Why was consanguineous marriage popular in ancient times?

Biological science was backward in the past, did not find this mystery, all attributed the reason to fortune or family luck above. The most powerful inbreeding is still the royal family, if they had known, they would have taken another measure.

Ancient times belonged to a class society, and there was a serious relationship between people as monarchs and ministers, masters and servants. Moreover, the concept of gentrification was very strong, and all of them demanded that the door be right for the family. In this way, the problem arose. If you are a rich man, you still have to marry a rich man. But there are only a few rich men, and you can't afford to marry a poor man. The range of choices is very narrow, and there are only a few families that come and go. Close relatives are inevitable.

Another reason is that transportation is not easy and people live locally. Marrying far away was a very unhappy affair. Those were the only people for hundreds of miles around, and anyway, if you wanted to marry, you married, and if you didn't, you were a bachelor. So a village is all about the same ancestors, the same family name, and then you marry back, which means you're a relative from the last few generations.

This problem also led to the dynasty to the end of the year, a serious shortage of heirs, directly broken. Until the dynasty was overthrown. They knew this, absolutely why bother in the beginning!