Category Archives: News

Hormone Measurements in Evolutionary Psychology Research, Part 2: The Prevalence of False Negatives

In a blog post a few weeks ago, I reviewed a study that highlighted the discrepancies between counting and hormonal methods in classifying women as either high or low conception risk in evolutionary psychology research. I concluded that evidence of such discrepancies may “challenge the reliability of some prior findings of cycle phase effects.”

What I mean to suggest with that sentence is not that previous findings of cycle phase effects are false positives, but rather that some null findings in unpublished studies may actually be false negatives, and/or that cycle phase effects may be stronger than currently suggested in the literature.

But why would using a messy, proxy measurement of conception risk (in this case, the counting method) result in false negative findings, or underestimates of a true effect size? Let’s use a simple thought experiment to make this a little clearer:

Say we have a population of 13 males and 13 females, and we are interested in whether there is a significant difference in height between the two sexes. We measure each individual’s height in inches, arrange them in order, and come up with these data. The pink cells represent values for females, and blue for males.

The two distributions overlap a bit, but overall, it looks like males on average are taller than females. We do an independent samples t-test on our small sample, and voila! At p<0.01, our statistical test is significant, and we can conclude that the average height for males and females differ.

Let’s say that for some reason, rather than asking individuals what their biological sex is, we’ll use a proxy measurement to determine biological sex: hair length. We decide that individuals with long hair will be classified as females, and individuals with short hair will be classified as males.

Unfortunately for us, that is a horrible way to differentiate between the biological sexes in this day and age. Plenty of females have short hair, while plenty of males have long hair (especially these days, with the popularity of man-buns reaching an all-time high).

Our data may end up looking a little more like this—our two columns, rather than being ‘female’ and ‘male,’ are ‘long hair’ and ‘short hair,’ because of how we decided to classify sex. Pink cells still reflect values for (truly) biological females, and blue for (truly) biological males.

The mean heights for these two groups still aren’t the same, but we do the same independent samples t-test that we did earlier, and our p value (p=0.12) is no longer statistically significant. This would lead us to conclude that there is no height difference between females and males; however, since we know this is not true, that conclusion would be a false negative.

In the thought experiment above, about 31% of the total sample was misclassified by sex, and this magnitude of misclassification was enough to lead us to a false negative finding. Looking at cycle phase research specifically, classification of days as being either low conception or high conception using the counting method may be incorrect up to 36% of the time when compared to more accurate, hormonal methods. While most of the women classified as high conception risk by counting methods are classified correctly and thus display a specific phenotype in behavior or preferences, mistakenly including low conception risk women (who display a different phenotype) in that group interferes with our ability to truly understand the full extent and magnitude of cycle phase effects.

Now, it has been suggested that some previously reported findings are false positives (rather than false negatives) due to something called ‘researcher degrees of freedom.’ Because the days of the menstrual cycle considered high or low conception risk days are not agreed upon, the classification schema used by a team of researchers to distinguish between phases of the menstrual cycle is in part arbitrary (see this article for a great chart showing the variability among studies in the way phases of the cycle are defined). If statistically significant cycle phase effects are not observed when using one classification schema, it could be that researchers change the days they consider to be high and low risk, and do so until the desired effect is significant.

Though this is possible, meta-analyses and examination of p-curves suggest that this is not the case, and that further inquiry on the extent and breadth of changes in behavior and cognition over the menstrual cycle is warranted.

Note: For those reading who are as interested in counting and hormonal methods of conception risk classification as I am, check out this cool recent article in Evolution and Human Behavior.

Special thanks to Adar Eisenbruch, a current evolutionary psychology graduate student, for his guidance on topics discussed in this post.

Are You Rolling On Dubs? The Evolutionary Psychology Of Vehicle Mods

Post by Jessica S. Kruger, a University of Toledo Health Education doctoral student with a cognate in Psychology, who did the research with her husband, evolutionary social psychologist Dr. Daniel J. Kruger, a Research Assistant Professor at the University of Michigan.


“ARE YOU ROLLING on dubs?” Not long ago, I only knew this as a tag line in a rap song.



