Emotional development has been shown to predict school achievement (Denham, 2019) and affect life chances (Eysenck, 2009). But how do emotions, and our ability to read them, emerge?
How much an individual is influenced by their biology or the environment has been debated since long before Galton (1869) phrased it as nature versus nurture (Denyer, 2008). New discoveries have led to a reappraisal of their influence and how they interact (Keating, 2011), with many now arguing that nature and nurture are inseparable (Wilson, 2022), while others isolate them by applying heritability across a population (Plomin, 2019). Partly addressing the presence of universality, let's consider the process of facial expressions of emotion in babies and infants.
Newborn babies have been found to spontaneously look at human faces, both real and schematic (Goren et al., 1975). More recent studies have found that faces are perceived within the first few days of life (Arcaro et al., 2017; Gandhi et al., 2017). Babies up to three-months of age also seem to prefer looking at happy faces than neutral ones (Rigato et al., 2011), and they may discriminate between positive and negative expressions (Cheries et al., 2016). However, many of these findings are based on time spent looking at faces. As babies are preverbal, this seems like a sensible technique, yet it is not enough to infer cause or that particular preferences exist. Infants may simply be responding more to familiar expressions, such as a smile, whilst others may be responding to novelty. Despite this, it is well established that faces are crucial for communication (Pascalis & Kelly, 2009). On balance, it appears that babies and infants have an innate preference for some basic-level facial expressions (Ekman & Friesen, 1976). Nature, therefore, may be providing babies with a head start in their emotional development, which Austerberry et al. (2022) claim is more heritable than cognitive or language development.
According to Uston et al. (2022), foetuses produce facial expressions. The researchers noted that exposure to kale flavour elicited an upper-lip raiser representative of disgust. However, the assumption of disgust is another perceiver-dependent inference, and such reverse inferences are unable to evidence emotion as only the expression is accessed (Barrett et al., 2019).
Whilst the early ability to make facial expressions may be adaptive, perhaps to keep caregivers near (Gaussen, 2001), it could be that the adults perceiving the expression are responding in way that reinforces their use. Perhaps a child learns that smiling elicits a desired response. For example, a scowling baby could be seen as feeling angry, yet Camras et al. (2016) found that babies often scowl before they cry. This has not prevented babies from being claimed to be able to recognise sadness, fear, surprise and anger (Caron et al., 1982; Denham, 1998; Izard, 1994). According to Widen and Russell (2008), a conceptual acquisition of these emotions is not present at birth and occurs gradually and beyond infancy, revealing a role of nurture.
Vicari et al. (2000) tested 120 children aged 5 to 10 on their ability to recognise the six basic or classic facial expressions (Ekman & Friesen, 1976). The children matched photographs of the facial expressions with appropriate verbal words. It was found that their perceptual and semantic scores were not only differential, the abilities developed independently and at different rates. Certain emotions were also much more likely to be decoded than others, with 30% of ten-year-olds unable to recognise disgust. This study, like many others, relies on posed, exaggerated facial expressions, that differ greatly from the actual facial movements and configurations an infants would typically see (Grossmann, 2010). A strength of the study was its inclusion of synonyms, accounting for verbal preference. The variation in how children are able to recognise emotions found in this study does not remove nature from the process. Rather than an exclusively innate ability, it shows that emotional development is complex and differs across and within individuals. Growing evidence suggests that the environment determines how this happens, allowing the brain to wire itself through experience, as discussed next.
Between the ages of six-to-twelve months, infants follow gaze direction (Deák, 2015) and look more at others’ mouths (Hunnius & Geuze, 2004). Seeking communication cues, such as intention signals, they are relying on others for this information. A study of 154 seven-month-olds by Geangu et al. (2016), found cultural differences in how infants attend to faces. Half their subjects were from the UK, the other half from Japan. It was discovered that each group visually discriminated facial expressions by means of culturally distinct strategies. Tracking eye movements, the researchers found that the Western infants fixated on the mouth more and for longer, whereas the Eastern infants tended to eye movements, matching cultural preferences found in adults (Jack et al., 2009). As infants match their own emotions to other people’s (Walker-Andrews, 2001), it seems that culture is shaping this process (Todorov, 2017). The different attentional strategies developed by infants are dependent upon the faces they regularly observe, as Nelson’s (2001) perceptual narrowing hypothesis proposed.
Nelson (2001) argued that babies arrive with a crude face-processing system that experience fine-tunes. Supporting this, Scott et al. (2007) hypothesised that children develop a greater sensitivity to faces similar to those they were regularly exposed to. Several studies have measured the percentage of own-race faces that infants see, for example: 92% in Las Vegas (Rennels & Davis, 2008), 96% in Toronto (Sugden et al, 2014), 99% in Hangzhou (Liu et al., 2015). This data informs the other-race effect (Liu et al., 2018), which demonstrates the impact of experience and explains the decline in the ability to discriminate between faces. Sugden and Marquis (2017) argue that infants need to be exposed to different types of faces before they are 9 months old, otherwise they will find it difficult to distinguish between unfamiliar-race faces later in life. This innate visual preference may occur after seeing over 90% own-race faces for the first 100 days (Lee et al., 2017). Unwanted consequences aside, it is evidence for an evolved perceptual narrowing (Quinn et al., 2018), allowing infants to be better able to distinguish between the types of faces they are most often exposed to. It is an evolved adaptation (nature) that relies upon input from the environment (nurture). This effect may also explain a child’s sensitivity to the emotions of members of their inner group.
Tully et al. (2008) found an association between a mother’s depression and her child’s emotional development. It made no difference whether the child was biological related to their mother or not. This seminal study, involving 568 adopted adolescents and 416 nonadopted adolescents, suggested an important non-genetic influence. Offering a similar argument, Eley et al.’s (1998) adoption study found that maternal depression and neuroticism influenced preadolescents’ internalizing symptoms. Whilst this suggests clear evidence of nurture, these parent-offspring results have not been replicated in twin studies which are better identifiers of nonadditive genetic factors. Perhaps an interaction between genes creates a sensitivity in adolescents to their mother’s mood that assumes, but does not rely upon, a close genetic tie.
Around half the variance in emotional development seems to be attributed to genetic factors. The other half is down to the environment and GE interaction. These influences are changeable between populations, and exposure to different environments can stifle or assist genetic potential. The dominant view in psychology - that emotional development is influenced by the genes and modified by the environment (Grantham-McGregor et al., 2007) - holds up. Whilst 0.1% of our DNA is responsible for much variation, there are also universal drivers, such as the preference for faces and social contact, that encourage development. Many experiences considered nurture may be initiated by our genes. What’s more, genetic differences often have a greater effect as a child grows and gains more control over their environment. As Keating (2011) noted, the debate is now more about how nature and nurture interact. This essay concludes that nature is the foundation of emotional development, as our DNA makes us who we are, but that the expression of DNA happens via nurture.
Twins
For a tractable means of separating nature and nurture, adoption and twin studies offer the most effective design. Twin studies demand large estimation errors but they have been favoured since the 1920s (Mukherjee, 2017), often producing well-powered results, especially when combined with adoption studies. Ideally, a large sample of monozygotic (MZ) twins would be followed from birth. One twin in each set would remain with their biological parents and the other would be adopted away, having no further contact. In reality, these incidences rarely happen. However, several large longitudinal classical twin design (CTD) studies have enabled the trait resemblance of MZ and zygotic (DZ) twins to be quantitatively measured (Verhulst, 2017).
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