Steven Pinker -- How the Mind Works - Hampshire High Italian ...

458 | HOW THE MIND WORKSIncest repugnance might be weaker, making him more likely to cross theline. It is a special case of the lower costs of reproduction for males andtheir less discriminating sexual desire, to which we will return.A father, moreover, can never be certain that a daughter is his, so thegenetic cost to him could be zero. That could weaken the suppression ofdesire even further compared to her brother, who is certain to be relatedto his sister because they share a mother. For stepfathers and stepbrothers,there is no genetic cost at all. It is no surprise, then, that betweenhalf and three-quarters of all reported incest cases are between stepfathersand stepdaughters, most of them initiated by the stepfather. Mostof the rest are between fathers and daughters, and virtually all arecoerced by the father. Some are between girls and other older male relatives,also mostly coerced. A mother gets no genetic benefit from a matingbetween her husband and her daughter (compared with a matingbetween her daughter and a son-in-law), but suffers the cost of defectivegrandchildren, so her interests are aligned with her daughter's and sheshould be a force opposing incest. Incestuous exploitation of girls mightbe even more common if their mothers were not around. These battlesare driven by strong emotions, but the emotions are not an alternative tothe genetic analysis; the analysis explains why they exist. And of course,in science as in detective work, to try to figure out the motive for a crimeis not to excuse the crime.People cannot directly sense their genetic overlap with another person;as with the rest of perception, the brain must combine informationfrom the senses with assumptions about the world to make an intelligentguess. Chapter 4 showed that when the world violates the assumptions,we fall prey to an illusion, and that is exactly what happens in theperception of kinship. The nineteenth-century anthropologist EdwardWestermarck conjectured that growing up in intimate closeness with aperson in the early years is the key information the brain uses to put the personin the category "sibling." Similarly, when an adult raises a child theadult should perceive the child as "son" or "daughter" and the childshould perceive the adult as "mother" or "father." The classifications thennegate sexual desire.These algorithms presuppose a world in which children who areraised together are biological siblings and vice versa. That is certainlytrue of foraging peoples. A mother's children grow up with her and usuallywith their father, too. When the assumption is false, people shouldbe the victim of a kinship illusion. If they grow up with a person who is