What are the contributions of the Xia Dynasty?

Angel, the first Chinese Almanac called Xia Xiao Zheng appeared during this time. Also the first law named Yu Xing also was made. Gao Yao, a capable official, also created the first prison in Chinese history. Most importantly, Yu changed abandoned abdication system and gave the throne to his son. This marks the establishment of the heredity system. The kings and emperors in latter dynasties followed him to give the throne to their sons.

Previously, the kings abdicated the throne to another noble and capable person. It can't be their kids.