Early Environmental Effects on Personality and Individual Differences
Various theories and models of evolutionary psychology posit that personality traits are part of adaptive strategies regulating behavioral adaptation to various environmental (ecological and/or social) conditions encountered during childhood. Life history theory provides the most comprehensive framework to understand how circumstances experienced in early life might influence personality. It proposes that personality traits develop into a certain profile depending on different conditional factors. Actual circumstances define resource allocation, that is, how the individual utilizes available resources (e.g., food, parental support, etc.) in order to maximize survival and/or reproduction. The most dominant environmental components to affect allocation strategies are level of mortality, level of stability or predictability of conditions, and level of heterogeneity of the trait in the local environment. Less favorable conditions (i.e., higher mortality rates and less parental investment) are suggested to form personality traits linked to more exploitative behavioral strategies with unrestrictive sexual behavior, whereas more advantageous circumstances proposedly shape rather prosocial behaviors and more restricted sexuality. Early childhood experiences (i.e., quality of caregiving, low socioeconomic status of the family) can be seen as indicators for such environmental factors which might also promote the development of personality profiles linked to certain life history strategies.
Initial stages of human development can be characterized with an extended period of vulnerability and dependence, so the survival of the individual depends mostly from parental effort. Quality of caregiving is formed by several factors such as availability of resources, ability to control resources, personality traits of parents, and numerous more (Buss 2009, 2015). Accordingly, the development of psychosocial processes during childhood is affected by various environmental conditions. This results in the emergence of personality traits which can be seen as functional strategies enabling the individual to adapt to specific challenges to survival or reproduction (Buss 2009, 2015). More specifically, children have to be flexible and to be able to adapt to the rearing styles of their parents/caregivers in order to maximize the time, effort, and other resources invested in them. With the help of these functional strategies, they can ensure their survival, gain more time and opportunity to develop their skills and abilities, and reach sexual maturity. Individuals with more advanced skillset (e.g., being more empathic or being an achiever) have improved access to resources or are able to control them more. Possessing preferable characteristics and sufficient resources leads to advantages in mating, creating more success in reproduction and better changes to survival and development of the individual’s offspring. Correspondingly, the genetic basis of advantageous traits which facilitate reproductive success will be transmitted to the next generation and spread in the population.
The evolutionary approach of personality emphasizes the adaptive function(s) of personality traits, but it also highlights a question in regard to individual differences. Namely, if some traits are more beneficial than others, it should be no variability or only a narrow variation in personality traits (Tooby and Cosmides 1990). Large body of research demonstrated the presence of consequential individual differences in personality traits which have heritable components and are stable over time (Nettle 2006). Former studies have found a heritability of around 50% for the major personality traits indicating that non-shared environmental effects might be as determinative for individual differences as genetic factors (Bouchard 2004). Consequently, individuals adopt a particular personality profile as a result of adaptive psychobiological processes responding to past or present environmental conditions (Buss 2009, 2015). An evolutionary psychological framework dedicated to describe the mechanisms how early-life conditions affect the development of certain personality traits is the life history theory (LHT).
Life History Theory and Adaptive Trade-Off Strategies
The model of life history theory provides a framework for understanding and describing the different strategies individuals develop for allocating their limited resources (e.g., energy, time, etc.) in order to maximize survival and reproduction. Resource scarcity necessitates trade-offs, that is, to prioritize the specific life domain(s) on which they divide up and utilize available resources (Kaplan and Gangestad 2005). Trade-offs determine whether the individual expends time and energy to its own further development or rather starts reproduction. After the onset of reproduction, resource limitations force individuals to recurrent decisions about resource expenditure between actual or future reproduction and supporting existing offspring or producing another (Kaplan and Gangestad 2005; Bjorklund and Ellis 2014). The adaptive value of resource expenditure strategy varies according to circumstances. For example, children and adults differ in their optimal energy allocation strategies based on their level of maturity, ability to access resources, and other characteristics: for children, it is more advantageous to invest more time and energy in their growth and development to reach maturity, while adults, who are mature and self-sufficient, benefit more from producing offspring or support their children and spend energy to their own survival. Accordingly, individual characteristics and differences in environmental conditions shape optimal allocation strategies, which may alter across the lifespan. More importantly, these trade-off strategies can be accounted for differences in timing of life events (e.g., maturation, reproduction, etc.) (Kaplan and Gangestad 2005; Bjorklund and Ellis 2014). Individual configuration of life history trade-offs determines the individual’s overall life history (LH) strategy (Kaplan and Gangestad 2005). Life history strategies enable an optimal adaptation to local conditions, yet, they show a wide range of variation across individuals within the same environmental constraints.
