Infants Are Social Strategists

Babies weigh costs and benefits to make social decisions.

Posted Sep 21, 2018

Jessica Sommerville
Social baby starer
Source: Jessica Sommerville

When my daughter was just over a month old, I would hold her in my arms and gaze into her eyes, in awe of my little miracle. She would gaze back, and we would stare at one another… for a long time.  A very, very long time. If I dared break the spell to glance at her emerging hairline, or inspect her delicate ear lobes, or admire her tiny fingers, she would protest. A lot.

Social babies

Despite the fact that I am a developmental psychologist who has been studying infants’ social perception, cognition, and behavior for over 20 years, I am amazed at how, well, social she is. Over the last year, as I’ve watched my daughter grow from a tiny newborn to a near toddler, I’ve been impressed with her emerging motor skills and problem-solving abilities. But mostly I’ve been fascinated by her sheer social-ness: the waves she gives to strangers in the customs and immigration line, the social bids she makes to waiters, and the mega-watt smiles she generously doles out to anyone who stops to engage with her.

When I tell my friends about the studies my colleagues and I conduct on infants’ social cognition and behavior, they are often unsurprised by the results. Of course infants are social! Of course they are fascinated by people and their behavior! Of course infants understand much more about the social world than we ever thought!

But, it turns out that infants are not only socially knowledgeable and socially engaged. Infants are also social strategists. They make active decisions about who they want interact with, when they want to interact with those individuals, and how much effort (or not) they are willing to put in to achieve those social interactions.

Making social decisions: Weighing up the costs and benefits

In a series of experiments in my lab, published recently in the journal Cognition, we examined 18-month-old infants’ willingness to help a fellow playmate.  Since a lot of prior research has shown that infants at this age can and do help other people complete their goals, our question was not merely whether or not infants could help the experimenter. Rather, we wanted to know how different factors would influence these toddlers’ willingness to help the experimenter.

For adults, a primary route to decision making (including social decision making) involves analyzing the costs and benefits of the outcomes our decisions generate. If we are deciding whether or not to can attend a colleague’s birthday party we consider the “costs” of our actions, such as how far we have to drive to get to the party and what other opportunities we might miss by attending, along with the “benefits” our decision might generate, such as how much we like this particular colleagues and whether we might see others we like or want to meet at the party.

We wondered if infants similarly weight costs and benefits in their social decisions. To pose this question, we presented infants with a simple situation: An experimenter sat on the other side of the room, building a tower from vinyl blocks. The experimenter was missing a block that she needed to complete her tower; a single block sat at the infant’s feet, and the experimenter asked the infant to bring her the block. The twist in this study, however, was how much the block beside the infant weighed. For half of the infants, the block was light, and for the other half it was heavy (infants were able to lift both the heavy and light blocks). We wanted to know whether infants could use the information about the weight of the block to determine the amount of effort required to help the experimenter, and whether this would influence their decision to help her or not.

Toddlers in our study were twice as likely to help the experimenter if the block was light, and required little effort to carry, than when it was heavy and required greater effort. Like adults who might pass on a colleague’s birthday party if attending requires an hour’s drive, but show up if the colleague lives 10 minutes away, infants considered whether helping the experimenter was “worth” the effort.

These findings demonstrate that infants consider costs when making social decisions, but we also wanted to know whether infants are sensitive to the potential benefits that social interactions might provide them. To ask this question, another group of infants were given the opportunity to carry a heavy block across a room to help an experimenter finish her tower. The twist in this experiment was that half of the infants had previously learned that the experimenter liked the same toys as they did; the other half learned that the experimenter liked different toys. Adults are often more motivated to interact with individuals that share their desires, preferences, or values, given the inherent benefits of doing so. In this case, infants were much more likely to help an experimenter if she shared their toy preferences than if she did not. That is, even when the costs were high, infants’ decided whether to help or not based on the social benefits of the situation.

Infants as social strategists

Our findings, along with those of other researchers in the field, are painting a new picture of infants: Not only are they social and socially knowledgeable, they are also socially savvy. Like adults, they make sophisticated social decisions that consider both what they will gain from social interactions, and what these social interactions require from them. In turn, we can leverage this new knowledge  to facilitate infants' and toddlers actual social behavior; for example, if your toddler is uncomfortable around a new playmate, think about how you can demonstrate the potential benefits of interacting with a new friend, and reduce the costs, in order to encourage them to play.


Sommerville, J. A., Enright, E. A., Horton, R. O., Lucca, K., Sitch, M. J., & Kirchner-Adelhart, S. (2018). Infants’ prosocial behavior is governed by cost-benefit analyses. Cognition, 177, 12-20.