We often think that our world is an infinite realm comprising great plains, jungles, and oceans, teeming with wild animals featured in memorable nature shows like the BBC’s Planet Earth. But the first global census of wild mammal biomass, conducted by Weizmann Institute of Science researchers, reveals the extent to which our natural world – along with its most iconic animals – is a vanishing one. 

An earlier, widely-discussed study by researchers from Prof. Ron Milo’s lab in Weizmann’s Plant and Environmental Sciences Department showed that in 2020, the mass of human-made objects – anything from skyscrapers to newspapers – had surpassed the planet’s entire biomass, from redwood trees to honeybees. In the latest study, the researchers offer a new perspective on humanity’s rapidly increasing impact on our planet, seen in the ratio between humans and domesticated mammals, and wild mammals.

To calculate the biomass of our warm-blooded class, the researchers collected existing censuses of wild mammal species and the defining characteristics of hundreds more. The new report shows that the biomass of wild mammals on land and at sea is dwarfed by the combined weight of cattle, pigs, sheep, and other domesticated mammals. 

Milo’s team found that the biomass of livestock has reached about 30 times the weight of all wild terrestrial mammals (approximately 20 million metric tons) and 15 times that of wild marine mammals (40 million metric tons).

“This study is an attempt to see the bigger picture,” says Milo. “The dazzling diversity of various mammal species may obscure the dramatic changes affecting our planet. But the global distribution of biomass reveals quantifiable evidence of a reality that can be difficult to grasp otherwise: It lays bare the dominance of humanity and its livestock over the far smaller populations of remaining wild mammals.”