In many instances throughout recorded history, cousins could marry each other with no one objecting. Brother and sister marriages, however, were a different matter.

Nevertheless, there were numerous cases where siblings got married to each other in ancient history, implying that incest between siblings was common in many societies at the time. Notably, these kinds of relationships were more common in royal families.

Today, we will try to explore brother and sister marriages in history.

Brother And Sister Marriages Among Kings

Brother and sister marriages were quite common among ancient kings. The custom came to be known as "royal incest." The female in such union was usually called a sister-wife.

Some of the most popular cases of brother and sister marriages were reported in ancient Egypt, where incestuous marriages were considered the norm.

For about three centuries, a significant number of marriages between brothers and sisters took place within Egypt's ruling class. Based on census returns from Roman Egypt, 22 out of 136 documented incestuous marriages between royals were brother and sister marriages.

Similarly, in ancient Athens, half-siblings could get married as long as they had different mothers. The practice was also common in Inca Peru, where marriages to full brothers or sisters took place among several royals.

In East Asia, between the 10th and the 20th century, there were many marriages between brothers and their half-sisters within the ruling class.

During the 5th century, Prince Konashi no Karu from Japan married his full sister, Princess Karu no Oiratsume. The country also had a couple of marriages between emperors and their half-sisters between the 6th and the 9th century.

The Hawaiian Islands also had several incestuous marriages between royal brothers and sisters or half-siblings. There are over two dozen documented cases of such unions in the region throughout history.

Additionally, medieval Europe also had its fair share of incest within the royal families. For instance, during the 15th century, John V of Armagnac married his full sister Isabelle of Armagnac.

There were also suspected cases of brother and sister relationships in history. One of the most popular cases involves Caligula and his full sisters Julia Livilla, Drusilla, and Agrippina the Younger.

Why Was Incest Between Brothers And Sisters Common Among Kings?

Among royals, incest was typically meant to achieve political goals. Under such circumstances, it was not considered taboo for close relatives to marry each other.

It was also common to associate incest among royals with divine incest that existed in popular mythology, which made it an exception. The Greek god Zeus, married Hera, his sister; and the Egyptian Osiris also married his sister Isis. Also, Inca god-king Manco Capac got married to his sister.

Due to such myths, marriage between a king and his sister was considered god-like.

Consequently, many pharaohs were following the example set by Osiris, a revered benevolent king. Nevertheless, sibling marriages among the people were rare.

In Zoroastrian Iran, incest between parents and children was encouraged with the perception that this could offer supernatural benefits. Still, this custom was only common in polygamous or upper-class families.

Furthermore, kings were considered to be above most laws in society, which is why they could get away with a lot of things, including incest. A king's sister was also considered a king's worthy peer since only she had shared his privileged heritage.

So, rather than settle for someone from a lesser dynasty, the king was forced to commit incest by marrying his sister.

Incest was also necessary to ensure royal families did not have other semi-royal families rivaling them due to connections through marriage.

What Makes Brothers And Sisters Get Attracted To Each Other?

According to experts, siblings are unlikely to engage in sexual relationships due to the closeness they had in childhood, a phenomenon known as the Westermarck effect.

Typically, brothers and sisters who grow up together don't usually experience any form of sexual attraction, even if they are not related by blood.

Therefore, in a lot of cases, siblings who end up in brother and sister marriages are usually separated at a young age, only to meet later in life. That is why some brother and sister marriages are caused by accidental incest.

For instance, a British brother and sister got married unknowingly only to discover they were twins who were adopted by different families when young. Similarly, a South African couple that was expecting a child discovered they were brother and sister before they got married after their parents met and told them they were siblings.

Similarly, the separation of siblings is cited as one of the reasons brother and sister marriages were common within ancient royal families. Royal siblings often had very little contact with each other while growing up, and once they met as adults, they were more likely to be attracted to each other romantically.

The Cost Of Brother And Sister Marriages

Royal families that engaged in inbreeding certainly paid the price for their unconventional relationships with relatives.

Many heirs died soon after birth, while others had to cope with crippling disabilities or lifelong health conditions. Generations of inbreeding are believed to have doomed the Habsburg royal family.

For the sake of keeping power and property within the family, the Habsburgs married within the family, and in a period of over 200 years, genetic issues accumulated and led to the extinction of the male lines.

The last Habsburg ruler, Charles II of Spain, also known as "the bewitched," had severe physical disabilities and was unable to produce an heir despite getting married twice.

However, despite these risks, ancient royal families could justify incest by claiming that most of their children ended up living healthy lives anyway. Problems only began setting in after several generations of incest.

Also, although the kings risked having unhealthy babies by marrying their sisters, they tended to have healthy children with other women.

These days, brother and sister marriages are clearly not as common as they were in ancient times. That said, debates about incest continue, with some countries considering incest a crime although others don't.