Marco Del Giudice

University of Trieste | UNITS · Department of Life Sciences

Many motivational constructs are opaque “black boxes,” and should be replaced by an explicit account of the underlying psychological mechanisms. The theory of motivational systems has begun to provide such an account. I recently contributed to this tradition with a general architecture of motivation, which connects “energization” and “direction” th...

Researchers are increasingly replacing ot supplementing Cronbach’s alpha with model-based coefficients of the omega family, including omega-total (the proportion of observed score variance explained by all the common factors of a test) and omega-general/omega-hierarchical (the proportion of observed score variance solely explained by the general fa...

Evolutionary research on emotion is increasingly converging on the idea that emotions can be understood as superordinate coordination mechanisms. Despite its plausibility and heuristic power, the coordination approach is still incomplete; most notably, it fails to explicitly address the relations between emotions and motivation. But motivation and...

The chapters in this Handbook shows that evolutionary scholars are making tremendous progress toward an integrated model of emotions. However, there remain a number of theoretical problems that will have to be resolved before integration can truly occur. In this concluding chapter I review and critically discuss what I see as the most pressing issu...

The life history approach to individual differences has become a major influence in evolutionary psychology, not least thanks to the contributions made by Jay Belsky and his collaborators over the last three decades. Today the approach is at a turning point, with a lively dialectic between proponents and critics and a menu of theoretical and empiri...

I highlight a problem that has become ubiquitous in scientific applications of machine learning and can lead to seriously distorted inferences. I call it the Prediction-Explanation Fallacy. The fallacy occurs when researchers use prediction-optimized models for explanatory purposes, without considering the relevant tradeoffs. This is a problem for...

Statistical indices of masculinity-femininity (M-F) summarize multivariate profiles of sex-related traits as positions on a single continuum of individual differences, from masculine to feminine. This approach goes back to the early days of sex differences research; however, a systematic discussion of alternative M-F indices (including their meanin...

Science is among humanity’s greatest achievements, yet scientific censorship is rarely studied empirically. We explore the social, psychological, and institutional causes and consequences of scientific censorship (defined as actions aimed at obstructing particular scientific ideas from reaching an audience for reasons other than low scientific qual...

This chapter discusses the influence of ideological bias in the psychological study of sex and gender, with a focus on academic psychology. After introducing the essence of the problem, the chapter examines the conceptual distinction between “sex” and “gender,” the binary nature of biological sex, and the challenges to the idea of a sex binary. The...

This paper introduces relative density clouds, a simple but powerful method to visualize the relative density of two groups in multivariate space. Relative density clouds employ k-nearest neighbor density estimates to provide information about group differences throughout the entire distribution of the variables. The method can also be used to deco...

The major domains of psychological variation are intrinsically multivariate, and can be mapped at various levels of resolution-from broad-band descriptions involving a small number of abstract traits to fine-grained representations based on many narrow traits. As the number of traits increases, the corresponding space becomes increasingly high-dime...

In this chapter, I present an emerging evolutionary framework for motivation, emotion, and personality. The framework is composed of three "layers", each building on the previous ones: (1) a theory of motivational systems; (2) an extended coordination approach to emotion, which describes a hierarchy of coordination mechanisms, from emotions to moti...

In this note, I describe data matrix disattenuation (DMD), a method for correcting measurement error in multivariate datasets. The method employs a vector of known or estimated reliabilities to disattenuate the correlations among a set of continuous variables, then corrects the data matrix to bring it in agreement with the disattenuated correlation...

In a recent meta-analysis, Harrison, Noble and Jennions (2022; Biological Reviews, 97, 679-707) set out to test the greater male variability hypothesis with respect to personality in non-human animals. Based on their non-significant results, they concluded that there is no evidence to support the hypothesis, and that biological explanations for gre...

Sex differences researchers are becoming increasingly interested in how differences in averages and variability jointly influence male and female representation at the tails of the distribution. This paper introduces the S-index, a novel index that provides a simple and robust summary of the shape of sex differences at the distribution extremes. Th...

Scree plots are ubiquitous in applications of exploratory factor analysis (EFA) and principal component analysis (PCA); they are used to visualize the relative importance of different factors/components and display the results of selection procedures (e.g., parallel analysis). Because the eigenvalues shown in the scree plot indicate the amounts of...

To achieve integration in the study of personality, researchers need to model the motivational processes that give rise to stable individual differences in behavior, cognition, and emotion. The missing link in current approaches is a motivational architecture—a description of the core set of mechanisms that underlie motivation, plus a functional ac...

