2012 February 05 Sunday
Sex Hormones Govern Genes That Control Behavior

At least in mice (and probably some day in humans) it is possible to separately tweak the expression of individual genes that are influenced by testosterone and estrogen.

Now a team of scientists at the University of California, San Francisco (UCSF) has uncovered many genes influenced by the male and female sex hormones testosterone and estrogen that, in turn, govern several specific types of male and female behaviors in mice.

Imagine being able to create humans who have very rare combinations of both female and male traits. That'll be possible eventually. Some prospective parents will opt to do it for a variety of reasons.

While testosterone and estrogen act to turn on and off groups of genes these scientists turned off individual genes from these groups to see what affect each gene's suppression caused.

The UCSF team selectively turned many of these genes off one by one and found they could manipulate individual behaviors in the mice, like their sex drive, desire to pick fights, or willingness to spend extra time caring for their young.

"It's as if you can deconstruct a social behavior into genetic components," said Nirao Shah, MD, PhD, an associate professor in the Department of Anatomy at UCSF who led the research, which is published in the 2/3/12 issue of the journal Cell. "Each gene regulates a few components of a behavior without affecting other aspects of male and female behavior.

Obviously this sort of experiment would be hard to do in humans for both ethical and practical reasons. While the ethical objections are obvious enough the practical obstacles are also quite high. Just carrying out an experiment by turning off individual genes at conception would require many experimental subjects as well as many years of waiting to see how each tweak changes cognitive processes and behavior.

But with humans lots of experiments happen naturally due to genetic mutations during fetal development or before. It is possible that with really cheap DNA sequencing scientists may be able to identify humans who already have mutations that turn off or at least turn down the expression of some of the genes that the UCSF researchers are studying in lab mice.

By Randall Parker    2012 February 05 11:29 PM   Entry Permalink | Comments (6)
2012 January 31 Tuesday
Testosterone Cuts Female Cooperation

Your friends getting along too well? Feeling like the group is stuck in a rut of conformity? Testosterone could give you the edge you need to break away and strike out on your own. Testosterone makes us place more value on our own opinions. Whether that is a good or bad thing depends on the quality of your opinions versus the opinions of those around you.

Testosterone makes us overvalue our own opinions at the expense of cooperation, research from the Wellcome Trust Centre for Neuroimaging at UCL (University College London) has found. The findings may have implications for how group decisions are affected by dominant individuals.

Problem solving in groups can provide benefits over individual decisions as we are able to share our information and expertise. However, there is a tension between cooperation and self-oriented behaviour: whilst groups may benefit from a collective intelligence, collaborating too closely can easily lead to an uncritical groupthink ending in decisions that are bad for all.

Attempts to understand the biological mechanisms behind group decision making have tended to focus on the factors that promote cooperation. Research has shown that people given a boost of the hormone oxytocin tend to be cooperative. Now, in a study published today in the journal Proceedings of the Royal Society B, researchers have shown that the hormone testosterone has the opposite effect – in other words, it makes people act less cooperatively and more egocentrically.

But will a lower willingness to cooperate always result in worse outcomes? Those with less need to go along with a group consensus have greater latitude to innovate in areas where the conventional wisdom is blocking development of different and much better approaches to problem.

Women can be made less cooperative with testosterone. One wonders whether the marginal impact on males would be as great.

Dr Nick Wright and colleagues at the Wellcome Trust Centre for Neuroimaging at UCL carried out a series of tests using seventeen pairs of female* volunteers who had previously never met. The test took place over two days, spaced a week apart. On one of the days, both volunteers in each pair were given a testosterone supplement; on the other day, they were given a placebo.

During the experiment, both women sat in the same room and viewed their own screen. Both individuals saw exactly the same thing. First, in each trial they were shown two images, one of which contained a high contrast target – and their job was to decide individually which image contained the target. If their individual choices agreed, they received feedback and moved on to the next trial. However, if they disagreed then they were asked to collaborate and discuss with their partner to reach a joint decision. One of the pair then input this joint decision.

I wonder whether it makes sense to have more and less cooperative states of mind at different times of the day and week in order to get combined benefits of both cooperation and independent thinking.

