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Sex Differences

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I recently watched the above video of a Demi Lovato song. I like Michelle Rodriguez’s stomach as much as the next guy (OK, perhaps more), but one thing that struck me in particular is that throughout the whole narrative arc Lovato, a 5’3 tall female, beats the crap out of many much larger men. Obviously this is a stylized fantasy, and the trope of “butt-kicking babes” is pretty well established in our culture now that we can slot it into the appropriate schema (Lara Croft?). But, recently I’ve been made aware of the magnitude of the strength differences between men and women, so these sorts of scenes are even more fantastical than were before. It’s almost as strange to me as an episode of Sailor Moon. It starts to violate the need for a “minimally counter-intuitive” scenario which is the criterion for a good realistic fantasy (yeah, that’s an oxymoron!).

sexdiff The table to the left is from Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity. I’m not too interested in the evolutionary psychological details at the heart of the paper. Rather, let’s focus on some statistics which are given. The key is to focus on the d column, this is the effect size, which indicates the differences between the means of the two distributions in standard deviation units. The mean ages of the two distributions were the same, 33. So d is naturally 0 for this measure. For height men are 1.75 standard deviations taller, on average, than women. This seems about right. You can see in body fat percentage that women have higher values than men. The d here is negative. It gets interesting once you get to muscles. These are measuring volumes. When it comes to arm muscles the average male has 2.5 standard deviation units more than the average female! I was also surprised by the thigh muscle, as arm musculature differences have always been more salient. Finally, there’s the fat free mass.

Some have pointed out to me before that the standard sexual dimorphism calculation in relation to humans may not be informative in the way we might think. There’s about a 10% size differences between men and women. But as you see in the “fat free mass” row the size difference is much more extreme if you account for the higher body fat of women. This is relevant because fat does not make you strong, it just adds more weight and volume. In terms of upper body muscle mass there’s less than a 10% overlap between the two distributions. The vast majority of men have more muscle mass than all women. 99.9% of females have less upper body muscle mass than the average male. The 61% greater average muscle mass in male upper bodies translates into 90% greater average strength (the respective values for the lower body are 50% and 61%). The authors of the paper note that “The sex difference in upper-body muscle mass in humans is similar in magnitude to the sex difference in lean body mass in gorillas, the most sexually dimorphic primate.” Obviously humans don’t engage in obligate harem building, and males are not totally devoted to agonistic behavior as their raison d’etre. So one should be cautious about extending the analogy too far. But this result will likely surprise many. It surprised me.

k10359 I spent a lot of time fixating on numbers above because I don’t beat women. More pointedly, I’ve never hit a woman. That’s not because of the way I was raised by my parents. Though they don’t countenance beating women, they came as adults to this country from Bangladesh, so their attitudes toward violence are more “liberal” in a literal sense than the average America. The culture in which I grew up though affected me more in regards to proper behavior in this dimension (the United States, and more particularly, middle class mores). I have a cousin who was beaten up by her husband several times (for the record, they both grew up in Bangladesh into their adulthood). She’s about 4’10 and he’s 5’8. Though I abhorred this behavior I didn’t have any concrete understanding of what this might have meant. I’ve gotten into fights, but only with guys, and they weren’t ever that much smaller than me. Now I understand better why a 5’8 man should never get violent with a 4’10 woman. The discrepancy is far greater than height would suggest, because the woman has less muscle mass per pound. I have some intuition about this because my wife is about my height and of athletic disposition for a woman, and when she tried to throw down my sorry out of shape ass it was pretty easy for me to prevent her. How is it possible that despite us being the same height, and her being in shape and me not being in shape*, I could still best her? Because I still had more upper body muscle mass due to being a male.

Now, mind you, there are a small minority of women who are stronger than a small minority of men. The statistics above make it clear. But it is very unlikely that in a pairwise interaction the very strongest females will randomly face the very weakest males. In terms of relationships, where domestic violence occurs, it is very unlikely for reasons of assortative mating that the very strongest females will be paired up with the very weakest of males. On the contrary.