Correspondingly, LH strategies can be considered as coordinated and integrated patterns of metabolic, cognitive, behavioral, and personality traits (Bjorklund and Ellis 2014; Del Giudice et al. 2015). It has been suggested that all LH traits vary on a slow-fast continuum, where humans are toward the slow end of the continuum, but similarly to other species, humans also display a variety of slow and fast life history traits (Del Giudice et al. 2015). Slow LH strategies are associated with future-oriented attitudes and with a preference of long-term focus in behavioral outputs such as the ability to delay gratification. Core features of slower strategies are higher parental investment (i.e., expend time and effort in caring for offspring) together with a restricted number of offspring. In contrast, fast LH strategies involve behavioral strategies with a relatively short-term focus and present-orientated attitude of taking risks in order to maximize immediate rewards. Furthermore, faster strategies can be characterized with an overall prioritizing of mating efforts in forms of early reproductive maturity, frequent mating, and little investment in social relationships or offspring (Belsky et al. 1991; Del Giudice et al. 2015).
Early Environmental Conditions, Life History Strategies, and Personality Development
Two critical environmental determinants of life history strategies were suggested: unpredictability and harshness (Brumbach et al. 2009). Unpredictability covers the predictability of change in environmental conditions, whereas harshness refers to the availability of resources and morbidity-mortality rates. Harshness represents the probability of disability or death caused by actual circumstances at each developmental stage within a population. Unpredictability can be seen as the spatial and temporal variability in harshness (Brumbach et al. 2009). Higher adult morbidity-mortality rates suggest that individuals have a narrow time-window of reproduction, because death or severe health problems occur more frequent at younger ages. In this case, acceleration of physiological development and sexual maturation (i.e., faster LH strategies) are more adaptive, but if morbidity-mortality can be reduced (e.g., through increased parental investment), so children have better chances to live longer and healthier – thus the age-range of reproduction lengthens – slower LH strategies become more adaptive. In other words, faster strategies are more advantageous if the future is uncertain and lifespan is unpredictable or mortality and morbidity rates appear to be high (i.e., high unpredictability); however more stable conditions reducing environmental threats on the survival of offspring favor slower LH strategies (Del Giudice et al. 2015; Brumbach et al. 2009).
Environmental conditions experienced in early-life form not only individual LH strategies but also influence responses to adversities or other life events in adulthood. For example, childhood socioeconomic status (SES) was established as a reliable indicator for environmental harshness (Belsky et al. 2012): low SES was found to be related to greater environmental harshness and can be also associated with higher levels of impulsivity and risk-taking, along with unrestricted sociosexual orientation (Belsky et al. 2012; Brumbach et al. 2009). Consequently, personality is influenced by early-life conditions in several ways, on the levels of interpersonal, socio-cognitive, and affective functioning (Bjorklund 2015; Brumbach et al. 2009). Exposure to unpredictable and harsh environments in childhood was found to be linked to heightened perception of risk, a more hedonistic attitude with relatively hostile and malevolent interpersonal styles and with relatively poor social skills (Belsky et al. 2012; Bjorklund 2015; Brumbach et al. 2009).
Accordingly, LH strategies can be linked to personality development in a relatively direct way as well. For instance, low self-control and impulsivity, openness to experience together with some facets of extraversion were related to indicators of faster LH traits (e.g., increased mortality, unrestricted mating behavior, and exploitative interpersonal behavior) (Belsky et al. 1991; Del Giudice 2014; Del Giudice et al. 2015). Conversely, agreeableness and conscientiousness from the Big Five along with honesty-humility were associated with reduced rates of mortality, reduced sociosexuality, and higher investment in factors influencing emotional stability and quality of parental effort (e.g., relationship quality and stability) (Del Giudice 2014; Del Giudice et al. 2015).
