What Stuff Weighs

 A single blue whale can weigh 400,000 pounds.  But suppose you could put every kind of mammal on your bathroom scale, not as individual organisms but as a species. Cattle would physically weigh the most, according to a new study by the Wiezman Institute of Science.  In a paper titled “The Global Biomass of Wild Mammals,,” published in the Proceedings of the National Academy of Science last March, researchers determined that dogs–our family pets–collectively weigh about as much as all 4,805 wild species of mammals combined.  Cats tip the scales at double the tonnage of savannah elephants.  

Watching Nature on PBS, with its migrating wildebeests, foraging bears and wallowing hippos gives a seriously distorted impression that the earth teems with wildlife.  In fact, human beings (weighing in at 390 million tons) and cows (totalling altogether 420 million tons) represent almost all of the globe’s mammalian biomass.  Adding in sheep, pigs and other animals cultivated for meat or dairy means that  livestock outweigh all wild mammals by a factor of thirty-fold.  

In a related study, the scientists recently determined that what they call “anthropogenic mass” (the total of human made artifacts like cars, coke bottles, skyscrapers and disposable diapers) has passed a tipping point.  People are producing or consuming the equivalent of their own body weight every week, on average, and this total is doubling roughly every twenty years.  In 2020, our species’ “anthropogenic mass” outran the sum of all the world's living biomass - not just overtaking the tonnage of mammals but of fish, forests, fungi, and all  other lifeforms.

Calculating the human footprint on nature by weight is just one measure of our impact, alongside extinction rates and loss of biodiversity.  But “The Global Biomass of Wild Mammals,” coming on the heels of demographic reports that the world’s population surpassed eight billion late last year, is a shocking indicator that nature’s scales have gone seriously out of balance.

Lead author Ron Milo, who  holds a PhD in Biological Physics and was the first fellow in Systems Biology at Harvard Medical School before joining the Department of Plant & Environmental Sciences at the Weizmann Institute, says “It is definitely striking, our disproportionate place on Earth. When I do a puzzle with my daughters, there is usually an elephant next to a giraffe next to a rhino. But if I was trying to give them a more realistic sense of the world, it would be a cow next to a cow next to a cow and then a chicken.”

Solving this puzzle starts with what’s on our plate.