What You Need to Know about Incest Law

Sexual activity between close relatives and family members is a cultural taboo. Most societies consider children of incestuous relationships as illegitimate. A common justification for prohibiting inbreeding is preventing genetic disorders in children. Children of parents with a close genetic relationship are at a great risk of death, physical disability, and congenital disorders.

A Brief History of Incest Law

Incest became an offense in England and Wales in 1908. According to the Incest Act of 1908, intercourse between a man and a woman that he knows to be his mother, sister, daughter, or granddaughter is illegal. However, statistics show that there have only been 26 prosecutions in the UK.

Prohibitions against inbreeding are not new. They have existed for millennia. In the Biblical book of Leviticus, God tells Moses, “No person should approach a close relative for sex.” However, Lot had sexual intercourse with his daughter but it was because of drunkenness.

In ancient China, it was illegal for first cousins with the same surnames to marry. In ancient Egypt, there were no laws prohibiting sibling marriages. Many pharaohs married their siblings.

The Roman civil law outlawed marriages within four degrees of consanguinity. Norse mythology has themes of brother-sister marriages.

Biological Motive

Incest law has a biological motive. It prevents the passing down of defective genes down the family line. People with blood relations have recessive genes. Thus, a child of incest is highly likely to have genetic defects.


In most countries, the law takes into account the issue of consent. In some nations, two consenting adults can have sex irrespective of their blood relations. In other countries, the issue of consent is irrelevant.

Non-Consensual Sex

This is a crime. Other laws such as assault, unlawful sexual intercourse, and rape laws also address the matter of non-consensual sex.

Familial Child Sex Abuse

The age of consent in most countries is 18 years. An adult having sex with a family member under the age of 18 years is familial child sex abuse. This attracts severe legal penalties.

Incest Law Differs By Country

Some countries have strict legal penalties while others have lax laws regarding incest. There are countries that have the death penalty. Most cultures around the world frown upon incest especially among close family members.


According to incest law, the degree of relationship determines the level of incest. The most severe case of incest is between parent and offspring. Other serious cases involve full siblings, identical twins, grandparent-grandchild, great-grandparent- great-grandchild, and first cousins.

United States

In the US, incest law varies by state. The definition of the offense as well as the penalties vary from jurisdiction to jurisdiction. In most states, sexual activity between a linear descendant and a linear ancestor is a legal offense. The state of Ohio only prosecutes parental offenders. In Michigan, Idaho, Montana, and Nevada, there is life imprisonment. Texas and Oregon are the other states with severe penalties.

Some states prohibit sex between first cousins while other states allow it. In New Jersey, there are no legal penalties if both parties are above 18 years.


The Indian Penal Code does not address the issue of sex between blood relations. However, sexual abuse of children is a crime in India.


Filipino law considers marriage between brothers and sisters as incestuous. Such a marriage is void. In addition, the marriage of collateral blood relatives up to the forth-civil degree is illegal.

Religious Laws

Religious laws prohibit incestuous relationships. Christianity, Judaism, Islam, and Hinduism view them as evil. Most faiths cannot carry out marriage between genetically close individuals.

The Bottom-Line

The law of a country defines marriage. In most countries, the definition of marriage is a union between two people of the opposite sex who do not have blood relations. Thus, marrying a blood relative or having sex with such a person is illegal.