Developmental trajectories of aggressive behavior in children from ages 8 to 10: The role of sex and hormones

Objectives This study explored the developmental trajectory of aggressive behavior from age 8 to age 10 in school‐aged children, taking into account possible sex differences, as well as the involvement of certain hormones. Methods Participants were 90 children (49 boys and 41 girls) from four schools. At the beginning of the study, the children were 8‐year old and were in 3rd grade of primary school. The second data collection phase was carried out two years later (at age 10) when the children were in 5th grade (primary). Their aggressive behavior was measured by the Direct and Indirect Aggression Scale, an instrument which uses peer rating. Hormone levels, testosterone, cortisol and estradiol were analyzed using an enzymoimmunoassay technique in saliva samples. Results The results revealed a difference in aggressive behavior between the ages of 8 and 10, in boys only, who were found to be more aggressive at age 10. A regression analysis revealed that cortisol and estradiol contributed to explaining the changes observed in aggressive behavior in boys. Boys whose cortisol levels rose most between the ages of 8 and 10 were also those whose aggressive behavior increased most during the same timeframe. Moreover, boys whose estradiol levels rose most between the ages of 8 and 10 were also those whose aggressive behavior decreased most during the same timeframe. Conclusions Our results highlight the importance of studying aggressive behavior from a longitudinal perspective, taking into account sex differences and biological measures. Am. J. Hum. Biol. 28:90–97, 2016. © 2015 Wiley Periodicals, Inc.