Because plants' sexual systems are varied-species may possess various combinations of male, female, or hermaphrodite systems-their evolution has long been of interest to scientists. This is especially the case in melons, whose sexual system-andromonoecy-carries both male and bisexual flowers and appears to have evolved recently. In this study, the researchers sought to understand what determines the recent formation of melons' new sexual system. "If we can understand how different sexual systems in plants have evolved, we can then begin to understand how sex in general evolves," explained Purugganan. The researchers focused on the role played by the hormone ethylene, which is known to help fruit ripen. The French group determined that an enzyme involved in making this gaseous hormone is also involved in the evolution of the sexual switch of female flowers to hermaphrodites. The finding links hormone levels to sex determination in flowers.