Brother and Sister Marriage: Ethical and Legal Aspects

Brothers and Sisters Marriages

Yesterday, I attended my close friend’s wedding. A basic social institution, marriage differs greatly between cultures and legal systems. A thought pooped in my mind. Is brother sister marriage real? Despite the common misconception that marriage laws are straightforward, the subject of real brother and sister marriage is actually quite complicated. I came back and did extensive research on this topic. I came across some legal, religious, ethical, and cultural aspects of this type of marriage. Through this blog I am going to share everything I find out. 

History of Siblings Marriage 

I started with checking the history of brother and sister marriage first. In many cultures throughout brother and sister marriage in history also referred to as sibling marriages have been documented, especially among royal families. For example, in order to maintain the royal line and consolidate power, Egyptian pharaohs often married their siblings. For comparable reasons, sibling marriage was customary among the Inca dynasty in Peru. In Zoroastrian Persia, including those involving siblings were occasionally recommended. It was thought that these unions would preserve purity and bolster dynastic authority. Yet, these customs were usually restricted to aristocratic or royal families and were frequently motivated by social, political, or religious goals as opposed to accepted cultural norms.

brother sister marriage

Legal Restrictions by Different Countries

I know there are some legalities involved. In almost all jurisdictions around the world, brother and sister marriages are strictly prohibited. This prohibition is rooted in laws designed to prevent genetic disorders that can arise from close interbreeding. Here are a few examples:

  • United States: All 50 states and the District of Columbia have laws against marriages between siblings.
  • United Kingdom : Marriages between siblings are illegal under the Marriage Act 1949.
  • India : The Hindu Marriage Act of 1955, among other personal laws, explicitly bans sibling marriages.
  • Australia : The Marriage Act 1961 prohibits marriages between siblings.

Religious Aspects of Marriage 

Different religions have different take on brother and sister marriage

  • Hinduism

In Hinduism, is brother -sister marriage possible? The concept of brother-sister marriages is largely prohibited and considered taboo. However, there are notable exceptions within certain sects and historical contexts. The practice of marrying close relatives, such as cousins, is seen in some communities to preserve family lineage and property.

  • Zoroastrianism

Zoroastrianism had unique views on sister brother marriage. Historical records indicate that brother-sister marriages were practiced among Zoroastrians, especially within the royal and priestly classes. These marriages were believed to promote social cohesion and religious purity. In contemporary Zoroastrian communities, such practices have largely ceased and are not endorsed by modern followers. 

  • Ancient Egyptian Religion

The ancient Egyptian religion provides one of the most well-documented instances of brother sister marriage. These practices were deeply embedded in the religious and cultural aspects of ancient Egypt. However, they do not continue in modern Egyptian society, which follows Islamic laws that prohibit such unions.

  • Judaism

Judaism strictly prohibits brother sister marriage, based on the laws outlined in the Torah. These prohibitions are important in Jewish law.  Orthodox, Conservative, and Reform Jews uniformly reject any form of incestuous relationship. 

  • Christianity

Christianity, encompassing a wide range of denominations, uniformly prohibits brother sister marriage. The Christian ethos upholds the sanctity of family relationships and views incest as a violation of moral and ethical standards. 

How are Genes Affected by This?

Being a research student, genes are always there in my research. I found the primary reason for these prohibitions is genetic. Siblings share approximately 50% of their genes. Marrying and having children with someone who shares such a significant portion of your genetic material increases the likelihood of recessive genetic disorders manifesting in offspring. This risk is a key driver behind the near-universal legal restrictions against brother sister marriage.

brother sister marriage

Implications on Ethics and Values

Beyond the legal and genetic aspects, there are profound ethical and social reasons for these prohibitions:

  • Family Dynamics : Allowing brother sister marriage could disrupt traditional family roles and relationships, creating complex and potentially harmful family dynamics.
  • Social Norms : Society’s moral and ethical frameworks generally view sibling marriages as taboo. These norms are deep and reflect familial roles and responsibilities.
  • Psychological Impact : Relationships between siblings are expected to be non-sexual and supportive. Introducing marriage in this could have imposed psychological impacts on family members and broadly on social groups.

Psychological Perspectives Linked with Siblings Marriages

From a psychological standpoint, the attraction between siblings, known as genetic sexual attraction (GSA), is a recognized phenomenon but remains rare. GSA occurs more often in cases where siblings meet for the first time as adults, after being separated at birth or at a very young age. The initial meeting can trigger an intense romantic or sexual attraction, which psychologists attribute to the unfamiliar familiarity they share.

Exceptions in Few Parts of World

While the prohibitions are nearly universal, some historical and cultural contexts have allowed brother sister marriage:

  • Ancient Egypt : The pharaohs often married their siblings to keep the royal bloodline pure.
  • Inca Empire : Similar practices were observed to maintain the purity of the royal lineage.

In modern times, these practices are almost entirely extinct, largely due to the understanding of genetic implications and evolving social norms.

Some Alternatives to Sibling Marriages 

You share a deep bond with a sibling but wish to formalize their relationship in some way, other legal arrangements might be more appropriate:

  • Power of Attorney : Siblings can grant each other power of attorney to make decisions on their behalf.
  • Living Together Agreements : Siblings can enter into legal agreements that define their cohabitation rights and responsibilities.
  • Estate Planning : Siblings can use wills and trusts to ensure their mutual care and financial security.


As we come to the end of the blog I hope my research has helped you on this topic broadly. If you are the one who is planning to marry their sibling you must know every aspect of such a decision, no matter in which part of the world you are living!!

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