Sequential hermaphrodites are organisms which are born with the sex organs of one gender and the capability of changing sexes later in life. Sometimes, sequential hermaphrodites change sex at a predestined time, as part of their development. In other cases, the sex change is an elective process, undertaken in response to environmental or biological triggers.
Before delving into the world of sequential hermaphrodites, it may help to know that a hermaphrodite is any organism which has sexual characteristics associated with both genders. This term is primarily used in the scientific community; using “hermaphrodite” in reference to a human with ambiguous sex organs is considered offensive. In addition to sequential hermaphrodites, it is also possible to see simultaneous hermaphrodites, which have active sex organs from both genders at the same time. Humans and many other mammals do not develop hermaphroditic tendencies under normal circumstances.
There are two types of sequential hermaphrodites. Animals which are born male with the ability to become female are said to be exhibiting the trait of protandry. Protogyny, on the other hand, is a trait in which animals are born as females, with the ability to become males later in life. Depending on the species, simultaneous hermaphrodites may change sex only once, or they may be able to flip back and forth between genders several times.
Many simultaneous hermaphrodites are fish, such as the clownfish. Some form harems, in which a single male supervises a school of females. If the male is killed, the dominant female in the harem transitions and takes his place. In such harems, the male is usually responsible for defending the school from invaders and protecting his territory to ensure that his flock does not wander astray or encounter potential dangers.
There are some evolutionary advantages to being a sequential hermaphrodite, or this trait wouldn't exist. The ability to change gender in response to biological or environmental pressures makes sequential hermaphrodites much more flexible, and able to deal with situations in which their populations are depleted. This trait ensures the preservation of the species by promoting biodiversity, as animals can exchange genetic material with each other in a variety of ways. Sequential hermaphrodites are also very interesting for biologists to observe, with numerous studies on their evolution and lifestyle being conducted at various points around the world.