Why were sons called "dogs" and daughters called "daughters" in ancient times?

The word "son of a dog" originally came from No.57, Volume 1 17 of Biography of Historical Records of Sima Xiangru. Sima Xiangru, born in Chengdu, Shu County, is evergreen. When I was young, I was good at reading and learning fencing, so I was called my son by my own name.

Emperor Wu of the Han Dynasty, Sima Xiangru read an article "Fu Lin" by Emperor Wu of the Han Dynasty. Emperor Wu liked this article very much and praised it greatly. It happened that dog supervisor Yang Deyi knew Sima Xiangru and recommended it to Emperor Wu of the Han Dynasty. Later, Emperor Wu summoned Sima Xiangru to thank him, and Sima Xiangru wrote Fu Lin for Emperor Wu. This article praised SHEN WOO, a wise man in Hanwu, and the great national strength of the Han Dynasty. From then on, Sima Xiangru became famous. Later, the famous dog was handed down, and everyone hoped that his son would be present like Sima Xiangru, so they called him a dog, which gradually evolved into a humble son.

There is a line in the Yuan drama "The Return of Xue": "Miss, I am the daughter of ordinary people, and you are the darling daughter of an official family. Help yourself. " After the Ming and Qing Dynasties, a good family was generally called "a daughter", and the title of "a good girl" was handed down, mostly used to describe girls.

Another theory is related to Wu Zixu. "Wu yue spring and autumn? Liao Wang's Biography of Childe records the story of a woman who gave her life to save Wu Zixu. Wu Zixu thought of repaying a debt of gratitude after she got revenge, but she didn't know the girl's address, so she put her daughter in the place where she dived at that time, so there was the saying of a good girl.

This is also in line with the concept that girls should be well-off now, and they all want their children to be outstanding, so they modestly call their daughters daughters.