In this paper we offer a new perspective on the relations between attachment and intelligence, a topic that has received relatively little attention in the recent decades of attachment research. Based on a review of relevant empirical work, a reanalysis of published data, and novel theoretical arguments, we advance a revised model of attachment and...

This chapter offers a concise, systematic introduction to quantification in sex differences research. The chapter reviews the main methods used to measure sex differences and similarities, including standardized distances (Cohen’s d and Mahalanobis’ D), indices of overlap, variance ratios, and tail ratios. Some less common approaches (e.g., relativ...

Hormone ratios are often used to capture the joint effect (or "balance") of two hormones with opposing or mutually suppressive effects. Despite some statistical and interpretative problems, hormone ratios are being increasingly used to examine associations of testosterone/cortisol, estradiol/progesterone, testosterone/estradiol, and other hormone p...

Harrison et al. (2021) set out to test the greater male variability hypothesis with respect to personality in non-human animals. Based on the non-significant results of their meta-analysis, they concluded that there is no evidence to support the hypothesis, and that biological explanations for greater male variability in human psychological traits...

The field of psychopathology is in a transformative phase, and is witnessing a renewed surge of interest in theoretical models of mental disorders. While many interesting proposals are competing for attention in the literature, they tend to focus narrowly on the proximate level of analysis and lack a broader understanding of biological function. In...

In this brief note, I wish to bring attention to a problem that has been discussed many times before, but whose implications are still not widely appreciated. As a result, many researchers (present author included) keep making distorted inferences about the relative size and importance of certain effects, by directly comparing the proportions of va...

In this primer, we unpack the generic concept of a “covariate” by reviewing three crucial roles that a variable can play in relation to an effect of interest (X → Y), namely mediator, confounder, and collider. We also describe some common variations and extensions, e.g., scenarios in which a variable is a mediator of a confounder, or a descendant o...

The topic of this tutorial is the effective dimensionality (ED) of a dataset, i.e., the equivalent number of orthogonal dimensions that would produce the same overall pattern of covariation. The ED quantifies the total dimensionality of a set of variables, with no assumptions about their underlying structure. The ED of a dataset has important impli...

A scientific approach to human health and behaviour cannot afford to ignore the insights provided by evolutionary biology. Pure socialisation accounts overlook key evidence on the relations between biological sex and health, leading to biased understanding and potentially counterproductive interventions. Many observed sex disparities in health refl...

Decisions made by researchers while analyzing data (e.g., how variables are measured, how outliers are handled) are sometimes arbitrary, with no alternative objectively justified over another. Multiverse-style methods (e.g., specification curve, vibration of effects) estimate an effect across an entire set of possible specifications, to expose the...

In this special issue paper we reflect on the next generation of attachment research with a focus on disorganization, a central but still poorly understood topic in this area. We suggest that progress will be facilitated by a return to attachment theory’s evolutionary roots, and to the emphasis on biological function that inspired Bowlby’s original...

The idea that individual differences in behavior and physiology can be partly understood by linking them to a fast-slow continuum of life history strategies has become popular in the evolutionary behavioral sciences. I refer to this approach as the “fast-slow paradigm” of individual differences. The paradigm has generated a substantial amount of re...

Trafimow (2017) used probabilistic reasoning to argue that more complex causal models are less likely to be true than simpler ones, and that researchers should be skeptical of causal models involving more than a handful of variables (or even a single correlation coefficient) [Trafimow, D. (2017). The probability of simple versus complex causal mode...

Notes on model selection with AIC (Akaike's information criterion) from my statistics courses

Objective: Sex differences in personality are a matter of continuing debate. In a study on the US standardization sample of Cattell’s 16PF (fifth edition), Del Giudice and colleagues (2012; PLoS ONE, 7, e29265) estimated global sex differences in personality with multigroup covariance and mean structure analysis (MG-CMSA). The study found a surpris...

The ability of parasites to manipulate host behavior to their advantage has been studied extensively, but the impact of parasite manipulation on the evolution of neural and endocrine mechanisms has remained virtually unexplored. If selection for countermeasures has shaped the evolution of nervous systems, many aspects of neural functioning are like...

Citing an earlier study on eminence in psychology, Simonton (2016) argued that associations between measures of scholars’ reputation, scientific productivity, and citation counts are only small to moderate [Simonton, D. K. (2016). Giving credit where credit’s due: why it’s so hard to do in psychological science. Perspectives on Psychological Scienc...

Jünger et al. (2018) conducted a preregistered study examining whether women particularly prefer muscular bodies when conceptive in their cycles. Despite an impressive number of participants and within-woman observations, they found no evidence for a preference shift; rather, they claimed, conceptive women find all male bodies more attractive. We p...

