Handshakes

Hand-to-hand contact may have an evolved purpose. Several non-human primate species appear to shake hands in the form of rhythmic overlapped fingers (Al-Shamahi, 2021), while some human-like palm-overlapping has also been observed during the movement (Hobaiter, 2020). Whilst this behaviour could represent convergent evolution, it could also be that a form of handshake has existed for millions of years. As Darwin (1872) noted, the open hand is the antithesis of a fist and, therefore, it may be a universal representation in primates of the opposite of threat. Chimpanzees have been recorded shaking their overlapping (mutually gripped) fingers after engaging in, or witnessing, a fight (Hobaiter, 2020), while primates use touch to reduce stress (Rosenbaum et al., 2020; Young et al., 2014). Chimpanzees have long been known to perform a grooming handclasp (McGrew & Tutin, 1978), promoting group cohesion (Dunbar, 2010). During the handclasp, a pair of chimpanzees each simultaneously extend an arm overhead to clasp each other’s palm (or wrist), often using their free hand to groom one another (van Leeuwen & Hoppitt, 2023). It could be that by gripping each other’s hand, chimpanzees are providing support in a similar way that humans do by holding hands.

From an early age humans begin to associate touch with stress reduction which later becomes an automatic response (Reite, 1990). This positive association with touch has been observed from the third trimester and through into old age (Cascio et al., 2019). The seemingly universal craving for touch may be driven by its ability to increase oxytocin (Morhenn et al., 2008), which can increase trust (Kosfeld et al., 2005) and lower stress and blood pressure (Grewen et al., 2003). It is reasonable to predict that these benefits extend to the handshake, an act itself associated with trust (Bedell, 2002). The ability of touch to communication trust and harmony (Navarro, 2013), may be why a typical handshake signals positive intent and promotes confidence (Nuszbaum et al., 2014).

Many thousands of years ago, on the African savanna, early humans may have used hand-to-hand contact to signal positive intent. This might explain why the handshake seems to be a natural and highly recognisable greeting behaviour (Eibl-Eibesfeldt, 1989). The primatologist Frans de Waal (2014) even reported that a matriarch chimpanzee used to offer her hand to him whenever they met. As mammals often greet one another with olfactory investigation (Wesson, 2013), the handshake’s use may have evolved from, or for, the purpose of social chemosignaling. Frumin et al. (2015) found that, following a handshake, humans are more than twice as likely to sniff their own hand (than after no handshake). The researchers also demonstrated that a handshake transmits body odour and increases breathing through the nostrils. Whilst the origin of the human handshake origin is debatable, historically its social meaning has mainly been as an expression of greeting and reconciliation (Bulwer, 1644).

Handshakes are used to greet others across human cultures (Schiffrin, 1974). Eibl-Eibesfeldt (1996) wrote of greeting members of the then largely uncontacted hunter-gatherer tribes of New Guinea with a handshake that was reciprocated. This may simply demonstrate behavioural mirroring, however, members of the Kukukuku and Woitapmin communities informed him that they had ‘always’ practiced the action. Unlike vocal greetings, a handshake requires immediacy as defined by Mehrabian (1972) as an interaction between two individuals involving close physical proximity. In allowing someone close enough to shake hands, it follows that a handshake is an important communicative device for displaying trust and positive intent.  

Handshake research has replicated many of the findings of other touch studies. As such, the focus has often been on positive effects with little investigation from a negative perspective, suggesting the literature may contain positivity bias. Collective studies have made the argument that a handshake can signal cooperative intent (Wiltermuth & Health, 2009) and convey trust (Burgoon & Newton, 1991), and encourage risk-taking in areas of finance (Levav & Argo, 2010) and health (Li & Cao, 2021). Merely observing a handshake has been found to produce greater nucleus accumbens activity (McGaughey, 2012), an area of the brain associated with reward (Cohen et al., 2012). Yet, as with other touch research, the quality and type of handshake is also important. 

Despite the positive effects of touch dominating the literature (Saleh et al., 2023), the quality of touch is an important variable. Stewart et al. (2008) demonstrated that the quality of a job candidate’s handshake positively correlated with their chances of being recommended for the job. Awkward handshakes communicate negative information (Edinger & Patterson, 1983; Schlenker, 1980), while a cold, wet, sticky or weak handshake elicits feelings of aversion (Stewart et al., 2008) and disgust (Saluja & Stevenson, 2019). It could be argued that a limp handshake acts as an evolved warning cue that the hand belongs to someone who may be weak from infection, with a hand’s texture and temperature cues to the presence of disease (Oum et al., 2011). This theory is supported by Leong et al.’s (2015) study which showed that grip strength is associated with mortality risk, with a weak grip being a better predictor of all-cause death than systolic blood pressure. Moreover, the impact of a handshake does not merely relate to its strength or tactile quality; other variables exert influence.

