Category Archives: Research

Applying the Evolutionary Science of Attachment Bonds

Attachment theory is one of the most enduring theoretical frameworks in psychology, spanning the areas of developmental psychology, social/personality psychology, and evolutionary psychology. Broadly, classical attachment theory, originally developed by John Bowlby, focuses on the development of attachment bonds between parents and infants, and how those early attachments influence social development throughout childhood and into adolescence, coalescing in adult romantic attachments.

During my doctoral studies I became interested in attachment utilizing an evolutionary framework after reading a classic (monster of a) paper from Dr. Marco Del Giudice. I was fascinated with questions of the functional nature of adult attachments: What purpose did pair-bonding and romantic attachments serve in adults? What was the relationship between romantic attachments and the diversity of sexual strategies in humans? In what ways are romantic attachment similar, and different, from infant attachments?

I began exploring these questions about attachment intensely, and for my comprehensive exams to advance to candidacy I wrote a novel theoretical framework for understanding the evolution and development of attachment systems. I am currently working on refining this framework to publish in a series of papers.

The first of this trilogy, The Nature of Attachment Systems, has just been accepted for publication in Social and Personality Psychology Compass. The primary thesis of this paper is that infant and adult attachments are fundamentally different in nature; that is, their evolutionary history, operation in social contexts, and functions are different. This diverges from classical attachment theory by way of proposing that what we commonly think of as “attachment” is comprised of two distinct evoled cognitive systems, rather than one as proposed by classical interpretations of attachment theory.

One hypothesis that I propose in this paper is the Mate Guarding Hypothesis of attachment, which states:

Once pair-bonding and consequent attachments are established, mate guarding ensures the optimization of resource investment for both males and females. Here, I propose that mate guarding is the primary manifestation of the romantic attachment system, whereby romantic attachment bonds are a primary motivational source underlying mate guarding behaviors. Mate guarding behavior occurs in response to threats to the pair-bonded relationship. Threats can be exogenous in origin (intrasexual competitors), or endogenous in origin (emotional detachment or disinterest of mate). Threats may be acute in nature (a present, intrasexual competitor), ongoing (chronic jealousy), or perceived (suspicion of partner’s activities). Threats to a pair-bonded relationship can thus be operationalized as endogenous or exogenous threats to the stability of the pair-bond that negatively affect optimal investment of resources into the mateship, for either partner. The romantic attachment system, then, is a suite of psychological mechanisms that primarily operate to prevent, correct, and address threats to the pair-bond most often by regulating mate guarding behavior, broadly construed.

Barbaro, in press, pp. 10-11.

This hypothesis follows from a line of empirical work that I have been leading since 2016 on the associations between attachment orientations, particularly anxiety (which is characterized by hyper-activation of the attachment system), and mate guarding outcomes (see here and here).

Essentially, what we understand to be mate guarding behaviors — that have been heavily researched by evolutionary psychologists — are a primary manifestation of the romantic attachment system, which actively monitors threats to one’s pair-bond (see figure). Why is this important? Because pair-bonded relationships are reliant on heavy resource investment from both parties. And, particularly for males, is quite divergent from the classical “promiscuous male” mating strategy that dominates the male mammalian kingdom. There is a reason that pair-bonding is rare among mammals — it’s got to be worth the time (evolutionarily speaking).

Conceptual depiction of the Mate Guarding Hypothesis of Romantic Attachment based on Barbaro, in press.

Okay, so why is any of this important? Because understanding how our mind monitors threats our romantic relationship can help us be more self-aware and understanding of our own (and our partner’s) behaviors within our relationship. Recently, Dr. Michael Bailey asked me to briefly discuss ways in which evolutionary psychology can be applied to our lives. What I shared with him (and his psychology class via video), touches on my recent attachment work, especially with regard to the mate guarding hypothesis. Below is the 12 minute clip (shared with permission).

