The Westermarck effect is when people who grow up together, regardless of relationship, don’t develop sexual attraction later in life. It’s named after Edvard Westermarck, a Finnish sociologist. The effect only applies to those raised together before the age of six. Studies show that unrelated individuals raised together also don’t develop sexual attraction. Siblings raised apart sometimes develop genetic sexual attraction. Historical examples of sibling marriages are not a good counterexample. Traditional Chinese families who adopt young girls with the intention of marrying them off often face issues later on.
The Westermarck effect is a phenomenon that has been observed in individuals who spend a lot of time with each other under the age of six. People who grew up together, regardless of relationship, tend to become numb to each other and generally won’t develop sexual attraction to each other later in life. A variety of studies have supported the concept of the Westermarck effect.
This idea is sometimes referred to as “reverse imprinting” and is named after Edvard Westermarck, a Finnish sociologist who worked and wrote in the late 1800s. He was particularly interested in marriage patterns and incest taboos, and his idea that people grown together will not develop sexual attraction contradicted the beliefs of Freud, an important contemporary. Over time, it has become apparent that Westermarck has been vindicated, as the evidence strongly suggests that Freud’s ideas are not supported by real evidence.
In addition to using data on siblings raised together, the Westermarck Effect researchers also looked at situations in which unrelated individuals are raised together. For example, in Israeli kibbutzim, children are often raised together in large peer groups, and members of the same peer group rarely develop relationships of a sexual nature with each other. This also applies to young children adopted into families with existing children.
Conversely, siblings who are raised apart sometimes develop a sexual attraction to each other when they meet later in life, developing what is known as genetic sexual attraction. Westermarck effect researchers also found that the six-year cutoff is very important; children raised together after the age of six do not show the Westermarck effect, indicating it has to do with early childhood development.
Opponents of this theory often point to historical examples of sibling marriages, such as those performed in ancient Egypt among the ruling classes. However, these marriages are not a good counterexample, because such marriages were typically entered into without consulting the people involved, and it was common for children of the ruling classes to be raised separately from each other, for a variety of reasons.
In an interesting modern example of the Westermarck effect at work, the researchers studied traditional Chinese families, who sometimes adopt a young girl into their families with the intention of marrying the girl off to their children. They found that girls are often strongly against such marriages when they come of age, and that these marriages are more prone to later dissolution, childlessness, or adultery.
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