Two years ago, we moved to a historic neighborhood in an urban area. As evolutionary researchers, we were fascinated by what we saw there. One thing we noticed was the high proportion of vehicles with large and shiny rims (wheels). There is even a store just a few blocks from where we live that sells these rims. After driving by so many times, I decided to stop in and investigate. I was stunned to learn how expensive they could be, and intrigued that we would often see very fancy vehicles parked in front of houses that were in various states of decay.

We understand these patterns through the framework of Life History Theory:

Life history theory … is a branch of evolutionary theory which predicts behavior based upon people’s [potential lifespans, vis a vis how stable or risky their environment is]. It suggests that as people believe they are likely to live longer, decisions related to certain milestones such as marriage, having babies, and divorce may be delayed in favor of other activities such as education. … Life history theory can help us understand how we make important decisions that affect our lives.

Some researchers describe life history as a continuum from slow to fast. This is because relatively “faster” species and individuals tend to reproduce earlier and more prolifically, but also tend to die earlier. In evolutionary terms, neither fast nor slow life histories are inherently good or bad. An individual’s life history is shaped in part by the environment in which it grows up. When conditions are unpredictable and the chance of early death is high, individuals seize opportunities when they can, before it is too late. If conditions are predictable and the chance of early death is low, individuals take a less risky, long-term approach.

Each individual has a limited amount of time and energy, so one has to make “trade-offs” in how much effort to invest in each aspect of life. One of these trade-offs is between mating effort (getting new sexual partners) and parenting effort (investing in offspring). For example, a male peacock has a big and beautiful tail. Charles Darwin was puzzled by peacock tails and wondered how they could have evolved, as they are cumbersome and could attract predators. He later realized that peacock tails did not evolve because they helped peacocks survive, but rather that this costly trait served as a signal of the male’s quality. The more brilliant the plumage, the more attractive it is to potential mates.

We concluded that the extravagant wheels we saw were a function of mating effort, a costly signal analogue to the peacock’s tail, used to gain status and attract partners. We decided to conduct a study to confirm this idea. We searched the Internet for before and after pictures of cars that had rim upgrades. We found suitable pictures of a Jeep Rubicon and a Chrysler 300. We predicted that people would rate a male owner of a car with upgraded rims as higher in mating effort, lower in parental effort, more interested in brief sexual affairs, and less interested in long-term committed relationships than men with stock vehicles.


The results from ratings of 339 college students generally confirmed our predictions. The patterns were stronger for male participants, and both cars seemed to be associated with a high mating effort (and lower parental effort, etc.) life history regardless of the wheels they had.

I am on the board of a grassroots non-profit inner-city gym for local youth. I was talking with people there about the project, and they were incredulous that we needed to do a study to figure this out; to them it was so obvious.

Rims can be thought of jewelry for your car and, in evolutionary terms, a display of resources to attract potential mates.

We are glad to shed more light on conspicuous consumption and explain an apparent paradox (why people in resource-scarce environment would spend so much on these products) with the strongest theoretical framework in the human sciences.

Screen Shot 2015-09-06 at 8.32.12 PM copy









I like to get into my research.


This research was presented by Jessica Sloan Kruger at NEEPS 2015, the NorthEastern Evolutionary Psychology conference. Dates and info on NEEPS 2016 and other the 2016 ev psych (and related) conferences here.

The Evolution Of Fun Names For Scientific Theories: The “Sneaky F*ckers” Strategy Has Company

The late British evolutionary biologist John Maynard Smith came up with the “Sneaky F*ckers” strategy — in short, explaining a way that beta males get the girl. DragonflyIssuesInEvolution explains:

The term “sneaky fuckers” was coined by evolutionary biologist John Maynard Smith to describe subordinate males who take advantage of the opportunity to mate with females while dominant males are otherwise occupied, leading to their reproductive success (Smith, 1993). It was originally thought that in some species such as deer and gorillas, only the dominate male mates successfully. But, through direct observation and DNA analysis, it is now known that often other males surreptitiously successfully mate when they can find the opportunity.

