Unpredictability, and Psychological Signature of Fast Life-History Pace

Socioeconomic status (SES) is one of the most commonly used measures in the social sciences, meant to proxy wealth and social status, but it is a “black box” that alone provides little insight above and beyond a general access to knowledge and resources (30). Objective SES indicators are indirect, and may depart from perceived status, standing, and well-being in local communities. SES thus taps into multiple dimensions of “lived experience” that can vary substantially within and among populations.

Two of these perceived dimensions related to SES are environmental harshness and unpredictability. Whereas much research in the social sciences has focused on the amount of social and economic resources, the predictability (i.e., stability) of resource access is a relatively underappreciated component underlying decision-making, with pervasive effects on evolved life history and psychological traits. A species’ life history reflects the effects of selection on the timing and duration of life stages and its events, including juvenile development, age of first reproduction, and rate of senescence. Living in harsh, unpredictable environments characterized by resource insecurity, ecological uncertainty, volatile safety nets, and unsafe neighborhoods can foster a present-oriented disposition that favors short-term benefits despite long-term costs, while discounting long-term benefits that carry short-term costs (31, 32). Present-oriented time preference reflects a “fast” life history. While species vary along a slow–fast life-history continuum as a function of mortality risks and predictability, similar logic and testing finds individuals in the same species varying in life-history pace as well. According to this view, people who perceive themselves living under harsh conditions that are difficult to control are more likely to abstain from healthy habits, including routine physical activity, a healthy diet, physician check-ups, and preventative care, not because of poor understanding of the health consequences of such abstention, but because other uses of time and money may take precedence if chronic disease risks at later ages are discounted (31, 33). Cigarette smoking, alcohol consumption, drug use, criminal behavior, overeating, risk taking, and other activities that provide short-term gains but long-term costs have all been associated with (perceptions of) living in an unpredictable, high-mortality environment (34, 35). Medical treatment compliance, safer sexual practices, regular physical exercise, and other activities that may provide long-term benefits but have immediate costs are instead associated with a predictable, low-mortality environment (36, 37). Faster life histories where future prospects look dim are also expected to shift priorities toward earlier and greater reproductive effort, including earlier sexual maturity, sexual activity and reproduction, greater short-term mating, and higher total fertility (38, 39).

Rural, underserved populations rarely studied in psychology are disproportionally affected by poor living conditions, high rates of disease, adverse effects of climate change, natural disasters, and displacement by governments or foreign entities. These and other cues of harsh environments tend to be associated with more present-oriented time preferences, as short-term fitness considerations may outweigh potential long-term gains that may never be realized (40). Consistent with this notion, young adults living in slums (favelas) of Rio de Janeiro were found to discount the future more heavily than age-matched Brazilian university students (41). Across 46 nations, those with greater life expectancy (proxy for better conditions) were more willing to wait for a larger but delayed reward (i.e., less present-oriented) (42).

Although less explored, these proxies of a faster life-history trajectory can be linked to other psychological traits. Dispositional attributes shaped by living under resource-insecure conditions include not only steep temporal discounting, but also higher impulsivity, less self-regulation, low self-efficacy, and an externalized locus of control: that is, believing that one’s own efforts may have only marginal effects on well-being (43). Thus, in terms of motivation to improve one’s health, a relatively stable environment with predictable resources and low extrinsic mortality risk should favor greater self-efficacy and a more internalized health locus of control orientation due to the payoffs from successful planning in matters of health. Such planning requires a sense of control and an ability to self-regulate in ways that help attain delayed gains at short-term cost, especially in the presence of numerous stressors. On the other hand, an environment characterized by resource unpredictability and high exogenous mortality risks should favor a more externalized locus of control orientation, greater temporal discounting, and lower self-efficacy in terms of health care decision-making. Consistent with this line of reasoning, experimental evidence reveals that low levels of control lead to a lower ability to focus on concrete goals (44), a belief that goals are not attainable (45), less motivation to realize goals (46), and greater future discounting (47). Across 43 nations using a World Values Survey, lower income within and among countries was associated with lower perceived control, intrinsic motivation, trust, and prosocial attitudes (48). Across countries, low income conditions also reduce self-efficacy, and increase vigilance and impulsivity (49, 50). Among seven postcommunist countries, the effects of SES and material deprivation on health were mediated largely by perceived control (49). Thus, resource limitation, harsh environment, and uncertainty about the future may lead to undervaluing long-term health. Further support is evident in a recent study of Tsimane Amerindians, who exhibit less internal and more external locus of control than representative, age-matched samples from the United Kingdom and Japan; Tsimane with external locus orientation are less likely to seek medical attention for common illnesses (10).

