While cousin marriage is legal in most countries, and avunculate marriage is legal in many, sexual relations between siblings are considered incestuous almost universally. Thus, many cases of sibling incest, including accidental incest, concern siblings who were separated at birth or at a very young age.

Why is it illegal to date your sibling?

Romantic and sexual relationships between siblings or other family members is called incest, and if one of the people involved are under the age of consent then it is illegal because its illegal for an adult to date a minor.

Can u marry your sister?

Is it legal to marry your sister? No, it is not legal to marry your sister in any state in the US, or in most countries around the world. It is not legal to marry your sister because a brother and sister share genetic material and this makes the chances of their child having a genetic disorder much higher.