For years, scientists have debated whether humans or the climate have caused the population of large mammals to decline dramatically over the past several thousand years. A new study from Aarhus University confirms that climate cannot be the explanation.

About 100,000 years ago, the first modern humans migrated out of Africa in large numbers. They were eminent at adapting to new habitats, and they settled in virtually every kind of landscape—from deserts to jungles to the icy taiga in the far north.

Part of the success was human’s ability to hunt large animals. With clever hunting techniques and specially built weapons, they perfected the art of killing even the most dangerous mammals.

But unfortunately, the great success of our ancestors came at the expense of the other large mammals.

It is well-known that numerous large species went extinct during the time of worldwide colonization by modern humans. Now, new research from Aarhus University reveals that those large mammals that survived also experienced a dramatic decline.