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Part II - Middle-Level Theories
Abstract
The interface of sexual behavior and evolutionary psychology is a rapidly growing domain, rich in psychological theories and data as well as controversies and applications. With nearly eighty chapters by leading researchers from around the world, and combining theoretical and empirical perspectives, The Cambridge Handbook of Evolutionary Perspectives on Sexual Psychology is the most comprehensive and up-to-date reference work in the field. Providing a broad yet in-depth overview of the various evolutionary principles that influence all types of sexual behaviors, the handbook takes an inclusive approach that draws on a number of disciplines and covers nonhuman and human psychology. It is an essential resource for both established researchers and students in psychology, biology, anthropology, medicine, and criminology, among other fields. Volume 1: Foundations of Evolutionary Perspectives on Sexual Psychology addresses foundational theories and methodological approaches.
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Males of some species use mate retention behavior and investment in ejaculate quality as anti-cuckoldry tactics concurrently while others do so in a compensatory fashion. Leivers, Rhodes, and Simmons (2014) reported that men who performed mate retention less frequently produced higher-quality ejaculates, suggesting that humans use these tactics compensatorily. We conducted a conceptual replication of this research in a sample of 41 men (18–33 years; M = 23.33; SD = 3.60). By self-report, participants had not had a vasectomy and had never sought infertility treatment. We controlled for several covariates known to affect ejaculate quality (e.g., abstinence duration before providing an ejaculate) and found no statistically significant relationships between mate retention behavior and four components of ejaculate quality: sperm velocity, sperm concentration, slow motility, and ejaculate volume. The present results provide little support for the hypothesis that human males deploy mate retention behavior and ejaculate quality investment compensatorily. We discuss the limitations of this study and highlight the need for research to address questions about the nature of anti-cuckoldry tactic deployment in humans, especially concerning investment in ejaculate quality.
Romantic love is a phenomenon of immense interest to the general public as well as to scholars in several disciplines. It is known to be present in almost all human societies and has been studied from a number of perspectives. In this integrative review, we bring together what is known about romantic love using Tinbergen’s “four questions” framework originating from evolutionary biology. Under the first question, related to mechanisms, we show that it is caused by social, psychological mate choice, genetic, neural, and endocrine mechanisms. The mechanisms regulating psychopathology, cognitive biases, and animal models provide further insights into the mechanisms that regulate romantic love. Under the second question, related to development, we show that romantic love exists across the human lifespan in both sexes. We summarize what is known about its development and the internal and external factors that influence it. We consider cross-cultural perspectives and raise the issue of evolutionary mismatch. Under the third question, related to function, we discuss the fitness-relevant benefits and costs of romantic love with reference to mate choice, courtship, sex, and pair-bonding. We outline three possible selective pressures and contend that romantic love is a suite of adaptions and by-products. Under the fourth question, related to phylogeny, we summarize theories of romantic love’s evolutionary history and show that romantic love probably evolved in concert with pair-bonds in our recent ancestors. We describe the mammalian antecedents to romantic love and the contribution of genes and culture to the expression of modern romantic love. We advance four potential scenarios for the evolution of romantic love. We conclude by summarizing what Tinbergen’s four questions tell us, highlighting outstanding questions as avenues of potential future research, and suggesting a novel ethologically informed working definition to accommodate the multi-faceted understanding of romantic love advanced in this review.
Zietsch and Sidari (2020) argue that life history theory does not offer an appropriate model for understanding inter-individual trait covariation. We examine in great detail four major claims of Zietsch and Sidari’s critique of life history theory as an explanation of inter-individual covariation among phenotypic, especially psychometric, traits. We review relevant theoretical and empirical research overlooked by Zietsch and Sidari and conduct reanalyses of comparative cross-species “pace-of-life” and human behaviour-genetic data. Our results challenge their arguments concerning (a) the implications for life history theory of the absence of individual-differences-level covariation in a variety of species and (b) the genetic aetiology of psychometric life history covariance. None of the four major claims made by Zietsch and Sidari withstand close scrutiny. Critiques of life history theory, such as the one developed by Zietsch and Sidari, should (if they are to be more persuasive) show what alternative theory might be at least as successful as life history theory in consiliently and parsimoniously explaining patterns of covariation among various traits within and between species, including the predictable absence of such covariation among certain traits. Evolutionary life history theory—as applied to non-human animals and humans—offers one of the broadest and empirically best-supported frameworks for understanding individual differences in physiology, cognition, behaviour, reproduction, and other traits and life outcomes.