By Randall Parker    2012 January 31 11:47 PM   Entry Permalink | Comments (4)
2011 October 24 Monday
Thoughts Of Mating Change Aversion To Losses

The willingness to take losses for larger gains depends on whether one has been primed to think about mating and also one's sex.

TEMPE, Ariz. – Could a passing mood influence your financial portfolio for decades to come? Can impulses you inherited from your cave-man ancestors influence your financial decisions in the modern world in ways that may have lifelong consequences?

In a word, yes.

Arizona State University researchers report new evidence that passing mood and deeply embedded human impulses can and do influence us as we make important financial decisions. The new findings, just released online by the American Psychological Association, suggest that our economic decisions change radically when either survival or reproduction is on our minds.

The old view of economic decision-making focuses on human beings as acting rational. In the last few years, cognitive psychologists have revolutionized economics by demonstrating that economic decisions are often irrational. One of the best-known examples of such irrationalities is the phenomenon of "loss aversion."

To a rational economist, $100 is worth exactly $100, whether it's in your pocket now or on the gambling table. But dozens of studies have demonstrated that the typical person places about twice as much psychological value on keeping the $100 bill in their wallet as they do when they place it on winning another $100.

From an evolutionary perspective the effects on men and women make sense. Though today we aren't in the environment for which we are evolutionarily adapted and as a result we are making decisions that are less than optional.

New research re-examines economic decisions in an evolutionary light and suggests that our decision biases may not be so irrational at all. In a series of three studies to appear in the March 2012 issue of the Journal of Personality and Social Psychology, a team of Arizona State University psychologists shows that loss aversion waxes and wanes in flexible ways, depending of whether or not the person is experiencing different fundamental motivational states, such as self-protection or looking for a mate.

Men in a mating frame of mind become less loss-averse while getting into a mating frame of mind has the opposite effect on women. This makes sense from an evolutionary perspective.

In the first study, research participants were asked how happy or unhappy it would make them to gain or lose $100, or to experience a 30-percentile boost in their financial assets. As in previous research, losses typically loomed slightly larger than gains. But all that changed for participants who answered the questions in a mating frame of mind (after imagining themselves having a romantic encounter with someone they found highly attractive).

According to Li, the first author of the study: "For men in a mating frame of mind, loss aversion completely disappeared and they became more focused on wins than losses. For women, on the other hand, mating motivation led them to be even more loss averse, to focus less on possible gains and even more on the pain of loss.

From an evolutionary perspective this makes sense because reproductive decisions are inherently much more costly for females, who pay higher costs of pregnancy and nursing.

So we've got innate differences hard wired into our brains. Whether the male or female tendency is adaptive depends on the situation.

I see all the tendencies of humans to react to their environments in ways that cut into our ability to think rationally as opportunities to better manage oneself. Set up cues and avoidance of cues on your subconscious to shape your biases in more adaptive directions.

By Randall Parker    2011 October 24 06:51 AM   Entry Permalink | Comments (2)
2011 September 11 Sunday
Higher Fetal Androgens Alter Female Brain Development

The rare genetic condition congenital adrenal hyperplasia (CAH) boosts androgen hormone exposure in the womb. Women with CAH have stronger interest in science, technology, engineering and mathematics (STEM) careers than women who have normal hormone levels. CAH does not appear to influence male career interests.

Teacher, pilot, nurse or engineer? Sex hormones strongly influence people's interests, which affect the kinds of occupations they choose, according to psychologists.

"Our results provide strong support for hormonal influences on interest in occupations characterized by working with things versus people," said Adriene M. Beltz, graduate student in psychology, working with Sheri A. Berenbaum, professor of psychology and pediatrics, Penn State.

Berenbaum and her team looked at people's interest in occupations that exhibit sex differences in the general population and are relevant to science, technology, engineering and mathematics (STEM) careers. The researchers studied teenagers and young adults with congenital adrenal hyperplasia -- a genetic condition -- and their siblings who do not have CAH.

This shouldn't be too surprising. Sex hormones alter brain development. But it reminds me of an interesting question: When the capability to intentionally alter fetal hormonal environment becomes pretty refined and powerful what will people do with this capability?

There's a legal angle to this: Suppose prospective parents 10 or 20 years from now decide to alter the womb environment in a female pregnancy in order to temporarily induce the conditions that CAH causes. Suppose they'll be able to do this without a doctor's help. Will prosecutors try to bring charges against them? If so, for what?

Imagine instead that prospective parents decide to reduce the level of hormones for a male fetus in order to create a feminized son. Again, legal grounds for charges to be brought? Should it be illegal to substantially alter the degree of masculine or feminine qualities developed in a fetus?

Do you believe parents should be free to create combinations of cognitive attributes that are currently quite rare? Is that cruelty to their future child and future adult? Consider that some combinations of attributes would be very hard to live with. Someone so altered might not be able to, for example, find someone to form a romance with who would have compatible desires.

By Randall Parker    2011 September 11 09:42 PM   Entry Permalink | Comments (24)
2010 December 21 Tuesday
Chimp Girls Show Doll Preference

Chimps show familiar human sex stereotypes with objects for playing.

Researchers have reported some of the first evidence that chimpanzee youngsters in the wild may tend to play differently depending on their sex, just as human children around the world do. Although both young male and female chimpanzees play with sticks, females do so more often, and they occasionally treat them like mother chimpanzees caring for their infants, according to a study in the December 21st issue of Current Biology, a Cell Press publication.

The findings suggest that the consistently greater tendency, across all cultures, for girls to play more with dolls than boys do is not just a result of sex-stereotyped socialization, the researchers say, but rather comes partly from "biological predilections."

"This is the first evidence of an animal species in the wild in which object play differs between males and females," said Richard Wrangham of Harvard University.

Earlier studies of captive monkeys had also suggested a biological influence on toy choice. When juvenile monkeys are offered sex-stereotyped human toys, females gravitate toward dolls, whereas males are more apt to play with "boys' toys" such as trucks.

Innate brain differences between males and females are the result of natural selection. It is natural that the young of a learning species will practice skills that better enable them to carry out adult responsibilities. Play times in youth are for learning.

By Randall Parker    2010 December 21 12:16 AM   Entry Permalink | Comments (10)
2010 November 10 Wednesday
Fetal Testosterone Exposure Boosts Male Risk Taking

Testosterone before birth make men take greater risks in all aspects of life.

Montreal November 9, 2010 – Potential investors might wish to examine the fingers of their financial advisor prior to signing over any savings. A new study from Concordia University has found the length between the second and fourth finger is an indicator of high levels of prenatal testosterone, risk-taking and potential financial success in men. The findings, published in the journal of Personality and Individual Differences, suggest that alpha males may take greater risks in relationships, on the squash court and in the financial market.

If your ring finger is longer than your index finger (the finger you use to point at things) then you were exposed to more testosterone. I bet most female CEOs have long ring fingers. Ditto for Wall Street traders and male CEOs for that matter.

You've got to take risks to achieve big successes.

"Previous studies have linked high testosterone levels with risky behaviour and financial success," says senior researcher Gad Saad, Concordia University Research Chair in Evolutionary Behavioral Sciences and Darwinian Consumption as well as a marketing professor at the John Molson School of Business. "We investigated the relationship between prenatal testosterone and various risk proclivities. Our findings show an association between high testosterone and risk-taking among males in three domains: recreational, social and financial."

"Since women tend to be attracted to men who are fit, assertive and rich, men are apt to take risks with sports, people and money to be attractive to potential mates. What's interesting is that this tendency is influenced by testosterone exposure – more testosterone in the womb can lead to more risks in the rink, the bar and the trading floor in later in life," says first author and Concordia doctoral student, Eric Stenstrom.

What I wonder: Once it becomes possible to control fetal testosterone exposure will expectant parents opt to make their male or their female babies more aggressive and masculine? To put it another way: Will the incidence of longer ring fingers be higher 50 years from now?

What I also wonder: Will ways be found to modulate and funnel risk-taking behavior to make it more focused on financial success? Will parents opt to make their kids rather like Ferengi with a stronger focus on acquisition? This seems doable. There are probably genes that boost risks of becoming gambling addicts that are separate from genes that boost more constructive forms of risk-taking.

By Randall Parker    2010 November 10 08:15 PM   Entry Permalink | Comments (11)
2010 September 26 Sunday
Estrogen Spikes During Ovulation Reduce Learning

Higher estrogen during ovulation reduces the ability of female rodents to pay attention.

