As we all know, Monopterus albus is a "daughter" at birth, but once it is sexually mature and lays eggs, the reproductive system will suddenly change and become a "boy". Therefore, all slim and emaciated eels are "ladies" and all bulky eels are "men". In this way, a stout "man" married a weak "woman", gave birth to a group of "women", and then became a "man", and so on. More than 20 red thick fish in the Red Sea form a polygamous family. In this family, the husband is not allowed to be interested in other males, and the females in the nest are not allowed to be brave. Otherwise, this brave female may become a male. Once the only husband disappears or dies, a strong woman will become a man, take her place and rule the family. If this husband runs away, the other female will immediately become a male, running and changing until the last one becomes a male. In fact, this phenomenon is not uncommon among lower marine animals. Red snapper, big snapper, parrotfish and crested snapper all live on coral reefs, while fine snapper, eel and anemone all change from male to female. Some fish are more exotic, such as groupers in coral reefs. When there are more males than females in this sea area, some male groupers will become females. When there are more females than males in this sea area, some female groupers will become males to ensure that they will give birth to many offspring. Stranger still, the blue striped grouper living off the coast of Florida and Brazil changes several times a day. Every dusk, the male and female blue striped grouper will have a sex change, which is repeated five times in a row. This phenomenon is called degeneration, hermaphroditism and cross fertilization. Scientists analysis, perhaps because fish eggs are much larger than sperm, if only females lay eggs, the burden is too heavy and the price is too high. And if both parties undertake the task of ovulation and ovulation, they will have more opportunities to reproduce. Interestingly, the male and female changes of females are changing year by year, that is, last year it was male, this year it became female, and the next year it was male, which is constantly changing every year. Every man changes at a different time, not at the same time. Why the sex of lower marine animals changes is still a mystery. Although scientists have different opinions, there is no conclusion. But in any case, this is also a unique function that some lower animals have evolved in order to adapt to survival and reproduce more smoothly.