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Raha Hassan * , Taigan L. MacGowan, Kristie L. Poole, and Louis A. Schmidt

McMaster University, Canada

Shyness reflects inhibition and anxiousness in social situations, and has been conceptualized as an emotion as well as an enduring characteristic of one’s personality (see Jones et al., 1986). Although shyness is a ubiquitous phenomenon that is observed across development, with estimates exceeding 90% of individuals experiencing it at some points in their lives (Zimbardo, 1977), a smaller percentage of children (~10–15%; Kagan, 1994) and adults (< 40%; Pilkonis, 1977) are characterized as dispositionally or temperamentally shy. Temperamental shyness is associated with a number of distinct physiological correlates of stress‐vulnerability, including greater relative right frontal EEG activity, high and stable heart rate at rest, and high morning basal cortisol levels (see Kagan et al., 1988; Schmidt & Miskovic, 2014; Schmidt & Schulkin, 1999, for reviews). Interestingly, these same distinct patterns of resting physiology have been identified in other mammals, including timid and cautious nonhuman primates (see Shackman et al., 2013), suggesting that temperamental shyness may be conserved across mammals. Temperamental shyness also has been linked to a range of internalizing problems (Findlay et al., 2009), but primarily social anxiety (Heiser et al., 2003; Hofmann et al., 2006; Poole et al., 2017). However, we know that not all individuals who are shy experience maladjustment. Some individuals who are shy appear to adapt reasonably well (Schmidt et al., 2017; Tang et al., 2017).

Shyness is an inherently interesting phenomenon to study, not only because of its ubiquity, but because social interaction and social connection are so fundamental to human existence, raising questions regarding the function of shyness and what purpose(s) it serves (see Schmidt & Poole, 2020a). In this chapter, we explore this broader question from evolutionary and neuroscientific perspectives. To this end, we address three specific questions organized around the broader former question: (1) Are there adaptive functions of shyness? (2) What are some of the regulatory mechanisms of adaptive shyness? and (3) How are these self‐regulatory mechanisms instantiated in the brain in adaptive shyness?

Temperaments are early‐emerging, biologically based, and stable traits that can provide individuals with diverse behavioral strategies that allow them to gain access to resources, reproduce, and coexist within a social hierarchy (Kagan, 1994). The shy‐bold continuum, for example, is commonly observed in nonhuman animal species of fish, birds, and mammals (Wilson et al., 1994). Within this continuum, some individuals are more biologically inclined to exhibit risk‐taking behavior and approach toward novel stimuli (i.e., bold behavioral strategy) whereas others will display fear and avoidance in response to unfamiliar objects, individuals, and situations (i.e., shy behavioral strategy; Groothuis & Carere, 2005; Koolhaas et al., 1999; Wilson et al., 1994). Similarly, temperamental behavioral inhibition can be assessed in humans, with these observed tendencies being evident from infancy throughout development (Kagan, 1994). While behavioral inhibition and the shy‐bold continuum tend to focus on the extent to which an individual experiences approach or avoidance motivations toward any unfamiliar stimulus, there are also individual differences in responses to unfamiliar stimuli that are of a social nature. Specifically, some individuals will exhibit bolder behaviors with social conspecifics while others tend to experience fear and anxiety when interacting with unfamiliar social partners and when encountering new social situations (see Schmidt & Schulkin, 1999, for a review). Although both responses can be viewed as adaptive, wariness and fear are not always acknowledged to have value in our evolutionary past or in more recent human history. Given how conserved the shy‐bold continuum and phenotype appear to be across a range of animal species, it likely has served an important function to species’ survival throughout evolution.