Once upon a time, there were many giants living in our world.
Actually, it wasn’t that long ago. Once the dinosaurs had had their day, our planet was home to a whole new range of gigantic animals, from human-sized sloths to woolly mammoths to enormous wombats and kangaroos to the magnificent giant goose.
Between about 50,000 and 10,000 years ago, nearly 200 of the world’s largest animal species disappeared forever, leaving nothing but their gigantic bones (and burrows). It’s unclear what ultimately claimed these magnificent creatures.
During the period in which the megafauna disappeared, the world warmed and an ice age ended, pointing to one possible mechanism: climate change. Meanwhile, our own species expanded into new lands, seeking the wealth of resources that came with the retreating ice. And so the debate raged over the role of these two possible contributing factors.
Now a new study into the decline of giant plant-eating mammals – megaherbivores – points the finger at humans.
Fossils show that 50,000 years ago there were at least 57 species of megaherbivores. Today, only 11 remain. These include remarkable giants such as hippos and giraffes, as well as several species of rhinoceros and elephants, many of which are still endangered.
According to researchers, such a dramatic decline cannot be explained by climate change as the sole cause.
“The large and highly selective loss of megafauna over the past 50,000 years is unique in the past 66 million years. Previous periods of climate change did not lead to large, selective extinctions, arguing against a major role for climate in megafauna extinctions,” says macroecologist Jens-Christian Svenning of Aarhus University in Denmark.
“Another important pattern arguing against a role for climate is that recent megafauna extinctions hit climatically stable areas with equal force as those in unstable areas.”
The new study is a comprehensive review of the available evidence since the dinosaurs went extinct 66 million years ago. This includes locations and times of extinctions, habitat and food preferences, estimated population sizes, evidence of human hunting, human population movements, and climate and vegetation data going back millions of years.
We know that humans coexisted with megafauna, and we have evidence that some species were hunted to extinction. We know that our ancestors were able to effectively hunt large animals.
“Early modern humans were effective hunters, even of the largest animal species, and clearly had the ability to reduce populations of large animals,” Svenning said.
“These large animals were and are particularly vulnerable to overexploitation because they have long gestations, produce few offspring at a time, and take many years to reach sexual maturity.”
The new research shows that these human hunters were effective enough to contribute significantly to many extinctions. The megaherbivores, the team found, went extinct under a range of climate scenarios in which they could have thrived effectively even during times of change. Most of them would have adapted well to a warming environment, the researchers found.
And they died at different times and to different degrees – but all of those times were after humans had arrived, or had developed the means to hunt them. In fact, the exploitation of mammoths, mastodons, and giant sloths was consistent pretty much everywhere humans went.
Perhaps the mammoths persisted on Wrangel Island after the mainland population disappeared because there were no people there.
It’s a sobering thought, especially since the megafauna that survive today are in decline due to human exploitation, as a 2019 study found. About 98 percent of endangered megafauna species are at risk of extinction because humans won’t stop eating them.
“Our results emphasize the need for active conservation and restoration efforts,” Svenning says. “By reintroducing large mammals, we can help restore the ecological balance and support the biodiversity that evolved in ecosystems rich in megafauna.”
It’s no wonder then that the rest of the animal kingdom is afraid of us.
The research was published in Cambridge Prisms: Extinction.