Melons have recently evolved a strange new sexual feature: When they bloom, their flowers are both male and bisexual. Their sexual system is called "andromonoecy," and it may provide a glimpse into what caused humans to evolve into male and female — as well as what we might evolve into next. Scientists in France and the United States looked at the history of the melon's evolution and discovered a key hormone that caused melons' sexual mutations. According to a release about the study:

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.

Though humans don't use this hormone, a similar mechanism might exist among humans that causes us to become male or female. Tweaks in that hormone could result in a transformation as dramatic as that found in melons. Humans might develop a third or fourth sex, or all of us might exhibit sexual characteristics of both. A gene for sexual switching in melons provides clues to the evolution of sex [Eurekalert]