To date, the few experiments testing effects of harshness on time preference and other psychological traits reveal similar findings as in observational and comparative studies. Inducing cues of poverty among Chinese students revealed more impulsivity and present-oriented preferences (51). Envisioning one’s future self, through letter-writing and virtual reality representation, also appears to reduce support for risky and delinquent behavior (52). Additional experiments show parallel relationships beyond humans. For example, European starlings in poorer condition (proxied by greater telomere attrition) act more impulsively, while having lower energy reserves resulted in steeper time discounting (53). Thus, observational and experimental evidence supports patterned variability in several psychological risk-related attributes that affect decision-making as coherent, functional responses to cues of socioecological context. Development of these psychological traits guiding preferences and decision-making may be especially shaped by exposures early in life (54), although additional changes over the life course as circumstances improve have also been observed (55).

Living in poverty with many stressors and low sense of power is also believed to induce greater “cognitive load,” and hence greater susceptibility to cognitive biases and poor decision-making (50). But in contrast to this “deficit” model where adverse environments are believed to result only in impairments and underachievement, an adaptive flexibility approach considers that individuals groomed in adverse or high-stress conditions develop traits that are better suited to managing these conditions (56). Indeed, evidence to date suggests enhanced abilities among vulnerable and at-risk populations or even when such stressful conditions are artificially induced in the laboratory. These include greater attention-shifting (57), memory for negative events (58), rapid tracking (56), recognition of angry and fearful faces (59), enhanced learning about animal dangers (60), enhanced early-life memory retention (61), and empathic accuracy (62). Understanding that different cognitive “biases” may be adaptive responses to sustained living under difficult conditions has important implications for what constitutes appropriate interventions in educational and employment settings (56).

This theoretical approach relating life-history pace, time preference, and psychological traits presents a promising direction for further exploration of population differences in a growing number of psychological and behavioral traits. Most critically, it requires sampling individuals from a wide range of socioeconomic backgrounds and developmental histories in WEIRD populations. For example, a study of urban middle school students in the industrial city of Flint, Michigan, showed that perceptions of a harsh neighborhood and social environment were associated with more present-oriented time preference, and itself associated with greater participation in risky behaviors, such as physical aggression and property crime (63). Similarly, community college students with shorter perceived time horizons and greater perceived future unpredictability engaged in more risk-taking behavior in areas of safety, health, sexual behavior, finances, and social relationships (40). Contrasting environments characterized by uncertainty, harshness, poverty, and danger with those distinguished by predictability, abundance, comfort, and safety requires that researchers sample beyond the university, broadly within one’s state and country, in addition to greater sampling of low-income countries.

The studies mentioned here represent just the beginning of a nascent life-history and socioecological approach to understanding plasticity in psychological traits. Exciting directions abound. For example, with improved health infrastructure and other forms of socioeconomic development occurring globally but at different rates, perceptions of uncertainty and environmental harshness should shift accordingly, with concomitant impacts on psychological traits affecting behavior. Natural disasters and other unexpected traumatic events can temporarily shift perceptions in the opposite direction, even in high-income countries. Indeed, exposure to catastrophes is associated with altered time and risk preferences (64). In low-income countries, floods and other disasters can lower aspirations and affect risk and time preferences in ways that help explain the difficulty of escaping poverty (65). Even when individuals experience similar traumas or inhabit similar environments, individual perceptions of events and future prospects can vary in key ways that affect decision-making related to resilience. This new body of research highlights the need to better understand how perceptions are formed in the first place. The question of perception formation and updating is especially relevant in the context of rapid cultural, socioeconomic, and political change.

Socioecological Complexity and Personality Diversification

A major area of psychology addresses the content of personality structure. The Five Factor Model (i.e., “Big Five”: openness, conscientiousness, extraversion, agreeableness, neuroticism/emotional stability) is often claimed to be the universal structure of human personality that transcends language, culture, history, economy, and ideology (66, 67). Although other structures have been described (e.g., ref. 68), with more or fewer factors, most are similar to the Big Five. It is largely non-WEIRD samples that to date have deviated most from the Big Five. For example, Tsimane personality structure supports two factors combining features across the Big Five: prosociality/leadership and industriousness (7). The failure of the Big Five to replicate among the Tsimane could not be explained by addressing the usual methodological culprits. Stratifying by sex, cohort, schooling, and Spanish fluency made little difference, nor did accounting for acquiescence and confirmation bias; spousal reports also showed a similar two-factor structure. Other findings with indigenous populations are instructive. For example, failure to demonstrate the Big Five has also been recently shown among both rural and urban Mossi in Burkina Faso (69). Among 12 isolated languages, including Maasai, Fijian, and Enga, a lexical approach documenting universal attribute concepts highlighted just two dimensions of dynamism and social self-regulation (70).

