Westermarck effect
Reverse sexual imprinting is also seen: when two people live in close domestic proximity during the first few years in the life of either one, both are desensitized to later close sexual attraction and bonding. This phenomenon, known as the Westermarck effect, was discovered by anthropologist Edvard Westermarck. The Westermarck effect has since been observed in many places and cultures, including in the Israeli kibbutz system, and the Shim-pua marriage customs of Taiwan, as well as in biological-related families.
But in the case of the Israeli kibbutz farms, these children grew up in a common children's house, away from their parents. They spent the entire day and night together. This did result in a generation that was not interested in the opposite sex within their class, and the program was dropped. It is an extreme example of grouping since the adults were also removed from the environment.
When this does not occur, for example where a brother and sister are brought up not knowing about one another, they may find one another highly sexually attractive when they meet as adults: a phenomenon known as genetic sexual attraction. This observation is consistent with the theory that the Westermarck effect evolved to suppress inbreeding.