Humans have been using fire for hundreds of millennia, creating an ancestral expansion toward the nocturnal niche. The new adaptive challenges faced at night were recurrent enough to amplify existing psychological variation in our species. Night-time is dangerous and mysterious, so it selects for individuals with higher tendencies for paranoia, risk-taking, and sociability (because of security in numbers). During night-time, individuals are generally tired and show decreased self-control and increased impulsive behaviors. The lower visibility during night-time favors the partial concealment of identity and opens more opportunities for disinhibition of self-interested behaviors. Indeed, individuals with an evening-oriented chronotype are more paranoid, risk-taking, extraverted, impulsive, promiscuous, and have higher antisocial personality traits. However, under some circumstances, such as respiratory pandemics, the psychobehavioral traits favored by the nocturnal niche might be counter-productive, increasing contagion rates of a disease that can evade the behavioral immune system because its disease cues are often nonexistent or mild. The eveningness epidemiological liability hypothesis presented here suggests that during the COVID-19 pandemic, the evening-oriented psychobehavioral profile can have collectively harmful consequences: there is a clash of core tendencies between the nocturnal chronotype and the recent viral transmission-mitigating safety guidelines and rules. The pandemic safety protocols disrupt much normal social activity, particularly at night when making new social contacts is desired. The SARS-CoV-2 virus is contagious even in presymptomatic and asymptomatic individuals, which enables it to mostly evade our evolved contagious disease avoidance mechanisms. A growing body of research has indirectly shown that individual traits interfering with social distancing and anti-contagion measures are related to those of the nocturnal chronotype. Indeed, some of the social contexts that have been identified as superspreading events occur at night, such as in restaurants, bars, and nightclubs. Furthermore, nocturnal environmental conditions favor the survival of the SARS-CoV-2 virus much longer than daytime conditions. We compare the eveningness epidemiological liability hypothesis with other factors related to non-compliance with pandemic safety protocols, namely sex, age, and life history. Although there is not yet a direct link between the nocturnal chronotype and non-compliance with pandemic safety protocols, security measures and future empirical research should take this crucial evolutionary mismatch and adaptive metaproblem into account, and focus on how to avoid nocturnal individuals becoming superspreaders, offering secure alternatives for nocturnal social activities.
Contemporary models for the evolution of learning suggest that environmental predictability plays a critical role in whether learning is expected to evolve in a particular species, a claim originally made over 50 years ago. However, amongst many behavioral scientists who study insect learning, as well as amongst neuroscientists who study the brain architecture of insects, a very different view is emerging, namely that all animals possessing a nervous system should be able to learn. More specifically, the capacity for associative learning may be an emergent property of nervous systems such that, whenever selection pressures favor the evolution of nervous systems, for whatever reason, the capacity for associative learning follows ipso facto. One way to reconcile these disparate views of learning is to suggest that the assumed default in these evolutionary models, namely the non-learning phenotype, is incorrect: The ability to learn is, in fact, the default but, under certain conditions, selection pressures can override that ability, resulting in hard-wired, or considerably less plastic, responses. Thus, models for the evolution of learning actually may be models for the conditions under which inherent plasticity is overridden. Moreover, what have been revealed as the costs of learning in insects may, instead, be costs associated with far more complex cognitive feats than simple associative learning – cognitive skills that researchers are just now beginning to reveal.
The COVID-19 pandemic has caused a global societal, economic, and social upheaval unseen in living memory. There have been substantial cross-national differences in the kinds of policies implemented by political decision-makers to prevent the spread of the virus, to test the population, and to manage infected patients. Among other factors, these policies vary with politicians’ sex: early findings indicate that, on average, female leaders seem more focused on minimizing direct human suffering caused by the SARS-CoV-2 virus, while male leaders implement riskier short-term decisions, possibly aiming to minimize economic disruptions. These sex differences are consistent with broader findings in psychology, reflecting women’s stronger empathy, higher pathogen disgust, health concern, care-taking orientation, and dislike for the suffering of other people—as well as men’s higher risk-taking, Machiavellianism, psychopathy, narcissism, and focus on financial indicators of success and status. This review article contextualizes sex differences in pandemic leadership in an evolutionary framework. Evolution by natural selection is the only known process in nature that organizes organisms into higher degrees of functional order, or counteracts the unavoidable disorder that would otherwise ensue, and is therefore essential for explaining the origins of human sex differences. Differential sexual selection and parental investment between males and females, together with the sexual differentiation of the mammalian brain, drive sex differences in cognition and behavioral dispositions, underlying men’s and women’s leadership styles and decision-making during a global pandemic. According to the sexually dimorphic leadership specialization hypothesis, general psychobehavioral sex differences have been exapted during human evolution to create sexually dimorphic leadership styles. They may be facultatively co-opted by societies and/or followers when facing different kinds of ecological and/or sociopolitical threats, such as disease outbreaks or intergroup aggression. Early evidence indicates that against the invisible viral foe that can bring nations to their knees, the strategic circumspection of empathic feminine health “worriers” may bring more effective and humanitarian outcomes than the devil-may-care incaution of masculine risk-taking “warriors”.
Sex differences in the neural processing of decision-making are of high interest as they may have pronounced effects on reward- and addiction-related processes. In these, the neurotransmitter dopamine plays a central role by modulating the responsiveness of the reward circuitry. The present functional magnetic resonance imaging study aimed to explore sex and dopamine transmission interactions in decision-making. 172 subjects (111 women) performed a behavioral self-control task assessing reward-related activation during acceptance and rejection of conditioned rewards. Participants were genotyped for six key genetic polymorphisms in the dopamine system that have previously been associated with individual differences in reward sensitivity or dopaminergic transmission in the human striatum, such as rs7118900 (dopamine receptor D2 (DRD2) Taq1A), rs1554929 (DRD2 C957T), rs907094 (DARPP-32), rs12364283 (DRD2), rs6278 (DRD2), and rs107656 (DRD2). The selected polymorphisms were combined in a so-called multilocus genetic composite (MGC) score reflecting the additive effect of different alleles conferring relative increased dopamine transmission in every individual. We successfully demonstrated that reward-related activation in the ventral striatum and ventral tegmental area (VTA) was significantly modulated by biologically informed MGC profiles and sex. When comparing men and women with low MGC profiles that may indicate lower dopamine transmission, only women displayed a reduced down-regulation of activation in the mesolimbic system during reward rejection and additionally, a significant non-linear u-shape relationship between MGC score and VTA activation. Taken together, by integrating neuroimaging and genetics, the present findings contribute to a better understanding of the effects of sex differences on the human brain.
