Origins of Morality: Puppet-Show Style!

Morality and convention are so mired in culture that it may seem near impossible to determine the extent to which biology and environment give rise to it. And yet it is possible to investigate the evolutionary origins of morality. Research with infants - especially pre-verbal infants - who have not yet been sufficiently exposed to most cultural institutions, can provide an opportunity to determine what the evolutionary and developmental building blocks are for complex moral reasoning.

Human adults evaluate individuals very quickly, on the basis of both physical and behavioral traits and characteristics. What are the origins of this capacity? One group of researchers wanted to determine if preverbal infants would distinguish individuals that might help them from individuals that might be harmful. In this study, 6- and 10-month-old infants watched a short puppet show in which a "climber" shape was struggling to climb up a hill. In some trials, the climber is helped by another shape, and in other trials, the climber is hindered by a third shape. By using simultaneously two methods common in infant studies, the researchers attempted to discern whether young infants were evaluating other individuals on the basis of their behavior.

The first method was the traditional looking-time measurement, also known as the violation of expectation paradigm. This method works because infants tend to look longer at something that is unexpected or surprising. After habituating the infant to alternating "helping" and "hindering" puppet shows, the "climber" would approach either the helpful shape or the harmful shape. If the infants had formed representations of the intentions of the "helper" and "hinderer" based on their actions, then the infants should be surprised - and therefore look longer - when the climber goes to hang out with the hinderer, than when the climber goes to hang out with the helper. The 10-month-olds looked significantly longer when the climber approached the hinderer, suggesting that they were surprised by the climber's behavior. However, the 6-month-olds showed no preference, and looked equally at both displays.

The second method was the toy-choice measurement, also known as the choice paradigm. After viewing the presentations, the infants were offered a tray from which they could reach for a replica of the helper and hinderer shapes used in the puppet shows. Would the babies rather play with the helper or the hinderer? The infants overwhelmingly reached for the helper: 87.5% of the 10-month-olds, and 100% of the 6-month-olds.

Why would it be that the six-month-olds would appear to have accurately encoded the social actions when using the choice task but not the looking-time measurement? It appears that both 6- and 10-month-olds can engage in the social evaluation of others, more generally, and therefore reached for the helper shape. However, it is possible that 6-month-olds are unable to infer the social evaluations of others, while 10-month-olds are. In order to be surprised that the climber chose to approach the hinderer, the infant would have to possess at least a rudimentary theory of mind. He or she would have to know that the climber had a mind that was also evaluating the behavior of the helper and hinderer.

In social situations, individuals must decide relatively quickly, based on limited information, whether or not to trust somebody else. That the ability to rapidly evaluate another individual on the basis of its actions towards another unrelated individual emerges so early in infancy suggests that it is critical to the processing of the social environment. This ability also seems critical for the development of more complex moral reasoning. The ability to distinguish the more fuzzy notions of right and wrong may emerge from the more basic evaluations of positive and negative actions. Indeed, the authors make exactly such an argument: "The social evaluations we have observed in our young subjects have (at least) one crucial component of genuine moral judgements: they do not stem from infants' own experiences with the actors involved...Their evaluations were made on the basis of witnessed interactions between unknown individuals: the infant, as an unaffected, unrelated (and therefore unbiased) third party, is nonetheless rendering a judgement about the value of a social act."

These findings support the claim that the social evaluations of others forms one building block for more complex moral thinking, and is potentially innate.

Hamlin JK, Wynn K, & Bloom P (2007). Social evaluation by preverbal infants. Nature, 450 (7169), 557-9 PMID: 18033298