Todd K Shackelford

Oakland University · Department of Psychology

Objectives: The phrase "level of sperm competition" is used only vaguely in the primate literature. There is also little distinction between the important elements of frequency and intensity of sperm competition, largely because the two current forms of measurement (socio-sexual system and relative testes size) are both proxies which allow neither...

Sperm competition theory can be used to generate the hypothesis that men alter the quality of their ejaculates as a function of sperm competition risk. Using a repeated-measures experimental design, we investigated whether men produce a higher-quality ejaculate when primed with cues to sperm competition (i.e., imagined partner infidelity), relative...

Research in evolutionary psychology, and life history theory in particular, has yielded important insights into the developmental processes that underpin variation in growth, psychological functioning, and behavioral outcomes across individuals. Yet, there are methodological concerns that limit the ability to draw causal inferences about human deve...

Traditional attachment theory posits that attachment in infancy and early childhood is the result of intergenerational transmission of attachment from parents to offspring. Verhage et al. (2016) present meta-analytic evidence addressing the intergenerational transmission of attachment between caregivers and young children. In this commentary, we ar...

A man whose romantic partner is sexually unfaithful is at risk of sperm competition and cuckoldry—unwitting investment in offspring to whom he is genetically unrelated. Men, therefore, may have evolved mechanisms to solve the adaptive problems of sperm competition and cuckoldry. The current research investigates another potential anti-cuckoldry tac...

The sustainability of a healthy, well-functioning citizenry depends on the acceptance and inclusion of people with disabilities. We investigated attitudes towards and communications with people with disabilities in Saudi Arabia by securing self-reports from 236 Saudi Arabian adults in a survey developed for this research, alongside demographic vari...

Previous research suggests that human males, like males of many mammalian and avian species, adjust their ejaculate quality in accordance with sperm competition risk. Men who spend less time with their regular female partner since the couple’s last copulation produce ejaculates with more sperm at the couple’s next copulation (Baker & Bellis, 1993)....

Citizens of a sustainably healthy population have the right to an education, and this right must be extended to citizens with disabilities. Visual impairment presents challenges to such sustainability insofar as it can negatively impact the social and educational experiences of affected students. The present study explores the challenges that stude...

Objective Research documents effects of skin features on assessments of age, health and attractiveness of female faces. Ethnic variation also has been reported for the impact of age‐related changes in skin features on face assessments. Here, we investigate women's self‐ratings across age cohorts and ethnic groups and discrepancies with (non‐expert)...

Sexual violence has likely been a feature of warfare throughout human history and may even have been present during prehistoric conflicts. In recent decades, international policymakers have improved efforts to prohibit and prosecute wartime sexual violence, including holding criminal tribunals for suspected perpetrators of wartime rape. Social scie...

Many people live with disabilities and many countries worldwide are acting to provide people with disabilities opportunities to find and sustain gainful employment. Notwithstanding, people with disabilities still do not have the same access to employment as their counterparts without disabilities. Although some research has investigated these issue...

Bullying among primary school students is a serious problem that often has multiple negative effects including poor academic performance and mental health problems. The current study used qualitative methodology to determine the role of communication in creating awareness and preventing bullying in a school setting through stakeholder intervention...

Humanity is now facing what may be the biggest challenge to its existence: irreversible climate change brought about by human activity. Our planet is in a state of emergency, and we only have a short window of time (7–8 years) to enact meaningful change. The goal of this systematic literature review is to summarize the peer-reviewed literature on p...

A scientific answer to suicidology’s central question, “Why do people kill themselves?” can take two forms, and they are complementary, not competing. A proximate explanation addresses mechanistic causation—psychological experiences, interactions of risk factors, and suchlike. An ultimate explanation speaks to the behaviour’s evolution in the human...

Erectile dysfunction (ED) can have negative consequences for men and their intimate partners. The purpose of the present research was to replicate and extend the results of previous studies concerning the connections that ED has with partner-directed behaviors using a sample of heterosexual romantic couples. Specifically, we used an actor-partner i...

Physical appearance plays an importan' ' in social perception and interaction. This presents findings of an evolutionary approach to female facial appearance within and between ethnic groups.

