Introduction

Are we born amoral creatures or do we come into this world with a rudimentary moral compass? Hamlin, Wynn, and Bloom [1] argue that at least one component of our moral system, the ability to evaluate individuals as good or bad, is present from a very early age. In their study, 6- and 10-month-old infants watched two social interactions: in one, infants observed the helper assist the climber achieve its goal of ascending the hill, whereas in the other, infants observed the hinderer prevent the climber from ascending the hill. Hamlin et al. [1] found that when given a choice, most infants chose the helper over the hinderer, suggesting that infants evaluated the helper as good and/or the hinderer as bad. The next question Hamlin et al. [1] addressed was whether infants' choices reflected a preference for the helper, an aversion for the hinderer, or both. To answer this question, the helper and hinderer were pitted against a neutral character that neither helped nor hindered the climber. Consistent with the notion that infants evaluated the helper as good and the hinderer as bad, infants picked the helper when it was paired with a neutral character and the neutral character when it was paired with the hinderer. On the basis of these findings, Hamlin et al. [1] concluded that the ability to evaluate individuals based on their social interactions is innate.

Hamlin et al.'s [1] Supplementary Videos show that two conspicuous perceptual events occur on helper and hinderer trials – 1) an aversive collision event when the climber collides with the helper on help trials and with the hinderer on hinder trials and, 2) a positive bouncing event when the climber reaches the top of the hill on help trials. We argue that it is these negative and positive events, rather than the ability to evaluate individuals as good or bad, that drive infants' choices. The helper is viewed as positive because, although associated with the aversive collision event, it is also associated with the more salient and positive bouncing event. In contrast, the hinderer is viewed as negative because it is only associated with the aversive collision event. In the present experiments, we test our alternative account by pitting Hamlin et al.'s [1] social evaluation hypothesis against an alternative, simple association hypothesis.

Results

First, to determine whether infants find the collision event aversive, in Experiment 1 we eliminated the climber bouncing at the top of the hill on help trials and pitted the helper against a neutral character. If infants find the collision between the climber and the helper aversive, then in the absence of the climber bouncing, infants should select the neutral character. In contrast, if infants' choices are based on social evaluation, they should select the helper because, even in the absence of the climber bouncing, the helper is assisting the climber. Second, to determine if infants find the bouncing event positive, in Experiment 2 we manipulated whether the climber bounced on help trials (bounce-at-the-top condition), hinder trials (bounce-at-the-bottom condition), or both (bounce-at-both condition). If infants' choices are driven by the bouncing event then they should select the individual, whether it is the helper or the hinderer, that is present on the trials when bouncing occurs; when the climber bounces on both help and hinder trials infants should show no preference. In contrast, if infants' choices are based on social evaluation, then independent of the bounce, infants should display universal preference for the helper because in all three conditions the helper is assisting the climber in achieving its goal of ascending the hill.

Consistent with the view that infants find the collision aversive, a significant number of infants picked the neutral character over the non-bouncing but colliding helper (7 of 8, binomial probability test, one-tailed P = 0.035). With respect to the bouncing event, consistent with the view that infants find the bouncing event positive, a significant number of infants picked the helper in the bounce-at-the-top condition (12 of 16, P = 0.038, Fig. 1), a significant number of infants picked the hinderer in the bounce-at-the-bottom condition (12 of 16, P = 0.038, Fig. 1), and, in the bounce-at-both condition, infants showed no preference with an equal number picking the helper and hinderer (8 of 16 selected the helper, P = 0.60, Fig. 1).

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Figure 1. Simple Associations May Explain Moral Reasoning in Infants.

Percentage of infants choosing the helper or hinderer, asterisk: one-tailed P<0.05.

https://doi.org/10.1371/journal.pone.0042698.g001

Discussion

The simple association hypothesis allows us to explain why Hamlin et al.'s [1] infants preferred the neutral character over the hinderer and the helper over the hinderer without invoking the notion of an innate moral compass. Experiment 1 demonstrated that, in the absence of bouncing, infants preferred the neutral character over the helper. This finding is consistent with our view that infants find the collision event aversive irrespective of whether the collision occurs between the hinderer and the climber or the helper and the climber. The finding is not consistent with the social evaluation hypothesis because that hypothesis predicts that infants will view the collision between the hinderer and the climber as qualitatively different from the collision between the helper and the climber (i.e., as helping and hindering respectively). Experiment 2 adds further support to the simple association hypothesis by demonstrating that the bouncing event predicts infants' choices. While the preference for the helper in the bounce-at-the-top condition is consistent with the social evaluation and the simple association hypotheses, the preference for the hinderer in the bounce-at-the-bottom condition and the lack of a preference in the bounce-at-both condition clearly conflicts with the social evaluation hypothesis. If infants' choices were based on social evaluation then, because the helper assists the climber in both the bounce-at-the-bottom and bounce-at-both conditions, infants should display preference for the helper in both conditions.

