This episode is also on Bilibili too.
I recently came across a popular question on Zhihu:
Why, no matter how beautiful a sister is, does her younger brother never think she’s beautiful?
Quite a few “younger brothers” showed up in the answers with firsthand accounts. The gist was: You outsiders have only seen my sister looking gorgeous, while I’ve watched her display countless ugly sides from childhood to adulthood—and she bullied me growing up, too. So in the eyes of her actual little brother, she’s an ugly shrew, a nasty shrew. Of course I can’t fall for her!
But I think those are only the surface explanations. From a psychological perspective, the deepest reason younger brothers can’t see their sisters’ beauty is—
Humans have an inborn aversion to incest.
When it comes to incest, many people have been led astray by Freud’s deeply unreliable claims. Freud said humans have a universal desire for incest: sons want to kill their fathers and marry their mothers—the famous Oedipus complex—while daughters want to kill their mothers and marry their fathers. To prevent incest, people supposedly invented all kinds of incest taboos, using the cultural, legal, and moral equivalent of heavy sticks to firmly suppress our inborn desire for incest. Freud also believed that many of our psychological problems were connected to this repressed desire for incest.
But the truth is actually the exact opposite!
What humans universally possess is fundamentally not a desire for incest, but an aversion to incest.
As the Zhihu question hints, brothers and sisters aren’t sexually attracted to each other. A younger brother certainly doesn’t become completely blind to his sister’s beauty; he just doesn’t see the kind of beauty she has as a member of the opposite sex, radiating sexual appeal. Not only is there no mutual sexual attraction between them, but sexual thoughts about each other actually make siblings feel extremely uncomfortable, even intensely repulsed.
This is an adaptive mechanism acquired under the pressure of natural selection. Individuals who fail to avoid incest are more likely to produce offspring with more defects and lower chances of survival. So individuals with an “aversion to incest” are favored by evolution, helping ensure that people mate with individuals who are not related to them.
Of course, humans can’t directly identify one another’s genes. In practice, we can only use visible, tangible, perceptible external clues to determine who our siblings and blood relatives are.
One of the most important external clues is this: Did a member of the opposite sex live closely with you during early childhood? If someone of the opposite sex lived intimately with us from childhood, we categorize that person as a blood relative and activate our aversion to incest.
Anthropologist Edward Westermarck (1862-1939) was the first to observe this. In The History of Human Marriage, he proposed: “Men and women who have lived closely together from early childhood—whether this applies to one or both parties—generally show little inclination to have sexual relations with each other, and this is undoubtedly a worldwide phenomenon” (quoted in Wu Baopei’s Lovers, Paramours, and Weirdos).
—This is the Westermarck effect. According to the Westermarck effect, even if two people of the opposite sex are not actually related by blood, if they grow up together in the same family—or in a similarly intimate, family-like relationship—they will regard each other as blood relatives and develop an aversion to incest, despite having no biological connection whatsoever.
There are three classic examples here:
1. Child Brides in China
In the mid-twentieth century, Stanford anthropologist Margery Wolf conducted a classic study of child-bride marriages in Taiwan, providing particularly clear evidence for the Westermarck effect.
The child-bride system was once widespread in traditional Chinese society. A child bride was a little girl sent to her future husband’s family shortly after birth, usually before the age of three. In this new home, she ate and slept with her future husband and lived with him like a biological sibling. Usually, it was not until puberty that they were told they weren’t brother and sister, but an engaged couple.
So would these little sweethearts become “childhood sweethearts, innocent and inseparable,” as literary types like to imagine?
No.
Their typical reaction was intense resistance to the marriage. And the reason was precisely that they had absolutely no “sexual attraction” to each other.
The child-bride couple’s resistance began on their wedding night. For ordinary newlyweds, the wedding night was something to eagerly anticipate; they were raring to go. But child-bride couples often ran away that very night, to the point that parents sometimes had to stand outside the bridal chamber with sticks to stop them escaping.
After marriage, child-bride couples were generally less happy and had more problems than ordinary couples. According to Margery Wolf’s survey data, in Taiwan at the time, the divorce rate for ordinary couples was only 1.2%, while among child-bride couples it reached 24.2%. Their fertility rate was 30% lower than that of ordinary couples. Their divorce rate was three times higher.