There are two reasons I’m posting this. First, I’m assuming most of my male readers have never beaten a woman, so they too lack good intuition about what they might be capable of if they did do such a thing. There isn’t the sort of thing you really want first-person experience of, so scientific research which can gain you some sense of the shape of reality is useful. Second, the general skepticism and rejectionism of biological differences in behavior between the sexes which is now common on the cultural Left can start to bleed into other domains in the most surreal ways. I’ve had friends with science backgrounds who balk somewhat when I attempt to start any discussion about sex differences with the contention that there is a difference in upper body strength. They don’t necessarily even want to concede this without dispute. In these earlier conversations I didn’t know of any research on the magnitude of the difference, it just seemed “common sense.” But perhaps the positive diminution of domestic violence in some sectors of American society has had the side effect that people forget how strong the magnitude of difference in strength is?

Related: Men Are Stronger Than Women (On Average). In which I report that the average German man has a grip strength more powerful than the majority of the woman’s Olympic level fencing team.

* This was in the past, now that I lift my upper body muscle mass has increased considerably.

• Category: Science • Tags: Sex Differences 
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Citation: Leyk, D., et al. “Hand-grip strength of young men, women and highly trained female athletes.” European journal of applied physiology 99.4 (2007): 415-421.

51bCI-7YlbL._SY344_BO1,204,203,200_ Every now and then there is a debate on who is more “anti-science”, the Left or the Right. I’m not too interested in the details of that, but, a few years ago I expressed my skepticism to Chris Mooney, author of The Republican War on Science, that liberals were somehow reflexively more “pro-science.” I suggested to him, for example, that when it comes to aspects of the biological basis of human behavior, with the exception of homosexual orientation, liberals are highly resistant to accepting any differences across groups because of their adherence to social constructionism. Chris brushed this off, suggesting that the “science wars” were over, and even when it came to evolutionary psychology (broadly construed) the liberal Left had conceded to the best evidence on hand. I was not moved, because I’ve had years of exchange with many liberal Left folk who defy Chris’ assurance to me. This is most notable when it comes to sex differences, which are usually seen as less controversial, and evolutionarily should have some prior expectation due to dimorphism.

To give a concrete example of how far this goes, there are many liberal Left people who won’t even accede to the proposition that men are, on average, stronger in terms of upper body strength than women. A few years ago this came up on social media, where a friend who has a biology background from an elite university, even expressed skepticism at this, when I was trying to get her to be open to behavioral differences between the sexes by starting with something I thought she would at least agree with as reasonable. When I saw the lack of unequivocal acceptance of this point I decided to opt out of the conversation. This was basically face to face with Left

This is not to say that people are totally in denial. Rather, the standard educated tack by those with progressive tendencies kicks in. There are “problematic” terms which need to be “contextualized,” and “difference” needs to be considered as an expression of socially preferred categories and measurement. After the critical theory verbiage is hurled usually sane people want to run out of the room.

But on Twitter recently I saw an article which quantifies the difference in concrete ways. To be honest the difference shocked me. The paper is Hand-grip strength of young men, women and highly trained female athletes. As you can see in the figure above the sample sizes are large. The N = 60 of top female athletes consisted of those who competed in judo and handball, to select for individuals who were already geared toward upper body activities. The very weakest male in the data set of nearly 1,700 males looks to be about at the 20th percentile for average women.


The upshot is that the very strongest female athletes are barely above the median of grip strength for men. The top 75th percentile of female athletes are below the bottom 25th percentile of men. Another way to look at it is cumulative distributions. You can tell looking at this that there is overlap between the two sample distributions. How much? Ten percent of women have stronger grips than the bottom five percent of men. The difference in distributions is big enough that the very strongest non-elite athlete female in the whole data set has a weaker grip than most of the men.

fig4 At this point the intelligent obscurantist will probably make an appeal to something about a confound. But the researchers had a data set of men and women in their early 20s, of a wide range of body types. To the right you see a plot of average grip strength as a function of lean body mass. The further to the right, the more muscular the individuals are. As you can see the more muscular men and women are, the stronger they are. But you can also observe that even the most muscular women can barely beat the least muscular men.

