why is it imorral for close blood relatives to marry? i know in the beginning, god allowed it since there wasn’t much choice. is it because love between brothers and sisters and married people is suposed to be different?

The word is consanguinity. The prohibition against marriage to close family members predates Christianity. It could be that society had witnessed the fact that the children of such unions were often born with disabilities or that society realized that incestuous relations were destructive to the family.

Indeed, the prohibition predates humanity. There are many species of mammals that have a strong preference for mating outside of their close relatives.

Although close family marriages were allowed very early (Abraham and Sarah for example), modifications to these rules quickly arose. These modifications were founded mainly upon the sharpened instincts of human nature and the importance of guarding against the dangers of corruption from the intimacy of very near relations, which prompted the cutting off all hope of covering past impurity by subsequent marriage. Undoubtedly this danger increased the instinctive natural repugnance to marriage between those connected by the closest ties of blood and family affection.

In the moral order the prohibition of marriage between near relations served as a barrier against early corruption among young persons of either sex brought habitually into close intimacy with one another; it tended also to strengthen the natural feeling of respect for closely related persons (St. Thomas, II-II.154.9; St. Augustine, XV.10City of God). Nature itself seemed to abhor the marriage of close kin, since such unions are often childless and their offspring seem subject to grave physical and mental weakness (epilepsy, deaf-muteness, weak eyes, nervous diseases), and incur easily and transmit the defects, physical or moral, of their parents, especially when the interbreeding of blood-relations is repeated.

see, e.g.

Its not just applicable to brothers and sisters. It goes out to the 4th degree of consanguinity which are 1st cousins.

Perhaps it is. At least the fruits of that love can be much different.

Brother and sister have the same or very similar upbringing which instills similar values, habits, traditions, ways of thought, and so on. They share many of the same strengths and weaknesses of character. If they were to marry, they would bring nothing new into their family. The shortcomings of the parents would be passed on to their children.

When two unrelated persons are attracted to each other, they tend to have similar cultural, educational, and economic backgrounds. However, they usually will have been brought up with different family habits, traditions, etc., and they will not share all the same personal strengths and weaknesses. There is a chance that they can compensate for each others shortcomings, thereby working more effectively together than they could as two separate individuals. They may also learn from each other, bring out the best in each other, and perhaps become better as individuals.

This certainly seems to be the case in my marriage.

The sons of blood relatives have a high porcentage of having something wrong, I think that is more than enough to make it sinful.

And then there are cases like Cleopatra who was both beautiful and brilliant with parents that were siblings.

That doesn’t make it any more moral though!

Of course it doesn’t I was merely pointing out that it doesn’t necessarily cause problems and that defects don’t pop up as fast as people think.

It is still immoral regardless of temporal consequences.


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