Montreal September 24, 2010 – Feeling a little sluggish and having trouble concentrating? Hormones might be to blame according to new research from Concordia University published in the journal Brain and Cognition. The study shows that high estrogen levels are associated with an inability to pay attention and learn – the first such paper to report how this impediment can be due to a direct effect of the hormone on mature brain structures.

"Although estrogen is known to play a significant role in learning and memory, there has been no clear consensus on its effect," says senior author Wayne Brake, an associate professor at Concordia's Center for Studies in Behavioural Neurobiology. "Our findings, using a well-established model of learning called latent inhibition, shows conclusively that high estrogen levels inhibit the cognitive ability in female rodents."

Since something similar happens with human females the researchers are happy that they've established a rodent model to use to study estrogen's effects on the brain.

Human females have high estrogen levels while they are ovulating. These high levels have also been shown to interfere with women's ability to pay attention.

Since very few ovulations result in pregnancy and most of the time women do not want to become pregnant while ovulating the interference in learning ability caused by estrogen imposes a big cost with perhaps no benefit most of the time. A method to either block the estrogen surge or block its cognitive effects would raise the mental performance of millions of ovulating women.

By Randall Parker    2010 September 26 11:48 AM   Entry Permalink | Comments (6)
2010 September 14 Tuesday
CEO Behavior And Testosterone Levels

“High testosterone responders tend to reject low offers even though this is against their interest.”

HANOVER, MD, September 8, 2010 – High testosterone levels in CEOs negotiating mergers and acquisitions are linked to a higher rate of dropped deals and an increase in hostile takeover attempts, according to a new study in the September issue of Management Science, a journal of the Institute for Operations Research and the Management Sciences (INFORMS®).

Deal or No Deal: Hormones and the Mergers and Acquisitions Game” is by Maurice Levi, Kai Li, and Feng Zhang of the Sauder School of Business at the University of British Columbia. The study appears in the current issue of Management Science.

A podcast interview with Prof. Levi is at www.scienceofbetter.org/podcast/levi.html.

Although observers might expect M&A bids to follow analysis of business advantage, the authors find that more human factors are also at work.

“We find a strong association between male CEOs being young and their withdrawal rate of initiated M&As,” the authors say, characterizing these rejectionist younger executives as showing dominance-seeking behavior. “High testosterone responders tend to reject low offers even though this is against their interest.”

Younger CEOs are 4% more likely to initiate an attempt to acquire another company than older men, the study finds. In a more marked finding, male CEOs’ relative youth increases their likelihood of withdrawing a merger/acquisition bid by as much as 20%.

It strikes me that what is needed is the ability to raise and lower testosterone as differing business condiions require different optimal testosterone levels. Turn the knob up or down to adjust your personality and behavior as needed. 50 years from now I expect personality modification will become widespread.

By Randall Parker    2010 September 14 12:10 AM   Entry Permalink | Comments (5)
2010 June 22 Tuesday
Gay Male Facial Recognition More Like Female Speed

Homosexual men can recognize faces faster than heterosexual men. Apparently women are faster than men at facial recognition.

TORONTO, June 22, 2010 – Gay men can recall familiar faces faster and more accurately than their heterosexual counterparts because, like women, they use both sides of their brains, according to a new study by York University researchers.

I'm curious to know how homosexual women score on facial recall speed. Are they slower at the task than heterosexual women?

I'm also curious to know what the adaptive advantage was for women to recall faces faster than men. Why would facial recognition speed provide a selective advantage for producing offspring that would survive?

The study, published in the journal, Laterality: Asymmetries of Body, Brain and Cognition, examined the influence of gender, sexual orientation and whether we're right-or-left-handed on our ability to recognize faces. It found that when memorizing and discriminating between faces, homosexual men show patterns of bilaterality – the usage of both sides of the brain – similar to heterosexual women. Heterosexual men tend to favour the right hemisphere for such tasks.

"Our results suggest that both gay men and heterosexual women code faces bilaterally. That allows for faster retrieval of stored information," says study lead author Jennifer Steeves, Associate Professor, Department of Psychology, Faculty of Health.

To put it another way: What was the selective advantage for men to use less of their left hemisphere for facial recognition? What does the left side of the male brain do instead of facial recognition?