Child-bride couples were also more likely to be unfaithful, go out looking for lovers, and—rather oddly—seem unconcerned when the other gave them a pair of green horns. The husbands’ reactions are especially revealing. In traditional Chinese society, a wife’s infidelity was a terrible humiliation for her husband, who would normally be furious. Yet in Margery Wolf’s survey, some husbands whose child-bride wives cheated on them didn’t care at all. They weren’t jealous because they simply had no interest in their wives. They stayed together only because they didn’t want to defy their parents’ wishes; in reality, each lived their own life, and felt perfectly at peace doing so.
These findings all match the predictions of the Westermarck effect: children who grow up as childhood companions don’t suffer under the pressure and torment of an “incest taboo” as adults. They actively avoid incest altogether.
2. Israeli Kibbutzim
In some parts of Israel, a communal system known as the kibbutz (Kibbutz) was once practiced. These communities were established by utopians in the early twentieth century to break up the traditional nuclear family and put communal living into practice. In a kibbutz, boys and girls of the same age lived together in the same dormitory from shortly after birth until puberty, raised collectively by caregivers and teachers.
Yet once these children reached adulthood, there was very little intermarriage among those who had grown up together, and very little extramarital sex either—even though nobody objected to their marrying and no rule or cultural norm prohibited it. Israeli anthropologist Joseph Shepherd examined records from more than 200 kibbutzim and collected information on over 2,700 couples. He found that not a single couple came from the same kibbutz where they had lived together as children.
These findings likewise match the predictions of the Westermarck effect: people of the opposite sex who share an intimate living environment during early childhood feel no sexual attraction to each other.
3. Evidence from the Other Direction
Conversely, people who engage in incest often did not grow up together.
The famous psychologist Steven Pinker wrote in How the Mind Works:
A Chicago study of incest between brothers and sisters found that the only pair who intended to marry had been raised apart.
The same pattern also operates in incest between parents and children. If parents spend a great deal of time with their children during early childhood, incest is extremely unlikely to occur. Conversely, if parents are separated from their children during those early years, the risk of incest rises.
How the Mind Works says:
Fathers who sexually abuse their daughters generally spent little time with them when they were young. If a stepfather and a biological father spend the same amount of time with a daughter, the stepfather is no more likely than the biological father to abuse her.
When Freud proposed the concept of the “incest taboo,” he used the story of King Oedipus from ancient Greek tragedy as an example. The basic plot goes like this:
Laius, king of Thebes, was warned by an oracle that his son would one day kill him. So after his wife Jocasta gave birth to Oedipus, Laius abandoned the baby in the mountains. Oedipus, unsurprisingly, didn’t die. As an adult, he happened to encounter his biological father Laius, whom he had never seen before, and killed him in an argument. He then defeated the Sphinx, the monster with a woman’s head and a lion’s body, and was rewarded by becoming the new king and marrying the newly widowed queen Jocasta—his biological mother, who had not been with him during his upbringing. By the time Oedipus finally learned the truth, he and his own mother had already had 4 children together.
Freud believed this story indirectly reflected men’s incestuous desire to “kill their fathers and marry their mothers.” But in fact, it contains precisely the high-risk factor for incest I just described: Oedipus was not raised by his biological mother.
So, why does a younger brother not think his sister is beautiful, no matter how beautiful she is? Because the Westermarck effect is at work. Because “men and women who have lived closely together from early childhood, whether this applies to one or both parties,” develop an aversion to incest—and that aversion completely zeros out the sexual appeal radiating from the other person.
References:
Steven Pinker. (2016). How the Mind Works: The Origins and Evolution of the Human Mind. Zhejiang People’s Publishing House.
Wu Baopei. (2015). Lovers, Paramours, and Weirdos: A Psychological Portrait of Human Desire. Electronic Industry Press.
Research on child-bride marriages:
Wolf, M. (1972).Women and the family in rural Taiwan. Stanford University Press.
Research on Israeli kibbutzim:
Tiger, L., & Shepher, J. (1975).Women in the Kibbutz. Harcourt Brace Jovanovich.
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