Why is most of the ancient Mandarin Henan dialect?

Xia Yan was the elegant dialect in ancient times, and the standard pronunciation of ancient Putonghua in China was Henan dialect, but today's Beijing dialect is actually Northeast dialect 400 years ago ... Do you believe these statements? Mr. Zheng Zhangshangfang, a researcher at the Institute of Linguistics, Chinese Academy of Social Sciences, has been engaged in language research for more than 50 years, especially in the field of ancient sounds and dialects. Recently, the reporter interviewed Mr. Zheng on the origin of Putonghua. & lt/p & gt； & ltp> Reporter: The oldest dictionary in China is Er Ya, which means to explain elegant words in order to approach correct pronunciation. Modern Chinese Dictionary says, "Elegant and standard." "Elegant language refers to the standard language prevailing in ancient times." Therefore, "elegant language" is an ancient standard language that conforms to the norms. As we know, in the era of Confucius, elegance was synonymous with * * * *. I wonder, is there an older source of elegance? & lt/p & gt； & ltp> Zheng Zhang: Yayan is from Xia Yan. There are many examples of the interaction between "elegance" and "Xia" in ancient times: Zuo Zhuan is "Gongziya" and Han Feizi is "Gongziya"; The bamboo slips unearthed in Guodian in recent years, Confucius' poetics, are "elegance" and "lesser" for "big summer" and "little summer"; Mozi quoted "Ya", also called "Xia". In particular, Xunzi's Honor and Disgrace says that "the more people are flat, the more people are flat, and the gentleman is flat", and Confucianism says that "living in Chu and Chu, living in more and more, living in summer and summer." This "elegance" or "summer" as opposed to Chu Yue obviously refers to the Central Plains. & lt/p & gt； & ltp> The ballads of Xia Dynasty recorded in pre-Qin ancient books may be recorded orally: Shangshu Tang Shi records that Xia Min called Xia Jie "mourning for the day?" Here, you're dead! Xia Zhen recorded in Mencius and Yi Zhou Shu all rhyme, and the rhyme system is similar to the ancient sound of Zhou Dynasty. So we can infer that the languages of Xia, Shang and Zhou are similar. & lt/p & gt； & ltp> Reporter: If the elegant characters in Xia, Shang and Zhou dynasties really come down in one continuous line, then the ancient "Putonghua" in China will have a long history of 4,000 years. & lt/p & gt； & ltp> Zheng Zhang: Yes. The ancient Huaxia people are the core of the Han nationality, and the Xia language they speak has great cohesion. Many ancient historical nationalities no longer appeared later, but in fact they all used Chinese characters to speak Chinese and merged into the Han family, as evidenced by the Gaiyuan family in the northern Wei Dynasty. & lt/p & gt； & ltp> Reporter: So what is the standard sound point of Yayan or Xia Yan? & lt/p & gt； & ltp> Zheng Zhang: