Why Does a Baby Strike Out in Anger? A Study Looks At The Family Risks

A baby is set on the floor to play with other babies and she yanks a toy away from a playmate or shoves him in frustration or anger.

What makes some infants aggressive? Does something adverse happen in the womb? Is it life with Mom and Dad that ramps up their anti-social behavior? Or both?

These are the questions that a group of Cardiff University psychologists—Dale Hay, Lisa Mundy, Siwan Roberts, Raffaella Carta, Cerith Waters, Oliver Perra, Roland Jones, Ian Jones, Ian Goodyer, Gordon Harold, Anita Thapar, and Stephanie van Goozen—are exploring in a large-scale, nationally representative longitudinal study of 271 British infants and their parents. The families are being assessed during the mother’s pregnancy, and at the infants’ ages of 6, 12, 21, and 33 months.

A portion of that study, looking at prenatal predictors of infantile aggression around the first birthday, has already yielded important insights. Happily, it finds that infantile aggression is the exception, not the rule.  But when it shows up, says Hay, “it is predicted by the same family factors that are known to predict aggressive behavior in older children and adolescents.” The findings will be published in an upcoming issue of Psychological Science, a journal of the Association for Psychological Science.

In the study, first, during the mother’s third trimester, both parents underwent a thorough psychological assessment and completed questionnaires about their education and work histories. The mothers also described their own conduct when they were young: Did they steal, lie, or cut school? This way the researchers created a profile of parental risks—including depression in the pregnant mom—for their child’s becoming aggressive.

At six months, family members completed an inventory of the baby’s emotions and behavior, such as tantrums or biting.

Then, at 12 months, three families came into the lab at a time, where they attended a simulated birthday party, with decorations and toys for the children to play with. “We wanted to see how they did in naturalistic, but somewhat challenging conditions,” says Hay. Observers counted the instances each baby used a toy or his own body against another child.

Analysis of the data revealed “small to medium, but statistically significant correlations” in two areas: Those few infants who often tugged on other babies’ toys had mothers who were depressed in pregnancy. Those who used their bodies against others had moms with troubled youths. No gender differences showed up. The lab observations at one year mirrored the families’ descriptions of the babies at six months—indicating a tendency to flail out in anger, not just a reaction to a stressful situation.

The results are partial, and questions about both genetic and environmental contributions remain, says Hay. But the study already offers hope to families whose infants are acting out. Rather than stigmatize or write off a baby as a lost cause, “the family can be given extra support in learning to deal with anger and frustration”—and in patiently nurturing an infant whose moods, for whatever reason, may be volatile.