Evolution/The changing sexual identity of creatures
Are there not some creatures whose sex changes in their life time?
Who are they? How does and when does this happen? When they are young?
Yes there are, and some have both sexes in the same animal. These are called hermaphrodites Earthworms for one, and snails for another, have both sexual structures. As a kid growing up in an area with horses, one horse breeder had a hermaphrodite horse. And he used it to see if the mares that came to have their mare bred to his advertised stallion, were ready to breed. He never wished to risk that valuable stud to a mare not ready to breed, who may injure his stud..... so he kept this small hermaphrodite and used it to test to see if the mare would accept a stallion.
Fish as well at times can switch from being a male to a female, and in fact we have some problems with that..... because women who take birth control pills, urinate into our sewage system. And tho it is all treated, and then emptied into the sea or a river, and is even drinkable, there is no way to get out the extra estrogen, so fish eggs exposed to this, tend to produce lots of female offspring. Sometimes, so few males are born, that the eggs are never fertilized.
In high school we are all taught that biological sex has to do with X and Y. Women have two X's, and men have one of each, X and Y.
But recently, scientists have learned that things might not be so simple. There are people whose biological sex can't be easily determined because they're born with both genitals or because the female presents with an XY and the male presents with the XX.
People with congenital abnormalities that leave them unable to be classified as male or female are considered "hermaphrodites" in humans. And most of these are, in this country, corrected to be either a male or female surgically. This surgery is usually done when they are still babies. Whether or not that is a good idea or not, it your call, not mine. In poor countries, these babies end up in freak shows, put there by their poor parents, as a way to make money. (And as an aside, humans are often born with a truly long tail. Some can even wag it. These are removed in First World countries when they are children.... but again, in poor places, like Indonesia, they are put on display to earn money for the family....and have no intention to remove the tail.)
In the animal world, though, hermaphrodites aren't the atypical abnormalities they are in the human world.
These species are evidence that there's more to biological sex than just genes and chromosomes -- sometimes, all it takes is an environmental factor to alter one's sex and gender. And as yet, for the most part, we don't know why this happens in humans.... i.e., was the mother exposed to some chemical? Or did she eat things that were contaminated.... with what, we don't know. Or was the father responsible for these anomalies? No one knows.
Reef fish are known to change sex even as adults.
You likely can google more.... try something such as, "What animals can have both sexes in one body?" And "What animals can change sex from male to female, and from female to male?" Try this one too, "What causes an animal that was male to become female?"
Fun question...even more fun are the answers.