Although I am obviously biased, I find the notion that your attachment bond and its manifestations within your relationship are strongly influenced, in part, by the relationship dynamics within that relationship context far more appealing than the still popular proposition that your early relationships with your parents set the course for your adult romantic relationships — but that’s a topic for the next paper…

Questioning the Role of Menarche Timing in Life History Models of Sexual Development

Life history models of sexual development are popular for understanding female sexual development as it relates to early experiences in the rearing environment. Broadly speaking, life history models suppose that early stressful environments will lead to accelerated maturation, manifesting as earlier timing of menarche, which subsequently leads to earlier age at first sex, and more unrestricted (and risky) sexual behavior.

Although there are subtle differences between the three primary life history developmental models (see Figure 1 for a conceptual depiction of predictions across the three models), they all have in common the prediction that menarche timing is, in part, regulated by early environmental stress, such that stress and father absence – a particular variable of interest within the literature – predict earlier menarche timing.

Figure 1. Conceptual model of the theoretical predictions derived from various life history models of development. Solid lines indicate predicted association. PA = psychosocial acceleration theory; CD = child development theory; PI = paternal investment theory.

The effect of father absence on menarche timing has been enjoying a rich discussion in recent years, with criticisms ranging from genetic confounding (which my colleagues and I outline here) to WEIRD effects not found in cross-cultural data. Other criticisms have focused on the issue of broader confounding factors such as socioeconomic status and body mass index. Although each of these criticisms and alternative explanations for menarche timing have been investigated independently in previous research, no previous study has attempted to comprehensively evaluate a broad array of proposed effects of life history antecedents on menarche timing (that are derived from life history developmental models) with a genetically informative research design.

In our recent research, we (co-authors, George Richardson, Joe Nedelec, & Hexuan Lui) sought to test a comprehensive model of theoretically relevant life history predictors on menarche timing and subsequent sexual behavior in girls using a twin subsample from Add Health. We took a two-stage approach to test the associations between father absence, specifically, and environmental stress, broadly, with age at menarche and sexual debut, and to identify potential genetic confounding of those associations.

In the first stage we tested and refined a measurement model specifying a latent environmental stress factor, and then built and tested a comprehensive structural equation model to test our life history hypotheses (see Figure 2). What is most striking about these results is what effects are not detected. There are no significant effects of environmental stress or father absence on age at menarche; only BMI is a significant predictor (a well-known predictor in the pediatrics literature.) There were, however, significant effects of early environmental stress on sexual debut, consistent with recent work in a Canadian sample.

Figure 2. Final SEM model. Only significant effects show.

In the next stage, we used univariate and multivariate behavior genetic models to identify whether significant associations between BMI and age at menarche, and between age at sexual debut and number of sexual partners and risky sexual behavior, were confounded by shared genetic covariation. Results here did not provide evidence of a nonshared environmental association (i.e., an association that survived control of genetic and shared environmental factors), suggesting the effect of BMI on age at menarche in our nongenetically informative model is likely spurious. Findings also did not provide evidence of a nonshared environmental association between age at sexual debut and risky sexual behavior. However, the association between age at sexual debut and number of sexual partners did survive control of genetic and shared environmental factors, suggesting it may reflect a causal effect of the former on the latter.

This study tested many other predictions in addition to the key findings presented above. Below in Table 1 is the tl;dr version of our primary aims and results summary.

Table 1. tl;dr summary of research aims and results.

What do all these results mean for life history models of sexual development? First, and in my view, most importantly, is that the null association between early environmental stress and father absence with menarche timing (the latest null result in a growing list) calls into question each of the three life history developmental models. Why? Because parental investment theory, psychosocial acceleration theory, and child development theory all rely on menarche timing as a key regulatory mechanism linking early environments to adolescent sexual behavior. (In our paper we discuss at great length the implications for each theory on preprint pp. 20-23).

Our behavior genetic models offer some interesting insights to life history models, too – just not for age at menarche. The evidence associated with age at sexual debut does suggest sexual behavior may be, in part, responsive to early environmental stress. Unlike age at menarche, age at sexual debut does reflect the shared environment in all the models we tested. Again, however, life history developmental models will have to reconcile the fact that the key regulatory mechanism of menarche timing is missing. Additionally, these results also do not provide evidence for my own hypothesis that the association between father absence and age at menarche is genetically confounded – because there appears to be no such association to confound!

