are humans earth's infection?

Now University of Washingtonpaleontologist Peter Wardhas proposed an alternate theory that suggests Earth is set up to kill off lifewhen it spreads too widely. Humans wouldn't be the first victims of thisperiodic biocide. The dinosaurs may have been killed off by an asteroid, he says, butduring the planet's other mass extinctions, millions of species were done in by good old Mom.

- Is nature one mean mother?