In order to investigate the nature of complex problem solving (CPS) within the nomological network of cognitive abilities, few studies have simultantiously considered working memory and intelligence, and results are inconsistent. The Brunswik symmetry principle was recently discussed as a possible explanation for the inconsistent findings because the operationalizations differed greatly between the studies. Following this assumption, 16 different combinations of operationalizations of working memory and fluid reasoning were examined in the present study (N=152). Based on structural equation modeling with single-indicator latent variables (i.e., corrected for measurement error), it was found that working memory incrementally explained CPS variance above and beyond fluid reasoning in only 2 of 16 conditions. However, according to the Brunswik symmetry principle, both conditions can be interpreted as an asymmetrical (unfair) comparison, in which working memory was artificially favored over fluid reasoning. We conclude that there is little evidence that working memory plays a unique role in solving complex problems independent of fluid reasoning. Furthermore, the impact of the Brunswik symmetry principle was clearly demonstrated as the explained variance in CPS varied between 4 and 31%, depending on which operationalizations of working memory and fluid reasoning were considered. We argue that future studies investigating the interplay of cognitive abilities will benefit if the Brunswik principle is taken into account.
The relationship between PISA 2012 maths test scores and relative poverty was tested in a sample of 35 Italian and Spanish regions, together with a larger sample that included Australian, Belgian, and Canadian regions. The correlation between mean scores in mathematics, adjusted for students' socioeconomic and cultural backgrounds, and poverty rates is ‐−0.84 for the Italian and Spanish sample, and −0.68 for the complete sample. In the regressions, the effect of relative poverty on mean scores in mathematics is highly significant (p < 0.01), robust to different specifications, and independent from students' backgrounds and regional development levels. It is proposed that disparities in average scores in mathematics across regions depend on the shares of low-performing students which, in turn, depend on the degree of relative poverty within regions. The implications for the thesis according to which, in Italy and Spain, regional disparities in educational achievements reflect genetic differences in the IQ of populations are discussed.
Indirect genetic effects, the effects of the genotype of one individual on the phenotype of other individuals, are environmental factors associated with human disease and complex trait variation that could help to expand our understanding of the environment linked to complex traits. Here, we study indirect genetic effects in 80,889 human couples of European ancestry for 105 complex traits. Using a linear mixed model approach, we estimate partner indirect heritability and find evidence of partner heritability on ~50% of the analysed traits. Follow-up analysis suggests that in at least ~25% of these traits, the partner heritability is consistent with the existence of indirect genetic effects including a wide variety of traits such as dietary traits, mental health and disease. This shows that the environment linked to complex traits is partially explained by the genotype of other individuals and motivates the need to find new ways of studying the environment.
In non‐human mammals, sexual conflict should be particularly intense because males rarely provide parental care. An expected consequence of sexual conflict is male aggression towards mates. Considering how complex measurements and interpretations of behaviours such as sexual aggression and sexual coercion are, I preferred to define operationally, as ‘sexual disturbance’, any male behaviour towards females during the pericopulatory period that can be costly for females.
The objectives in this review were as follows: 1) to estimate how widespread sexual disturbance is among mammals, 2) to analyse the types of female response to sexual disturbance, and 3) to characterise the costs of sexual disturbance to females. I conducted a systematic review by searching the literature in the Web of Knowledge database using the search tools available for 19 main journals, and I conducted a qualitative review via a taxon‐by‐taxon analysis.
Sexual disturbance was frequent in four of the 32 mammalian orders: Primates, Artiodactyla, Carnivora, and Cetacea, which all include highly polygynous taxa. The most common expression of sexual conflict around copulation is seen in behaviours associated with female retention attempts that cause minor harm. Research suggests that the most common response of females to sexual disturbance comprises female grouping around a dominant male.
The past half century has seen the development of the field of post-ejaculatory sexual selection, the sequel to sexual selection for mate-acquisition (pre-ejaculatory) described by Darwin. In richness and diversity of adaptations, post-ejaculatory selection rivals that of pre-ejaculatory sexual selection. Anisogamy—and hence two sexes—likely arose by primeval gamete competition, and sperm competition remains a major force maintaining high sperm numbers. The post-ejaculatory equivalent of male–male competition for matings, sperm competition was an intense ancestral form of sexual selection, typically weakening as mobility and internal fertilization developed in many taxa, when some expenditure became diverted into pre-ejaculatory competition. Sperm competition theory has been relatively successful in explaining variation in relative testes size and sperm numbers per ejaculate and is becoming more successful in explaining variation in sperm phenotype. Sperm competition has generated many other male adaptations such as seminal fluid proteins that variously modify female reproduction towards male interests, and copulatory plugs, prolonged copulations and post-ejaculatory guarding behaviour that reduce female remating probability, many of which result in sexual conflict. This short survey of conceptual developments is intended as a broad overview, mainly as a primer for new researchers.
