For years, scientists have debated whether humans or climate caused the dramatic decline in large mammal populations over the past few thousand years. A new study from Aarhus University confirms that climate cannot be the cause. The first modern humans migrated in large numbers f

Prehistoric man is attacking an elephant. New research suggests that humans, not climate, caused the dramatic decline of nearly all of Earth's megafauna 50,000 years ago. Image source: First published in Bryant & Gay, 1883. Wood carving by E. Bayard. Part of the reason for

's success is humans' ability to hunt large animals. With their ingenious hunting skills and specially crafted weapons, they have perfected the art of killing the most dangerous mammals. But unfortunately, our ancestors' great success came at the expense of other large mammals.

It is well known that many large species became extinct during the global colonization of modern humans. Now, new research from Aarhus University shows that those large mammals that survived also experienced dramatic declines.

Eastern gorillas are one of the most declining mammals. Today, it only lives in a small area in the Democratic Republic of Congo. Source: Michalsloviak

By studying the DNA of 139 living species of large mammals, scientists found that populations of nearly all species declined dramatically about 50,000 years ago.

Jens-Christian Svenning, director of the Center for Ecodynamics of Novel Biospheres (ECONOVO) at the Danish National Research Foundation and professor at Aarhus University, is the initiator of this research.

Another large mammal in decline is the greater one-horned rhinoceros. It lives in India and is one of the only five species of rhinoceros left. Image source: Mayank1704

"We studied the evolution of large mammal populations over the past 750,000 years. For the first 700,000 years, the populations were fairly stable, but around 50,000 years ago, the curve broke and populations declined sharply. Nor has it recovered. Over the past 800,000 years, the world has fluctuated between glacial and interglacial periods approximately every 100,000 years. If climate was the cause, then when the climate changed 50,000 years ago, we should Bigger fluctuations were seen. But we didn't. So humans are the most likely explanation."

For decades, scientists have debated the reasons why large mammals became extinct or declined rapidly over the past 50,000 years. One group of scientists believes that rapid and violent fluctuations in climate are the main reason. For example, they believe the woolly mammoth went extinct because much of the cold mammoth steppe disappeared. On the contrary, some people believe that the prevalence of modern humans (Homo sapiens) is the main reason. They believe that our ancestors hunted these animals to the point where they were either completely extinct or largely wiped out.

The most important piece of evidence in the debate so far is fossils dating back 50,000 years. These fossils show that the strong, selective extinction of large animals in time and space roughly coincides with the global spread of modern humans. Therefore, animal extinctions are difficult to link to climate. However, the debate continues. New data from

new research sheds new light on this debate. By studying the DNA of 139 species of large mammals, researchers were able to find that the numbers of these animals had also declined over the past 50,000 years. This development appears to be related to the spread of humans rather than climate change.

The Tahr is closely related to the goat, but is actually a type of antelope. It lives in the mountains of southern India and its population was once much larger. Image credit: Ameshshenai

Over the past 20 years, there has been a revolution in DNA sequencing. It has become easy and cheap to map entire genomes, and as a result, the DNA of many species has now been mapped.

Juraj Bergman, lead researcher of the new study and assistant professor at Aarhus University, explained that genome maps of species around the world are freely available on the Internet, and the Aarhus University research team is used this data.

"We collected data on 139 species of large mammals and analyzed a huge amount of data. There are approximately 3 billion data points per species, so it takes a long time and a lot of computing power: DNA contains a lot of information about the past . Most people know about the tree of life, which shows where different species developed and what common ancestors they had. We do the same with DNA variation. By grouping mutations and building family trees, we can estimate the The population size of a species over a period of time. The larger the population of an animal, the more mutations occur. This is actually a simple mathematical problem. Take elephants as an example. Every time an elephant becomes pregnant, some mutations are likely to occur and Pass these mutations on to future generations. More births means more mutations."

As shown in the picture, the Pere-David elk no longer live in the wild. Today the only remaining animals live in zoos and animal parks. Image credit: Tim Fells

The 139 large mammal species examined in this study are all living species today. These include elephants, bears, kangaroos and antelopes, among others. There are an estimated 6,399 species of mammals on Earth, but this study selected 139 living megafauna species to examine how their populations have changed over the past 40,000 to 50,000 years, when similar large animals became extinct .

Large mammals are also known as megafauna - defined as animals that weigh more than 44 kilograms as an adult. Therefore, humans are also considered megafauna. In this study, however, the researchers looked at a species that weighed just 22 kilograms, so every continent was represented except Antarctica.

The one in the water is Lin Ling. This is a kind of antelope that lives in many countries in Africa. The forest antelope lives in swamp areas and was once more numerous. Image credit: Kennyannydenny

However, the size of the elephant population is not the only factor that affects the number of mutations.

If the area where elephants live suddenly dries up, the animals would be stressed, which could affect the composition of the variation. The same effect would occur if two isolated elephant populations suddenly met and mixed genes.

If it wasn't just the size of the population that affected the number of mutations, you would think the results would be inconclusive. But that's not the case, explains Juraj-Bergman.

"Only 10% of mammalian genomes are active genes. Strong selection pressure from the environment or migration will mainly lead to genetic mutations. The remaining 90% of genes are relatively neutral, so we studied the genes in the genome that are least susceptible to environmental influences. Mutations in parts of the population. These parts tell the story of population size over time."

Takin live in the Himalayas. It lives in bamboo forests and feeds on fresh leaves and grass. 50,000 years ago, the takin population was essentially extinct. Source: Eric Kilby

Much of the debate over what led to the extinction or decline of large animals has focused on the woolly mammoth. But that's not a good example because, as Jens-Christian Svenning explains, most extinct megafauna species were associated with temperate or tropical climates.

He said: "The classic argument for climate as an explanatory model is based on the fact that when ice melted and habitat types disappeared, woolly mammoths and some other species associated with the so-called 'mammoth steppe' disappeared with them. . This is basically an unsatisfactory explanation model, because the vast majority of extinct megafauna species at that time did not live on the mammoth steppe at all. They lived in warmer areas, such as temperate and tropical forests or savannahs. In In our study, we also found that many of the surviving megafauna species experienced sharp declines during this period, and that they came from a variety of different regions and habitats."The end of the

debate may not yet be decided, but Jens-Christian Svenning believes that the debate on climate as an explanation is difficult to continue.

" What seems unimaginable is that it is possible to propose a climate model that explains why all continents and large fauna groups have experienced extinctions and continued declines since about 50,000 years ago. Over the past 66 million years, This selective extinction of megafauna is unique despite dramatic climate change."

Given the wealth of data we now have, it is also difficult to deny that, instead, it was due to the global spread of humans from Africa and subsequent human population expansion increase.

compiled from: ScitechDaily