Basically, while the alpha male is off, oh, fighting the war, the beta male is sneaking sex with their woman. Maynard Smith has long held the lead for fun names of theories, but there’s a now nice showing from the Los Angeles contingent.

Yes, we’ve got some Americans losing the stuffy on theoretical names, with the “Crazy Bastard Hypothesis.” Evolutionary social psychologist Frank T. McAndrew covers the fun on his blog at Psychology Today:

Recently, a team of anthropologists at UCLA led by Dan Fessler tested what they called the “Crazy Bastard Hypothesis” in a series of studies. They gathered data online from thousands of Americans and in person from dozens of individuals in the Fiji Islands. They had people read short scenarios about individuals who engaged in risky, daredevil behavior or in more cautious, risk-averse behavior. They then asked them to make judgments about the characteristics that they thought the person in the story might possess. Among other things, the daredevil was perceived to be taller, stronger, and generally more physically formidable than the cautious individual.


Their “Crazy Bastard Hypothesis” gives us a fun and more complete way of thinking about risky male behavior.  Now, it is no longer just about advertizing genetic quality, but it is also about advertizing how one might behave as an adversary or an ally. If you see a “crazy bastard” who behaves with apparent disregard for his own personal well-being by doing things that would scare ordinary men away, you definitely end up wanting to have this person as a friend rather than as an enemy. Even though the crazy bastard’s behavior is not overtly aggressive, one can easily imagine the terror of dealing with such a reckless opponent in combat and the comfort that one might have going into battle with that individual as a comrade. Going way back to the dawn of recorded human history one can find rituals (often involving excessive consumption of alcohol) used by warriors to at least temporarily make themselves feel and appear to be formidable crazy bastards as a way of intimidating their enemies and taking the fight out of them before the battle even began.


Perhaps the “Crazy Bastard” is not so crazy after all?

Buy Frank T. McAndrew’s book, Environmental Psychology.

Boy Next Door or Abs Galore: The Discrepancy Between What Men Think Is Hot and Reality

Keeping in line with my short-running streak of posting about getting in with the opposite sex, guys, do I have more good news for you!

A study commissioned by the U.K. underwear company, Jacamo, finds that women aren’t really that into the super cut men you see in men’s underwear ads, but rather the ones you see mowing the lawn shirtless on weekends.

“72 percent of women in the UK actually prefer men with the “boy next door” look as opposed luscious hulks.”

The study also shines light on the very interesting discrepancy between what men think women think and what women actually think:

“While men state that a woman’s ideal man would be made up of Justin Bieber’s hair, Gerard Butler’s [chiseled] face, Hugh Jackman’s moviestar arms, David Gandy’s tight abs and Cristiano Ronaldo’s smooth legs, the response from women showed a contrasting view, set to be welcomed by men across the country.

“… In reality, women in the UK lust over Prince Harry’s smile and comedian James Corden’s hair, research says.

“Men with well-toned bodies are, initially, regarded as attractive, but it is the man with the little bit of excess flab around the waist who often wins the day,” states Jacamo’s press release.”

This is interesting from a mating perspective, since what men are pursuing as a desired standard isn’t actually what their target audience is after at all (I have my own concerns over the ladies’ love of Prince “Hairy” here). Even further, the social stress to obtain and the desirability mismatch of this “ideal” body type may be having a negative impact on men’s self esteem.

Dove has famously campaigned for acceptance of all female body types; however, men are a little short on body-type support groups. The article ends concludes with the notion that men and women aren’t so far apart in fretting about body image:

“… as many as 62 percent of men in the UK are still persuaded that ladies would rather go for a man with “the gladiator look,” and that many men suffer “pangs of anxiety when they fail to match up this image.

“Who says body confidence is only women’s issue?”

Sex Disparities in the Workplace: Is Competitiveness to Blame?

It’s no secret—across many cultures, men and women aren’t equal in the workplace. Men are more likely to hold high positions, and earn higher salaries than their women counterparts on most rungs of the corporate ladder. A study performed by Drs. Corin Apicella and Anna Dreber, published in this September’s issue of Adaptive Human Behavior and Physiology, suggests that that some of these workplace disparities may exist because men are more willing to engage in competition than are women, though this willingness to compete may differ depending on the type of task.

Participants were all members of the Hadza hunter-gatherer group, which is a group living in remote areas of Tanzania. The Hadza population is often studied when determining whether certain psychological traits, like mate preferences or competitiveness, may have been present in our early ancestors.

Participants engaged in 3 different tasks: a gender-neutral task, a female-centric task, and a male-centric task. Results suggested that:

“Hadza boys and men are more competitive than Hadza girls and women. This difference, however, is only significant for the gender-neutral task (skipping rope) and the male centric-task (handgrip strength)”.

However, when it came to actual performance,

“Boys and men are significantly more competitive than girls and women in skipping rope, even though they perform equally well when it comes to both practice jumps and actual performance. The sex difference in competitiveness found for handgrip strength, with men competing more than females, is less surprising since men are typically stronger than women.”

In the female-centric task (bead collection), women performed better on the task than men, but they did not display significantly different levels of competitiveness than men.

The sex differences in competitiveness observed in the Hadza population across all age groups, though only present in certain tasks, tend to support the idea that

“Financial and labor outcome disparities… may, in part, result from sex differences in economic preferences such as willingness to compete.”

While we have previously assumed the existence of evolutionary sex differences in competitiveness in humans, these assumptions have come largely from work done in nonhuman primates. Some prior work in humans has suggested sex differences in competitiveness, though Apicella and Dreber provide us with some of the first data on these sex differences across different task types.

Evolutionary Tradeoffs: Too Materialistic To Marry And Have Children?

Evolutionary social psychologist Norm Li and his colleagues have posted an interesting open access study at PLOS ONE, exploring materialism’s relationship to attitudes toward marriage and having children. They studied subjects in Singapore, finding that:

Materialistic values led to more negative attitudes toward marriage, which led to more negative attitudes toward children, which in turn led to a decreased number of children desired. Results across two studies highlight, at the individual level, the tradeoff between materialistic values and attitudes toward marriage and procreation and suggest that a consideration of psychological variables such as materialistic values may allow for a better understanding of larger-scale socioeconomic issues including low fertility rates among developed countries.

There’s a drop in fertility in prosperous countries:

In many modern societies, native populations are shrinking as citizens are delaying marriage and having less children. This is especially the case in East Asia, where countries like Singapore, Hong Kong, and South Korea have fertility rates that are far short of what is required to sustain a population. Although this trend seems to be related to economic development, relatively little is known—especially from a psychological perspective—regarding what it is about economic development that may be responsible for inducing aversions to marriage and procreation. In this paper, we considered the possibility that a key factor prevalent in modern societies—materialistic values—may negatively influence the value that individuals place on marriage and children.

They further explain at the end of the paper:

Materialistic values may, from an early age, compete with and displace values relating to cooperation and interpersonal warmth. Such displaced values may directly or indirectly decrease the desire for marriage and family.

There seems to be an evolutionary mismatch here — between our evolved psychology and the modern world:

Modern-day materialism may involve a maladaptive engagement of mental processes evolved to impel individuals to acquire social status and signal their status to others. Although status signaling may be a manageable process in an ancestral village of 100 to 150 individuals, in the modern day, rapid technological advances combined with global competition induce symbols of social status to change at increasingly faster rates and luxury goods to lose their luster exceedingly quickly. Thus, it is not possible for most modern people to acquire what feels like enough status for very long or at all, and materialistic desires may lock individuals into a costly and futile pursuit of status targets perpetually moving upwards. Ironically, then, the pursuit of status may be leading to decreased reproduction in the modern day.

As for possible solutions, Norm Li explained in an email:

As long as evolved mechanisms for social status exist, accompanied by capitalism, technology, globalization, and advertising, there will likely be competitive materialistic processes. However, consistent with our previous findings and those of others, materialistic appetites can be curbed by improving the strength of personal relationships and finding ways to boost overall life satisfaction. At the individual level, though, one can reduce one’s own exposure to mass media, and associate with individuals and communities who aren’t so caught up in the materialistic game. My collaborators and I are looking into new ways to approach the materialism-reproduction tradeoff.  Stay tuned.