This article is part of the theme issue ‘Fifty years of sperm competition'.
Studies of the yellow dungfly in the 1960s provided one of the first quantitative demonstrations of the costs and benefits associated with male and female reproductive behaviour. These studies advanced appreciation of sexual selection as a significant evolutionary mechanism and contributed to the 1970s paradigm shift toward individual selectionist thinking. Three behaviours in particular led to the realization that sexual selection can continue during and after mating: (i) female receptivity to remating, (ii) sperm displacement and (iii) post-copulatory mate guarding. These behaviours either generate, or are adaptations to sperm competition, cryptic female choice and sexual conflict. Here we review this body of work, and its contribution to the development of post-copulatory sexual selection theory.
This article is part of the theme issue ‘Fifty years of sperm competition’.
Across the world, millions of couples get married each year. One of the strongest predictors of whether partners will remain in their relationship is their reported satisfaction. Marital satisfaction is commonly found to be a key predictor of both individual and relational well-being. Despite its importance in predicting relationship longevity, there are relatively few empirical research studies examining predictors of marital satisfaction outside of a Western context. To address this gap in the literature and complete the existing knowledge about global predictors of marital satisfaction, we used an open-access database of self-reported assessments of self-reported marital satisfaction with data from 7178 participants representing 33 different countries. The results showed that sex, age, religiosity, economic status, education, and cultural values were related, to various extents, to marital satisfaction across cultures. However, marriage duration, number of children, and gross domestic product (GDP) were not found to be predictors of marital satisfaction for countries represented in this sample. While 96% of the variance of marital satisfaction was attributed to individual factors, only 4% was associated with countries. Together, the results show that individual differences have a larger influence on marital satisfaction compared to the country of origin. Findings are discussed in terms of the advantages of conducting studies on large cross-cultural samples.
Women’s mating strategies are dependent on multiple factors, such as identifying which men advertise physical features indicating high genetic quality, as well as identifying which men are willing to invest in offspring. Research has suggested that women pursuing short-term mating prioritize physical attraction to facilitate the acquisition of good genes. Although it is known that physical characteristics are important in mate choice, research investigating the saliency of physical features in assessing male fitness has not been readily explored. The current study used an eye-tracking paradigm to investigate the role of short-term mating in women and their attraction and visual attention to men’s waist to chest ratios (WCRs). Women’s short term mating orientation (N = 130) was associated with attraction to men with low WCRs; however, their visual attention was not influenced by their mating strategy. Interestingly, women who perceived themselves as attractive rated men with low WCRs as more attractive and allocated attentional resources to physical features important in mate choice, such as the head and midriff region. The findings from this study lend some support to sexual strategies theory (Buss & Schmitt, 1993) and strategic pluralism (Gangestad & Simpson, 2000), and they suggest that mate preferences may be calibrated as a function of one’s mate value.
Genetic quality may be expressed through many traits simultaneously, and this would suggest a phenotype-wide fitness factor. In humans, intelligence has been positively associated with several potential indicators of genetic quality, including ejaculate quality. We conducted a conceptual replication of one such study by investigating the relationship between intelligence (assessed by the Raven Advanced Progressive Matrices Test-Short Form) and ejaculate quality (indexed by sperm count, sperm concentration, and sperm motility) in a sample of 41 men (ages ranging 18 to 33 years; M ¼ 23.33; SD ¼ 3.60). By self-report, participants had not had a vasectomy, and had never sought infertility treatment. We controlled for several covariates known to affect ejaculate quality (e.g., abstinence duration before providing an ejaculate) and found no statistically significant relationship between intelligence and ejaculate quality; our findings, therefore, do not match those of Arden, Gottfredson, Miller et al. or those of previous studies. We discuss limitations of this study and the general research area and highlight the need for future research in this area, especially the need for larger data sets to address questions around phenotypic quality and ejaculate quality.
Over the past decade, there is increasing interest in the ways in which environmental unpredictability shapes human life history development. However, progress is hindered by two theoretical ambiguities. The first is that conceptual definitions of environmental unpredictability are not precise enough to be able to express them in statistical terms. The second is that there are different implicit hypotheses about the proximate mechanisms that detect unpredictability, which have not been explicitly described and compared. The first is the ancestral cue perspective, which proposes that humans evolved to detect cues (e.g., loss of a parent, residential changes) that indicated high environmental unpredictability across evolutionary history. The second is the statistical learning perspective, which proposes that organisms estimate the level of unpredictability from lived experiences across development (e.g., prediction errors encountered through time). In this paper, we address both sources of ambiguity. First, we describe the possible statistical properties of unpredictability. Second, we outline the ancestral cue and statistical learning perspectives and their implications for the measurement of environmental unpredictability. Our goal is to provide concrete steps toward better conceptualization and measurement of environmental unpredictability from both approaches. Doing so will refine our understanding of environmental unpredictability and its connection to life history development.
