Willem E. Frankenhuis

Big and Mighty: Preverbal Infants Mentally Represent Social Dominance

Infants use size as a predictor in judging which contestant will win. Human infants face the formidable challenge of learning the structure of their social environment. Previous research indicates that infants have early-developing representations of intentional agents, and of cooperative social interactions, that help meet that challenge. Here we report five studies with 144 infant participants showing that 10- to 13-month-old, but not 8-month-old, infants recognize when two novel agents have conflicting goals, and that they use the agents’ relative size to predict the outcome of the very first dominance contests between them. These results suggest that preverbal infants mentally represent social dominance and use a cue that covaries with it phylogenetically, and marks it metaphorically across human cultures and languages, to predict which of two agents is likely to prevail in a conflict of goals.

The evolution of predictive adaptive responses in human life history

Many studies in humans have shown that adverse experience in early life is associated with accelerated reproductive timing, and there is comparative evidence for similar effects in other animals. There are two different classes of adaptive explanation for associations between early-life adversity and accelerated reproduction, both based on the idea of predictive adaptive responses (PARs). According to external PAR hypotheses, early-life adversity provides a ‘weather forecast’ of the environmental conditions into which the individual will mature, and it is adaptive for the individual to develop an appropriate phenotype for this anticipated environment. In internal PAR hypotheses, early-life adversity has a lasting negative impact on the individuals somatic state, such that her health is likely to fail more rapidly as she gets older, and there is an advantage to adjusting her reproductive schedule accordingly. We use a model of fluctuating environments to derive evolveability conditions for acceleration of reproductive timing in response to early-life adversity in a long-lived organism. For acceleration to evolve via the external PAR process, early-life cues must have a high degree of validity and the level of annual autocorrelation in the individuals environment must be almost perfect. For acceleration to evolve via the internal PAR process requires that early-life experience must determine a significant fraction of the variance in survival prospects in adulthood. The two processes are not mutually exclusive, and mechanisms for calibrating reproductive timing on the basis of early experience could evolve through a combination of the predictive value of early-life adversity for the later environment and its negative impact on somatic state.

When do adaptive developmental mechanisms yield maladaptive outcomes

This article discusses 3 ways in which adaptive developmental mechanisms may produce maladaptive outcomes. First, natural selection may favor risky strategies that enhance fitness on average but which have detrimental consequences for a subset of individuals. Second, mismatch may result when organisms experience environmental change during ontogeny, for instance, because they move from one environment to another. Third, organisms may learn about their environment in order to develop an appropriate phenotype; when cues indicate the environmental state probabilistically, as opposed to deterministically, sampling processes may produce mismatch. For each source of maladaptation, we present a selection of the relevant empirical research and illustrate how models from evolutionary biology can be used to make predictions about maladaptation. We also discuss what data can be collected to test these models in humans. Our goal is to show that evolutionary approaches not only yield insights into adaptive outcomes but can also illuminate the conditions leading to maladaptation. This perspective provides additional nuance to the dialectic between the developmental psychopathology model and evolutionary developmental psychology.

Simpson's paradox in psychological science: a practical guide

The direction of an association at the population-level may be reversed within the subgroups comprising that population—a striking observation called Simpsons paradox. When facing this pattern, psychologists often view it as anomalous. Here, we argue that Simpsons paradox is more common than conventionally thought, and typically results in incorrect interpretations—potentially with harmful consequences. We support this claim by reviewing results from cognitive neuroscience, behavior genetics, clinical psychology, personality psychology, educational psychology, intelligence research, and simulation studies. We show that Simpsons paradox is most likely to occur when inferences are drawn across different levels of explanation (e.g., from populations to subgroups, or subgroups to individuals). We propose a set of statistical markers indicative of the paradox, and offer psychometric solutions for dealing with the paradox when encountered—including a toolbox in R for detecting Simpsons paradox. We show that explicit modeling of situations in which the paradox might occur not only prevents incorrect interpretations of data, but also results in a deeper understanding of what data tell us about the world.

Does Early-Life Exposure to Stress Shape or Impair Cognition?

A predominant view in psychology is that early psychosocial adversity (e.g., abuse) impairs cognition, because children from stressful backgrounds (e.g., violent households) score lower on standard tests of intelligence, language, memory, inhibition, and other abilities. However, recent studies indicate that these people may exhibit improved detection, learning, and memory on tasks involving stimuli that are ecologically relevant to them (e.g., dangers), compared with safely nurtured peers. These findings contradict the view that cognition of stressed people is generally impaired; they suggest, rather, that these people’s minds are developmentally specialized toward local environmental conditions. Here, we review recent research supporting this hypothesis. In addition, we propose that novel studies should examine whether stressed children show not only improved detection but also improved memory and reasoning on tasks involving stimuli that are ecologically relevant to them. Finally, we discuss clinical implications of switching from conceptualizing stressed minds as “adapted” rather than “impaired.”

