Some toddlers get mad easily. They are quick to hit, bite, kick, or fight with people when they don’t get their way. Are their parents doing something wrong?
It’s tempting to be judgmental, particularly if you haven’t been challenged by a physically aggressive toddler yourself. But a new study adds support to the idea that some babies are born with traits that make them more combative. That doesn’t mean these babies are doomed to become anti-social misfits. But it does suggest that their parents have to work harder to help their kids learn peaceful ways of getting along.
The study, which surveyed the mothers of 667 twins, tracked the development of physical aggression across three time points – when kids were 20, 32, and 50 months old. Moms were asked how often their toddlers hit, bit, kicked, or attacked another person.
When Eric Lacourse and his colleagues analyzed the data, they confirmed what we know from previous studies: Physical aggression tends to peak between the ages of 2 and 4 years. But the researchers also found evidence for substantial individual differences. At just 20 months old, some babies were more aggressive than others. And at every time point, the lion’s share of the variation between individuals (50-60%) could be explained by genetic factors.
The rest was attributed to mistakes in data collection (like the inevitable failure of mothers to be perfectly and consistently accurate when describing each twin) and to environmental factors that children –even identical twins — don’t share with their siblings. Kids might live in the same household and have the same parents, but they don’t have exactly the same relationship with their parents, nor do they have the same experiences at school. Such influences accounted for a modest amount of variation in physical aggression. Environmental factors that siblings share — like socioeconomic status — seemed to have little or no effect.
What are the implications?
Studies like these rely on comparisons between monozygotic twins (who share almost 100% of their genes) and dizygotic twins (who share only about 50% of their genetic makeup). When monozygotic twins show greater similarity in their behavior, the difference is chalked up to heritability, and researchers have a basis for estimating the relative importance of genes and the environment.
The process is complicated, and the resulting estimates are rough and subject to error. But even if we assume these estimates are a bit inflated, we’ve still got evidence that genetic factors account for a lot of the variation between toddlers.
The take away? Your child’s level of physical aggression isn’t merely a reflection of your parenting style. There’s a lot more going on, and much of it isn’t your fault. Instead of playing the blame game, we’re better off looking for ways to help frazzled parents stay calm, authoritative, and emotionally supportive.
Kids aren’t all alike, and their personality differences inevitably influence the way we relate to them. To read more about it, see my post, “Kids aren’t passive players in their own development.” For more thoughts about the development of aggression — and what parents can do about it — see my post, “Can you tell if a baby is going to become an aggressive kid?” And for some research-based tips on coping with toddler anger, aggression, and impulsivity, check out my post, “How do you handle temper tantrums?” and my Parenting Science article, “Teaching self-control.”
Reference: Lacourse E, Boivin M, Brendgen M, et al. 2014. A longitudinal twin study of physical aggression during early childhood: evidence for a developmentally dynamic genome. Psychological Medicine, FirstView article pp 1-11.
Have you ever felt you were negatively judged for your todder’s aggressive behavior?