Background: In Mongolian-origin ethnic groups digit ratio (2D:4D; a proxy for prenatal sex-steroids) is sexually dimorphic (males < females), as reported for other ethnicities. Most studies measured 2D:4D from soft tissue (directly from the digits, or indirectly from hand scans), or from radiographs. Evidence on the correspondence of 2D:4D measure...

Objective Research indicates the impact of skin colour, tone evenness and surface topography on ratings of age, health and attractiveness in women. In addition to subjective assessments, these effects have been quantified with objective measures derived from skin image analysis. Signs of skin ageing may manifest differently across ethnic groups. Ho...

We present an overview of the role, benefits, and drawbacks of theory in scientific research, particularly in the social and behavioral sciences. We discuss what theory is and what it is not. We also focus on some key elements of theory, such as its ability to explain phenomena at multiple parallel levels of analysis. Evolutionary theory is offered...

Parenting communication and parenting style, including expressions of fear, worry, and threat, may contribute to children’s anxiety and apprehension. This study examined the degree to which perceptions of parental communication (both verbal and nonverbal) and parenting style are linked with childhood anxiety. This is among the first studies to inve...

This exploratory, qualitative study investigated the perceptions of Saudi Arabian parents of elementary school‐aged children with learning disabilities with regard to their involvement in their children's education. Guided by results of previous research conducted primarily with Western samples, and using a semistructured interview methodology foll...

Psychopathic men sometimes direct sexual aggression toward prospective female partners (e.g., using sexually aggressive behavior on a first date) and such behavior may be indicative of a high mating effort strategy. Less research has investigated the role of psychopathy in men’s use of sexually coercive behaviors in their intimate relationships (e....

The present studies investigated the relationships between men's perceived risk of experiencing sperm competition (i.e., when the ejaculates of two or more men simultaneously occupy the reproductive tract of a single woman), and their use of strategies to detect, prevent, and correct their partner's sexual infidelity. We investigated these associat...

This exploratory study investigated whether factors such as gender, age, level of education, monthly income, and the number of family members are associated with verbal and non-verbal communication in Saudi Arabian families. A convenience sampling procedure was used to recruit 182 Saudi Arabian adults who responded to a self-report survey. Verbal a...

We offer a commentary on Gaffney, Adams, Syme, and Hagen (2022; Depression and suicidality as evolved credible signals of need in social conflicts. Evolution and Human Behavior, 43, 242–256). Gaffney et al. argue that suicidality and other depressive behaviors evolved as mechanisms by which otherwise powerless individuals obtain concessions from ot...

This study investigated in the Saudi Arabian context the relationship between student-instructor interaction and students’ academic attainment. A survey secured reports from university students (n = 167) of their age, gender, interactions with instructors, and cumulative grade mean score for the previous three semesters. The results indicated a sig...

The Oxford Handbook of Human Mating covers the contributions and up-to-date theories and empirical evidence from scientists regarding human mating strategies. The scientific studies of human mating have only recently risen, revealing fresh discoveries about mate attraction, mate choice, marital satisfaction, and other topics. Darwin’s sexual select...

The Oxford Handbook of Human Mating covers the contributions and up-to-date theories and empirical evidence from scientists regarding human mating strategies. The scientific studies of human mating have only recently risen, revealing fresh discoveries about mate attraction, mate choice, marital satisfaction, and other topics. Darwin’s sexual select...

This study explored the association of interpersonal communication style (ICS) with personal and professional growth among Saudi Arabians in the context of the work environment. It was hypothesized that different ICSs are differently associated with personal and professional growth. The participants were 143 Saudi Arabian adults, including members...

We investigated the relationship between borderline symptoms in women and their partner’s desire to continue the relationship and relationship commitment in an aversive living environment using an experimental design. We aimed to highlight the adaptive mechanisms of borderline symptoms, which may materialize in reproductive advantages for women in...

Personality dimensions have been found to be associated with a range of sexual attitudes and sexual behaviors. The present research aimed to replicate and extend previous work showing associations between basic personality dimensions and men’s experience with erectile dysfunction (ED) in heterosexual romantic relationships. In Study 1, we collected...

