First author

As social creatures, humans must be able to distinguish allies from adversaries. Adult humans rapidly and unconsciously evaluate others on both behaviour and physical features. But can infants do the same? Kiley Hamlin, a graduate student at Yale University, and her colleagues set out to answer this question using puppet shows depicting helping and hindering behaviour. On page 557, they report that even 6-month-old infants have a surprisingly uniform ability to choose 'good' guys over 'bad'.

Why study infant social skills?

Infants have an 'untouched' nature — they are pre-linguistic and have been explicitly taught very little — so they can give us a sense of the underlying capabilities of humans. Adults are automatic evaluators of others' behaviour. If this evaluation is so pervasive in adults and essential for survival in a social world, we proposed that infants should be able to do it too. But, until now, nobody has reported any work in children younger than three years old.

Did you find what you expected?

We were intrigued by the dissociation we found between infants' ability to predict others' social preferences (indicated by their looking time) and the infants' expression of their own preferences (indicated by their reaching behaviour). We found that infants have their own strong preferences before they are able to predict what others should prefer.

What was the biggest surprise?

We were shocked by the strength of the responses. We thought infants would be sensitive to the behaviour of others, but didn't anticipate the extent of this. Infant research rarely achieves anywhere close to a 100% response rate. We used physically neutral 'puppets' — circles, squares or triangles with affixed eyes — to role play the behaviours. And we expected some infants' shape or colour preferences to influence their choice, but, in our experiments, almost every single baby chose to play with the helper puppet over the hinderer after watching their behaviour.

If infants can distinguish good and bad, how does ugly factor in?

Infants are definitely savvy. They are always evaluating other people. There's a lot of research showing that babies prefer to look at attractive over unattractive people. In addition to evaluating others on the basis of surface characteristics, however, our work shows that they also base decisions on internal characteristics. But we don't yet know how they integrate these features — in other words, how they would rank an 'ugly helper'.