Taiwan's historical "minor marriages," where unrelated children were raised as future spouses, show culture can override behavior but not underlying psychology. These unions had more divorces and affairs, demonstrating the persistence of the Westermarck effect's sexual aversion despite societal pressure.
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Evolution designed an economical system where a single, subconscious "kinship estimate" for each person dictates both altruism towards them and sexual aversion. It's one calculation for two different social behaviors, determining how close your heart should be and how far your genitals should be.
When asked to imagine incestuous acts, women's disgust is uniformly high. Men's responses show a much wider variance. This reflects the catastrophic evolutionary cost of a single bad reproductive choice for a female (nine months of gestation) versus the far lower opportunity cost for a male.
The widespread and instinctual revulsion toward incest provides a strong case for emotivism. When pressed for a logical reason why it's wrong (beyond pragmatic concerns like birth defects), most people fall back on emotional expressions like 'it's just gross.' This suggests the moral judgment is rooted in a fundamental emotion, not a rational principle.
Historically, marriage was a pragmatic institution for resource sharing, political alliances, and acquiring in-laws. The now-dominant concept of marrying for love and personal attraction is a relatively recent cultural development, primarily from the 18th and 19th centuries.
Contrary to the "get it out of your system" theory, a higher number of past sexual partners is a strong predictor of future relationship instability. For both men and women, it correlates with higher rates of divorce, cheating, and lower satisfaction in long-term relationships.
In scenarios like Jonathan Haidt's "Mark and Julie" experiment, where incest is harmless and consensual, people still condemn it. This reaction may be less about a moral calculation of harm and more about an individual's fear of being seen publicly opposing a powerful social norm.
The 'lie' of monogamy is not that it's a bad choice, but that culture has sanctified it as the only valid path. This framing turns non-monogamous people into villains and ignores that polygyny is the biological norm for most animals, including pre-agrarian humans.
When sperm donor half-siblings meet as adults, they may feel attraction. This isn't an innate desire for kin, but a consequence of shared genes creating highly similar preferences. They seem like a "perfect match" because the usual childhood-developed sexual aversion is absent.
The strong emotional recoil many feel about incest is a developed response, not innate. Only children, who never experienced the necessary childhood cues (like co-residence with a sibling), understand incest is wrong intellectually but lack the deep, gut-level aversion that is programmed in others.
Despite social progress, a man's identity remains deeply tied to his economic status. When a woman in a relationship earns more than her male partner, the likelihood of divorce doubles, and his use of erectile dysfunction medication triples. This reveals a persistent and powerful link between masculinity, money, and relationship stability.