Mystery Solved: The Way To A Woman’s Heart Is Through Her Stomach

In new research by clinical psychologist Alice Ely, there’s some light shed on the conundrum that has plagued men for centuries: “How do I get this lady to like me?”

In a new study published online in the journal Appetite, researchers found that women’s brains respond more to romantic cues on a full stomach than an empty one. The study explored brain circuitry in hungry versus satiated states among women who were past-dieters and those who had never dieted…

“We found that young women both with and without a history of dieting had greater brain activation in response to romantic pictures in reward-related neural regions after having eaten than when hungry,” said Ely.

So far, studies have found support for stronger reward responses while hungry, but Ely’s research provides a view of the other side of the coin: When you’re hungry, you’re preoccupied with finding food, but once you’ve chowed down, you can focus on other priorities.

“In this case, they were more responsive when fed,” she said. “This data suggests that eating may prime or sensitize young women to rewards beyond food. It also supports a shared neurocircuitry for food and sex…

“The pattern of response was similar to historical dieter’s activation when viewing highly palatable food cues, and is consistent with research showing overlapping brain-based responses to sex, drugs and food,” said Ely.

Maybe those dinner dates aren’t so overrated after all!

Evolutionary Scientists: Collaborate With Local Teachers To Help Them Teach Evolution Better

Dustin Eirdosh, AEPS’s main man in spreading evolutionary education in the schools, writes:

AEPS Members in the US (and all evolutionary scientists): The National Center for Science Education has just started its “Scientists in the Classroom” program, and they are seeking evolution scientists willing to collaborate with local teachers who want help teaching evolution better.


Please consider joining the effort. If you do join, drop me an email [dustin at unitoliara dot info] so we can strengthen our relationship with the important work that NCSE does!

Dustin Eirdosh (on Research Gate) is a curriculum designer at the Berlin-based NGO Big Red Earth (, an organization that supports a university-led development approach in southwestern Madagascar. This region is characterized by high food insecurity, poverty, low quality of education and unsustainable use of natural resources, while it is at the same time an important biodiversity hot spot. Utilizing perspectives in Evolutionary Educational Psychology (Evo-Edu) and the tools of cultural evolution studies, Dustin has developed a governance education program focused on connecting university classrooms with sustainable development initiatives in the region.

Meet The Greats Of Evolutionary Psychology: The HBES Founders Videos

BELOW ARE THREE TERRIFIC VIDEOS — 15-minute interviews with three major evolutionary scientists: Steven Pinker, David Buss, and Leda Cosmides. There is also a link to many more from the series.

About the videos: In 2013, evolutionary psychology professors Catherine Salmon and Barry X. Kuhle videotaped oral histories of the researchers who founded the major international organization for evolutionary psychology, the Human Behavior and Evolution Society, and who were substantial in fostering the emergence of evolutionary psychology as a science of public import. (The taping of these videos coincided with the 25th anniversary of HBES.)

Thus far, with funding from HBES, and the participation of filmmaker Dave Lundberg Kenrick, Salmon and Kuhle have taped interviews with David Buss, Steven Pinker, Leda Cosmides, John Tooby, Douglas Kenrick, Martin Daly, Randy Thornhill, Mark Flinn, William Irons, Napoleon Chagnon, Sarah Hrdy, Don Symons, Raymond Hames, Bobbi Low, Peter Richerson, David Sloan Wilson, Dick Alexander, Randy Nesse, and E. O. Wilson. (The entire series of interviews can be found here.)

(Sadly missing from this series are pioneers and pillars of sociobiology and evolutionary psychology who’ve passed on, including Bill Hamilton, Dave Rowe, Dev Singh, John Maynard Smith, George C. Williams, and Margo Wilson.)