To a great extent I feel like an idiot even writing this post. Who doesn’t know the extent of this biological difference? Well, lots of people at a minimum pretend not to. I’ve interacted with people about genetics for 13 years now. I’m someone who leans to the Right, but I want to think the best of everyone, and really empirical data is my summum bonum. It doesn’t make me happy to know that the flight from reality has gone so far in some sectors. I am aware that most reasonable people on the Left half of the political distribution would have no problem assenting to the facts here. The problem is that a vocal minority who will “problematize” what should be rock solid facts are not marginalized. This group is so loud and fixated on these topics that they begin to shape perceptions. After all, it isn’t every day that a man is going to challenge a woman to an arm wrestling match. And if you watch superhero movies you know that there are plenty of “butt kicking babes” who more than hold their own. But here’s the thing: superheroes don’t exist, movies are made up!

Perhaps these ideas are stronger than I think, because I’ll be honest that I was a bit surprised by the magnitude of the difference. It is fashionable, and defensible, to talk about averages, but these results point to the possibility that on some biophysical metrics men and women exhibit disjoint distributions. In other words, it is reasonable to treat them as distinct and separate categories in near totality.

Mind you, in a population of millions there will be many strong women who can beat many men. But the results from top level athletes should make us aware just how rare these individuals will be. As individuals they are somewhat sui generis. On the whole I am willing to grant the value of individualism on the legal level. Men and women should be allowed to become fire fighters with sex or gender no bar, and honestly I feel the same for volunteer combat troops. There are women who are physically and mentally in the population capable of competing with and besting most men at tasks which they would have traditionally been barred from on account for their sex. But for some traits they are very rare, because sex matters a lot in development. That is a biological fact.

• Category: Science • Tags: Sex Differences 
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There’s a new paper in PLoS ONE, The Distance Between Mars and Venus: Measuring Global Sex Differences in Personality*, which suggests that by measuring variation of single observed personality traits researchers are missing larger underlying patterns of difference. The Distance Between Mars and Venus: Measuring Global Sex Differences in Personality:

In conclusion, we believe we made it clear that the true extent of sex differences in human personality has been consistently underestimated. While our current estimate represents a substantial improvement on the existing literature, we urge researchers to replicate this type of analysis with other datasets and different personality measures. An especially critical task will be to compare self-reported personality with observer ratings and other, more objective evaluation methods. Of course, the methodological guidelines presented in this paper can and should be applied to domains of individual differences other than personality, including vocational interests, cognitive abilities, creativity, and so forth. Moreover, the pattern of global sex differences in these domains may help elucidate the meaning and generality of the broad dimension of individual differences known as “masculinity-femininity”…In this way, it will be possible to build a solid foundation for the scientific study of psychological sex differences and their biological and cultural origins.

I’m curious about the reaction of people in psychology to this result. The reason is that I am generally confused or skeptical about measurements of personality difference. I’m not confused or skeptical of differences in personality between individuals or groups. I agree that these exist. I just don’t have a good sense of the informativeness of the measures of difference. People may criticize psychometrics intelligence testing all they want, but at least their methods are relatively clear.

From what I can gather the authors discovered that the differences between sexes on personality were much clearer once you looked for the correlation across numerous single measured traits. This strikes me as similar to what you see in population genetics when you move from variation in one gene across populations to many. While a single gene is not very informative in terms of population differences (e.g., the standard assertion that ~15 percent of variation is between races), synthesizing the variation of many genes allows one to easily distinguish populations, because there is such strong discordance in the correlation of differences. An analogy with traits makes understanding this easy. If you were told that population X tended toward black hair, that would not be very informative. Nor if you were told that population X tended toward straight hair. And what if you were told that population X tended toward light skin? All these traits are common across many different populations. But if you told that population X tended toward straight black hair and light skin, the set of populations which intersect at those three traits together in this direction is far smaller than evaluating on a trait-by-trait basis.