The findings of our experiments speak to a number of important issues in developmental psychology. In the context of a nativist explanation for morality, our data cast doubt on Hamlin et al.'s [1] claim that “the capacity to evaluate individuals on the basis of their social interactions is universal and unlearned.” Our data also speak more generally to the issue of rich interpretations of infant behaviour. In his seminal article, “Who put the cog in infant cognition: Is rich interpretation too costly?” Haith [2] noted that rich interpretations had begun to dominate developmental psychology and he suggested that, in many cases, the data could be explained by much simpler mechanisms. In a companion paper, Spelke [3] argued that, just like the rich interpretations that Haith [2] castigates, intellectual attitudes like Haith's [2] also impede research on infant cognition. Spelke [3] challenged those researchers who were sceptical of rich accounts of infant cognition to put their simpler explanations to the test, and she listed four guidelines for such tests. To test the validity of the simple association hypothesis, below, we address each of these guidelines.

Spelke's [3] first three guidelines are: 1) “Theories should be evaluated in relation to evidence,” 2) “No hypothesis should be considered guilty until proven innocent,” and 3) “those who would explain infants' performance by appealing to sensory or motor processes must provide evidence for those processes.” The present experiments were designed with these guidelines in mind: We evaluated our theory in relation to evidence (Guideline 1) and, in doing so, provided evidence that positive and negative perceptual events determined infants' preferences (Guideline 3). Also, the fact that we pitted our simple association hypothesis against Hamlin et al.'s [1] social evaluation hypothesis demonstrates that we did not treat either hypothesis as guilty until proven innocent (Guideline 2). Spelke's [3] fourth guideline deals with the issue of generalizability and makes the point that a study should not be viewed in isolation. On this note, below we briefly discuss two of Hamlin and colleagues' more recent studies.

In the first follow up to Hamlin et al. [1], Hamlin, Wynn, and Bloom [4] tested 3-month-old infants using the hill paradigm and measured looking time, rather than object choice, to assess infants' preference. When presented with the helper and hinderer, 3-month-old infants displayed a significant preference for the helper (Looking time: Helper 13.12 sec vs. Hinderer 6.22 sec). When paired with a neutral character, 3-month-old infants displayed no preference for the helper over the neutral character (Looking time: Helper 8.64 sec vs. Neutral 8.17 sec), but showed a significant preference for the neutral character over the hinderer (Looking time: Neutral 12.32 sec vs. Hinderer 2.86 sec). Hamlin et al. [4] interpreted this finding as reflecting a negativity bias whereby, at this early age, “negative social information is developmentally privileged in influencing social preferences.” In our view, this finding may simply reflect the fact that 3-month-old infants find the bouncing event less appealing than do 6- and 10-month-old infants, or that they have greater difficulty distinguishing between the collisions and bouncing events. Either of these interpretations would explain Hamlin et al. [4] finding and spare one from having to explain why previous work suggests that a positivity bias, rather than a negativity bias, exists prior to 6 months of age [5], [6].

More recently, Hamlin and Wynn [7] tested 3-, 5-, and 8-month-old infants on two new paradigms and again found that they preferred an individual that helped over an individual that hindered. Similar to the hill paradigm, the help and hinder conditions in these new paradigms are also confounded by salient perceptual events that may be driving infants' choices. Given the ease with which we shifted infants' preferences on the hill paradigm, we believe that by manipulating these salient perceptual events, one could also shift infants' preferences on these new paradigms. One final point of contention may be Hamlin, Wynn, Bloom, and Mahajan's [8] remarkable finding that 8-month-old infants prefer an individual who helps, rather than hinders, a prosocial individual, and an individual who hinders, rather than helps, an antisocial individual. While a full explanation of these findings is beyond the scope of the present paper, it is important to note that they can also be subsumed under the simple association hypothesis [9], [10], and need not reflect infants' innate preference for those who help prosocial individuals and hinder (i.e., punish) antisocial individuals.

In summary, we have followed Spelke's [3] four guidelines and demonstrated that our simple association hypothesis is a plausible alternative to Hamlin et al.'s [1] social evaluation hypothesis. When combined with the arguments against the very concept of moral nativism [11], [12], [13], our findings call into question the view that infants enter this world with an innate moral compass. Outside of the social realm, our findings add momentum a movement in both developmental [14], [15], [16] and comparative [17], [18], [19], [20] psychology toward more parsimonius interpretations of behavior. With respect to evolution, Darwin [21] argued that there is grandeur in a view of life in which complexity and diversity develop from simplicity. With respect to development, we would argue that there is also grandeur in the view that infants' complex and diverse behaviours can be explained using simple mechanisms. Much like evolution, once we understand these simple beginnings, we can begin to uncover the origins of our complex cognitive abilities.

Methods

The research was approved by the University of Otago Human Ethics Committee and all infants participated with written consent from their parents.

Supporting Information

Acknowledgments

We thank Karen Tustin, Molly McCormick, and Sabrina Goh for their help with data collection. Also, we thank Mark S. Blumberg and David J. Lewkowicz for their comments on an earlier draft of the manuscript.