This paper, currently under peer-review, contributes to the ongoing critical discussions in the life history literature particularly regarding developmental models, facultative adjustment, and genetic confounding. We look forward to hearing your comments!

Preprint (19 June 2020)

OSF project and pre-registration

Is (Online) Education Hackable? (Spoiler: NO)

Brief psychological and behavioral interventions are popular in education, with promises of big impacts on academic outcomes for students. However, these kinds of brief interventions nearly all suffer from the same problem: generalizability. It’s one thing to demonstrate that an intervention works in a particular class, school, or sample, it is another beast entirely to claim that an intervention is effective across education broadly.

So, is education hackable? Can we really improve student’s education outcomes with a 30-minute video or activity?

Unfortunately, probably not.

A new study published in the Proceedings of the National Academy of Sciences tested how different behavioral science interventions fared in massive online open courses, or MOOCs – a rigorous test of generalizability with around a quarter million students involved across the world. The overall study design was iterative whereby pilot-type results for interventions were done first, followed by a year of randomly embedding the interventions in MOOCs, then they revised and registered their hypothesis for year two of randomly embedding the interventions in the MOOCs.

The key outcome metric was course completion rates, and the interventions were “plan making” (planning out their coursework at the beginning of the term), “mental contrasting with implementation intentions” (planning to overcome obstacles), “social accountability” (identifying people to check in with regularly about their course progress), and “value relevance” (write about how the course is connected with a personal important goal or value).

What was the result? That no single intervention had beneficial effects on course completion rates across courses and countries, and the effect sizes were in some cases an order of magnitude smaller than initial pilot-like studies suggested. Instead, the effects of interventions varied by country type (e.g., individualistic, developed), or whether the intervention occurred in the first year or the second year of the study. Interventions such as “plan making” only increased course engagement for the first week, but had no long-term effects. In some cases, the “value relevance” intervention had negative effects in some courses depending on country-context. Overall, the results show that noise and small, inconsistent effects that are highly context dependent are the norm in this kind of intervention work.

So, if these types of psychological-behavioral interventions are highly-context dependent, then what we need to do is identify the students that would benefit from the intervention and then deliver to them the intervention, rather than random or blanket assignment of interventions to all students. In theory this is a great solution, but one that is not easily executed.

A key context variable identified in the research was what the authors call the ‘global gap’ defined by courses in which course completion rates differ between less developed countries and more developed countries; interventions had positive effects on students in less developed countries but only if the courses had a global gap. The problem here is that the global gap index for a course is only known after the course has run, and is inconsistent across time. A predictive model the researchers developed couldn’t identify which courses would have a global gap the following year better than chance. Moreover, identifying individual students to target with interventions using machine-learning techniques did not increase course completion rates above what would be the case if interventions were randomly assigned.

The results of this massive research effort are important for educators and institutions. This research confirms what many educators and scientists know from experience: that context matters. But these results shouldn’t be touted as a “See! Context matters! We just need to individualized interventions!” because this study shows that we have no idea how to actually do that yet at scale. Yes, we need to be more intentional about educational interventions and more holistic in the ways in which we strive to improve academic outcomes for students, but saying that is the solution and actually being able to do it are two very different things. As higher education continues to move online at scale, we need to shy away from hackable, short-sighted “solutions” and focus on holistic, personalized and responsive education.

Ethnic Spaces on Campus Positively Impact Minorities, but Not Whites: What are Potential Inclusive Solutions?

A new study published in Social Psychological and Personality Science tests how ethnic and cultural spaces on college campuses impact perceptions, experiences, and outcomes for minority and White students. Ethnic spaces increased minority students sense of belonging, their perception of how much the university values minority students, their felt support by the university, and their reported academic engagement. For White students, however, ethnic spaces decreased their perceived support from the university and lowered their reports of future campus engagement; ethnic spaces did increase White’s perception of how much the university values minority students.