But in regards to the evolution of sex differences there is something that I feel that I can say here. Humans seem to lay between other ape lineages in terms of physical dimorphism. For example, in size the difference between males and females is not as extreme as gorillas, but not as equitable as among gibbons. These differences are traditionally correlated with social structure. Groillas are highly polygynous, and there is a great deal of male-male competition, therefore driving sexual selection. In contrast, gibbons tend toward monogamy (at least in the ideal, as with “monogamous birds” the reality seems to differ from the ideal).

But there is also an evolutionary genetic aspect to sexual dimorphism we must consider: in Genetics and Analysis of Quantitative Traits the authors note that evolution of sex specific traits is not going to occur fast. The reason is simple: aside from the peculiarities on the sex chromosomes males and females are genetically the same. This implies that sex differences on the genetic level may emerge via modulation of gene expression across networks of genes tuned by some “master controllers” associated with differential sex development. All of this added complexity takes time to evolve, with the rough result that sexual differences in trait value take about an order of magnitude longer than other traits to come to the fore. The intuition here is simple: if there is selection for large males, there will be selection for large daughters indirectly. Modifiers which dampen this effect need to emerge, so that sex-specific selection doesn’t have the side effect of dragging the other sex along in terms of trait value (this is a concern when you have traits, such as high testosterone, which might increase fitness in males, but reduce it their daughters). Therefore, if there are sex differences in behavioral tendencies which are biologically rooted (I believe there), they will tend to be universal across human societies and have a very deep evolutionary history.

So that would be the strategy to understand differences in personality across the sexes. Go beyond W.E.I.R.D. populations, as they did in this study. And look for traits where males and females seem to exhibit consistent differences across these range of social environments. I suspect environment does effect the magnitude of differences, but I would be willing to bet money that some differences are going to persist (e.g., inter-personal violence is an area where males will differ due to size and personality).

* I’m really sick of the use of the Mars vs. Venus dichotomy in the scholarship.

• Category: Science • Tags: Psychology, Sex Differences 
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Big Think has a post, Do Women Value Ethnicity Over Income in a Mate?:

The results are striking. An African-American man would have to earn $154,000 more than a white man in order for a white woman to prefer him. A Hispanic man would need to earn $77,000 more than a white man, and Asian man would need, remarkably, an additional $247,000 in additional annual income.

So do women value ethnicity over income in a mate? They certainly seem too. If income was the more important factor in mate choice these numbers would be small; it would take very little additional income to entice a woman to date a man of a different race. The fact that the numbers are so large suggests that a man’s race is significantly more important that his income.

And men? Well the problem is that men don’t seem to care about income at all. So even though their behaviour suggests they care less about their partner’s race than women do, the income needed to encourage them to make the trade-off between races is incalculably large. To really estimate how much men care about race you would have to find a different measure, like perhaps physical beauty.

First, there has been research controlling for physical beauty. So the white male disinclination toward black females can be accounted for mostly by the fact that they aren’t as physically attracted to them. When you limit the sample of black women to those which they are physically attracted to the discrepancy mostly disappears. In contrast, when you similarly constrain the samples of black men which white women judge as attractive the discrepancy in dating preference remains (the same when you do so for Asian men).

All this is not new. I blogged this two years ago, and have gotten bored with the topic (there a regular series of papers which confirm the finding in different circumstances). The sex difference in race preference in the dating literature seems relatively robust. Women care about the race of their partners far more than men, all things equal (in fact, much of the literature suggests men are not concerned about race very much when you control for other background variables). If a site brands itself as “Big Think”, it would be nice to add some value.

I’ll offer a hypothesis in keeping with Ann Althouse’s rule-of-thumb in regards to discussing sex differences in polite company: make sure to make it seem as if women are superior in some fashion. Perhaps women simply have a lower time preference? That is, they’re thinking of long-term consequences. Interracial divorce rates are higher, so women may be making implicit calculations as to the probable success of a relationship as opposed to the short-term benefits of a pairing which men fixate upon. Additionally they may be more liable to “think of the children.” Though I’m generally skeptical of the social science research in this area which indicate that mixed-race children experience stress because of their background, there are plenty of high profile media accounts of people of mixed-race and their “struggles” with their identity. This may shape perceptions of the quality of life of the children. In other words, women aren’t being shallow at all, race is an excellent proxy for all sorts of social-cultural variates which might effect the outcomes of a relationship success, and also the fullness of life which their offspring may experience. Women are then in this model being prudent by using a coarse variate, race, as a proxy for the multi-textured reality of how race is lived in America, and how it matters deeply in the lives of human beings.

