Origin Story: A Big History of Everything

by David Christian

In 1890, human impacts on the nitrogen cycle were insignificant. Each year, humans extracted about fifteen megatons of nitrogen from the atmosphere, mainly through farming, while wild plants extracted about one hundred megatons, or almost seven times as much. One hundred years later, humans and plants had swapped roles. By 1990, the area of farmed land had increased to such a degree that wild plants were extracting only about 89 megatons, while human extraction of nitrogen through farming and fertilizer production had risen to 118 megatons. Our impact on other large mammals has also been profound. In 1900, wild land mammals accounted for the equivalent of about ten megatons of carbon biomass. Humans already accounted for about thirteen megatons, while domesticated mammals—our cows, horses, sheep, and goats—accounted for an astonishing thirty-five megatons. In the next century, these ratios would get even more warped. By 2000, the total biomass of wild land mammals had fallen to about 5 megatons, while that of humans had increased fast (not surprising, given what we know of population growth) to about 55 megatons and that of domesticated mammals to an astonishing 129 megatons. This is a powerful indicator of the extent to which expanding human activities have squeezed out other species of large animals by taking more and more of the biosphere’s resources. The point is a general one. Most species of animals and plants that are not of immediate value to humans are declining i...