Decades of research in behavioral endocrinology has implicated the gonadal hormone testosterone in the regulation of mating effort, often expressed in primates in the form of aggressive and/or status-striving behavior. Based on the idea that neuroendocrine axes influence each other, recent work among humans has proposed that links between testoster...

The argument against innatism at the heart of Cognitive Gadgets is provocative but premature, and is vitiated by dichotomous thinking, interpretive double standards, and evidence cherry-picking. I illustrate my criticism by addressing the heritability of imitation and mindreading, the relevance of twin studies, and the meaning of cross-cultural dif...

Sex differences in attachment styles have been found in adulthood, emerge as early as middle childhood, and can be sizable when described at the appropriate level of analysis. However, they have received relatively little attention in mainstream attachment research. Here I review the evidence of sex differences in attachment, including what is curr...

The assumption that early stress leads to dysregulation and impairment is widespread in developmental science and informs prevailing models (e.g., “toxic stress”). An alternative evolutionary-developmental approach, which complements the standard emphasis on dysregulation, proposes that early stress may prompt the development of costly but adaptive...

Synopsis: The term "stress" is used to capture important phenomena at multiple levels of biological organization, but finding a general and rigorous definition of the concept has proven challenging. Current models in the behavioral literature emphasize the cognitive aspects of stress, which is said to occur when threats to the organism are perceiv...

SAMPLE CHAPTER: Chapter 6 - The Life History Framework and the FSD Model. Abstract: The chapter presents a life history framework for psychopathology and describes the FSD model, a three-way taxonomy that distinguishes between fast spectrum (F-type), slow spectrum (S-type), and defense activation disorders (D-type). Each type of disorder is associ...

Trade-offs between advantageous but conflicting properties (e.g., speed vs. accuracy) are ubiquitous in cognition, but the relevant literature is conceptually fragmented, scattered across disciplines, and has not been organized in a coherent framework. This paper takes an initial step toward a general theory of cognitive trade-offs by examining fou...

Behavioral researchers have increasingly become interested in the idea that chronic, low-grade inflammation is a pathway through which social and behavioral variables exert long-term effects on health. Much research in the area employs putative inflammatory biomarkers to infer an underlying state of inflammation. Interleukin 6 (IL-6) and C-reactive...

In a previous paper (Del Giudice, 2017 [Heterogeneity coefficients for Mahalanobis’ D as a multivariate effect size. Multivariate Behavioral Research, 52, 216-221]), I proposed two heterogeneity coefficients for Mahalanobis’ D based on the Gini coefficient, labeled H and EPV. In this addendum I discuss the limitations of the original approach and n...

Developmental plasticity is a widespread property of living organisms, but different individuals in the same species can vary greatly in how susceptible they are to environmental influences. In humans, research has sought to link variation in plasticity to physiological traits such as stress reactivity, exposure to prenatal stress-related hormones...

Expectations about the shape of statistical interactions play a crucial role in the study of differential susceptibility and other types of person–environment interplay. These expectations shape methodological guidelines and inform the interpretation of empirical findings; however, their logic has never been explicitly examined. This study is the f...

Baumert and colleagues make a compelling case for integration in personality research, but fall short of presenting a convincing program for achieving it. I argue that evolution is the “missing catalyst” of integration and that the field is destined to remain fragmented until it fully embraces the evolutionary paradigm. I illustrate the heuristic a...

Statistical tests of differential susceptibility have become standard in the empirical literature, and are routinely used to adjudicate between alternative developmental hypotheses. However, their performance and limitations have never been systematically investigated. In this paper I employ Monte Carlo simulations to explore the functioning of thr...

The Mahalanobis distance D is the multivariate generalization of Cohen’s d, and can be used as a standardized effect size for multivariate differences between groups. An important issue in the interpretation of D is heterogeneity, that is, the extent to which contributions to the overall effect size are concentrated in a small subset of variables r...

According to models of differential susceptibility, the same neurobiological and temperamental traits that determine increased sensitivity to stress and adversity also confer enhanced responsivity to the positive aspects of the environment. Differential susceptibility models have expanded to include complex developmental processes in which genetic...

In their widely publicized paper, Joel et al. (1) make two empirical claims about sex differences in features of the human brain: (i) “…internal consistency [in individuals’ sex-differentiated brain features] is rare” (p. 15472) and (ii) the amount of overlap in sex-differentiated features of male and female brains “undermines any attempt to distin...

In recent years, tremendous progress has been made in mapping the structure of comorbidity between psychiatric disorders. In particular, empirical findings have suggested the existence of a general p factor of susceptibility to psychopathology. In the present study, simulation methods were used to test whether the observed structure of psychiatric...