Source

These results are a net positive for universities. As the authors suggest, ethnic spaces are one way in which universities can foster a sense of belonging for minority students on campus—and important component to closing equity gaps in academic outcomes.

Ethnic spaces on college campuses, however, are also subject to debate. There has been a lot of controversy over the years about who can use these spaces, and whether barring White students from these campus spaces is racist (it is), and whether the spaces are being used enough to justify their building cost.

Findings of this new study in SPPS shed some light on some of these controversial issues. On the one hand, ethnic spaces do positively impact minority students, but on the other hand, White students feel less supported. Additional analyses in the paper also show that the positive effects for Black and Hispanic students (the majority of the underrepresented minority sample in this research) are not dependent on actual or perceived usage of the space, “suggesting that [ethnic spaces] served as a signal of a more welcoming university context for underrepresented students” (emphasis added).


So, what are some practical insights that can be gathered from these new findings? First, creating a sense of belonging for underrepresented groups is important and can have a positive impact on those students. Higher education institutions that want to better academic outcomes for all of their students should focus on the idea of institutional belonging. Are ethnic spaces the best way to foster a sense of belonging? Maybe. In my opinion, I think that universities can both create spaces to celebrate ethnic diversity, be inclusive to all students, and be a good financial investment for the university. Finding the sweet spot of all these goals is possible.

It seems that the primary goal of ethnic centers is to give students a space to hang out, be themselves, be around like others, and hold events. For example, here is a description of ethnic spaces at Virginia Tech:

“These centers consist of a room or several rooms, ranging from 564 to 1,400 square feet each, equipped with televisions, sofas, chairs, tables, and bookshelves. But they are more than physical spaces for students to hang out, do homework, rest, and host club meetings, choir rehearsals, and other gatherings. They are judgment-free spaces where students say they can be themselves.”

This is another description of ethnic spaces that were used in the SPPS study at University of Washington:

“In support of the goals of the University of Washington, the Ethnic Cultural Center promotes an inclusive and educational environment by providing programs and services which enhance the communication and exchange of multicultural perspectives and values. The Ethnic Cultural Center provides programs and a learning environment where students and student organizations collaborate, develop and implement programs while building leadership and organizational skills.”

It seems that the goal of ethnic centers should be more than to provide spaces for particular students to hang out, and more focused on supporting particular students in the academic journeys. A good example of a ethnic center that has a clear mission is the University of Utah:

“Using a pan-African lens, the Black Cultural Center seeks to counteract persistent campus-wide and global anti-blackness. The Black Cultural Center works to holistically enrich, educate, and advocate for students, faculty, and staff through Black centered programming, culturally affirming educational initiatives, and retention strategies.

This new center will enact this mission through intentional programmatic learning outcomes, envisioned to build a sense of belonging and community at the U, with the goal of increasing the recruitment and retention of Black students, faculty, and staff. Supporting academic and cultural activities, this center is designed to promote and explore Blackness, equity, justice, and other progressive social change initiatives on campus and within the larger African diasporic community. The broader public mission of the Center is marked by a commitment to community activism and collaboration.”

Ethnic centers should, like the University of Utah, be aiming to provide academic resources for underserved populations, and serve as educational resources for all students, rather than barring certain students from these spaces. Rather than ethnic spaces serving as a signal of belonging, as the research suggest, ethnic centers should aim to be mission-oriented and educationally-based for all students, and the local community.

How could ethnic spaces be inclusive to all students, while still promoting belonging for underrepresented populations? Potentially, the spaces could be educational in their focus, which would also align with the missions of universities. Such spaces could be thought of as museums of sorts, that celebrate human diversity, showcase student and faculty work in relevant areas, and motivate academic engagement within the center. The public could be charged a small admission fee (free for all university students and staff) to help support student organizations. Providing opportunity and incentive for student engagement would likely promote greater use of the centers, too.

