Accidental incest is incest that is committed by two partners who do not know they are biologically related. It can occur when two people who are unaware of their biological relationship become sexually intimate. When two related people meet as adults, and become sexually attracted, it is known as genetic sexual attraction. When a biological relationship is suspected, DNA testing may be used.
Artificial insemination with donated sperm may result in accidental incest. Because sperm donation is often anonymous, many people conceived in this manner are usually unaware of any biological half siblings they have. The likelihood of accidental incest is kept low with doctors limiting the number of times that each donor's sperm can be used. Some countries have laws limiting the number of children a donor can father in order to reduce the likelihood.Taiwan allows those conceived by artificial means to receive testing to determine if they are related to a person they are considering marrying.
In 2008, it was reported that a British brother and sister, who were twins separated at birth, married without knowing of their relationship. According to the report, the relationship was discovered soon after their wedding, and the marriage was annulled. The case has raised the issue regarding whether adoptions should be kept secret. Concerns have been raised, however, about whether the story is, in fact, true.
An engaged couple in South Africa, who had been together for five years and were expecting a child, discovered that they were brother and sister just before their wedding. They were raised separately and met as adults in college. Just before the wedding, their parents met and they came to realize that they were siblings. The couple broke off the relationship after the discovery.