By Randall Parker    2010 June 22 11:03 PM   Entry Permalink | Comments (8)
2010 June 13 Sunday
Men Suffer More From Relationships Gone Bad?

Women aren't the emotionally more sensitive in relationships?

Winston-Salem, NC -- Contrary to popular belief, the ups and downs of romantic relationships have a greater effect on the mental health of young men than women, according to a new study by a Wake Forest University sociology professor.

In the study of more than 1,000 unmarried young adults between the ages of 18 and 23, Wake Forest Professor of Sociology Robin Simon challenges the long-held assumption that women are more vulnerable to the emotional rollercoaster of relationships. Even though men sometimes try to present a tough face, unhappy romances take a greater emotional toll on men than women, Simon says. They just express their distress differently than women.

Simon's research is published in the June issue of the Journal of Health and Social Behavior. Anne Barrett, associate professor of sociology at Florida State University, co-authored the article.

"Our paper sheds light on the association between non-marital romantic relationships and emotional well-being among men and women on the threshold of adulthood," Simon says. "Surprisingly, we found young men are more reactive to the quality of ongoing relationships."

The researchers argue that women have more non-romantic relationships to fall back on that make break-ups easier on them. But I suspect the evolutionary roles of men and women also account for part of the difference seen here. Men pursue women. Women choose. A woman who knows she'll get to make choices among future suitors can afford to feel less is at stake if the current relationship doesn't last.

What would be interesting to know: Do better looking women feel less upset when relationships go bad? Also, do women feel more upset the higher the status of the guy they are breaking up with?

By Randall Parker    2010 June 13 11:38 PM   Entry Permalink | Comments (10)
2010 May 25 Tuesday
Testosterone Makes Naive Women Less Trusting

Only the most socially naive women were made less trusting by 0.5 milligrams of testosterone.

A study in the Proceedings of the National Academy of Sciences asked adult women to rate the trustworthiness of photos of strangers' faces.

The hormone testosterone, normally linked to competition and dominance, made the most socially naive women more vigilant.

If these results are significant then would lowering testosterone make women more trusting? Also, what about men?

Here's an excerpt from the abstract.

Testosterone, a steroid hormone associated with competition and dominance, is often viewed as an inhibitor of sociality, and may have antagonistic properties with oxytocin. The following experiment tests this possibility in a placebo-controlled, within-subjects design involving the administration of testosterone to 24 female subjects. We show that compared with the placebo, testosterone significantly decreases interpersonal trust, and, as further analyses established, this effect is determined by those who give trust easily. We suggest that testosterone adaptively increases social vigilance in these trusting individuals to better prepare them for competition over status and valued resources. In conclusion, our data provide unique insights into the hormonal regulation of human sociality by showing that testosterone downregulates interpersonal trust in an adaptive manner.

I would like to know whether women who are more inclined to feel trust have lower blood testosterone. Ditto for more trusting men.

The researchers above mention oxytocin's role in making people more social. Well, other research finds that oxytocin makes men more empathic. I hear Ray Davies of the Kinks singing "Lola": "Girls will be boys and boys will be girls". This is possible to achieve with copious use of hormones.

48 healthy males participated in the experiment. Half received an oxytocin nose spray at the start of the experiment, the other half a placebo. The researchers then showed their test subjects photos of emotionally charged situations in the form of a crying child, a girl hugging her cat, and a grieving man. The test subjects were then invited to express the depth of feeling they experienced for the persons shown.

In summary, Dr. René Hurlemann of Bonn University´s Clinic for Psychiatry was able to state that "significantly higher emotional empathy levels were recorded for the oxytocin group than for the placebo group", despite the fact that the participants in the placebo group were perfectly able to provide rational interpretations of the facial expressions displayed. The administration of oxytocin simply had the effect of enhancing the ability to experience fellow-feeling. The males under test achieved levels which would normally only be expected in women. Under normal circumstances, the "weak" sex enjoys a clear advantage when it comes to the subject of "empathy".

By Randall Parker    2010 May 25 09:53 PM   Entry Permalink | Comments (4)
2010 January 25 Monday
Men Feel Less Guilt Than Women?

The reaction of the researchers to their findings is as interesting as the research itself.

Although changing social and cultural contexts mean guilt has less power today than it once did, a new study has shown that in the West this emotion is "significantly higher" among women. The main problem, according to the experts, is not that women feel a lot of guilt (which they do), but rather that many males feel "too little".

