Incest marriage and one lineage

It is well known that the Spanish Hupsburg family lost their descendants due to excessive incest, and the throne passed to the French Bourbon family in the early 18th century. It can be said that it is miraculous that Japan's imperial family has been succeeded by the male line for over 1,000 years.

A few years ago, Dr. Ayao Hirashita, an orthodontist, explained the genetic influence of a long face and protruding lower lip in his book ``700 Years of Facial Changes in the Habsburg Family''. European feudal lords often had their painters draw their own portraits, so although they may have been slightly modified to make them look like beautiful men or women, you can get a glimpse of their facial features. Of course, hemophilia in the British royal family is not limited to the face, but it has become a genetic disease shared by all descendants of Queen Victoria, and is shared by European royal families.The effects of hemophilia, including early death and mental illness, are countless.

In the case of Japan, the last emperor for whom half-brother-sister marriage can be confirmed was Emperor Seiwa (850-881), and his mistress, Seiko Minamoto, was his half-sister. According to Wikipedia, there were 26 wives, so I guess his feeling would be carefree attitude like ... woops are you my sister? Under restrictions such as Catholicism, where marriage is a contract with God and divorce is not easy, and illegitimate children cannot inherit the throne, succession to the throne by members of the same family is always in danger of being cut off, and marriage with the royal family of another country or female descent I can understand the background behind the recognition of inheritance.

On the other hand, in Japan, the male line of succession is the basic principle that cannot be compromised, and they have managed to maintain a one-line system for all generations while always maintaining a spare family through polygamy. The era when the Emperor ruled directly is a long time ago (the last time was more than 800 years ago during the Insei(government by a retired emperor)era, but since then, there have been many political changes and changes in rulers, and the Japanese imperial family has been ruled by the best of each era. Incorporating the lineage of heroes, it seems that it has become a natural hedge genetically.

I'm a fan of initial female emperor (not female line succession), but at least the emperor is the true proponent of Japanese history and culture. For example, when people of Japanese descent visit to Japanese community in South America or Hawaii, they think of their hometown and are comforted. I hope that they will continue to be that kind of person.

Now, there is no clear evidence of the influence of consanguineous marriage among successive emperors. However, as far as I know, the suspects of madness include Emperor Yozei, the son of Emperor Seiwa, and the Emperors Reizei and Kazan, who were father and son, and I don't deny it was because of the frequent marriages between a limited number of relatives during the Sekkan period. Emperor Kazan is more of a sex-crazy than a madman, but he also has excellent artistic talent, and may even be a kind of genius.

Emperor Sanjo, who was forced to abdicate by Michinaga Fujiwara, was the son of the above-mentioned Emperor Reizei. He was healthy, but apparently he became blind after drinking a longevity medicine (Sentan). At that time, Sentan contained hydrogen sulfide and arsenic, and was considered a poisonous substance. How could be Emperor Sanjo depicted in Hikaru Kimi e (long-running TV drama by NHK in 2024)?