The total mass of all humans and domestic animals increased by nearly 3.5 times from 1900 through the early 21st century. This increase is thought to be the result of more easily accessible sources of food. The population of wild animals did not follow the same trend as domestic animals — it actually decreased by an estimated 25% from 1960 through the early 2000s. For example, in 1900, the total mass of all humans was four times more than the world’s elephants, and by the year 2000, humans accounted for 200 times more mass than elephants. This was because of an increase in the human population and a decrease in the elephant population.
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