The Swedish botanist and cytogeneticist Gunnar Östergren in 1945 noted how chromosomes may spread in a population because of their own ”parasitic” nature. Discussing B chromosomes in plants he wrote: ”In many cases these chromosomes have no useful function at all to the species carrying them, but that they often lead an exclusively parasitic existence … [B chromosomes] need not be useful for the plants. They need only be useful to themselves.” - Gunnar Östergren.