A formula for the ‘perfect’ handshake was devised by Geoffrey Beattie (Schneider, 2010). This concerned 12 variables including the grip and pumping action, while Schriffin (1974) described three distinct types of handshakes: openers, closures and collapses. Most research has focused on openers, a future-oriented handshake, befitting the handshake’s role as a greeting ritual, and suggesting its importance in directing future behaviour.

Human behaviour is strongly influenced by expectations being met (Pillutla & Chen, 1999). According to Melnyk and Hénaff (2019), within a second of contact, a handshake typically produces synchrony between its two actors which regulates their grip, movement and release. As with all ritualistic expectations, a violation of these rules of anticipated synchrony creates incongruence causing unease (Collet, 2016). These implicit standards (Dalton et al., 2010) guide social expectation and reactions (Liu et al., 2011). A deviation from such standards can evoke a threat response similar to that caused by a more obvious counter-stereotypic behaviour (Mendes et al., 2007).

Melnyk and Hénaff (2019) deconstructed the handshake into four phases: preparation, grip, rhythm and release. Of these phases, research has prioritised the grip but its release may be just as important. It is assumed that when one actor releases their grip, the other will instantly reciprocate. The shared timing of a handshake’s release is a good example of how behavioural mimicry occurs with little to no conscious awareness (Lakin & Chartrand, 2003). As one actor releases their grip, this a natural and instantaneous response is triggered. Failure to reciprocate may be taken as a warning that further predicted standards of behaviour will be unmet. People are highly vigilant to such cues of untrustworthiness (von Hippel & Trivers, 2011).

Whereas mimicry signals a desire to affiliate, fostering trust (Chartrand & van Baaren, 2009; Maddux et al., 2008), deliberate non-mimicry can evoke a lack of trust. Feelings of trustworthiness, gained from mirroring, have been linked to signals from the brain’s insula region (Meyer-Lindenberg, 2008), while violations of implicit mimicry standards have been found to induce feelings of physical coldness (Leander et al., 2012). It seems that the difference between the mutual and unconscious release of a handshake, and a consciously prolonged grip, result in very different reactions.

The release of a handshake usually occurs after 2 to 3 seconds of contact. This duration was recorded in 93% of the 1,542 handshakes observed by Feldhutter et al. (1990). However, there is some evidence for social context influencing duration, with Huwer (2003) and Melnyk and Hénaff (2019) reporting that a handshake of consolidation lasted longer than one conducted when greeting. Nevertheless, handshakes rarely last beyond 3 seconds, as a study of athletes at the Olympic Games attested (Nagy et al., 2011).

In a more recent experiment, Nagy et al. (2020) studied the effects of a handshake’s temporal violation on nonverbal behaviour. This is an understudied area, despite many high-profile examples of a prolonged handshake being employed. President Donald Trump, for example, - who gripped President Jinping’s hand for 19 seconds before finally releasing (Garber, 2020) - was subsequently on the receiving end of a 29 second handshake by President Emmanuel Macron whose handshake style has been claimed to be a symbol of status and power, used to exert dominance and demonstrate authority (Nagy et al. (2020). Indeed, President Macron has acknowledged that his handshake is symbolic, not innocent and having a deep significance (Watkins & Koran, 2017).

A handshake study by Nagy et al. (2020) compared how people reacted to being on the receiving end of a typical (2-3 second) handshake with those enduring a prolonged handshake (>3 seconds). This small temporal difference was designed to break the established expectations regarding duration and release. After a prolonged handshake, participants laughed less and displayed more spontaneous facial self-touching and self-hand-to-hand contact. These observations led the researchers to assume that the longer handshakes induced discomfort and social anxiety in their receiver, whereas the typical handshakes evoked similar reactions to the no handshake group. The Nagy et al. (2020) study therefore indicates that a handshake’s quality can induce emotional discomfort. 

Handshakes have the power to influence behaviour and perception, yet this impact is typically unharnessed. Something to consider the next time you shake hands.  

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