Most organisms are normally diploid, meaning they have two sets of chromosomes — one set inherited from each parent. Polyploidy may occur due to abnormal cell division. It is most commonly found in plants, but it does sometimes happen in animals. Some estimates suggest that 30-80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes. Huge increases in angiosperm (flowering plants) diversity have coincided with the timing of ancient genome duplications shared by many species. 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase.