PAPER Broadening horizons: Sample diversity and COLLOQUIUM socioecological theory are essential to the future of psychological science Michael D. Gurvena,1 aDepartment of Anthropology, University of California, Santa Barbara, CA 93106 Edited by Daniel Hruschka, Arizona State University, and accepted by Editorial Board Member Susan A. Gelman April 10, 2018 (received for review December 15, 2017) The present lack of sample diversity and ecological theory in flourished in areas of anthropology and economics, but have had psychological science fundamentally limits generalizability and relatively limited impact in psychology. Psychology has been obstructs scientific progress. A focus on the role of socioecology in considered more a proximate level explanation detailing mech- shaping the evolution of morphology, physiology, and behavior anism, complementing the ultimate-level functional approach of has not yet been widely applied toward psychology. To date, behavioral ecology. Evolutionary psychology has been remark- evolutionary approaches to psychology have focused more on ably influential in showcasing hypothesized design features of finding universals than explaining variability. However, contrasts psychological mechanisms, but emphasis in practice has been between small-scale, kin-based rural subsistence societies and more on uncovering human universals than explaining variability. large-scale urban, market-based populations, have not been well The overwhelming emphasis on Western, educated, industrial- appreciated. Nor has the variability within high-income countries, ized, rich, democratic (WEIRD) samples in psychological studies or the socioeconomic and cultural transformations affecting even is now well recognized (2), but recognition has had little impact the most remote tribal populations today. Elucidating the causes on broadening the sample pools or research directions in much and effects of such broad changes on psychology and behavior is a of psychology (3). One strategy to improve representation is to fundamental concern of the social sciences; expanding study increase sampling of small-scale contemporary hunter-gatherers participants beyond students and other convenience samples is COGNITIVE SCIENCES and horticulturalists, as these populations possess lifeways more PSYCHOLOGICAL AND necessary to improve understanding of flexible psychological similar to our preindustrial past, and thus represent a deep reaction norms among and within populations. Here I highlight contrast with WEIRD populations. Such inclusion has become two examples demonstrating how socioecological variability can more common when testing the universality of different traits or help explain psychological trait expression: (i) the role of environ- preferences, often revealing noteworthy differences that chal- mental harshness and unpredictability on shaping time preference lenge traditional ideas about human universals (e.g., refs. 4 and and related traits, such as impulsivity, vigilance, and self-efficacy; 5). For example, working with Tsimane Amerindians of the and (ii) the effects of industrialization, market integration, and Bolivian Amazon over the past two decades, colleagues and I niche complexity on personality structure. These cases illustrate have found that Tsimane parents provide minimal infant- how appropriate theory can be a powerful tool to help deter- directed speech compared with other populations (6), the Big mine choices of diverse study populations and improve the Five personality trait structure fails to replicate (7), there are no social sciences. midlife psychological crises (8), no sex differences in dead- reckoning skills (9), Tsimane exhibit a highly externalized health socioecology | diversity | personality | time preference | cross-cultural locus of control (10), and there is no evidence of heart dis- ease despite high systemic inflammation, a meat-rich diet, and he past four decades have witnessed greater consilience in low HDL cholesterol (11). Together, these findings question Tthe understanding of human behavior due to the common previously assumed universals in human behavior, psychology, thread of evolutionary and ecological theory weaving together and health. the social and life sciences. Recognizing that human psychology Diversifying samples is clearly necessary for assessing the and behavior are shaped by similar selection pressures as in other universality of traits, or testing any theory about the human animals is a powerful and humbling starting point when studying phenotype. A second and equally compelling motivation for the human animal. The existence of population variation, in- sampling beyond urban students is to help generate and test cluding “cultural differences,” is often believed to complicate the theories about human psychology and behavior. In behavioral study of humans by obviating generalizability. Instead, variability ecology, the concept of “reaction norms” describes how a phe- within and among populations is grist for the theoretical mill. notype varies in expression across a range of environments and The field of behavioral ecology applies evolutionary and eco- logical theory to consider adaptive solutions to a wide range of problems typically experienced in the life course of an organism, This paper results from the Arthur M. Sackler Colloquium of the National Academy of given competing demands on limited resources. It emphasizes Sciences, “Pressing Questions in the Study of Psychological and Behavioral Diversity,” held September 7–9, 2017, at the Arnold and Mabel Beckman Center of the National Acade- how socioecological factors affect costs and benefits bearing on mies of Sciences and Engineering in Irvine, CA. The complete program and video record- decision-making. These include factors shaping food acquisition ings of most presentations are available on the NAS website at www.nasonline.org/ (e.g., patchiness of resources in the environment, technologies pressing-questions-in-diversity. available, distance between food patches), marriage and mate Author contributions: M.D.G. designed research, performed research, and wrote choice (e.g., sex ratio, wealth holdings), and social learning (e.g., the paper. number and expertise of models, frequency of relevant envi- The author declares no conflict of interest. ronmental change), to name a few (1). Given its roots in ecology This article is a PNAS Direct Submission. D.H. is a guest editor invited by the Editorial and ethology, behavioral ecology takes diversity in life and life- Board. ways as fundamental and in need of explanation. Published under the PNAS license. To date, behavioral ecology and related approaches in evo- 1Email: [email protected]. lutionary social science (e.g., dual inheritance theory) have www.pnas.org/cgi/doi/10.1073/pnas.1720433115 PNAS Latest Articles | 1of8 Downloaded by guest on September 27, 2021 conditions. The broad range of physical and social environments the human species has experienced over its evolutionary history leads to a general expectation of a flexible expression of phe- notype (i.e., “phenotypic plasticity”) that leads to systematic differences across locales, situations, and over time. Even among hunter-gatherers, many features of subsistence, grouping, mo- bility, and mating vary in predictable ways along a number of socioecological dimensions (12). Some features of the psycho- logical phenotype are canalized during development (e.g., at- tachment style, personality), others remain situationally flexible (e.g., loneliness, self-regulation), sometimes varying over the life course (e.g., time preference, libido), while others may show evidence of transgenerational inheritance (e.g., stress reactivity). Diversifying sample pools thus is necessary, not only for assessing trait universality, but for testing causal theories about how the Fig. 1. Schematic framework contrasting Gemeinschaft (community) char- environment shapes human behavior and psychology in system- acteristics with those of Gesellschaft (society). Adapted from ref. 21. Ge- atic, predictable ways. sellschaft characteristics mirror those reflected by the WEIRD acronym, while The key concern with WEIRD samples is that they often re- Gemeinschaft reflect preindustrial Europe and low income countries, and flect a limited and largely unrepresentative portion of the world anthropological populations. Text in purple and yellow boxes refer to ex- population. However, within industrialized countries typically amples described in the text. labeled as WEIRD, there are large, understudied rural, working class, and ethnically diverse subpopulations (i.e., “inconvenient” Changes along the dimensions shown in Fig. 1 can be expected samples), whose inclusion could greatly benefit the social sci- to have important impacts on numerous traits. For example, ences. To the extent that WEIRDness is unrepresentative of greater abstract representation, innovation, and less “scaffolded most of our species history and much of the current world guidance” were found among Zinacantec Mayan weavers shifting population, a critical question to consider is how WEIRDness “ ” from subsistence agriculture and minimal schooling to wage la- and global WEIRDification itself affects psychology and be- bor and increased schooling over a period of four decades (18, havior. Indeed, different versions of this question have pervaded 19). Another study in Mexico found that children were less co- the social sciences and humanities for several centuries. For operative and more