An Evolutionary Ecological Framework for Understanding Human Behavioral Syndromes: Commentary on Lukaszewski et al. 2017

Socioecological Theory of Personality Traits’ Covariation

Personality traits correlate between themselves, both in humans (Van der Linden, te Nijenhuis, & Bakker, 2010) and other animals (Sih & Bell, 2008), but this phenomenon is poorly understood. Recently, a behavioral ecological theory for understanding correlations between personality traits in humans has been proposed. It is labeled as Socioecological complexity theory since it proposes that the complexity of human societies is inversely related to the shared variance between personality traits (Lukaszewski, Gurven, von Rueden, & Schmitt, 2017). The rationale behind this assumption is that complex societies are composed of a large number of different socioecological niches that allow for the behavioral specialization of individuals. Conversely, in less complex societies, individuals face a wide array of similar adaptive challenges that may result in a lower degree of specialization and produce a higher degree of covariation between personality traits.

We agree with the authors that human personality science can immensely benefit from theoretical concepts developed in behavioral ecology. In fact, we recently argued for a similar research direction as well (Međedović, 2018). Hence, we welcome the proposition of Lukaszewski, Gurven, von Rueden, and Schmitt (2017). In the present text, we would like to further advance the evolutionary ecological framework for understanding personality traits’ covariation in humans by pointing to a more specific target of the analysis—behavioral syndromes. Interestingly, Lukaszewski et al. mentioned the term behavioral syndromes in the key words of their manuscript, but it was never mentioned in the body of the text. Furthermore, behavioral syndromes are missing from their subsequent manuscripts on the same topic as well (M. D. Gurven, 2018; Smaldino, Lukaszewski, von Rueden, & Gurven, 2019). This is why we believe that the theory and behavioral ecological account on human personality, in general, would benefit from our proposal.

Behavioral Syndromes

In animal behavioral ecology, the correlations between functionally different behaviors (or personality traits) are called behavioral syndromes (Sih & Bell, 2008). Probably the most robust and replicable is the boldness–aggressiveness syndrome that is found in several species (Bell, 2005; Dochtermann & Jenkins, 2007; Moretz, Martins, & Robison, 2007). Activity is often related to aggressiveness (Kortet & Hedrick, 2007), these two traits can be positively correlated with exploration tendency (Adriaenssens & Johnsson, 2013), and there are data of positive correlations between boldness, aggressiveness, activity, and risk-taking (Garamszegi, Markó, & Herczeg, 2013). It is very important to note that syndromes usually have genetic underpinnings reflected in pleiotropy (e.g., Norton et al., 2011).

Behavioral syndromes are highly important for understanding personality since they are responsible for personality structure in animals and humans. Furthermore, they are considered to be one of the evolutionary puzzles of personality (Bergmüller & Taborsky, 2010). Behavioral syndromes reflect decreased flexibility in behavior which could lead to suboptimal behavioral responses. However, if behavioral syndromes are a maladaptive feature of personality, why did natural selection not decouple the shared genetic basis for different phenotypic behavioral traits? Behavioral ecologists often assume that behavioral syndromes may be adaptive instead, especially in certain ecologies. For example, in harsh, hostile environments with scarce resources, individuals who are both bold and aggressive may have the highest fitness. If this would be the case, correlated selection may increase the frequency of gene alleles which influence both boldness and aggressiveness—this would lead to a behavioral syndrome on a population level. Indeed, empirical data showed that an environment with elevated predation risk can generate boldness–aggressiveness syndrome (Bell, 2005; Bell & Sih, 2007), which is in line with this hypothesis.

An obstacle for exploration of the behavioral syndromes in humans is the fact that personality traits studied in animals cannot be directly translated to the complex personality traits depicted in lexical models of personality such as the Big Five. First, we must translate the personality characteristics studied in animals into the terms of the Big Five traits of human personality (Međedović, 2018): Boldness could be mapped on the negative pole of Neuroticism (as a lack of fear) and elevated Extraversion (social boldness); exploration is a characteristic associated with Openness to experience; aggressiveness would depict the negative pole of Agreeableness; impulsiveness and risk-taking could be mapped on the negative pole of Conscientiousness, while sociability is a central feature of Extraversion as well.

In sum, we propose that the research of ecological factors that generate personality traits’ covariation should primarily be aimed at behavioral syndromes. The main reason is that different environmental characteristics would not produce covariation in personality traits in general but to personality traits that may interactively contribute to fitness in that specific environment. By paying attention to which exact syndromes are related to various ecological parameters, we could gain new important information not only regarding the personality structure but adaptive functions of personality traits as well. Furthermore, this research direction would have comparative attributes as well, which may lead to more general interspecies knowledge about personality.

