Where does sex come from?

I asked my son, who graduated from high school this year, "How does evolution explain the origin of sex between men and women?" Suddenly I was curious and asked my son without any questions. The son made a puzzled look and said, "Well."

I could not explain it. Suddenly the water was a question, so it was not an easy question to answer if you did not think about it.

In fact, when did humans and animals all originate in the sexes of females and males? It is also the same. Men and women must be made contemporaneously, but animals that are divided into male and female must be made simultaneously or contemporaneously, so descendants are created. And in the world, whether men and women or females and males should exist.

I have confirmed that it is impossible for me to claim that the origin of life is so. In order for the birth of life to take place, the existence of man and woman must be simultaneous or contemporaneous, and even if it is done at the same time, the functions and structures must be mutually interlinked and the same life It is impossible to be born and born in the womb by chance.

So how do you explain it?
If it is impossible to be created by itself
What makes a person and an animal castle and makes the function work?
If it can not be created by itself, someone would have made it.

I was curious as to how the evolutionary theory explains how sexuality was determined at the same time, because the birth of life was made through sexual intercourse between men and women, and could not have been evolved by men or women alone.

The same is true of animals. One can not evolve first among females or males because they can not bear life by themselves. Although it is said that the core of evolution is going through a process of evolution for a long time, the birth of life must be made at the same time or at the same time. It is because the birth of life is accomplished even if the sexual union is made.

So I tried to find out how to explain it on the Internet.