Rather than having a separate student union-like buildings or spaces for particular groups, a potential solution could be a single ‘multicultural’ center on college campuses that could showcase and promote unity on campus, rather than exclusion. Such centers would be a place for all students to visit, learn, and engage with, and hold events, with the goal of promoting positive perceptions and belonging for all students on campus.

Research, such as this new study in SPPS, is necessary to evaluate the effects of such spaces on student outcomes. Because ethnic centers are themselves diverse across campuses, it would be useful to compare student perceptions and experiences based on key features of such centers that already exist. Do centers that have a clear educational mission like University of Utah promote a stronger sense of belonging than generic student union-like spaces like at Virginia Tech? Does a single multicultural center that celebrates all types of human diversity have positive effects for minority and White students?

Rather than being just “signals”, universities should strive to create ethnic centers that further educational goals, foster community belonging, and have positive effects on all students.

Open Science as a Solution for Rigorous and Impactful EdTech Research

High quality research is the foundation from which effective and impactful EdTech is built on. Educators, institutions of learning, and companies depend on research to make informed decisions about what products and interventions to implement. There is, of course, some responsibility on those choosing products to do their due diligence on the research backing such products. But, on the other hand, the greater responsibility should fall on the companies and researchers conducting studies.

Why is research so important? Because we want to know what actually helps students and the impact that EdTech products are having on our populations of focus. If EdTech is interested in building long-term, effective, and sustainable solutions to drive innovation, then credible and rigorous research is essential to accomplish these goals.

Our research practices and policies at WGU Labs were designed to ensure that the research we’re doing on EdTech products and educational interventions is rigorous, transparent, and impactful. There are three problems that EdTech focused companies, especially those like WGU Labs that also work with third-party EdTech products, must solve to produce rigorous research:

  1. The Research Problem
  2. The Credibility Problem
  3. The Accessibility Problem

This post appeared on WGU Labs’s blog on 15 April 2020. Click here to continue reading.

Does Spanking Cause Negative Developmental Outcomes? Yes, But Our New Research Suggests That Effects Are Probably Smaller Than What We Think.

The debate over whether it is moral to spank children is well-regarded as ‘over’ in that there is a strong consensus both publicly and scientifically that it is immoral to spank children. Spanking, defined here as hitting a child on their buttocks or extremities using an open-hand with the intention of modifying undesirable child behavior, is banned in a large number of developed countries with global movements dedicated to banning the behavior. Journalists covering the research on spanking and its effects on child development are equally strong in their conclusions with a number of publications stating that yes, “The spanking debate is over.”

What is behind this consensus view? Mountains of research across family studies, developmental psychology, and social psychology that have culminated on the following conclusions:

  1. Spanking is not associated with any positive outcome.
  2. Spanking does not correct problem behavior. In other words, spanking is not effective.
  3. Spanking is associated with only negative outcomes in children.

The most recent contribution to the spanking literature is an excellent and comprehensive meta-analysis published in 2016 by Elizabeth Gershoff from the University of Texas at Austin, and Andrew Grogan-Kaylor from the University of Michigan. Despite the consensus views regarding the negative outcomes for children as a result of spanking, their meta-analysis addresses some remaining concerns in the literature.

One primary concern addressed in the 2016 meta-analysis is ensuring that spanking (as defined above) is not confounded with harsher forms of physical punishment perpetrated against children (e.g., hitting children with objects; abusive behaviors including choking and beating, in other words, what would be considered physical abuse). This distinction is important: whereas there is a clear consensus that child physical abuse can be detrimental for child development, it is less clear – and still debated – whether controlled spanking is: (1) an effective form of positive punishment that reduces problem behavior, and (2) directly (and causally)associated with negative psychosocial outcomes throughout development and into adulthood.

The results of the Gershoff and Grogan-Kaylor (2016) meta-analysis suggest that spanking is, indeed, associated with wide-ranging negative psychological and behavioral outcomes across development. Psychosocial outcomes resulting from spanking vs. non-spanking, importantly, did not differ as a function of study design (e.g., retrospective, longitudinal), measurement (e.g., observational, child-report, parent-report), or age of children at the time of spanking (ranging from toddlerhood to adolescence). In summary, the results of Gershoff and Grogan-Kaylor align with the general consensus that spanking is consistently associated with poor developmental outcomes, appears to be largely ineffective at reducing problem behavior, and has not been shown to have any positive effects on child development. (Articles covering this paper can be found here and here.)

