Polyploidy is prevalent in plants and has played a significant role in the evolution of almost all angiosperm genomes. For example, many domesticated crops are either polyploids (e.g., wheat, coffee, cotton and peanut) or paleopolyploids (e.g., rice, maize, soybean and sorghum). After polyploidization, particularly in allopolyploidy, the subgenomes may reduce potential genetic incompatibilities through rediploidization, a process that involves rapid gene losses. Despite the important role of diploidization in the evolutionary innovation of new genes and new species, the evolutionary forces that drive the diploidization process and their underlying mechanisms remain unclear.