In this chapter we situate developmental psychopathology in an evolutionary perspective and demonstrate how the discipline can benefit by embracing modern biological theory. We begin by presenting the integrative approach of evolutionary-developmental psychology and exploring the interplay between adaptation and maladaptation in the origin of disor...

Evolutionary models predict systematic sex differences in romantic avoidance and anxiety; however, observed effect sizes are typically small. Here I explore the possibility that larger and more reliable differences may emerge at the level of narrower attachment facets. In two datasets from the US and Italy, five facets could be identified in the Ex...

Sex differences in attachment are absent during infancy and early childhood, emerge in middle childhood with self-reports and doll-play tasks, and persist into adulthood, when they are most reliably detected in romantic attachment styles. In our previous work, we hypothesized that sex differences in attachment develop under the influence of adrenal...

In this chapter we present an overview of life history theory and review its main psychological applications. We first discuss basic trade-offs in life history allocations and introduce the concept of life history strategies. We then consider the evolution of life history strategies at the population level and their development at the individual le...

Individual differences in plasticity have been classically framed as genotype-by-environment interactions, with different genotypes showing different reaction norms in response to environmental conditions. However, research has shown that early experience can be a critical factor in shaping an individual's plasticity to later environmental factors....

Middle childhood is a key transitional stage in the development of attachment processes and representations. Here I discuss the middle childhood transition from an evolutionary-developmental perspective and show how this approach offers fresh insight into the function and organization of attachment in this life stage. I begin by presenting an integ...

The scientific study of gender differences has yielded a wealth of robust generalizations about the way males and females differ across domains, cultures, and developmental stages. This article provides a descriptive overview of gender differences in personality, social cooperation and competition (including aggression and play), and verbal and non...

In this chapter, I situate self-regulation in an evolutionary perspective, and explore the implications of an evolutionary approach for the study of individual differences in self-regulation. I begin by reviewing the two basic strategies of behavior control (feedback and feedforward control), compare their relative advantages and disadvantages, exa...

According to recent theoretical models, autistic-like and schizotypal traits can be regarded as opposite sides of a single continuum of variation in personality and cognition, and may be diametrically associated with individual differences in life history strategies. Schizotypy is hypothesized to constitute a psychological phenotype oriented toward...

In this article, I outline a general framework for the evolutionary analysis of mental disorders based on the concepts of life history theory. I synthesize and extend a large body of work showing that individual differences in life history strategy set the stage for the development of psychopathology. My analysis centers on the novel distinction be...

I respond to commentaries on my target article “An Evolutionary Life History Framework for Psychopathology.” I start by addressing criticism of my basic assumptions about life history strategies and their implications for individual differences in human behavior. Next, I examine the theoretical structure of the proposed framework and respond to the...

Stress experienced early in life exerts a powerful, lasting influence on development. Converging empirical findings show that stressful experiences become deeply embedded in the child's neurobiology, with an astonishing range of long-term effects on cognition, emotion, and behavior. In contrast with the prevailing view that such effects are the mal...

Middle childhood is a crucial phase of human development characterized by a global shift in cognition, motivation, and social behavior. In this article, I review recent work on middle childhood from an evolutionary-developmental perspective and show how contributions from a range of disciplines can be synthesized into an integrated model of this li...

In the study of group and sex differences in multivariate domains such as personality and aggression, univariate effect sizes may underestimate the extent to which groups differ from one another. When multivariate effect sizes such as Mahalanobis D are employed, sex differences are often found to be considerably larger than commonly assumed. In thi...

In this chapter we present an evolutionary–developmental framework for individual differences in stress responsivity, the Adaptive Calibration Model (ACM). We argue that the core propositions of the ACM provide a context for the integrative biological analysis of the stress response system, exemplified by Tinbergen’s “four questions” of mechanism,...

How do exposures to stress affect biobehavioral development and, through it, psychiatric and biomedical disorder? In the health sciences, the allostatic load model provides a widely accepted answer to this question: stress responses, while essential for survival, have negative long-term effects that promote illness. Thus, the benefits of mounting r...

Humans are able to mentally adopt the spatial perspective of others and represent the visual world from their point of view. Here, we present neuropsychological evidence that information inaccessible from an egocentric perspective can be accessed from the perspective of another person. Patients affected by left neglect were asked to describe arrays...

A review of the book Principles of social evolution by Andrew F. G. Bourke (2011).

With the exception of a few model species, individual differences in cognition remain relatively unstudied in non-human animals. One intriguing possibility is that variation in cognition is functionally related to variation in personality. Here, we review some examples and present hypotheses on relationships between personality (or behavioural synd...