Parental Investment and Personality Development
Quality of parental care is also crucial to the development of socio-cognitive, affective, and interpersonal personality functions, and nurturing may mediate the effects of environmental factors on development (Belsky et al. 2012; Bjorklund and Ellis 2014). Furthermore, in early childhood children’s social, emotional, and physiological responses to environmental factors are shaped primary by the quality of care they receive from their primary caregivers (in most cases the parents, especially the mother). The quality of parental care is proximately determined by an emotional bond between the child and the primary caregiver, also referred to as attachment (Bowlby 1980). Higher parental investment in care creates a more consistent and predictable socio-emotional environment for the child, resulting in a secure attachment style. In contrast, lower-quality parental care and conflict between the child and his or her caregivers lead to insecure attachment, which is associated with social and emotional developmental difficulties (Griskevicius et al. 2013; Young et al. 2017).
The quality of the parent-offspring relationship is not only a key component of personality development; it also influences behavioral and neuroendocrine responses to stress. There is a large body of evidence showing that negative familial experiences, such as parental absence or parent-offspring conflict, can alter the epigenetic regulation of hypothalamic-pituitary-adrenal functions (for review see Ellis 2013). Correspondingly, experiencing insecure or unstable emotional environment during childhood unquestionably changes stress responsivity and influences adult functioning. Greater exposure to stress in early life (e.g., parent-offspring conflict) was found to be related with indicators of fast LH strategies (Young et al. 2017). Thus, quality of parental care can be linked to certain adult personality traits (Bowlby 1980; Young et al. 2017), suggesting that parental investment modulates both LH trade-offs and personality development.
Social Environments: The Frequency of Personality Traits in Others
Although families create an influential environment to form personality, the traits of other people, that is, the distribution of traits within the local population, also impact the development of personality trait. As pointed out earlier, in certain conditions individual differences can be maintained even in heritable traits (Nettle 2006). Frequency-dependent selection can create such circumstances, where adaptive traits show both high heritability (i.e., having strong genetic basis) and an appreciable variation within the population (i.e., there are individuals who are low on the trait; others show moderate level of this trait, whereas others are high on that certain personality feature) (Buss 2009; Nettle 2006). Limited resources or the limited access to resources create a competition within the population enhancing the importance of interindividual variation. The adaptive value of a trait depends not only on its character or output, but it is affected by the traits of others in the group (Simpson et al. 2011). For example, being aggressive toward other competitors might be advantageous if the majority of the peers are peaceful or submissive. However, if aggressive behavior becomes more frequent and large proportion of the group acts more aggressively, the adaptive advantage of this trait will decrease (Nettle 2006).
Evolutionary models of trait variability underline that there are trade-offs linked to every level of a certain trait. In other words, being high or low on a certain trait produces both cost and benefits for the person (Buss 2009; Nettle 2006). For example, individuals high on neuroticism may be more vigilant to threatening stimuli, which help them to avoid potential dangerous or harmful situations. Conversely, high neurotic individuals are more prone to depression, showing an increased sensitivity to stress and a decreased likelihood to having stable relationships (see Nettle 2006 for citations). Nevertheless, the costs and benefits also depend on the frequency of the variations of that trait across contestants.
Research on personality offers a comprehensive taxonomy about the structure of personality and a wide-scale field of studies about the behavioral outputs or neurobiological processes linked to certain personality traits (Mischel and Shoda 1999). However, despite the superabundance of knowledge about personality and its longitudinal developmental characteristics, investigating the possible evolutionary origin or specific conditions which evoke the development of certain personality traits is still wanting. Evolutionary personality psychology covers personality traits as adaptations, that is, evolved psychological mechanisms tailored to solve recurrent social problems our ancestors faced throughout our evolution (Buss 2009).
Childhood environmental conditions alter the adaptive strategies to solve evolved problems of survival or reproduction. Different circumstances create specific environments in which the adaptive value of personality traits varies according to several life history trade-offs. These trade-offs necessitate condition-dependent strategies in personality development in order to prioritize resource allocation. Resource expenditure strategies and associated personality traits enable individuals to maximize benefits within a specific, personalized environment which is shaped by local mortality-morbidity rates, stability of environmental conditions, parental investment, and interindividual variability of the traits.
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