Significance: Rapid impressions of trustworthiness can have extreme consequences, impacting financial lending, partner selection, and death-penalty sentencing decisions. But to what extent do people disagree about who looks trustworthy, and why? Here, we demonstrate that individual differences in trustworthiness and other impressions are substantial and stable, agreeing with the classic idea that social perception can be influenced in part by the “eye of the beholder.” Moreover, by examining twins, we show that individual differences in impressions of trustworthiness are shaped mostly by personal experiences, instead of genes or familial experiences. Our study highlights individual social learning as a key mechanism by which we individually come to trust others, with potentially profound consequences for everyday trust decisions.
Abstract: People evaluate a stranger’s trustworthiness from their facial features in a fraction of a second, despite common advice “not to judge a book by its cover.” Evaluations of trustworthiness have critical and widespread social impact, predicting financial lending, mate selection, and even criminal justice outcomes. Consequently, understanding how people perceive trustworthiness from faces has been a major focus of scientific inquiry, and detailed models explain how consensus impressions of trustworthiness are driven by facial attributes. However, facial impression models do not consider variation between observers. Here, we develop a sensitive test of trustworthiness evaluation and use it to document substantial, stable individual differences in trustworthiness impressions. Via a twin study, we show that these individual differences are largely shaped by variation in personal experience, rather than genes or shared environments. Finally, using multivariate twin modeling, we show that variation in trustworthiness evaluation is specific, dissociating from other key facial evaluations of dominance and attractiveness. Our finding that variation in facial trustworthiness evaluation is driven mostly by personal experience represents a rare example of a core social perceptual capacity being predominantly shaped by a person’s unique environment. Notably, it stands in sharp contrast to variation in facial recognition ability, which is driven mostly by genes. Our study provides insights into the development of the social brain, offers a different perspective on disagreement in trust in wider society, and motivates new research into the origins and potential malleability of face evaluation, a critical aspect of human social cognition.
Keywords: trustface evaluationfirst impressionsbehavioral geneticsclassical twin design
Discussion
Here, we find large and stable individual variation in key facial evaluations of trustworthiness, dominance, and attractiveness, consistent with the classic idea that these visual judgments can be shaped by “the eye of the beholder.” Using a twin study, we show that this variation in facial evaluation is largely shaped by people’s personal experiences, rather than by genetic factors or shared environments. Highlighting the scope of personal experience to affect trust offers a different perspective on the fundamental basis, nature, and origin of individual trust and on our capacity to change whom we trust, for good or for ill. As our lives are increasingly affected by highly personalized social experiences, especially online (1, 2), our findings suggest that disagreements about whom we trust are also likely to increase.
Notably, our finding that variation in facial evaluation is driven by personal environments stands in sharp contrast to variation in facial recognition ability, which is almost entirely genetically driven (25). Multivariate modeling showed that the environmental factors driving individual differences in trustworthiness, dominance, and attractiveness evaluations were also largely independent. This pattern suggests that individual differences in impression formation are based on different experiences, and largely not based on overall or general familiarity, typicality, or overall statistical learning (20⇓–22). Instead, our results are supportive of social learning theories, whereby unique social encounters shape individual associations between facial cues and associated traits (35, 36), or could also motivate new statistical learning theories which can account for the social context. Our results shed light on a core aspect of human social perception and indicate a remarkable diversity in the architecture of individual variation across different components of face processing.
As well as revealing the etiology of individual differences in trustworthiness and dominance evaluation, our results replicate and extend a behavioral genetics study of individual aesthetic judgments, which also found that individual differences in facial attractiveness are driven by people’s personal experiences (18). Our current study used a new, more diverse (e.g., in age) and more naturalistic sample of faces. This demonstration of generalizability is especially critical here because the faces used will strongly affect the types of facial cues people can use to judge attractiveness and, consequently, available individual differences (9, 27).
Interestingly, our results do not necessarily imply that familial environment is unimportant even though the shared environment was not a major contributing factor. Siblings, including twins, can have remarkably unique familial environments (reviewed in ref. 29). For example, maternal affection can be very different even across identical twin pairs (29). Early caregiver or familial social experiences could therefore still influence unique mappings of facial cues to impressions.
Finally, it is important to be clear that our findings about individual differences do not argue against the claim that facial impressions of trustworthiness are adaptive, as suggested by leading facial impression theories (5⇓–7, 26). Major evolutionary models of impressions have been based on consensus impressions (see ref. 17 for a review) whereas twin studies are concerned with individual variation. Facial cues that are critical for survival or successful reproduction may in fact be particularly strongly selected for, leading to consensus across individual perceivers. Indeed, consensus impressions, particularly of trustworthiness, are remarkably similar across cultural contexts, although there may be cultural “dialects” in impressions (37⇓–39).
Our results suggest that a priority for future research should be to understand the development of social evaluation of faces. Especially, it will be critical to discover the developmental drivers of individual differences in face impressions, rather than focusing on potential genetic influences. We know little about how early in development these individual differences occur or which kinds of experiences are most consequential. One suggestion, based on our current findings, is that individual interactions with strangers, peers, and caregivers will be especially critical. A key methodological contribution of the current work is to provide a set of reliable tests of individual variation in trust and other impressions, which will benefit developmental and other research into individual differences in facial impression formation. As individual differences in facial impressions and identity recognition show distinctive etiologies, the perceptual and neural mechanisms driving variation in facial impressions will likely differ from those discovered in face recognition perception so far (reviewed in ref. 25). In terms of perceptual mechanisms, little is known about which facial features drive idiosyncratic impressions although a wealth of research has illustrated which facial features underlie consensus impressions (e.g., smiling, femininity, and raised eyebrow height are generally perceived as trustworthy) (6, 7). Idiosyncratic impressions could result from individually specific weighting of the same features that drive consensus trustworthiness impressions, as well as associations with additional features with trust or mistrust. Indeed, different facial features are likely to drive trustworthiness variation for different people, depending on their personal experiences (for example, one person may rely heavily on emotional expression to judge trustworthiness whereas another person relies on gender). Regarding neural mechanisms, plausible candidate neural regions driving individual impressions include the amygdala and caudate, which encode associative facial trust learning at the participant group level (23). Finally, the importance of individual experience, highlighted by our findings, motivates research to determine the long-term malleability of facial evaluations. This research aim is particularly critical, given the potential for these impressions to bias important social decisions, from online dating to courtroom sentencing (3, 17).
To conclude, we provide compelling evidence for substantial individual differences in impression formation and show that these differences are largely driven by unique personal environments, not genes (or shared environment). We also provide reliable tests of individual differences in impression formation. Our findings will speak to any scientist, philosopher, journalist, artist, or curious person who wonders why we judge a book by its cover, to what extent impressions lie in the eye of the beholder, and how our experiences with family, friends, partners, or the media might shape how we view the world.
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