The Medea hypothesis is a term coined by paleontologist Peter Ward for the anti-Gaian hypothesis that multicellular life, understood as a superorganism, is suicidal. In this view, microbial-triggered mass extinctions are attempts to return the Earth to the microbial-dominated state it has been for most of its history. The metaphor refers to the mythological Medea (representing the Earth), who kills her own children (multicellular life).

Peter Ward also believes that the current man-made climate change and extinction event may also be considered to be the most recent Medean event, due to them both being caused by humans, concluding that Medean events are not necessarily caused by microbes, but also by intelligent life as well. He also believes that the final mass extinction of complex life, roughly about 500 million years in the future, will also be considered as a Medean event as well, as plant life that still exists by then will be forced to adapt to a warming and expanding Sun, causing them to remove even more carbon dioxide from the atmosphere and ultimately accelerating the complete extinction of complex life by making carbon dioxide levels drop down to just 10 ppm, below which plants can no longer survive, much faster and sooner than anticipated.

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