Sexually antagonistic (SA) genetic variation—in which alleles favored in one sex are disfavored in the other—is predicted to be common and has been documented in several animal and plant populations, yet we currently know little about its pervasiveness among species or its population genetic basis. Recent applications of genomics in studies of SA genetic variation have highlighted considerable methodological challenges to the identification and characterization of SA genes, raising questions about the feasibility of genomic approaches for inferring SA selection. The related fields of local adaptation and statistical genomics have previously dealt with similar challenges, and lessons from these disciplines can therefore help overcome current difficulties in applying genomics to study SA genetic variation. Here, we integrate theoretical and analytical concepts from local adaptation and statistical genomics research—including FST and FIS statistics, genome‐wide association studies, pedigree analyses, reciprocal transplant studies, and evolve‐and‐resequence experiments—to evaluate methods for identifying SA genes and genome‐wide signals of SA genetic variation. We begin by developing theoretical models for between‐sex FST and FIS, including explicit null distributions for each statistic, and using them to critically evaluate putative multilocus signals of sex‐specific selection in previously published datasets. We then highlight new statistics that address some of the limitations of FST and FIS, along with applications of more direct approaches for characterizing SA genetic variation, which incorporate explicit fitness measurements. We finish by presenting practical guidelines for the validation and evolutionary analysis of candidate SA genes and discussing promising empirical systems for future work.
Introduction:
A limited number of scientific studies explore the frequency with which various sexual positions are used in human populations and the potential of particular sexual position to facilitate female coital orgasm.
Aim:
The aim of this study was to provide data about the prevalence and frequency of various sexual positions, their rated pleasurability, and their association with female coital orgasm consistency (COC).
Methods:
A sample of Czech heterosexual population (11,225 men/9,813 women) were presented with a list of 13 sexual positions in black-and-white silhouettes. For each position, they indicated frequency and pleasurability. COC was assessed as the proportion of penile-vaginal intercourse with a current partner which led to orgasm.
Main outcome measure:
Participants reported the frequency of use of sexual positions and rated their pleasurability. Using ordinal logistic regression, association between the COC and frequency of use of coital positions was tested.
Results:
In both men and women, the most commonly used sexual positions were face to face/male above, face to face/female above, and kneeling/rear entry. Nonetheless, there emerged some gender differences in the rating of pleasurability of various positions (all P < .001). We found that a higher proportion of female coital orgasms are positively associated with the frequency of use of face to face/female above (odds ratio [OR] = 1.005, P < .001) and sitting/face-to-face positions (OR = 1.003, P < .001) and negatively associated with the frequency of kneeling/rear entry position (OR = 0.996, P < .001).
Conclusions:
Our findings suggest that there are no gender differences in the frequency of use of sexual positions, but their rated pleasurability differs between men and women, and higher frequency of use of face-to-face positions with female above increases the likelihood of achieving coital orgasm during penile-vaginal intercourse. Most results, however, were of small effect sizes, and more research is needed to further explore this issue. Krejčová L, Kuba R, Flegr J, et al. Kamasutra in Practice: The Use of Sexual Positions in the Czech Population and Their Association With Female Coital Orgasm Potential. Sex Med 2020;8:767-776.
The Triangular Theory of Love (measured with Sternberg’s Triangular Love Scale – STLS) is a prominent theoretical concept in empirical research on love. To expand the culturally homogeneous body of previous psychometric research regarding the STLS, we conducted a large-scale cross-cultural study with the use of this scale. In total, we examined more than 11,000 respondents, but as a result of applied exclusion criteria, the final analyses were based on a sample of 7332 participants from 25 countries (from all inhabited continents). We tested configural invariance, metric invariance, and scalar invariance, all of which confirmed the cultural universality of the theoretical construct of love analyzed in our study. We also observed that levels of love components differ depending on relationship duration, following the dynamics suggested in the Triangular Theory of Love. Supplementary files with all our data, including results on love intensity across different countries along with STLS versions adapted in a few dozen languages, will further enable more extensive research on the Triangular Theory of Love.
Many religions emphasize the importance of sexual morality. This article argues mating strategies are central to understanding religion. I highlight the reproductive-religiosity model, which suggests that religious behavior is partly motivated by preferences for restricted mating strategies. I then discuss how religion can lead to reproductive benefits. Specifically, religions can make parenting a relatively safer strategy by increasing paternal certainty, which drives men toward parental investment, and alloparenting, which reduces offspring mortality rates. Next, I discuss the social implications of reproductive-religiosity, including mate selection and trust. Finally, I discuss the potential role of mating strategies in the evolution and cultural evolution of religion and discuss future directions for developing an approach to religion rooted in mating interests.
A central question in ecology and evolution is to understand why sexual selection varies so much in strength across taxa; it has long been known that ecological factors are crucial to this. Temperature is a particularly salient abiotic ecological factor that modulates a wide range of physiological, morphological and behavioural traits, impacting individuals and populations at a global taxonomic scale. Furthermore, temperature exhibits substantial temporal variation (e.g. daily, seasonally and inter‐seasonally), and hence for most species in the wild sexual selection will regularly unfold in a dynamic thermal environment. Unfortunately, studies have so far almost completely neglected the role of temperature as a modulator of sexual selection. Here, we outline the main pathways through which temperature can affect the intensity and form (i.e. mechanisms) of sexual selection, via : (i ) direct effects on secondary sexual traits and preferences (i.e. trait variance, opportunity for selection and trait–fitness covariance), and (ii ) indirect effects on key mating parameters, sex‐specific reproductive costs/benefits, trade‐offs, demography and correlated abiotic factors. Building upon this framework, we show that, by focusing exclusively on the first‐order effects that environmental temperature has on traits linked with individual fitness and population viability, current global warming studies may be ignoring eco‐evolutionary feedbacks mediated by sexual selection. Finally, we tested the general prediction that temperature modulates sexual selection by conducting a meta‐analysis of available studies experimentally manipulating temperature and reporting effects on the variance of male/female reproductive success and/or traits under sexual selection. Our results show a clear association between temperature and sexual selection measures in both sexes. In short, we suggest that studying the feedback between temperature and sexual selection processes may be vital to developing a better understanding of variation in the strength of sexual selection in nature, and its consequences for population viability in response to environmental change (e.g. global warming).
