Humans form only a minuscule part of life on earth

A first-of-its-kind census says they have outsize influence on fellow creatures

Updated - May 23, 2018 12:19 pm IST

Published - May 22, 2018 08:51 pm IST

 The study examines the nature of our world and the impact humans have on it.

The study examines the nature of our world and the impact humans have on it.

When you weigh all life on the 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-its-kind global census of the footprint of life on the planet.

The planet’s real heavyweights are plants.

Plants outweigh all

They outweigh people by about 7,500 to 1, and make up more than 80% of the world’s biomass, a study in Monday’s Proceedings of the National Academy of Sciences said.

Bacteria are nearly 13% of the world’s biomass. Fungi yeast, mold and mushrooms make up about 2%. These estimates aren’t very exact, the real numbers could be more or less, 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%, the study said.

Domesticated animals

Now domesticated cattle and pigs outweigh all wild mammals by 14 to 1, while the world’s chickens are triple the weight of all the 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,” Mr. Milo said.

Mr. Milo and colleagues took earlier research that looked at biomass for different types of life, combined them, factored in climate, geography and other environmental issues, 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 for scientists 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.”

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