It happens[1]. In part because people tend to find those who look similar to themselves most attractive[2]. There is a countering instinct to be repulsed by the

It happens[1]. In part because people tend to find those who look similar to themselves most attractive[2]. There is a countering instinct to be repulsed by the idea of sex with people one was raised with[2], but this countering instinct doesn't happen if one wasn't raised with a family member. 1 - https://www.dailymail.co.uk/news/article-1311238/Brother-sister-didnt-know-related-marry--despite-knowing-union-illegal.html https://www.dailymail.co.uk/news/article-1311238/Brother-sis... > The couple, who hailed from different towns, about 100 miles apart, were both out with friends when they met in a nightclub in a third town several years ago. > So strong was their mutual attraction that just one week after meeting, they both felt they had known each other for a lifetime. 2 - https://www.psychologytoday.com/us/blog/the-mysteries-love/201505/are-we-attracted-people-who-look-us https://www.psychologytoday.com/us/blog/the-mysteries-love/2...