Undoubtedly, Charles Darwin can be considered as the father of plant breeding system studies. In his two books The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom, and The Different Forms of Flowers on Plants of the Same Species, Darwin pioneered work on self- incompatibility, inbreeding depression, heteromorphy, gynodioecy, pollination biology and gene flow, although he himself had no concept of the gene. The discovery of plant chromosomes, and the important role played by chromosomal mechanisms in plant evolution dominated plant evolution- ary genetics in the first half of the 20th century. Despite the lead taken by Darwin, studies on plant breeding systems proceeded very slowly during this period, although work during the 1920s revealed the genetic basis of self-incompatibility mechanisms. At least two generations ahead of his time, Sewall Wright was providing a sound and sophisticated model basis to the subject, the complexity and relevance of which is still being revealed today.