Research in nonhuman animals (including insects, birds, and primates) suggests a trade-off in males between investment in competitive traits and investment in ejaculate quality. Previous research reported a negative association between perceived strength and ejaculate quality, suggesting that this trade-off also applies to human males. We conducted novel analyses of data secured as part of a larger project to assess the relationship between competitive traits (shoulder-to-hip ratio, handgrip strength, and height) and ejaculate quality (indexed by sperm morphology, sperm motility, and sperm concentration) in a sample of 45 men (ages ranging 18–33 years; M = 23.30, SD = 3.60). By self-report, participants had not had a vasectomy and had never sought treatment for infertility. We controlled for several covariates known to affect ejaculate quality (e.g., abstinence duration before providing an ejaculate) and found no statistically significant relationships between competitive traits and ejaculate quality; our findings therefore do not accord with previous research on humans. We highlight the need for additional research to clarify whether there is a trade-off between investment in competitive traits and investment in ejaculate quality in humans.
Life history theory is a fruitful source of testable hypotheses about human individual differences. However, this field of study is beset by unresolved debates about basic concepts and methods. One of these controversies concerns the usefulness of instruments that purport to tap a unidimensional life history (LH) factor based on a set of self-reported personality, social, and attitudinal variables. Here, we take a novel approach to analyzing the psychometrics of two variants of the Arizona Life History Battery: the Mini-K and the K-SF-42. Psychological network analysis generates models in which psychological variables (thoughts, feelings, or behaviors) comprise the nodes of a network, while partial correlation coefficients between these variables comprise the edges of the network. Centrality indices (strength, closeness, and betweenness) operationalize each node's importance, based on the pattern of the connections in which that node plays a role. Because childhood environments are hypothesized to influence adult LH, we tested the hypothesis that among the Mini-K items, and the K-SF-42 scales, those that tap relationships with parents are central to the networks (pairwise Markov random fields) constructed from these instruments. In an MTurk sample and an undergraduate sample that completed the Mini-K, and an MTurk sample that completed the K-SF-42, this hypothesis was falsified. Indeed, the relationships with parents items were among the most peripheral in all three networks. We propose that network analysis, as an alternative to latent variable modeling, offers considerable potential to test hypotheses about the input-output mappings of specific evolved psychological mechanisms.
Although early-life adversity can undermine healthy development, children growing up in harsh environments may develop intact, or even enhanced , skills for solving problems in high-adversity contexts (i.e., “hidden talents”). Here we situate the hidden talents model within a larger interdisciplinary framework. Summarizing theory and research on hidden talents, we propose that stress-adapted skills represent a form of adaptive intelligence that enables individuals to function within the constraints of harsh, unpredictable environments. We discuss the alignment of the hidden talents model with current knowledge about human brain development following early adversity; examine potential applications of this perspective to multiple sectors concerned with youth from harsh environments, including education, social services, and juvenile justice; and compare the hidden talents model with contemporary developmental resilience models. We conclude that the hidden talents approach offers exciting new directions for research on developmental adaptations to childhood adversity, with translational implications for leveraging stress-adapted skills to more effectively tailor education, jobs, and interventions to fit the needs and potentials of individuals from a diverse range of life circumstances. This approach affords a well-rounded view of people who live with adversity that avoids stigma and communicates a novel, distinctive, and strength-based message.
The image of mother and child as a harmonious unit with mother willing to sacrifice all for the well-being of her child is ubiquitous. At the same time, it is certainly not always accurate. From an evolutionary perspective, offspring are the vehicle of parental fitness and as such parent-child interactions can be highly cooperative, but they can also involve significant conflict. There may be agreement about the general goal of offspring fitness, however, conflict can occur over allocation of investment in one offspring versus another. Activities that advance the fitness of one offspring can potentially reduce the lifetime success of the mother and vice versa. In general, we would expect individuals to allocate their parental investment among their offspring in ways that optimize their own inclusive fitness. All other things being equal, parents are equally related to all their offspring. However, we would expect individual offspring to have a somewhat different perspective as they are more closely related to themselves than their siblings and as such might benefit from extracting more than their share of maternal resources. In this chapter, we will examine the zone of conflict between mothers and infants with a particular focus on maternal-fetal conflict and weaning conflict.