Although research does clearly show that spanking is associated with negative psychosocial outcomes, not all confounds have been adequately addressed. This limitation of the literature is where my coauthors Eric Connolly, Madi Sogge, Todd Shackelford, Brian Boutwell, and I decided to focus our empirical efforts. The confound we were interested in was genetic confounds. Genetic confounds in this context would reflect the idea that being spanked and the psychosocial outcomes of interests such as externalizing behavior and self-regulation, for example, covary at the genetic level; meaning that the genetic variation underlying children’s propensity to be spanked are the same, to some extent, as the genetic variation underlying their problem behaviors presumed to be an outcome of spanking.

Some research addressing these genetic confounds have been conducted with results generally supporting the notion that genetic covariation can account for a large proportion of the association between spanking and psychosocial outcomes. A study by Sara Jaffee et al. in 2004 found that genetic covariation between spanking and antisocial behavior accounted for 86% of the observed association, whereas the remainder of the effect was primarily explained by nonshared environmental covariation. Another twin study conducted by Button and colleagues in 2008 found that genetic covariation between parental punitive punishment and children’s externalizing behaviors explained between 61% and 98% of the association. (Importantly this is NOT the case for the association between physical abuse and psychosocial outcomes).

Genetically informed research is hard to come by in the spanking literature. Whereas the non-genetic literature includes a wide range of psychosocial outcomes – 17 in the Gershoff and Grogan-Kaylor (2016) meta-analysis – the available genetically-informative research on spanking includes only a limited range of outcomes, such as internalizing and externalizing problems, and antisocial or conduct behavioral problems. The purpose of our research was to use all the information available in the spanking literature to provide an up-to-date analysis of the role that genetic confounds may play in a wide range of psychosocial outcomes. Specifically, we provided probable ranges of estimates of the degree to which genetic and nonshared environmental covariation could explain the reported associations from the Gershoff and Gorgan-Kaylor meta-analysis.

We conducted two studies to address our aims. The first study reported results from the Children of the National Longitudinal Survey of Youth (CNLSY). Similar to the results of earlier studies, our analyses showed that for alcohol use, delinquency, and depression, 49%, 66%, and 80% of the association, respectively between spanking and the outcomes was accounted for by genetic covariation between the traits, with the remainder explained by non-shared environmental covariation.

Our second study took a simulation modeling approach to estimate the extent to which the association between spanking and 17 psychosocial outcomes was likely to be explained by genetic covariation and non-shared environmental covariation. For all outcomes, with the exception of physical abuse, the estimates showed that genetic covariation could potentially account for the majority of the association between spanking and the psychosocial outcome of interest. Non-shared environmental covariance accounted for a relatively small, but non-trivial amount of the association between spanking and psychosocial outcomes.

So, what do these results mean for our understanding of how spanking effects children psychologically? First, our results are consistent with the notion that it is plausible to suggest that spanking, in some cases, may exert a negative impact, and certainly not a positive impact, on psychosocial development across the life course. However, there is an important caveat to this claim: The effect sizes are likely to be much smaller than what the current literature suggests. Overall, the results of genetically informative research suggesting moderate-to-large degrees of genetic covariation between spanking and psychosocial outcomes imply that once genetic variation is considered, the environmentally-mediated (casual) effects of spanking on psychosocial outcomes will be much smaller in magnitude than what non-genetically-informed studies suggest.

That the true effects of spanking on child development are likely smaller is magnitude than what the reported literature suggests is not at all to say that the negative effects of spanking on child development are non-existent. The extant research and the data in our new study strongly suggest that non-shared environmental covariation explains a non-trivial proportion of the phenotypic effect – a finding that is, in fact, consistent with causal interpretations of the negative effects of spanking.

