"Biezi as ancestor" originally referred to letting the son other than Zongzi (the heir) start his new clan and become its first ancestor. There were two stages in the Zhou Dynasty for this custom. In the Western Zhou Dynasty

the first heir was the son and the second heir was the younger brother. Biezi could refer to any son without inheritance rights

including the eldest Dizi (son from the first legitimate wife). During the Spring and Autumn Period and the Warring States Period

the system for the eldest Dizi as heir gradually dominated. The eldest Dizi became the only legal heir. Biezi could no longer start his own clan as ancestor

and the eldest Dizi was no longer included in the Biezi group. The custom of killing the first son was before the custom for Biezi or the eldest Dizi as ancestor. The patriarchal law was the law of the clan. It is incorrect to judge whether the patriarchal law was implemented by finding whether there was the system for the eldest Dizi as heir or whether the eldest Dizi was distinguished from other sons. Corresponding to the two stages

the patriarchal clan system in the Zhou Dynasty also presented two different forms. In the Western Zhou Dynasty

the youngest son was the actual heir of the major clan while the eldest son and Biezi became ancestors of their respective minor clan

and the elder sons were inferior to the younger sons. Since the Spring and Autumn Period and the Warring States Period

the eldest Dizi had become the heir of the major clan

and younger sons were inferior to the elder sons.