Babies With a Sense of Justice

I always find articles about cognitive development in babies to be fascinating, because they show the threshold of what we consider to be quintessential human traits. Now a study out of the University of British Columbia shows that somewhere between 5 and 8 months old, babies go from always preferring helpful individuals to preferring individuals who are helpful or not according to the behaviour of the recipient.

The research is pretty well described by LiveScience:

So the researchers set up a series of experiments using puppets to act out scenarios of helping and harming while each of 32 5-month-olds and 32 8-month-olds watched separately. After each experiment, the infants indicated their preference for the puppets’ behaviors by picking their favorite puppet to hold.

The puppets — a series of cheerful characters, including moose, elephants and a yellow duck — were first shown interacting in either nice or mean ways. One puppet would struggle to open a box containing a toy, while another either jumped in to help or cruelly slammed the lid shut.

Next, the infants watched as the puppet that had helped or hindered played with a ball and dropped it. A third puppet then came into the scene, either to take the puppet’s ball away or to hand it back…

The researchers wanted to know if the babies would prefer the ball-giving puppet or the one that took the ball away. They found that 5-month-olds always preferred the ball-giver, no matter whether the puppet that had dropped the ball had been mean or helpful in the previous scene. At this young age, the babies simply liked puppets to be nice in the moment.

But 8-month-olds were more discerning. They liked it when the third puppet gave the ball back to a previously helpful puppet. But they didn’t like it when the third puppet helped out a previously unhelpful puppet. In scenarios involving the mean, toy box-slamming puppet, 8-month-olds favored a third puppet taking its ball away by 13 to three.

The researchers then repeated the experiments with 32 toddlers ages 19 months to 23 months, this time adding a twist. The toddlers got to watch puppets being nice or mean to each other and then got to play the role of rewarder or punisher. Some toddlers were shown one nice puppet and one mean puppet and asked which they’d like to share a treat with. Others were shown a nice puppet and a mean puppet, both with treats, and were asked to take a treat away from one.

In all cases, the toddlers meted out justice according to the puppets’ earlier actions. Thirteen of 16 gave a treat to a nice puppet, while 14 of 16 took treats away from a mean puppet.

LiveScience also has a video of the puppet show and the babies choosing a puppet – it’s kind of adorable.

This finding is pretty cool. I wonder what the physical switch is that enables babies to be more discerning, if there is one distinct switch? For some small context, here’s a graph of a person’s change in brain weight over time, where blue is male and red is female:

Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978, via University of Washington

Notice that babies at the ages used in this experiment (5 or 8 months) have brains less than half the size of an adult, and maybe half that of a 3-year-old. They have a long way to go before everything clicks.

This study, to me, raises the question of which behaviours are learned, and which are ingrained. It seems clear here that a sense of justice, in the sense shown, is probably inherent, or at least the capability to learn it is. I’m also kind of surprised that the babies could distinguish between different puppets who were only distinguished by the colour of their clothes. It’s never caught my interest as a field of study, but I’m starting to understand why people might like developmental biology… 


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