Although the spanking debate may be ‘over’ with regard to whether spanking negatively effects children’s development, our understanding of the effects from a genetically informative perspective is far from resolved. Our work demonstrates how little genetically informative research has actually been done on the topic, and the potential impact that genetically informative research can have on the estimates we rely on to make informed policy decisions and moral arguments. So, yes, all research points to spanking having negative effects on psychosocial outcomes, but the magnitude of the effect is likely to be much smaller thank what we currently think to be the case.

You can find the OSF project here, and the pre-print of our paper here, which is currently under review for publication.

Photo by Caleb Woods on Unsplash

How Can Evolutionary Psychology Help Explain Intimate Partner Violence?


Jaimie has been out of town for nearly a week at her annual industry conference. Despite having been together for over a year, her boyfriend, Johnathan, still feels anxious when she is away on business trips. His anxiety has deepened because Jaimie has been “too busy to talk on the phone.” When Jaimie does finally return home, Johnathan ignites an argument, accusing her of spending time with her male co-workers. The argument escalates to shouting, with Johnathan accusing her of cheating on him while away. As Jaimie continues to plead her innocence and faithfulness to Johnathan, he pins her against the wall, with his hand around her neck, as he threatens to strike her if she refuses to admit her infidelity.

At some point in their lifetime, 10 to 35 percent of people experience intimate partner violence. (The numbers vary depending on the sample studied and precise definition of “intimate partner violence.”)

Why is violence among partners so common? Social scientists have proposed several theories, which primarily fall under two umbrellas: sociological explanations, and biological and psychological explanations. (Because the existing literature primarily focuses on violence in heterosexual relationships, my discussion is limited to violence between a man and a woman.)

To continue reading, click here.

This post originally appeared at Behavioral Scientist on 21 September 2017.

Are Life History Trade-Offs Based On Function? A New Study [IN BUGS] Suggests Caution of Basic Theoretical Assumption


When I get to my office in the morning, I go through my email and read my journal alerts of the newest academic papers published. I often come across papers that are interesting, but today I came across a paper that really blew me away. Why? Because it used a clever research design to yield big theoretical implications — my favorite kind of paper.

The paper, “A Weapons-Testes Trade-Off In Males Is Amplified in Female Traits,” by Christine Miller, Paul Joseph, Rebecca Kilner, and Zachary Emberts published in Proceedings B caught my attention. My lab recently published a paper on trade-offs in male ejaculate quality using a life history framework, so I was interested to see how the findings of this new paper contributed to this broader research area. The research did not disappoint. The results certainly found trade-offs between weapons and testes as the title implies, but with a significant twist, humbly reflected by the last part of the title “amplified in female traits.”

To continue reading, click here.

This article was originally published on my Medium account on 1 August 2019.

Why Men Have More Sex Partners Than Women


I got to my office the other morning with the goal of organizing my last data set needed for my PhD dissertation. The study is a small survey data set of 52 heterosexual couples, mostly adults in their 20s, who reported on a variety of self-report sexuality and relationship measures — pretty standard psychological research.

My topical expertise in psychology centers primarily around human sexuality. After years of studying in this area, there are two observations about human sexuality that I have more or less taken for granted at this point:

(1) Men have more sex partners than women, on average. This means that if you approach a random man on the street and ask him how many people he’s had sex with, his answer is likely to be larger than a random woman’s answer to the same question. (I don’t recommend using this approach strategy, however.)

(2) The variance, or range, of the number of sex partners within the sexes is different, with men as a group having a greater range as compared to women as a group. This means that it is likely that the most sexually successful man you know has a much larger number of sex partners than the most sexually successful woman who you know.

After my data were organized, I ran a simple analysis comparing the mean average number of lifetime sex partners between men and women to see if these basic observations held. It was unsurprising to see that my data conformed to both points: In my sample, men had a higher mean and a larger variance compared to women in their response to the question, “How many partners have you had sexual intercourse with in your lifetime?”

To continue reading, click here.

This post was originally published on my Medium account on 16 July 2019.