Monthly Archives: September 2015

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is not that previous findings of cycle phase effects are false positives, but rather that some null findings in unpublished studies may actually be false negatives, and/or that cycle phase effects may be stronger than currently suggested in the literature.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

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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.
RubiconPre

RubiconPost

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.

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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?”