Koalas nearly vanished 60,000 years ago. And humans had nothing to do with it

Photo: pixabay.com

Scientists from the University of Sydney and Texas A&M University studied the genetic material of 457 modern koalas. The analysis allowed them to reconstruct the history of their population over tens of thousands of years. It turned out that all modern koalas are descended from a relatively small group of animals that managed to survive a period of sharp decline in the species' numbers.

The researchers paid particular attention to the mutation rate — natural genetic changes that gradually accumulate in organisms. By determining the rate at which such changes occur in koalas, scientists were able to more accurately pinpoint when critical events in the species' history took place. It turned out that the mutation rate in koalas is approximately half that of humans.

The study results showed that about 100,000 years ago, the koala population began to decline, and approximately 60,000 years ago, it reached a critically low level. Such a state is called a "genetic bottleneck." This means that very few individuals survived, so the genetic diversity of the species significantly decreased. When the number of animals becomes too small, the risk of extinction increases, as the species becomes less resilient to diseases and environmental changes.

Previously, some scientists believed that the main decline in koala numbers could have been linked to the arrival of the first humans in Australia about 65,000 years ago. However, new data showed that the crisis began much earlier. This means that the main cause was not humans, but natural climatic processes.

Over millions of years, Australia has changed significantly. Once, a large part of the continent was covered by dense, humid forests. But due to the gradual northward movement of the Australian tectonic plate, the climate became increasingly dry. During glacial periods, droughts intensified, and fires occurred more frequently. As a result, many ecological systems were severely altered.

About 70,000 years ago, the large arid Nullarbor Plain formed, effectively dividing the koala's habitat into eastern and western parts. Because of this, populations became isolated from each other. The western population eventually disappeared completely, while the eastern one, though very small, managed to survive.

When the climate became more favorable and a relatively warm interglacial period arrived, koala numbers began to increase. Approximately between 16,500 and 6,000 years ago, they once again spread across a significant portion of eastern Australia and divided into several genetic groups, from which modern populations are descended.

Today, koalas are once again under threat, but for different reasons. They are affected by deforestation, the construction of roads and cities, wildfires caused by climate warming, and various diseases. In a number of Australian regions, the species is officially recognized as endangered.

Scientists believe that understanding how koalas survived the ancient climatic crisis will help better organize their protection today. The information obtained may also be useful for studying the history of other Australian animals and determining how they reacted to climate change in the distant past.

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