To test this sort of model we need data from other societies. There are confounds in this analysis in the USA because Asians, for example, are a small minority who as a matter of necessity can’t really limit their dating pool as much as whites. Additionally, it would be useful to take a fine-grained look at Hispanic dating patterns. About ~50% of Hispanic/Latino Americans identify as white, ~40% as “other”, while ~10% a mix with a substantial number of blacks. The race preference may be mostly a function of perception of cultural values, in which case you’d see that Hispanics don’t exhibit any sex bias in race at all. Then it would not be a matter of women being more racist, but being far less cosmopolitan! Oops, I mean that the low time preference is not operating through a racial proxy but a cultural proxy which is correlated with race. In other words, women are culturally sensitive, while men are culturally insensitive.

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Earlier I pointed to the possibility of biophysical constraints and parameters in terms of inheritance shaping the local trajectory of evolution. Today Olivia Judson has a nice post [link fixed] on how the existence of two sexes in many species results in a strange metastable tug-of-war in terms of phenotypic evolution:

In sum, the traits that make a “good” male are often different from those that make a “good” female. (Note: I’m only talking about “good” in evolutionary terms. That means a trait that improves your chance of having surviving offspring.) Since many of these traits have a genetic underpinning, male and female genes are thus being sculpted by different forces.

But — and this is the source of the tension I mentioned — males and females are formed from the same underlying set of genes. After all, in humans, whether you’re a boy or a girl comes down to whether you have a Y chromosome or not: boys do, girls don’t. The rest of the genes occur in both sexes.

The X choromosome in mammals spends about 2/3 of its time in females and 1/3 in males.* And obviously the Y is found only in males. But the rest of the genome is found in both males and females. Judson notes that traits which may be attractive in males may not in females, and which may be attractive in females may not in males. There’s a fair amount of evolutionary psychological work in humans in this vein in regards to the heritability of testosterone and estrogen levels in females and males and how it effects the same and opposite sex (in short, there is suggestive data that “sexy” individuals of one sex, those who exhibit strong secondary sexual characteristics, may be prone to having less sexy offspring of the opposite sex).

Of course you can overcome the balancing tug of war; that’s why you have sexual dimorphism in things like size or facial proportion. But these sorts of traits emerge very slowly because of the equilibrium described above, modifier genes and sex-specific gene expression have to slowly engineer around the overwhelming problem that males and females are genetically no different on a sequence level aside from the Y chromosome. Some estimates put the rate of evolutionary change of sexual dimorphism, that is, trait differences between sexes, between 1 and 2 orders of magnitude slower than conventional population level evolution. Ergo, one would expect that sexual dimorphism differences varying across populations have great time depth, and are probably more interspecific than intraspecific (for example, gorillas vs. humans).

There is naturally a whole field devoted to the study of the origin of sex. But whatever its ultimate rationale and utility an evolutionary context, its existence as a background condition in many taxa may result in a constraint of the exploration of phenotype space, as species divided into two sexes characterized by strong phenotypic differences dance between two sex-specific phenotypic optima.

* Sex determination varies by taxon.

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American Religious Identification Survey 2008 has a new survey, American Nones: The Profile of the No Religion Population. Not surprising, but interesting:

There are a couple of additional findings worth noting here. Looking at retention by gender, Nones are more likely to retain men than women: 66% of men who reported no religion at age 12 were Nones at the time of their participation in ARIS 2008, but only 47% of females who reported no religion at age 12 remained Nones. Of those who reported having a religion at age 12, 15% of men left while only 9% of women did. It appears that American women have a greater affinity for religion than men. And conversely men have greater affinity for secularity than women.

Also, 49% of male “Nones” are atheists & agnostics in terms of stated beliefs. 36% of female “Nones” are. In terms of asserting that one is an atheist or agnostic, 11% of male “Nones” admit to that, while 8% of females do.