Without a theory of personality formation, it is unclear whether different environments should generate true differences in personality structure in the first place. An evolutionary hypothesis proposes that temporally stable aspects of affect, cognition and behavior (i.e., personality) are adaptations that over generations tended to maximize biological fitness. However, this middle-range expectation alone does not carry enough specificity to guide research on personality variation across populations. Thus, it is critical to understand how low-order traits are coordinated to assemble into higher-order factors. The Big Five’s successful replication in many countries could be an artifact of living in a large urban, literate population. Even in prior studies demonstrating cross-population evidence for the Big Five, low congruence scores were obtained in samples in India, Botswana, Morocco, and Nigeria (66). An old but still unstudied question thus is to ask whether and why personality and its structure might differ substantially among populations. Levels of specific traits, such as extraversion and openness, certainly vary among populations (71), but the notion that the number and content of factors itself might vary is more complicated to resolve.

A behavioral ecological perspective would suggest that personality items should covary to the extent that they act synergistically to help individuals achieve fitness-relevant goals. Fitness effects of particular trait covariance structures should vary across socioecological environments with distinct ways of gaining status, obtaining mates, caring for children, producing and defending resources. Big Five personality covariance will be greater to the extent that meeting these goals requires facets cross-cutting the five factors. With this guiding logic, my colleagues and I recently proposed a hypothesis that greater societal complexity, defined by a greater number of diverse specialized social and occupational niches, should favor more weakly intercorrelated higher-order personality factors in a population. This “socioecological complexity hypothesis” (72) suggests that beginning with the Neolithic agricultural revolution, life in large, dense, and stratified populations became increasingly marked by greater niche diversification and divisions of labor; later technological and industrial revolutions, and expansion of markets in a monetized economy further expanded the number and specialized character of niches. More niches means more ways of being successful, and of maximizing fitness or proxies of fitness, such as wealth and prestige. Urbanization intensifies labor, mating, and social markets by concentrating larger numbers of people, and by incentivizing novel forms of specialization (73). Whereas hunter-gatherers are more likely to be “Jacks and Jills of all trades,” industrialized populations rely on highly specialized roles for producing goods and services. Personality diversification should map onto this high degree of occupational and social diversification if phenotypic specificity favors a more optimal performance within specialized niches. Another possibility is that having a greater number of niches open to individuals loosens whatever constraints on personality expression that might otherwise arise with having fewer options. For example, successful leaders in small-scale horticulturalist populations, such as the Tsimane, must not only be gregarious, but also generous, agreeable, hard-working, conscientious, and emotionally stable; under such conditions, we might expect greater interfactor correlations among the traditional Big Five factors, as is found among Tsimane. In industrialized populations, a project leader on an engineering project could be highly organized and creative, but shy, introverted, and unpleasant. Thus, a straightforward prediction is that populations characterized as having greater socioecological complexity should show greater personality diversification. In terms of the Big Five, we would expect lower correlations among the factors in more complex societies.

The first test of this hypothesis, by my colleagues and me, compared 55 nations (comprising 17,637 adults) tested using the same Big Five Inventory (72). Socioecological complexity was operationalized as a composite of three variables: human development index (United Nations index that combines data on levels of education, gross domestic product, and life expectancy), urbanization (percentage of nation’s population living in an urban vs. rural setting), and sectoral diversity (a measure of a country’s volume and diversity of exported products). Complex countries have citizens who are relatively, wealthy, literate, long-lived, residing in cities, and both producing and exporting a large and diverse set of goods and products. According to this composite measure, Japan, Belgium, and the United States are on the high end of socioecological complexity, while Ethiopia, Tanzania, and Bangladesh are on the low end. We found that a nation’s socioecological complexity was inversely associated with its average interfactor Big Five correlation (Pearson’s r = −0.54, P < 0.001). The average Big Five interfactor correlation spans from 0.14 (France) to 0.45 (Tanzania) across the 55 countries. For comparison, Tsimane horticulturalists, the only small-scale society studied using the same personality instrument, had an average interfactor correlation of 0.54 (7). Accounting for differences in sample size, geography, literacy, acquiescence, negative item, and evaluative bias did not substantially reduce the magnitude or significance of the relationship between socioecological complexity and interfactor correlation (72). It is notable that the Big Five factor combinations whose associations diminished most strongly with greater socioecological complexity tended to involve openness and conscientiousness more than emotional stability, agreeableness, or extroversion.