The literature regarding the Dark Triad of personality (i.e., narcissism, psychopathy, and Machiavellianism) has expanded rapidly during recent years with researchers evaluating the connections that these personality traits have with a variety of phenomena including philosophical beliefs and moral decision-making. The goal of the present study was...

A global initiative has emerged in recent years to highlight early childhood education and care as a foundation for later learning and development. The goal of this study was to investigate the choices that Saudi Arabian parents made for their children’s preschool education. In a qualitative, exploratory study, we investigated parental selection of...

Evolutionary psychiatry attempts to explain and examine the development and prevalence of psychiatric disorders through the lens of evolutionary and adaptationist theories. In this edited volume, leading international evolutionary scholars present a variety of Darwinian perspectives that will encourage readers to consider 'why' as well as 'how' men...

At a time when pandemics such as the novel coronavirus (COVID-19) spread rapidly, the deployment of online education is essential. However, to successfully leverage online education in such times, it is important to investigate learners’ motivations and beliefs about online education and associated barriers as well as the role of religious and soci...

Erectile dysfunction (ED) has been shown to be associated with several negative aspects of intimate relationships. Our goal for the present research was to examine whether ED was associated with men’s use of sexual coercion in their intimate relationships (which may include the use of physical coercion, psychological manipulation, or emotional mani...

Psychological research has produced a rich body of empirical data documenting humanity’s propensity to commit infidelity in the context of long-term relationships, but comparatively little work has been dedicated to synthesizing these data into an integrated framework that encompasses the full range of its processes, from why it occurs in the first...

Mate poaching is "behavior intended to attract someone who is already in a romantic relationship." We investigated actor and partner effects of the five-factor personality traits and the dark triad traits on several mate poaching experiences. We used actor-partner interdependence modeling with data secured from both members of 187 heterosexual marr...

There has been much debate around the ultimate explanation of cultural displays such as music and art. There are two main competing hypotheses for the function of music: sexual selection or byproduct of the complexity of the human brain. Although there is evidence that playing music increases male attractiveness, the sexual selection explanation ma...

Ejaculation latency is the time from penile intromission to ejaculation. This chapter does not pretend to exhaustively cover all aspects related to this parameter of copulatory behavior, but selectively reviews anatomical, intrinsic, and environmental factors involved in its regulation, mainly in laboratory rats and in humans. Except in humans, sho...

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 Perspectiv...

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 Perspectiv...

Mate poaching is engaging in premeditated behaviors to attract either short-term or long-term mates by luring them away from their already established relationship. It is unique as compared to other ways to initiate a relationship because it involves specific behaviours and consequences, given that the target is already mated. Despite the potential...

At first glance, the relationship between parent and offspring seems to begin in perfect harmony. In particular, the image of human parents’ devotion to their infant is one that has been depicted in art for thousands of years. And yet it often seems a sharp contrast to the modern Western image of the adolescent–parent relationship, full of strife a...

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 Perspectiv...

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 Perspectiv...

Polygyny is common around the world both historically as well as contemporaneously. The evolutionary goals supporting and incentivizing the practice, particularly for men, are clear. However, polygyny does not come without serious economic, social, and political costs for both men and women in the current environment. Like the innate taste for swee...

Compared to the body of literature on male homosexuality, the continuum of bisexual orientations between the exclusively homosexual and heterosexual poles has been largely overlooked in the scientific and evolutionary literature. Possibly, male bisexuality is not as hard a puzzle to evolutionary thinking because it does not reduce individual direct...

Human offspring require intensive and extended parental care. While the needs of offspring have been argued to drive paternal investment, the evolution of male care and its patterning across cultures defy any simple story. Because human paternal investment, while often substantial in relation to other animals, is facultative rather than obligatory,...

Copulatory urgency is produced by a psychological adaptation that evolved to solve the adaptive problem of sexual conflict resulting from the use of conditional mating strategies. Deployment of a long-term mating strategy, in which individuals invest substantially in the formation and maintenance of an enduring, committed relationship with one part...

Organisms carry a large number of adaptive traits, i.e., traits that enable them to obtain resources and acquire sex partners from their social, biotic, and abiotic environments, and escape the negative factors of these environments. When we recognize an adaptive trait, we typically assume that it is a product of some form of selection, either of n...

