Quote from : the Hot Zone Book

In a sense, the Earth is mounting an immune response against the human species. It is beginning to react to the human parasite, the flooding infection of people, the dead spots of the concrete all over the planet, the cancerous rot-outs in Europe, Japan and the United States, thick with replicating primates, the colonies enlarging and spreading and threatening to shock the biosphere with mass extinctions. Perhaps the biosphere does not 'like' the idea of five billion humans.