Personality trait covariance among Big Five at the nation level may reflect other aspects of national character or personality that are not typically studied by considering socioecological underpinnings. One achievement of cultural psychology has been to develop country-specific measures describing different aspects of culture, including “tightness,” “individualism,” and “power distance.” For example, cultural tightness reflects having many strong social norms and low tolerance of deviant behavior (74), while power distance describes the extent to which a community accepts and endorses authority, power differences, and status privileges. I expect personality trait covariance to be higher in places identified as tight, ranking low in individualism and high in gender egalitarianism. Indeed, Table 1 reports significant positive correlations between nation-level personality trait covariance and cultural tightness, and negative associations with Hofstede’s Individualism Index and GLOBE’s Gender Egalitarianism Values. Though not explicitly predicted, trait covariance also associated positively with Hofstede’s Power Distance Index and GLOBE’s Assertiveness Values Index. Adjusting for gross domestic product (GDP) reduces but does not eliminate many of these associations. Thus, even after accounting for the fact that trait covariance is greater in low-income countries, nations with higher trait covariance have greater cultural tightness, less cultural emphasis on gender egalitarianism, and more cultural emphasis on the role of assertion and confrontation in social relationships.

Despite the usual limitations of country-level comparative studies, together these findings introduce important questions about how personality structure might vary among populations in ways that have yet to be addressed, due in part to assumptions and repeated claims about universal structure. Greater sampling of diversity is needed on several empirical fronts. First, more research is needed among populations varying widely in socioecological dimensions. Second, populations experiencing rapid changes over time in socioecology (Fig. 1) could be sampled throughout this process to determine whether personality structure shifts accordingly. Along these lines, it will be interesting to assess Tsimane personality structure again in another decade after further modernization and acculturation. Third, children of immigrants who migrated from areas of lower to higher or higher to lower socioecological complexity may expect to show reflective differences in personality structure compared with their parents. Fourth, developmental research will need to focus on how coordinated traits might be facultatively calibrated in different environments during childhood and adolescence. Some evidence supports this view: Tsimane men and women who are physically stronger or obtain schooling are more likely to be extraverted (75). Similarly, exposures to stressors early in life may calibrate one’s later susceptibility to stress, possibly reflecting differences in neuroticism (76). Finally, formal models will be necessary to more explicitly consider the verbal argument about the evolution of personality structure described here, especially the role of feedback effects between successful specialized role fulfillment and trait-related behaviors.

Socioecology and Culture

Calls to diversify samples in the social sciences are poised to expand the range of cultural diversity. My emphasis and the two examples discussed in this paper, however, focused on socioecological factors as key drivers of population variability, rather than any explicit consideration of culture. Many socioecological characteristics directly or indirectly affect the expression of cultural traits. There is a long history of modeling cultural traits as adaptations to social and physical environment in small-scale societies, and socioecological features figure prominently in studies of the historical origins of cultural institutions in large-scale societies. For example, a history of defending herds among mobile pastoralists in the absence of police authorities has been linked to the cultural complex of honor in the United States South and elsewhere (28). The cultural legacy of agriculture, however, is not uniform, but depends on how crops are produced. A history of rice farming requiring cooperative irrigation and intensive labor in southern China was associated with more interdependent cultural traits, whereas wheat farming requiring minimal cooperation was associated with traits emphasizing independence (27). Countries with a heritage of capital- and strength-intensive plow agriculture with gendered divisions of labor show less-equal gender norms, whereas those with a history of shifting cultivation have norms and practices emphasizing greater gender equality (77). Operational sex ratio has also been shown to affect a variety of norms related to marriage, mating, and relationship dynamics (78).

My point here is that a renewed focus on the socioecological drivers of culture permits an initial framework for considering cultural variation. Sampling across the spectrum of socioecological conditions within and among populations therefore ensures a wider range of cultural variation as well. That being said, cultural evolution can direct norms and behavior in nonadaptive or maladaptive directions, or lead to multiple adaptive equilibria depending on initial conditions (79). In the examples above, the legacy of historical economic practices affects cultural traits in the present, despite massive changes in economic livelihoods over the past few centuries. Thus, even when socioecological conditions change, certain cultural traits and behavioral expression are less flexible and show path-dependence. The opposite scenario is also not uncommon: even when socioecological conditions are relatively uniform, distinct patterns of behavior may exist among subpopulations. For example, distinct fairness norms and cooperative behavior were found to exist among Tsimane villages, despite these villages inhabiting a very similar cultural and ecological environment (80). These cases where similar behaviors are found in distinct socioecologies, or where disparate behaviors are encountered in similar socioecologies, suggest that direct consideration of social learning and cultural transmission using the tools and methods of cultural evolutionary theory will be necessary to explain these discrepancies (79, 81). Sampling across populations identified as having distinct (similar) cultures despite sharing similar (distinct) socioecological features could lead to new insights about how ethnohistorical trajectories and transmission dynamics shape psychology and behavior.