Related: Male vs. female religiosity difference.

H/T Talk Islam

• Category: Science • Tags: Religion, Sex Differences 
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Look before you leap: Are women pre-disposed to be more risk averse than male adventurers?:

“It’s not at all that women are risk averse,” says Jody Radtke, program director for the Women’s Wilderness Institute in Boulder, Colorado. When men are confronted with challenging situations, they typically produce adrenaline, which is what causes them to run around, hollering like frat boys at a kegger. An adrenaline rush is a good feeling, but when confronted with the same situation, women produce a different chemical, called acetylcholine.

“Pretty much what (acetylcholine) does is it makes you want to vomit,” says Jody.

Because women don’t have the same positive chemical reward, they tend to be less pumped about confronting stressful situations. This leads them to rely on decision-making. Essentially, they want the whole picture before they go diving in.

Research, Jody says, shows women have more cross-networking between the two hemispheres of the brain, which subconsciously allows them to evaluate different sensory cues, facts and emotions when making decisions. The cause of this difference probably lies somewhere in the debate of nature versus nurture and the history of evolution.

Marvin Zuckerman, professor emeritus at the University of Delaware, has studied risk for decades. He found men are typically more likely to take risks when seeking novel or exciting sensations, and that comes from both genetics and environment.

What’s important seems to be the environment that isn’t shared by siblings in the same family,” he says.

The above was originally published by Women’s Adventure Magazine. The last reference is to the repeated finding that non-shared environment matters a great deal but isn’t well accounted for. Obviously both men and women vary in terms of psychological attributes, and there have been plenty of attempts to adduce the variation to different quantities of neurochemicals (the “chemical soup” model is easy to translate into prose).

The content of the piece isn’t too surprising, you see it all the time. Suggesting innate differences between men and women is totally acceptable so long as it is perceived to be neutral, or, better yet, casts women in a positive light. Michael Lewis’ recent article on the Icelandic financial turmoil hints to sex differences and male psychology as a root problem. He presented a rather conventional stereotype of men as financial cowboys willing to take outsized risks for reward, while women were risk averse socialists. During the run up to the Iraq War and afterward I recall many people, mostly but not always women, calling into Leftish radio shows promoting a sex determinist theory that war was the result of the male nature, and the fact that men are head of states of most nations was the ultimate problem (this argument crops up in science fiction as well).

The interesting point to me is the sort of articles which highlight “different ways of thinking” between the sexes and how they might be rooted in biological differences have implications which point in different directions in terms of positive or negative valuation depending on your perspective and circumstance. As a specific example, the risk taking predispositions of many males can be seen to be folly and lack of prudence, but, risk often entails both an upside and a downside. Decisions which may seem foolish and wrongheaded viewed through a conventional mainstream lens are often lauded in hindsight as visionary. Unfortunately the nature of uncertainty is such that one has little idea which risks will pay off and which will simply extract a downside cost. It is likely that human societies dominated by those who are only risk averse, or those who are only risk accepting, would not be those which we would truly wish to live in. Variation in human personalities is probably beneficial in an aggregate sense when it comes to human progress. There are downsides risks to both the risk averse and risk accepting strategy, so it is probably best to have some of both. In an economic scenario what I’m talking about is straightforward; consider two individuals with degrees in computer science, one who goes to work for IBM and another who founds a start-up. You wouldn’t want everyone to aspire to become a corporate employee, where would the innovation which drives productivity growth come from? On the other hand, there are only so many start-ups which succeed and there is a need for individuals who work in less sexy sectors who service older established technologies which are at the heart of the current economy. In other words, you want to be able to squeeze more juice from the oranges you have, as well be funding research which might result in the discovery of jucier varietals.

Addendum: Obviously what I’m saying here isn’t too novel. It’s rooted in human nature itself: our minds are cobbled together from disparate competencies and subfunctions, and our unitary consciousness is a delusion very successfully promoted by the prefrontal cortex. But even when it comes to concepts and assumptions which are the purview of the prefontal cortex its priority isn’t usually to keep its story straight. Rather it seem geared toward generative ad hoc narratives which are only proximately consistent. Yes it can engage in rationality, but most of the time its forte is rationalization. And why not? Rationalizing the contradictory feels good! It was almost certainly highly adaptive in the past, and likely is today, in terms of keeping everyone in the group on the same page.

