eastern Australia since 2022.
