Genetic sexual attraction
You're 40, happily married - and then you meet your long-lost brother and fall passionately in love. This isn't fiction; in the age of the sperm donor, it's a growing reality: 50% of reunions between siblings, or parents and offspring, separated at birth result in obsessive emotions. We revisit Alix Krista’s Guardian article from back in 2003 on the affliction termed “Genetic Sexual Attraction”.
From The Guardian