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 Perspectiv...

Orangutan females live semi-solitarily, spending 50–80 percent of their time alone, with only their dependent offspring for company (van Schaik, 1999). They are philopatric (Arora et al., 2012; van Noordwijk et al., 2002) and establish their home ranges in an area that overlaps with their natal range as well as with those of other females, both mat...

Evolutionary psychology has been suggested to be a promising method to explain the incidence of sexual offending. We identify and discuss three major theoretical approaches to the explanation of sexual offending (specifically male rape). First, we discuss selectionist approaches, which position rape as a distinct outcome of evolutionary processes r...

Pornography has long been a subject of interest to researchers, policy makers, and the general public. This chapter provides an overview of recent findings in pornography research with an emphasis on male sexuality. First, we present a brief summary focused on the definition of pornography. Then we outline the results of studies on pornography use...

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 Perspectiv...

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 Perspectiv...

Compared to the male orgasm, the female orgasm is poorly understood in humans. There is continuing debate about whether female orgasm is an adaptation or if it is a byproduct of the male orgasm. Additionally, even among scholars who agree that the female orgasm does serve an adaptive function, there are multiple proposed hypotheses as to what that...

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 Perspectiv...

The present chapter advances the view that women’s mate preferences can be grouped into at least two overarching domains: competitiveness and fatherhood. Theoretical and empirical considerations suggest that female mate preferences evolve in contexts of male competitiveness and often amplify the effects of male–male competition. Evidence for the im...

In this introductory chapter, we discuss the nexus between evolutionary theory and behavioral genetics, using it to elucidate the biological origins of human behavior and motivational predispositions. We introduce relevant behavioral genetics methods and evolutionary theoretical background to provide readers with the necessary conceptual tools to d...

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 Perspectiv...

Darwin found that many animals had characteristics that were difficult to explain in terms of natural selection (i.e., the gradual process in which organisms better adapted to their environment survive and reproduce more successfully over sufficiently long time periods). He proposed a new selective force, sexual selection, which refers to the proce...

Unlike extensive research conducted on courtship, foreplay, and intercourse, what happens after ejaculation is one of the most neglected dimensions of human sexual behavior. As described in this chapter, postejaculatory adaptations have important and diverse implications for such things as penis hypersensitivity, the refractory period, female infid...

Same-sex attraction can impair the reproductive success of women, as it motivates them to direct their mating effort toward same-sex outlets from which offspring cannot be produced. This reproductive cost could translate into strong negative selection pressures, reducing this trait to a very low frequency in the population. Apparently, this did not...

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 Perspectiv...

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 Perspectiv...

Sperm competition occurs when a female copulates with two or more males within a sufficiently brief period, resulting in sperm of the different males competing to fertilize ova. Sperm competition has been documented or inferred to occur across many species, ranging from insects to primates, including humans. To open the chapter, the theory of sperm...

The main purpose of this chapter is to review the recent literature on male sexual fantasies. Topics that are analysed include sexual fantasies’ definitions and functions; methodological issues related to the disparate measures used across studies; the distinction between fantasies, interests/desires, and experiences; how general and unusual fantas...

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 Perspectiv...

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 Perspectiv...

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 Perspectiv...

Many vertebrate animals engage in masturbation and it is also prevalent in primates. Given the gregarious nature of this order, this is perhaps surprising, since, by definition, it occurs to the exclusion of others. Our research maps the masturbatory landscape of the primate order, highlighting the distribution and diverse forms self-stimulation of...

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 Perspectiv...

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 Perspectiv...

Much of evolutionary psychology has focused on species-typical behavior or sex differences. However, recent attention has turned to considering the role of individual differences in shaping human behavior, in particular in the realm of sexual strategies. While some research still focused broadly on sex differences, there is a growing body of work t...

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 Perspectiv...

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 Perspectiv...

This chapter focuses on the behaviors employed by men in the service of attracting mates, which we discuss as having emerged to solve specific reproductive problems faced by women. We consider behaviors employed by men to attract mates in short-term mating and long-term mating contexts, given the differential valuation on certain behavioral reperto...