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The Medea hypothesis is a term coined by paleontologist Peter Ward for a hypothesis that contests the Gaian hypothesis and proposes that multicellular life, understood as a superorganism, may be self-destructive or suicidal. In this view, microbial-triggered mass extinctions result in returns to the microbial-dominated state it has been for most of its history. The metaphor refers to the mythological Medea , who kills her own children.
Past regressions include:
The list does not include the Cretaceous–Paleogene extinction event, since this was, at least partially, externally induced by a meteor impact.
Peter Ward proposes that the current man-made climate change and mass extinction event may be considered to be the most recent Medean event. As these events are anthropogenic, he postulates that Medean events are not necessarily caused by microbes, but by intelligent life as well and that the final mass extinction of complex life, roughly about 500–900 million years in the future, can also be considered a Medean event. Plant life that will still exist 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. However, Ward simultaneously argues that intelligent life such as humans may not necessarily just trigger future Medean events, but may eventually prevent them from occurring.