And now…those videos: 

Steven Pinker (introduction below by David Sloan Wilson)

Looking back, Pinker recalls how he first adopted an evolutionary perspective, based on thinkers such as Noam Chomsky and Jerry Fodor, who stressed the need to posit a nativistic dimension to human cognition and language. Looking forward, Pinker advises new students to think of themselves as psychologists first and evolution as an essential perspective for the study of all aspects of psychology, rather than a sub-discipline of the field. He describes the self-described field of evolutionary psychology as a stepping stone toward this end. He calls for more integration with evolutionary genetics and more generally the fully rounded approach associated with Nobel Laureate Niko Tinbergen, who stressed that all evolved traits should be studied from functional, mechanistic, developmental and phylogenetic perspectives. He also shares his own best idea that has not yet received the attention that it deserves.

Buy books by Steven Pinker (for which AEPS gets a wee kickback, at no cost to you).



David Buss (introduction below by Diana Fleischman)

This interview in the series “On the Origin of the Human Behavior and Evolution Society” is with David Buss, Professor of Psychology at the University of Texas at Austin. David is one of the founders of evolutionary psychology but initially made significant contributions to personality psychology. He is perhaps best known for groundbreaking work in human sex differences and mating including jealousy, cross-cultural mate preferences, and the strategies people use to retain a mate. Oftentimes his discoveries come with their own snappy nomenclature like “mate poaching” and “exploitability.” David professes he is especially interested in the “dark side” of human nature. Many of the initial forays David made into new territory have spawned whole new lines of research.

Some highlights of this interview include David’s rebellious roots and how an early hypothesis about dominance was purely designed to upset one of his teachers, how he began to acclimatize to John Tooby and Leda Cosmides’ night owl schedule when they became fast friends at Harvard, the advice he would give to graduate students and the way he demonstrates how to derogate a rival male on his interviewer and former graduate student Barry X. Kuhle, maybe a little too effectively.

Buy books by David Buss (for which AEPS gets a wee kickback, at no cost to you).



Leda Cosmides (Introduction below by Robert Kurzban)

Leda is one of the pioneers of the field of evolutionary psychology. She is a professor at the University of California Santa Barbara, where she co-founded the Center for Evolutionary Psychology (CEP) with husband and collaborator John Tooby. Leda’s impact on evolutionary approaches cannot be overstated. Her awards and honors are numerous, and include the prestigious National Institutes of Health Director’s Pioneer Award. Even if you are very familiar with Cosmides’ work, you’ll learn a lot from this video, including how being 5 minutes late to a meeting with E. O. Wilson (when she was an undergrad at Harvard) was “key to her future,” how her seminal and award winning 1989 paper on cheater detection took four years and several rejections before getting published in Cognition, why she called the field she and John helped start “evolutionary psychology” as opposed to “human sociobiology,” and much more.

Buy books by Leda Cosmides and her colleagues.


Also check out the fantastic interviewers and their research and thinking: 

Barry X. Kuhle’s Psychology Today page can be found here.

Catherine Salmon’s Psychology Today page can be found here. Buy books by Catherine Salmon (for which HBES gets a wee kickback, which we very much appreciate).

The Personal is Universal: How To Put Your Science Out for the General Public

A big part of putting out applied science is communicating to the general population in a language they can understand. A post by editor Katie L. Burke at American Scientist on how to do this (and much more) has some helpful tips.

This is one of the most important:

8. If you want people to understand that a problem addressed by your research affects real people, you need to illustrate the problem by telling a story about real people.

Scientists often want to connect with the public by talking about how their research affects issues of widespread concern. But they are used to talking about these effects in abstract ways, such as giving statistics about groups of people. The stats are important, but they’ll hold more weight and be more memorable for the reader if real people are also written as characters in the narrative. When scientists rattle off statistics but do not talk about how they connect to people’s lives, they risk coming off as cold and distant. Anecdotes may not have a place in science writing, but they are absolutely essential to journalistic and literary nonfiction.

Personal stories are stories that connect with people. We care about people. We don’t connect over big social issues we can do nothing about.

David Carr, the late media columnist at The New York Times, spoke about this at an alternative weekly newspaper conference in around 2008, saying (best I can recall), “Don’t talk about poverty; talk about how little Tasha doesn’t get lunch.”

Garry Shandling puts this another way: “The more personal it is, the more universal it is.”