The idea that males feel too little guilt brings to mind a recent post by Roissy, The Medicalization of Maleness. Any time a male behaves in ways to cause widespread disapproval (e.g. Tiger Woods) experts on behavioral disorders (in Woods' case treatment for supposed sexual addiction) come out of the woodwork to proclaim the need for professional treatment. I see the use of drugs for hyperactive male school children in a similar light. The drugs might be useful. But their use rests on the idea that a more male behavioral tendency is a medical disorder.

Females feel more guilt according to these researchers.

"Our initial hypothesis was that feelings of guilt are more intense among females, not only among adolescents but also among young and adult women, and they also show the highest scores for interpersonal sensitivity", Itziar Etxebarria, lead author of the study and a researcher at the University of the Basque Country (UPV/EHU), tells SINC.

The research, published in the Spanish Journal of Psychology, was carried out using a sample from three age groups (156 teenagers, 96 young people and 108 adults) equally divided between males and females. The team of psychologists asked them what situations most often caused them to feel guilt. They also carried out interpersonal sensitivity tests – the Davis Empathetic Concern Scale, and a questionnaire on Interpersonal Guilt, created purposely for this study.

When it came to comparing the measurements of intensity of habitual guilt of these groups, the researchers saw that this score was significantly higher for women, in all three age groups. "This difference is particularly stark in the 40-50-year-old age group", points out Etxebarria.

With younger women cheating on their spouses almost as much as younger men do I do not see the greater feelings of guilt doing much to restrain infidelity. Maybe the women feel worse about it but do it anyway.

Of course cheating heterosexual husbands need a woman to cheat with. Turns out lots of single women prefer taken men. Makes sense from an evolutionary perspective. A man who has a woman looks more appealing to other women because one woman already rated him as worthy.

By Randall Parker    2010 January 25 09:06 PM   Entry Permalink | Comments (5)
2009 December 07 Monday
Angry Female Faces Look Less Female

Interesting results on how fast gender gets recognized.

Rockville, MD – "Why is it that men can be bastards and women must wear pearls and smile?" wrote author Lynn Hecht Schafran. The answer, according to an article in the Journal of Vision, may lie in our interpretation of facial expressions.

In two studies, researchers asked subjects to identify the sex of a series of faces. In the first study, androgynous faces with lowered eyebrows and tight lips (angry expressions) were more likely to be identified as male, and faces with smiles and raised eyebrows (expressions of happiness and fear) were often labeled feminine.

The second study used male and female faces wearing expressions of happiness, anger, sadness, fear or a neutral expression. Overall, subjects were able to identify male faces more quickly than female faces, and female faces that expressed anger took the longest to identify.

We are wired up to have different expectations for male and female faces and the emotions they express.

Hess said that the same cues that make a face appear male – a high forehead, a square jaw and thicker eyebrows – have been linked to perceptions of dominance. Likewise, features that make a face appear female – a rounded, baby face with large eyes – have been linked to perceptions of the individual being approachable and warm.

Male anger is seen as more intense than female anger while female happiness is seen as more intense than male happiness.

"This difference in how the emotions and social traits of the two sexes are perceived could have significant implications for social interactions in a number of settings. Our research demonstrates that equivalent levels of anger are perceived as more intense when shown by men rather than women, and happiness as more intense when shown by women rather than men. It also suggests that it is less likely for men to be perceived as warm and caring and for women to be perceived as dominant."

So angry girls and happy guys aren't taken seriously.

So what are the implications of these results for our daily lives? Should guys try harder to seem happy or not even bother to make the effort? Should women hold up cue cards saying things like "I am really angry now"? Or just start throwing dishes?

By Randall Parker    2009 December 07 07:13 AM   Entry Permalink | Comments (3)
2009 October 26 Monday
Testosterone Makes Men Less Generous In Game

Another nail in the Blank Slate coffin where men and women supposedly get socialized into their different preferences and behaviors. Researcher Karen Redwine at Whittier College and Paul Zak at Claremont University found that a testosterone cream made men less generous. DHT (dihydrotestosterone) had an even more dramatic effect.

The testosterone cream worked. The next day, twice as much of the potent sex hormone coursed through the veins of volunteers, on average.

