Why did the Tang, Song and Yuan Dynasties rarely keep genealogy?

Starting with the "ancestor" of the village.

Genealogy generally does not start from the most famous ancestor in history, but from the "ancestor" of the village. People will simply introduce the inheritance of descendants under the famous ancestors, and then carefully write down the names of their descendants and the surnames of their spouses from their ancestors.

Villages in China generally have one or three surnames with a large number, and each surname has a common ancestor. The present village pattern in China was fixed after Hongwu immigrants and Judy immigrants in Ming Dynasty.

Many places were empty before, because from the end of the Song Dynasty to the end of the Yuan Dynasty, the situation was turbulent and famine continued, and many villages were empty. Therefore, the imperial court decided to emigrate from Shanxi and other populous places to Shandong and Henan. Many villages in northern China were established in the early Ming Dynasty.

The genealogy of the Yuan Dynasty and before is often lost, and at the same time, because a very perfect genealogy system has not been established, the genealogy of most surnames has not been handed down, so we have to start with the "moving ancestors" in the Ming Dynasty. There are some exceptions here. For example, the family tree of the Kongs is perfect.