Humanity moves more biomass than all land animals

Every living thing moves matter, and the sum of that movement, the shifting of biological material across the face of the Earth, is one of the great ecological forces, the circulation system of the biosphere. The movement made by animals, the migrations, the foraging, the transport of seeds and nutrients, has been studied for as long as ecology has existed. A paper in the 28 October issue of Nature Ecology & Evolution adds a new actor to the account, and the addition changes the arithmetic: the movement of biomass by humans, the food, timber, livestock and plant matter loaded onto our vehicles and ships and railways, may be up to forty times greater than the combined biomass movement of all land animals put together.

The comparison is the paper’s central device, and its power is in the scale of the number. The study, by an international team, assembles the data on how much biological material humans transport, as food for cities, as wood for construction, as feed for animals, as commodities for trade, and sets it against the best estimates of how much biomass the world’s land animals move in their normal lives, the migrations and carrying of the bison and the wildebeest, the seed-spreading birds, the foraging of everything in between. The human figure, the team reports, exceeds the animal figure by up to forty times, a ratio that reframes the question of who runs the biosphere’s transport.

The mechanism behind the number is familiar but newly visible at this scale. Agriculture and global trade have concentrated and moved biomass on a scale no species has ever approached: the grain of a continent’s harvest crossing an ocean, the timber of one forest building the houses of another region, the livestock raised in one ecosystem and consumed in a distant city. The movement is the biological signature of civilisation, and the paper’s estimate makes its magnitude legible for the first time.

The implications run in several directions. For ecology, the finding complicates the map of nutrient flows: the same rivers and oceans now carry a cargo of movement that dwarfs the natural circulation, with consequences for the distribution of nutrients, for invasive species hitching rides, and for the ecosystems at both ends of the world’s freight lines. For the study of humanity’s environmental footprint, it adds a dimension that carbon accounting misses: the sheer physical mass of biological material in transit, an index of the scale at which human activity has reorganised the planet’s matter.

There is a humbling arithmetic in the result. The migrations that ecologists once saw as the great movements of the biosphere, the herds that reshaped continents, turn out to be a small fraction of the traffic the modern world runs in a year. Humanity does not merely participate in the movement of biological matter; it dominates it, forty times over, and the paper’s number is the measure of a quiet and total reorganisation of the planet’s transport. The biosphere has a new circulation system now, and its volume, the study shows, is ours.