Balancing sampling and specialization: an adaptationist model of incremental development

Development is typically a constructive process, in which phenotypes incrementally adapt to local ecologies. Here, we present a novel model in which natural selection shapes developmental systems based on the evolutionary ecology, and these systems adaptively guide phenotypic development. We assume that phenotypic construction is incremental and trades off with sampling cues to the environmental state. We computed the optimal developmental programmes across a range of evolutionary ecological conditions. Using these programmes, we simulated distributions of mature phenotypes. Our results show that organisms sample the environment most extensively when cues are moderately, not highly, informative. When the developmental programme relies heavily on sampling, individuals transition from sampling to specialization at different times in ontogeny, depending on the consistency of their sampled cue set; this finding suggests that stochastic sampling may result in individual differences in plasticity itself. In addition, we find that different selection pressures may favour similar developmental mechanisms, and that organisms may incorrectly calibrate development despite stable ontogenetic environments. We hope our model will stimulate adaptationist research on the constructive processes guiding development.

Adaptive explanations for sensitive windows in development

Development in many organisms appears to show evidence of sensitive windows—periods or stages in ontogeny in which individual experience has a particularly strong influence on the phenotype (compared to other periods or stages). Despite great interest in sensitive windows from both fundamental and applied perspectives, the functional (adaptive) reasons why they have evolved are unclear. Here we outline a conceptual framework for understanding when natural selection should favour changes in plasticity across development. Our approach builds on previous theory on the evolution of phenotypic plasticity, which relates individual and population differences in plasticity to two factors: the degree of uncertainty about the environmental conditions and the extent to which experiences during development (‘cues’) provide information about those conditions. We argue that systematic variation in these two factors often occurs within the lifetime of a single individual, which will select for developmental changes in plasticity. Of central importance is how informational properties of the environment interact with the life history of the organism. Phenotypes may be more or less sensitive to environmental cues at different points in development because of systematic changes in (i) the frequency of cues, (ii) the informativeness of cues, (iii) the fitness benefits of information and/or (iv) the constraints on plasticity. In relatively stable environments, a sensible null expectation is that plasticity will gradually decline with age as the developing individual gathers information. We review recent models on the evolution of developmental changes in plasticity and explain how they fit into our conceptual framework. Our aim is to encourage an adaptive perspective on sensitive windows in development.

Why Are Childhood Family Factors Associated With Timing of Maturation? A Role for Internal Prediction

Children, particularly girls, who experience early familial adversity tend to go on to reach sexual maturity relatively early. This feature of adolescent development is believed to be an evolved strategy that arose because individuals with genes that caused them to mature relatively early under certain conditions left behind more descendants than those who did not. However, although much has been done to uncover the psychological and physiological mechanisms underlying this process, less attention has been paid to the evolutionary reasons behind why it might be advantageous. It has previously been suggested that this strategy evolved because early familial adversity accurately indicated later environmental adversity, under which conditions early reproduction would likely maximize evolutionary fitness. In this article, we contrast this “external prediction” model with an alternative explanation, which builds on the existing explanation and is mutually compatible with it but also distinct from it. We argue that accelerated development is advantageous because early adversity detrimentally affects the individual’s body, increasing later morbidity and mortality; individuals may adapt to this internal setback by accelerating their development. Unlike the external prediction model, this “internal prediction” relies not on temporal environmental continuity but on long-term effects of early circumstances on the body.

What Can Cross-Cultural Correlations Teach Us about Human Nature?

Many recent evolutionary psychology and human behavioral ecology studies have tested hypotheses by examining correlations between variables measured at a group level (e.g., state, country, continent). In such analyses, variables collected for each aggregation are often taken to be representative of the individuals present within them, and relationships between such variables are presumed to reflect individual-level processes. There are multiple reasons to exercise caution when doing so, including: (1) the ecological fallacy, whereby relationships observed at the aggregate level do not accurately represent individual-level processes; (2) non-independence of data points, which violates assumptions of the inferential techniques used in null hypothesis testing; and (3) cross-cultural non-equivalence of measurement (differences in construct validity between groups). We provide examples of how each of these gives rise to problems in the context of testing evolutionary hypotheses about human behavior, and we offer some suggestions for future research.

Individual Differences in Developmental Plasticity May Result From Stochastic Sampling

The ability to adjust developmental trajectories based on experience is widespread in nature, including in humans. This plasticity is often adaptive, tailoring individuals to their local environment. However, it is less clear why some individuals are more sensitive to environmental influences than others. Explanations include differences in genes and differences in prior experiences. In this article, we present a novel hypothesis in the latter category. In some developmental domains, individuals must learn about the state of their environment before adapting accordingly. Because sampling environmental cues is a stochastic process, some individuals may receive a homogeneous sample, resulting in a confident estimate about the state of the world—these individuals specialize early. Other individuals may receive a heterogeneous, uninformative set of cues—those individuals will keep sampling. As a consequence, individual variation in plasticity may result from different degrees of confidence about the state of the environment. After developing the hypothesis, we conclude by discussing three empirical predictions.