By merging analytical approaches from the fields of historiometrics and behavior genetics, a social pedigree-based estimate of the heritability of eminence is generated. Eminent individuals are identified using the Pantheon dataset. A single super-pedigree, comprised of four prominent and interrelated families (including the Wedgwood–Darwin, Arnold–Huxley, Keynes-Baha’u’lláh, and Benn-Rutherford pedigrees) is assembled, containing 30 eminent individuals out of 301 in total. Each eminent individual in the super-pedigree is assigned a relative measure of historical eminence (scaled from 1 to 100) with noneminent individuals assigned a score of 0. Utilizing a Bayesian pedigree-based heritability estimation procedure employing an informed prior, an additive heritability of eminence of .507 (95% CI [.434, .578]) was found. The finding that eminence is additively heritable is consistent with expectations from behavior-genetic studies of factors that are thought to underlie extraordinary accomplishment, which indicate that they are substantially additively heritable. Owing to the limited types of intermarriage present in the data, it was not possible to estimate the impact of nonadditive genetic contributions to heritability. Gene-by-environment interactions could not be estimated in the present analysis either; therefore, the finding that eminence is simply a function of additive genetic and nonshared environmental variance should be interpreted cautiously.
Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior—largely independent of each other. Here we reconcile these two fields under a dual inheritance framework, offering a more nuanced understanding of the interaction between genes and culture. Going beyond typical analyses of gene–environment interactions, we describe the cultural dynamics that shape these interactions by shaping the environment and population structure. A cultural evolutionary approach can explain, for example, how factors such as rates of innovation and diffusion, density of cultural sub-groups, and tolerance for behavioral diversity impact heritability estimates, thus yielding predictions for different social contexts. Moreover, when cumulative culture functionally overlaps with genes, genetic effects become masked, unmasked, or even reversed, and the causal effects of an identified gene become confounded with features of the cultural environment. The manner of confounding is specific to a particular society at a particular time, but a WEIRD (Western, educated, industrialized, rich, democratic) sampling problem obscures this boundedness. Cultural evolutionary dynamics are typically missing from models of gene-to-phenotype causality, hindering generalizability of genetic effects across societies and across time. We lay out a reconciled framework and use it to predict the ways in which heritability should differ between societies, between socioeconomic levels and other groupings within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetic approach cuts through the nature–nurture debate and helps resolve controversies in topics such as IQ.
The Scarr–Rowe effect is a gene × environment interaction, which is characterized by a negative association between exposure to low socioeconomic status (SES) environments and the additive heritability of cognitive ability. Utilizing a polygenic score for educational attainment (EA3), it was found that the two-way interaction between EA3 and parental educational attainment (EA; used as a proxy for parental SES) was a significant positive predictor of participants’ composite cognitive ability (IQ) score (β = .018, SE = .008, p = .028) after controlling hierarchically for the direct effects of (population-stratification-controlled) EA3, parental EA, and 20 distinct interaction terms (10 involving the interactions between the principal components [PCs] and EA3, and 10 involving the interaction between the PCs and parental EA). The presence of this interaction is consistent with the Scarr–Rowe effect, as the expressivity of EA3 on cognitive ability increases with increasing parental EA. No statistically significant sex differences in the effect magnitudes were found, although the effect was significantly present in the female but not male sample.
Research has long noted that there are differences between men’s and women’s responses to casual sexual requests. In this study, we sought to replicate and extend the Clark and Hatfield paradigm while exploring the influence of requestor attractiveness, sexual orientation, and two individual difference measures: sociosexuality (which is how open to sexuality a person is) and personal mate value (which is how high quality of a mate the person is). We found that attractiveness matters in the likelihood of a request being accepted (the more attractive the requester, the higher the proportion of agreement); sexual orientation matters for the overall proportion of responses agreed to (heterosexuals were most impacted by the attractiveness of the target), and that sociosexuality moderates the likelihood of agreeing to the requests (such that participants with higher sociosexuality scores were more likely to agree to requests).
Bipolar disorder is a mental health disorder characterized by extreme shifts in mood, high suicide rate, sleep problems, and dysfunction of psychological traits like self-esteem (feeling inferior when depressed and superior when manic). Bipolar disorder is rare among populations that have not adopted contemporary Western lifestyles, which supports the hypothesis that bipolar disorder results from a mismatch between Homo sapiens’s evolutionary and current environments. Recent studies have connected bipolar disorder with low-grade inflammation, the malfunctioning of the internal clock, and the resulting sleep disturbances. Stress is often a triggering factor for mania and sleep problems, but stress also causes low-grade inflammation. Since inflammation desynchronizes the internal clock, chronic stress and inflammation are the primary biological mechanisms behind bipolar disorder. Chronic stress and inflammation are driven by contemporary Western lifestyles, including stressful social environments, unhealthy dietary patterns, limited physical activity, and obesity. The treatment of bipolar disorder should focus on reducing stress, stress sensitivity, and inflammation by lifestyle changes rather than just temporarily alleviating symptoms with psychopharmacological interventions.
Introduction
The nature of the following work will be best understood by a brief account of how it came to be written. During many years I collected notes on the origin or descent of man, without any intention of publishing on the subject, but...