Empirical Example: Conscientiousness–Agreeableness Syndrome in Lukaszewski et al. Data

Lukaszewski et al. (2017) were focused on general covariation of personality traits in their manuscript. They did show the correlations between Socioecological complexity on a national level with specific correlations of every pair of Big Five traits, but they did not interpret the specific syndromes. As an example of the behavioral syndromes framework, we will analyze the syndrome that had the highest correlation with Socioecological complexity: Conscientiousness–Agreeableness syndrome (r = −.54, p < .001). When adding the original data published by Schmitt et al. (2007), we can see that Socioecological complexity is negatively related to the mean levels of Conscientiousness (r = −.41, p < .01) and Agreeableness (r = −.43, p < .01) as well; the correlations between Socioecological complexity, Extraversion (r = .02, p > .05), Neuroticism (r = .16, p > .05), and Openness (r = .01, p > .05) are statistically not different from zero. Furthermore, the negative association between Socioecological complexity and Conscientiousness–Agreeableness syndrome is significant even when mean levels of these traits are controlled in the analysis (r_partial = −.44, p = .001).

Conscientiousness–Agreeableness syndrome is fruitful for the behavioral ecological analysis since it is closely related to impulsiveness–aggressiveness syndrome if we observe two traits from their opposite poles. This syndrome is reliably found in humans; furthermore, the phenotypic correlation between the traits can be partially attributed to the shared genetic basis underlying these two traits (Dinić, Nikolašević, Oljača, & Ignjatović Bugarski, 2018). The data of Lukaszewski et al. (2017) can now offer a more specific and in-depth hypothesis about the covariation between the two traits. Low Socioecological complexity produces lower levels of Conscientiousness and Agreeableness together with the higher correlation of these two traits on a population level. Could this combination of traits be fitness-enhancing in low socioecological complexity societies? Previous research showed that lower Conscientiousness is related to higher reproductive success as a crucial fitness component (Berg, Lummaa, Lahdenperä, Rotkirch, & Jokela, 2014; Skirbekk & Blekesaune, 2014; but see Gurven, von Rueden, Stieglitz, Kaplan, & Rodriguez, 2014, for opposite results). On the other hand, the data usually show that higher Agreeableness is beneficial for fitness (e.g., Jokela, 2012; Međedović, Šoljaga, Stojković, & Gojević, 2018), although these studies did not analyze the potential moderating role of the environmental conditions. In any case, it is certainly plausible to assume that aggressive and more risk-prone individuals would have fitness benefits in less complex environments, which are in fact marked with elevated scarceness and environmental harshness. This hypothesis would be in line with the existing data in animals as well (Bell, 2005; Bell & Sih, 2007).

Other Issues and the Suggestions for Future Research

There are several additional issues that directly emerge from the previous analysis. The first one is related to the Socioecological complexity measure per se. We believe that the theorizing of Lukaszewski et al. (2017) is sound, but additional effort is needed to empirically show that Socioecological complexity cannot be reduced to environmental harshness. Human Development Index is used as one of the central measures of Socioecological complexity, but it, in fact, may better represent the harsh versus beneficial environment. Authors state that the associations between Socioecological complexity and behavioral syndromes remain significant after controlling for the markers of environmental harshness, but this may be due to unmeasured indicators of harshness. Note that the interpretation of Lukaszewski et al. findings would be exactly the same if we use environmental harshness as an exploratory concept instead of Socioecological complexity, but the former explanation would be more parsimonious compared to the latter.

Secondly, the researchers interested in using the evolutionary ecological framework in explaining personality traits’ covariations should analyze the adaptive benefits of these covariations in different environments. This could be used by measuring reproductive success or other fitness components. The hypothesis is that individuals with highly pronounced traits (or low expression of the traits, since both combinations can produce behavioral syndromes) may have elevated fitness benefits in a certain environment. Hence, we expect a three-way interaction between two personality traits and the environment in the prediction of fitness. This is the only way to test the ultimate explanation of behavioral syndromes, the one that involves natural selection as the cause of syndromes.

Finally, it must be taken into account that complex, lexically derived traits may not be ideal personality models for such scientific endeavor. In order to facilitate the functional explanation of the syndrome and to keep the comparative nature of the research, scholars may use personality models that more directly describe basic behavioral tendencies like risk-taking, aggressiveness, and boldness (e.g., Davis, Panksepp, & Normansell, 2003).

Conclusions

We certainly welcome the proposition of Lukaszewski et al. (2017). The increased usage of behavioral ecological theory would largely increase our knowledge of the basic features of personality. In our opinion, the research of ecological underpinnings of personality traits’ covariation would benefit if behavioral syndromes were the central target of this research direction. Addressing the evolutionary puzzle of behavioral syndromes could provide additional insight into why the most flexible behavior is not always adaptive and why natural selection in some cases may support diminished behavioral plasticity. This may lead to an increased understanding of the functional outcomes of personality in a biological sense and advance the exploration of human personality in a behavioral ecological context.