Over the years, a consensus has been established among researchers studying aggression: males tend to be more aggressive than females (Archer, 2004a; Archer, 2004b; Archer & Haigh, 1997; Bettencourt & Miller, 1996; Crane-Ross, Tisak & Tisak, 1998; Eagiy & Steffen, 1986; Tappere & Boulton, 2004). In a meta-analytic review of the social-psychological literature, Eagly and Steffen (1986) found that 89% of social-psychological reports indicated that males were more aggressive than females. Moreover, Bettencourt and Miller (1996) and Archer (2004a) obtained a close to moderate effect size of 0.33 and 0.42, respectively for the finding that males scored higher than females for general aggression.
Other studies examined different aspects of aggression such as indirect, verbal, and physical aggression and the findings suggest that sex differences may differ for each type of aggression. In one study, Crick, Bigbee, and Howes (1996) found that girls cited more indirect aggressive acts to express anger, as compared to boys. However, in a meta-analytic review of sex differences in aggression in real-world settings, measured using self reports, Archer (2004a) reported a negligible effect size of 0.02, illustrating that girls were not higher on indirect aggression compared to boys.
Past research on verbal aggression supported the consensus that males tend to be verbally more aggressive than females (Archer, 2004a; Archer 2004b; Tapper & Boulton, 2004). However, the magnitude of the effect sizes for the differences found in verbal aggression varied from study to study, even when similar methods were used. For example, Archer (2004a) summarized the findings of 40 studies using self-reports in a meta-analysis and reported an effect size of 0.30. In a different study, also using self-reports, Archer and Haigh (1997) reported a much smaller effect size of 0.11. In contrast, the studies on physical aggression yielded relatively conclusive findings, compared to those on indirect and verbal aggression. In these studies, which involved children (Tapper & Boulton, 2004), adolescents (Crane-Ross et al., 1998), and adults (Archer, 2004a; Archer, 2004b; Archer & Haigh, 1997; Bettencourt & Miller, 1996; Eagly & Steffen, 1986), males were shown to have higher scores for physical aggression as compared to females. For most of these studies, moderate effect sizes were found for sex differences in physical aggression. For instance, Tapper and Boulton (2004) calculated the number of aggressive acts per hour for children aged three to six and found that boys engaged in a greater number of physically aggressive acts per hour as compared to girls. This finding had a moderate effect size of 0.63. Using self-reports, Archer (2004b) found similar sex differences among undergraduates. Male undergraduates reported more physical aggression than did female undergraduates, with a moderate effect size of 0.62.
Aggressiveness among males was particularly pronounced when their opponents were males (Hoppe, 1979), probably because males usually have more approving beliefs and intentions about aggression toward other males (Harris, 1994). In one study, using hypothetical events, Archer and Haigh (1997) showed that among students, males scored higher on instrumental beliefs supporting same-sex physical aggression. There was a similar finding by Winstok and Enosh (2007). In their study, they found that among Israeli adolescents, males were most concerned with the gender of the provocateur and had intentions to react more aggressively in terms of physical aggression toward male provocateurs. To explain this phenomenon, past research has provided plausible reasons from evolutionary and social perspectives.
According to the evolutionary perspective, males and females had different selection pressures as a result of their different amount of parental investment. For females, parental investment in their offspring is usually great; in order to maximize survival, they had to be very selective, obtaining males with good genes and resources. …