The first comprehensive synthesis on development and evolution: it applies to all aspects of development, at all levels of organization and in all organisms, taking advantage of modern findings on behavior, genetics, endocrinology, molecular biology, evolutionary theory and phylogenetics to show the connections between developmental mechanisms and evolutionary change. This book solves key problems that have impeded a definitive synthesis in the past. It uses new concepts and specific examples to show how to relate environmentally sensitive development to the genetic theory of adaptive evolution and to explain major patterns of change. In this book development includes not only embryology and the ontogeny of morphology, sometimes portrayed inadequately as governed by "regulatory genes," but also behavioral development and physiological adaptation, where plasticity is mediated by genetically complex mechanisms like hormones and learning. The book shows how the universal qualities of phenotypes--modular organization and plasticity--facilitate both integration and change. Here you will learn why it is wrong to describe organisms as genetically programmed; why environmental induction is likely to be more important in evolution than random mutation; and why it is crucial to consider both selection and developmental mechanism in explanations of adaptive evolution. This book satisfies the need for a truly general book on development, plasticity and evolution that applies to living organisms in all of their life stages and environments. Using an immense compendium of examples on many kinds of organisms, from viruses and bacteria to higher plants and animals, it shows how the phenotype is reorganized during evolution to produce novelties, and how alternative phenotypes occupy a pivotal role as a phase of evolution that fosters diversification and speeds change. The arguments of this book call for a new view of the major themes of evolutionary biology, as shown in chapters on gradualism, homology, environmental induction, speciation, radiation, macroevolution, punctuation, and the maintenance of sex. No other treatment of development and evolution since Darwin's offers such a comprehensive and critical discussion of the relevant issues. Developmental Plasticity and Evolution is designed for biologists interested in the development and evolution of behavior, life-history patterns, ecology, physiology, morphology and speciation. It will also appeal to evolutionary paleontologists, anthropologists, psychologists, and teachers of general biology.
Male primates, carnivores and rodents sometimes kill infants that they did not sire. Infanticide by males is a relatively common phenomenon in these groups, but tends to be rare in any given species. Is this behavior pathological or accidental, or does it reflect a conditional reproductive strategy for males in certain circumstances? In this book, case studies and reviews confirm the adaptive nature of infanticide in males in primates, and help to predict which species should be vulnerable to it. Much of the book is devoted to exploring the evolutionary consequences of the threat of infanticide by males for social and reproductive behavior and physiology. Written for graduate students and researchers in animal behavior, behavioral ecology, biological anthropology and social psychology, this book shows that social systems are shaped not only by ecological pressures, but also social pressures such as infanticide risk.
Male primates, carnivores and rodents sometimes kill infants that they did not sire. Infanticide by males is a relatively common phenomenon in these groups, but tends to be rare in any given species. Is this behavior pathological or accidental, or does it reflect a conditional reproductive strategy for males in certain circumstances? In this book, case studies and reviews confirm the adaptive nature of infanticide in males in primates, and help to predict which species should be vulnerable to it. Much of the book is devoted to exploring the evolutionary consequences of the threat of infanticide by males for social and reproductive behavior and physiology. Written for graduate students and researchers in animal behavior, behavioral ecology, biological anthropology and social psychology, this book shows that social systems are shaped not only by ecological pressures, but also social pressures such as infanticide risk.
Male primates, carnivores and rodents sometimes kill infants that they did not sire. Infanticide by males is a relatively common phenomenon in these groups, but tends to be rare in any given species. Is this behavior pathological or accidental, or does it reflect a conditional reproductive strategy for males in certain circumstances? In this book, case studies and reviews confirm the adaptive nature of infanticide in males in primates, and help to predict which species should be vulnerable to it. Much of the book is devoted to exploring the evolutionary consequences of the threat of infanticide by males for social and reproductive behavior and physiology. Written for graduate students and researchers in animal behavior, behavioral ecology, biological anthropology and social psychology, this book shows that social systems are shaped not only by ecological pressures, but also social pressures such as infanticide risk.
By showing how and why human nature is what it is, evolutionary theory can help us see better what we need to do to improve the human condition. Following evolutionary theory to its logical conclusion, Death, Hope and Sex uses life history theory and attachment theory to construct a model of human nature in which critical features are understood in terms of the development of alternative reproductive strategies contingent on environmental risk and uncertainty. James Chisholm examines the implications of this model for perspectives on concerns associated with human reproduction, including teen pregnancy, and young male violence. He thus develops new approaches for thorny issues such as the nature-nurture and mind-body dichotomies. Bridging the gap between the social and biological sciences, this far-reaching volume will be a source of inspiration, debate and discussion for all those interested in the evolution of human nature and the potential for an evolutionary humanism.
Veiling is an ancient cultural practice endorsed by religion, social institutions, and laws. Recently, there have been adaptive arguments to explain its function and existence. Specifically, it is argued that veiling women is a form of male mate guarding strategy, which aims to increase sexual fidelity by decreasing overt displays of his mate's physical attractiveness, thereby helping to secure his reproductive success. Furthermore, it is suggested that such mate retention strategies (veiling) should be more important when child survival is more precarious, as cues to sexual fidelity support higher paternal investment. Using publicly available data from the PEW Research Center encompassing 26,282 individuals from 25 countries, we tested the hypotheses that men should be more supportive of women's veiling and this support should be more important in harsher environments, particularly those with poor health and high mortality rates, where paternal care is presumably more important. Our results show that men were more supportive of veiling than women, and this support increased as the environments became harsher. Overall, these findings support the male mate retention argument as well as the idea that the practice of veiling is sensitive to environmental differences.