It's a feature that involves Genetic Sexual Attraction.
Two days later, Melissa drove two hours at night during a Monday Midwestern snowfall to meet her brother. And when she saw him standing in the frigid air outside his office building, she felt a connection that was instantaneous and electric.
"It was love at first sight, absolutely the craziest thing I have ever experienced," Melissa says. "The sexual force was like I was levitating off the earth. Your body instantly craves the other person."
The feeling was mutual: The pair shyly hugged and they had trouble looking at each other, in part because it was like gazing in a mirror, they looked so similar. "It was trippy, like seeing yourself in the opposite form," Brian says. "Everything inside you is just vibrating. Your cells know that this is your person."
The article does explore the possible science behind GSA.
Social scientists and psychologists have long researched how societies' prohibition against incest evolved: It's essentially nature's way of protecting humans from passing along the genetic mutations and disease risks that happen more commonly with close relatives, explains Dr. Debra Lieberman, a professor of Psychology at the University of Miami. The dominant theory, first proposed by Finnish social scientist Edward Westermark, is that people become desensitized to those they are raised alongside.
"Westermarck's hypothesis and my research have shown that siblings use clues like living under the same roof and being cared for the same parents to develop a sexual aversion," Lieberman says. "But if you don't grow up together, no aversion naturally develops."And not everyone who does grow up together experiences the Westermarck Effect.
The flip side is something Lieberman calls her "template hypothesis." All people form a template for the world based on the people and their surroundings during development: what men and women look like, what their roles are, etc. Then, they seek that out in a mate. This is common for non-related couples, too, psychologist and sex expert Isadora Alman notes.
"Many couples experience the feeling of being instantly attracted to someone that is familiar in some way, whether it's a physical reminder of someone beloved or something else they can't put their finger on," Alman says. "Love at first sight is a real phenomenon."
But it's been suggested that this feeling is even stronger for consanguineous (a.k.a. related) couples, especially those who don't develop the ick factor from growing up together. Why? "Genes tend to shape our preferences, talents, and attitudes — and familiarity creates comfort, so we look for someone similar," Lieberman says. "For siblings, this drives an enhanced sexual attraction." Which is exactly what happened to Melissa and Brian.
Start reading through our series on myths about GSA.