You’re just a speck

Humans account for little next to plants, worms and bugs

When you weigh all life on Earth, billions of humans don’t amount to much compared to trees, earthworms or even viruses. But we really know how to throw what little weight we have around, according to a first-of-itskind global census of the footprint of life on the planet.

Humans only add up to about one 10,000th of the life on Earth, measured by the dry weight of the carbon that makes up the structure of all living things, also known as biomass.

The planet’s real heavyweights are plants. They outweigh people by about 7,500 to one, and make up more than 80 per cent of the world’s biomass, a study in Monday’s Proceedings of the National Academy of Sciences said.

Bacteria are nearly 13 per cent of the world’s biomass. Fungi — yeast, mould and mushrooms — make up about two per cent. These estimates aren’t very exact, but they give a sense of proportion, said study lead author Ron Milo, a biologist at the Weizmann Institute of Science in Israel.

“The fact that the biomass of fungi exceeds that of all animals sort of puts us in our place,” said Harvard evolutionary biology professor James Hanken, who wasn’t part of the study.

Still, humans have an outsized influence on its more massive fellow creatures. Since civilization started, humans helped cut the total weight of plants by half and wild mammals by 85 per cent, the study said.

Now domesticated cattle and pigs outweigh all wild mammals by 14 to one, while the world’s chickens are triple the weight of all wild birds. Instead of children’s books about elephants and lions, a more honest representation of Earth’s animals would be “a cow next to another cow, next to another cow next to a chicken,” Milo said.

Milo and colleagues took earlier research that looked at biomass for different types of life, combined them, factored in climate and geography, to come up with a planetwide look at the scale of life on the planet.

Taking water out of the equation and measuring only dry carbon makes it easier to compare species. About one-sixth the weight of a human is dry carbon. Humans are about two-thirds water.

Duke University conservation scientist Stuart Pimm called the study “a very important compilation of big numbers that speak to the nature of our world and the impact we humans have on it.”