Do you remember the movie "Finding Nemo"? The cute and mischievous clownfish's adventures in the Australian deep sea attracted many viewers. However, the real clownfish living in the ocean prefer to live in groups and are not adventurous. Moreover, they have a big secret: clownfish are truly "hermaphrodites", sometimes "male", sometimes "female", and sometimes it's impossible to tell. This is really incredible.
Scientists studying clownfish found that they always live together with anemones in nature, so they are also called anemone fish. In a large anemone, there are always many clownfish accompanying it, forming a large family. This family hierarchy is strict. The strongest female fish is the only "female" with absolute dominance. She always chooses the largest male fish as her spouse, and to consolidate her position, she will chase and suppress other family members. Those small male fish and un-characterized young fish can only move around in unimportant corners near the anemone. More incredibly, if the "dominant" female fish dies or leaves, the original male spouse will suddenly become a "female" and continue to choose the largest male fish to mate and take on the responsibility of raising offspring. This is the very unique physiological phenomenon of clownfish. The same individual has both female and male reproductive organs, that is, "hermaphrodites".
In fact, there are many hermaphrodites in nature, such as the very familiar earthworm, which is a typical example. However, unlike clownfish, each earthworm individual is hermaphrodite, that is, having both male and female characteristics, and this remains unchanged throughout its life.
Why do animals exist with "hermaphroditism"? This question has also not been given a definitive answer. However, scientists speculate that this may be related to natural selection caused by competition for mating opportunities among individuals of the same sex (usually males). Some species have difficulty finding mates in harsh environments, so hermaphroditism has emerged in these animals through natural selection. This can ensure the reproduction and increase of the species. For example, clownfish balance the population size by switching genders; hermaphroditic earthworms can mate with any individual, which is more conducive to the reproduction of the species.