The students then played a simple economic game with another participant via a computer. One volunteer is tasked with splitting $10 with another volunteer in any way he likes. The other volunteer either accepts the offer or rejects it as unfair, in which case no one gets any money. Each volunteer played this game in both roles, on and off the testosterone gel.

Overall, the testosterone cream caused a 27 per cent reduction in the generosity of the offers, from averages of $2.15 to $1.57, Redwine and Zak found.

Testosterone also made men more inclined to punish people who made unfair offers. Testosterone is therefore the enforcer of justice. One wonders what is the net effect of combining a smelly room with testosterone. War or an efficient system of justice?

An experiment I'd like to see: Do finasteride and dutasteride make men basically less selfish? These drugs block the conversion of testosterone into DHT. Also, do these drugs cause a long term decrease on the ability to do spatial reasoning? Or perhaps testosterone causes some male cognitive features and DHT causes others. So perhaps the drugs cause increases in some male tendencies and decreases in others.

By Randall Parker    2009 October 26 10:58 PM   Entry Permalink | Comments (5)
2009 October 24 Saturday
Brain Sex Differences In Gene Expression Start Early

Cognitive differences in the brain start early. Y chromosome genes turn on and alter brain development in fetuses before birth.

Prenatal sex-based biological differences extend to genetic expression in cerebral cortices. The differences in question are probably associated with later divergences in how our brains develop. This is shown by a new study by Uppsala University researchers Elena Jazin and Björn Reinius, which has been published in the latest issue of the journal Molecular Psychiatry.

Do any ideologues still maintain that fundamental sexual differences in cognition are a product of social environment? The science doesn't seem like it leaves any room for a serious argument along those lines.

Professor Elena Jazin and doctoral student Björn Reinius at the Department of Physiology and Developmental Biology previously demonstrated that genetic expression in the cerebral cortices of human beings and other primates exhibits certain sex-based differences. It is presumed that these differences are very old and have survived the evolutionary process. The purpose of the new study was to determine whether they appear during the process of brain development or first upon the conclusion of that process. Identifying the initial genetic mechanisms that prompt the brain to develop in a female or male direction is a long-range research objective.

The Uppsala University researchers analysed data, on the basis of sex, from another extensive study of the prenatal human brain.

"The results show that many of the genes situated on the Y chromosome are expressed in various parts of the brain prior to birth and probably provide a developmental basis for the sex-based differences exhibited by adult brains," according to Elena Jazin.

More than a third of Y-chromosomal genes appear to be involved in sex-based human brain differentiation. Some of the genetic activity in question is evident in the adult brain, while other of it only appears at earlier stages of brain development. It is yet unknown whether the differences in genetic expression among female and male brains have any functional significance.

It would be interesting to know how how prenatal brain gene expression differs in people who grow up to be homosexual. But it seems hard to conduct such a study. Sexual orientation wouldn't become clear for many years.

By Randall Parker    2009 October 24 11:52 PM   Entry Permalink | Comments (2)
2009 September 30 Wednesday
Women Prefer Taken Guys

Oklahoma State University researchers Melissa Burkley and Jessica Parker demonstrate an aspect of female desire that I've certainly experienced: women prefer taken guys.

Unknown to the participants, everyone was offered a fictitious candidate partner who had been tailored to match their interests exactly. The photograph of "Mr Right" was the same for all women participants, as was that of the ideal women presented to the men. Half the participants were told their ideal mate was single, and the other half that he or she was already in a romantic relationship.

"Everything was the same across all participants, except whether their ideal mate was already attached or not," says Burkley.

The most striking result was in the responses of single women. Offered a single man, 59 per cent were interested in pursuing a relationship. But when he was attached, 90 per cent said they were up for the chase.

You might think these women are unethical.

Roissy would not find these results surprising. Lots of us have had the experience of getting hit on by more women after they've seen a really attractive women hanging on us. That's been my experience.

So what's going on here? Women go with the herd. If some woman likes a guy enough to want to be attached to him this becomes evidence for other women that he's worth going after. For a guy a beautiful woman can serve as a powerful demonstration of higher value. I think there's a potential business here for a specialized escort service where women sell time with them in public places to guys who want to advertise their desirability.

