Megaevolution
![When it was first described, the Cambrian fossil Opabinia was thought to be unrelated to any known phylum. Later discoveries have shown it to be closely related to the ancestors of arthropods.](/Images/godic/202501/26/Opabinia_BW22708.jpg")
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![Dickinsonia, an organism of the Ediacaran Period that precedes the Cambrian, whose affinity is still unknown.](/Images/godic/202501/26/DickinsoniaCostata2708.jpg")
Megaevolution describes the most dramatic events in evolution. It is no longer suggested that the evolutionary processes involved are necessarily special, although in some cases they might be. Whereas macroevolution can apply to relatively modest changes that produced diversification of species and genera and are readily compared to microevolution, "megaevolution" is used for great changes. Megaevolution has been extensively debated because it has been seen as a possible objection to Charles Darwin's theory of gradual evolution by natural selection.