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.

Our nervous system is wired to gravitate towards familiar patterns, confusing them with safety. This is why people unconsciously recreate painful or traumatic childhood dynamics in adult relationships. It is a biological pull toward the known, not a conscious desire for pain, making it a cosmically unfair default setting.

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.

From a young age, we suppress our authentic selves (intuition) to maintain connection with caregivers. This creates a lifelong pattern of seeking external validation over internal knowing, leading us to distrust our gut feelings.

Emotions are not superfluous but are a critical, hardcoded value function shaped by evolution. The example of a patient losing emotional capacity and becoming unable to make decisions highlights this. This suggests our 'gut feelings' are a robust system for guiding actions, a mechanism current AI lacks.

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.

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.

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.