Sex Differences in Psychopathology

In a previous post (Men’s Struggle for Status and Relevance), I touched on male-male competition and men’s use of dominance (e.g., physical threats) and prestige (learning culturally important skills) to increase their status and level of resource control in the communities in which they reside. Across cultures, historical periods, and deep into our evolutionary history (as assessed by genes on the Y chromosome), men who were successful at these endeavors had more surviving offspring than did their lower-status peers. Status striving typically involves a mix of cooperative and competitive behaviors and a mix of behaviors that are focused on achieving dominance (e.g., being a little too assertive) or prestige (e.g., contributing to a team victory). There are, however, some boys and men who persistently use a dominance-related approach and many of them will be diagnosed as having some form of psychopathology, such as antisocial personality disorder for men or conduct disorder for boys. Common features of these disorders included the use of behavioral aggression or threat of aggression to get what they want, often accompanied by little regard for the well-being of others.

These behaviors are often maladaptive in modern contexts and hence their categorization as a psychopathology. These same behaviors and social attitudes are often very adaptive outside of the modern world, and can be understood from an evolutionary perspective [elaborations can be found in Del Giudice (2018) and Martell (2013)]. The basic idea is that the expression of externalizing behaviors is an evolutionary legacy of physical one-on-one and coalitional male-male competition. During much of human history, dominance-based status striving was a common feature of men’s reproductive strategies and often included the intimidation and murder of ingroup or outgroup rivals. Perpetrators of violence in turn often enjoyed an increase in social status and marriage and reproductive prospects. This form of status striving is suppressed in developed nations today and directed into prestige-based competition (e.g., education, earned income), but the dominance-based legacy remains evident throughout the modern world; there “is no known human society in which the level of lethal violence among women even approaches that among men” (Daly & Wilson, 1988b, p. 146).

In an analysis of same-sex homicide rates across developing and developed nations, including homicide records dating from more than 700 years ago, Daly and Wilson found that male-on-male homicide occurs between 30 and 40 times more frequently than does female-on-female homicide. Male-on-male homicide occurs most frequently during the initial mate-finding stage of the lifespan (i.e., late teens through mid-20s) and more frequently among unmarried than married men. Moreover, roughly 2 out of 3 male-on-male homicides occur as a result of social conflict rather than during the commission of a crime (e.g., robbery), and more than half of the homicides are associated with “matters of status competition and the maintenance of face” (Daly & Wilson, 1988, p. 175). An extensive analysis of more than 290,000 homicides in the United States revealed that 87% of them were perpetrated by men and that the largest cluster was male-on-male homicides among acquaintances in their 20s. In contrast, about 2% of homicides involved a woman killing another woman.

The sex difference in the propensity to commit homicide is mirrored by a sex difference in nonlethal forms of behavioral aggression and, as noted, in externalizing forms of psychopathology among children and adolescents. As with adults, across time and nations, there are about two to four boys for every girl with common externalizing disorders, including conduct disorder. The most severe and persistent form of conduct disorder begins in early childhood, continues into adulthood, and manifests as the repeated use of aggression and intimidation to achieve one’s goals. Among these individuals, there are 10 or more boys and men for every girl or woman. The latter conclusion is based on Moffitt and colleagues’ seminal longitudinal study of more than 1,000 New Zealanders who were followed from childhood to adulthood. They found that 10% of the boys and 1% of the girls had a persistent pattern of externalizing behaviors, including poor attentional control and frequent physical fights with peers.

Many of these children (and adults) also exhibit a tendency toward callousness and emotional indifference to the well-being of others, that is, a subset of these children and adolescents lack empathy and guilt. This is not to say that all children with externalizing disorders will become violent offenders (most won’t), but they are at higher risk of engaging in various forms of antisocial behavior, including physical aggression, as they move into adolescence and adulthood. Erskine and colleagues’ (2016) meta-analysis indicated that children with conduct disorder are 3.5 times more likely to commit a violent crime in adulthood than are other children. Many of these individuals have a host of other problems (e.g., poor educational outcomes) that undermine their ability to be successful in prestige-based endeavors as adults, but at least some of their traits (e.g., instrumental aggression, callousness) would be more functional in contexts with frequent male-male physical competition.

Although these social strategies have an evolutionary history, their expression can be influenced by current and developmental experiences. Adults can up-regulate or down-regulate these tendencies so that boys are better prepared for the type (i.e., dominance, prestige) and intensity of competition they will encounter as adults. In cultures with intense male-male warfare, child rearing practices and boys’ initiation rites (into adulthood) are harsh and likely increase callousness and emotional indifference to the suffering of others, as well as encourage behavioral aggressiveness. Individuals who are prone to physical aggression and with high levels of callousness and emotional indifference have, on average, lower levels of fear and anxiety, discount the potential consequences (e.g., punishment) of their behavior, and engage in more predatory aggression than do other individuals. This is a constellation of traits that seems to be well suited for violent male-on-male physical aggression, especially when directed toward people in an outgroup.

Harsh parenting and other early stressors can also up-regulate these attitudes and behaviors in the modern world. For many children, especially boys, these stressors can increase callousness, emotional indifference, and aggressiveness and thus increase their rates of violating the rights of others. In other words, most boys can be socialized to be more or less callous and aggressive, reflecting a plasticity in the traits that evolved through physical dominance-related male-male competition. On this view, it is not a coincidence that parenting practices become more child-centered and less punitive as societies become more peaceful and dependent on competition in prestige-based economic niches, rather than direct physical confrontations.