Table 1.

Examples of how the human perceptual system has evolved to decipher perceptual cues across diverse social landscapes.

Detecting social danger. Humans are particularly attentive to social expressions of threat, whether by direct expression of anger or indirectly via the observation of fear in others (Calder et al., 2011). Although humans are only minimally affected by predatory attacks from other animals, our predatory defense systems have evolved to cope with social threats arising from members of our own species. In our social environment, an angry face—or antagonistic tone of voice—presents robust cues that others are aggressive and possibly dangerous (Ceravolo et al., 2016).

Detecting kin and group members. The detection of kinship and of conspecifics is crucial for survival in humans. Evolutionary models show that people favor behaviors that benefit others who share genes. Kin detection is certainly observed in more basal species and increases exponentially in complexity as one moves to more socially complex creatures. Dawkins (1989) proposed the ‘green beard effect’, suggesting that animals, and potentially humans, possess recognition alleles that aid in the visual detection of genetically similar individuals.

Detecting disease and health. Especially before the invention of modern antibiotics, it was critical to avoid highly infectious diseases, such as ebola, smallpox and influenza (i.e. contamination fears). According to the disease-avoidance model, disgust functions to protect us from contiguous diseases (Oaten et al., 2009). Studies indicate that people can detect disease from both physical cues (e.g. others’ appearances and behaviors) and psychological cues (e.g. ‘depressed’ vs ‘not depressed’). Facial (e.g. facial masculinity and maturity), vocal (e.g. pitch and tone of voice) and body (e.g. motion and movement and speed) features can signal physical strength/weakness (Fink et al., 2007; Sundelin et al., 2015; Von Kriegstein et al., 2006).

Fitness and beauty. Most females and males want to copulate with those that exude beauty and health, which is a proxy for ‘good genes’ (Buss, 2016). Facial attractiveness is a facial attribute that conveys significant biological advantages (Shen et al., 2016) [e.g. as expressed in mating success (Pashos and Niemitz, 2003), earning potential (Frieze et al., 1991) and longevity (Henderson and Anglin, 2003)]. There is a long line of research showing that the waist–hip ratio is a predictive measure of female attractiveness (Singh, 1993), while height, body shape and penis size in males predict female attraction (Mautz et al., 2013).

Trust and cheaters. The ability to spot cheats, free-riders and the complementary capacity to trust others and evaluate the grounds for such trust is crucial for mutualism. Several studies have shown that some faces are perceived as more trustworthy than others (Winston et al., 2013). Stirrat and Perrett (2010) showed that men with greater facial width were more likely to exploit the trust of others. This suggests that facial phenotypes provide good indicators of another’s trustworthiness. Rhodes et al. (2013) found that women are better at predicting unfaithfulness than men and that perceived masculinity was the most dominant cue in detecting cheaters. Barkow,Cosmides and Tooby (1992, 2004) have proposed the existence of a cheater-detection module, and this has been supported by research showing that people have enhanced memory for cheaters (Bell and Buchner, 2009); similar proposals include a module for evaluating the trustworthiness of others, a so-called suspicion system (Gold and Gold, 2015).

Protection and competence. Todorov et al. (2005) showed that ratings of a political candidate’s face predicted electoral success. Others have shown that ratings of leadership ability from CEO faces predicted company profits (Rule and Ambady, 2008). It has been demonstrated that ratings of perceived competence of others (i.e., their ability to protect us) in a potentially threatening situation is a crucial component of threat assessment, which can influence levels of anxiety and defensive actions. For example, functional MRI studies show that under threat of pain, neural systems involved in pain anticipation show reduced activity when subjects rate others as higher in competence (Tedeschi et al., 2015). This suggests that inferences of competence act as predictors of protection and reduce the expectation of physical harm.

Status and dominance. Alan Fiske has proposed that during social interactions, individuals rank authority by ‘attending to their linear order’. Nonhuman primates will pay to view social images of high-status individuals (Deaner et al., 2005). Our own work has indicated that people show more conformity to individuals with higher reputations—manipulated by reputation ratings in uncertainty decisions (Qi et al., 2018).