Aggression in Children Makes Sense—Sometimes
Does a strategy of opposing traits explain humanity’s success?
Walk into any preschool classroom and you’ll see that some 4-year-olds are always getting into fights—while others seldom do, no matter the provocation. Even siblings can differ dramatically—remember Cain and Abel. Is it nature or nurture that causes these deep differences in aggression?
The new techniques of genomics—mapping an organism’s DNA and analyzing how it works—initially led people to think that we might find a gene for undesirable individual traits like aggression. But from an evolutionary point of view, the very idea that a gene can explain traits that vary so dramatically is paradoxical: If aggression is advantageous, why didn’t the gene for aggression spread more widely? If it’s harmful, why would the gene have survived at all?
Two new studies suggest that the relationship between genes and aggression is more complicated than a mere question of nature vs. nurture. And those complications may help to resolve the evolutionary paradox.
In earlier studies, researchers looked at variation in a gene involved in making brain chemicals. Children with a version of the gene called VAL were more likely to become aggressive than those with a variation called MET. But this only happened if the VAL children also experienced stressful events like abuse, violence or illness. So it seemed that the VAL version of the gene made the children more vulnerable to stress, while the MET version made them more resilient.
A study published last month in the journal Developmental Psychology, by Beate Hygen and colleagues from the Norway University of Science and Technology and Jay Belsky of U.C. Davis, found that the story was even more complicated. They analyzed the genes of hundreds of Norwegian 4-year-olds. They also got teachers to rate how aggressive the children were and parents to record whether the children had experienced stressful life events.
As in the earlier studies, the researchers found that children with the VAL variant were more aggressive when they were subjected to stress. But they also found something else: When not subjected to stress, these children were actually less aggressive than the MET children.
Dr. Belsky has previously used the metaphor of orchids and dandelions to describe types of children. Children with the VAL gene seem to be more sensitive to the environment, for good and bad, like orchids that can be magnificent in some environments but wither in others. The MET children are more like dandelions, coming out somewhere in the middle no matter the conditions.
Dr. Belsky has suggested that this explanation for individual variability can help to resolve the evolutionary puzzle. Including both orchids and dandelions in a group of children gives the human race a way to hedge its evolutionary bets. A study published online in May in the journal Developmental Science, by Dr. Belsky with Willem Frankenhuis and Karthik Panchanathan, used mathematical modeling to explore this idea more precisely.
If a species lives in a predictable, stable environment, then it would be adaptive for their behavior to fit that environment as closely as possible. But suppose you live in an environment that changes unpredictably. In that case, you might want to diversify your genetic portfolio. Investing in dandelions is like putting your money in bonds: It’s safe and reliable and will give you a constant, if small, return in many conditions.
Investing in orchids is higher risk, but it also promises higher returns. If conditions change, then the orchids will be able to change with them. Being mean might sometimes pay off, but only when times are tough. Cooperation will be more valuable when resources are plentiful. The risk is that the orchids may get it wrong—a few stressful early experiences might make a child act as if the world is hard, even when it isn’t. In fact, the model showed that when environments change substantially over time, a mix of orchids and dandelions is the most effective strategy.
We human beings perpetually redesign our living space and social circumstances. By its very nature, our environment is unpredictable. That may be why every preschool class has its mix of the sensitive and the stolid.