• Category: Science • Tags: Genetics, Human Biodiversity, Sex Differences 
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A randomized trial of the effect of estrogen and testosterone on economic behavior:

Existing correlative evidence suggests that sex hormones may affect economic behavior such as risk taking and reciprocal fairness. To test this hypothesis we conducted a double-blind randomized study. Two-hundred healthy postmenopausal women aged 50–65 years were randomly allocated to 4 weeks of treatment with estrogen, testosterone, or placebo. At the end of the treatment period, the subjects participated in a series of economic experiments that measure altruism, reciprocal fairness, trust, trustworthiness, and risk attitudes. There was no significant effect of estrogen or testosterone on any of the studied behaviors.

• Category: Economics, Science • Tags: Economics, Sex Differences 
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Evidence of gender differences in the ability to inhibit brain activation elicited by food stimulation:

Although impaired inhibitory control is linked to a broad spectrum of health problems, including obesity, the brain mechanism(s) underlying voluntary control of hunger are not well understood. We assessed the brain circuits involved in voluntary inhibition of hunger during food stimulation in 23 fasted men and women using PET and 2-deoxy-2[18F]fluoro-D-glucose (18FDG). In men, but not in women, food stimulation with inhibition significantly decreased activation in amygdala, hippocampus, insula, orbitofrontal cortex, and striatum, which are regions involved in emotional regulation, conditioning, and motivation. The suppressed activation of the orbitofrontal cortex with inhibition in men was associated with decreases in self-reports of hunger, which corroborates the involvement of this region in processing the conscious awareness of the drive to eat. This finding suggests a mechanism by which cognitive inhibition decreases the desire for food and implicates lower ability to suppress hunger in women as a contributing factor to gender differences in obesity.

ScienceDaily has a lot more:

“The finding of a lack of response to inhibition in women is consistent with behavioral studies showing that women have a higher tendency than men to overeat when presented with palatable food or under emotional distress,” Wang said. “This decreased inhibitory control in women could be a major factor contributing to the observed differences in the prevalence rates of obesity and eating disorders such as binge eating between the genders, and may also underlie women’s lower success in losing weight while dieting when compared with men.”

Here’s a question: do the sexes differ in time preference?

• Category: Science • Tags: Sex Differences 
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Gender Differences in the Mu Rhythm of the Human Mirror-Neuron System:

The present findings indirectly lend support to the extreme male brain theory put forward by Baron-Cohen (2005), and may cast some light on the mirror-neuron dysfunction in autism spectrum disorders. The mu rhythm in the human mirror-neuron system can be a potential biomarker of empathic mimicry.

Don’t know enough about this stuff to comment, but figure readers would find it of interest….

• Category: Science • Tags: Sex Differences 
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Check out this post. I found it via Research Blogging. I’m going to try out the RSS when they get it up and see if it’s worth it….

• Category: Science • Tags: Sex Differences 
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Dienekes points me to this piece in The American Journal of Physical Anthropology which concludes that there isn’t greater sexual dimorphism in skin color in areas where social/sexual selection could presumably operate because of relaxation of natural selection. Remember that sexual dimorphism tends to evolve very slowly (you need to have sex-linked or developmentally modified loci since men and women share almost all the same genes [except for the Y]), perhaps an order of magnitude more slowly than standard phenotypic evolution given the same selection pressure.

• Category: Science • Tags: Pigmentation, Sex Differences 
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Since very few of you have likely read Fair Women, Dark Men: the Forgotten Roots of Racial Prejudice by Peter Frost, I’d like to you point you to his website, where he introduces many of his ideas in a series of essays. Steve also has an essay on based on Frost’s ideas, and you might find this paper by Frost, European hair and eye color A case of frequency-dependent sexual selection?, of interest.

• Category: Science • Tags: Pigmentation, Sex Differences 
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