By Randall Parker    2009 September 30 09:58 PM   Entry Permalink | Comments (17)
2009 September 09 Wednesday
Pretty Women Make Guys Dumber

Guys should avoid taking classes that have good-looking women in them if the goal is to learn anything. The cognitive performance of men declines after interacting with attractive women.

The present research tested the prediction that mixed-sex interactions may temporarily impair cognitive functioning. Two studies, in which participants interacted either with a same-sex or opposite-sex other, demonstrated that men’s (but not women’s) cognitive performance declined following a mixed-sex encounter. In line with our theoretical reasoning, this effect occurred more strongly to the extent that the opposite-sex other was perceived as more attractive (Study 1), and to the extent that participants reported higher levels of impression management motivation (Study 2). Implications for the general role of interpersonal processes in cognitive functioning, and some practical implications, are discussed.

Spend your cognitive resources wisely. Guys, trying to impress women is often counterproductive. Plus, it diminishes your ability to do other things.

Being in a relationship didn't help guys maintain their ability to think about mentally challenging tasks.

In their second study, the researchers had 53 male and 58 female college participants interact with each other, instead of using a confederate for the interactions (like they did in the first study). Men (but not women), likewise, displayed a decline in performance on a different, very cognitively demanding task, requiring both task-switching and inhibition. Also, just like the first study, this effect held independent of whether the participant was currently in a relationship.

Curiously, that subset of women who admitted they were trying to impress the guy also experienced declines in cognitive performance. So fewer women than men try to impress. But those who do become dumber just like men do.

This all demonstrates how we are slaved to our genes.

Psychologist Dr George Fieldman, a member of the British Psychological Society, said the findings reflect the fact that men are programmed to think about ways to pass on their genes.

'When a man meets a pretty woman, he is what we call 'reproductively focused'.

Of course all that reproductive focus is defeated by birth control. Nature is foiled until natural selection creates future generations with stronger desire to make babies.

By Randall Parker    2009 September 09 11:12 PM   Entry Permalink | Comments (2)
2009 August 24 Monday
Higher Testosterone Pushes Women Toward Riskier Careers

Given enough testosterone women gravitate toward higher risk career choices.

CHICAGO (Aug. 24, 2009) – The battle of the sexes rages on, this time from the trading floor. While there has long been debate about the social and biological differences between men and women, new research by the Kellogg School of Management at Northwestern University, the University of Chicago Booth School of Business and the University of Chicago's Department of Comparative Human Development explores how the hormone testosterone plays an important role in gender differences in financial risk aversion and career choice.

Prior research has shown that testosterone enhances competitiveness and dominance, reduces fear, and is associated with risky behaviors like gambling and alcohol use. However, until now, the impact of testosterone on gender differences in financial risk-taking has not been explored.

The new paper, "Gender differences in financial risk aversion and career choices are affected by testosterone," has been published in the Aug. 24, 2009 early edition of the Proceedings of the National Academy of Sciences (PNAS). The research was conducted by Paola Sapienza, Associate Professor, Kellogg School of Management at Northwestern University; Luigi Zingales, Robert McCormick Professor, University of Chicago Booth School of Business; and Dario Maestripieri, Professor in Comparative Human Development, University of Chicago.

"In general, women are more risk averse than men when it comes to making important financial decisions, which in turn can affect their career choices," said Sapienza. "For example, in our sample set, 36 percent of female MBA students chose high-risk financial careers such as investment banking or trading, compared to 57 percent of male students. We wanted to explore whether these gender differences are related to testosterone, which men have, on average, in higher concentrations than women."

It all comes down to the testosterone baby.

The researchers, using an economic-based measure of risk aversion, found that higher levels of testosterone were associated with a greater appetite for risk in women, but not among men. However, in men and women with similar levels of testosterone, the gender difference in risk aversion disappeared. Additionally, the researchers reported that the link between risk aversion and testosterone predicted career choices after graduation: individuals who were high in testosterone and low in risk aversion chose riskier careers in finance.

You've got to ask yourself one question: Do I feel lucky? If you do, that means you've got a lot of testosterone.

What I want to know: Does testosterone decrease the C-V distance and increase orgasmic potential in women? Click thru and you'll see what I'm talking about.

By Randall Parker    2009 August 24 10:36 PM   Entry Permalink | Comments (4)
2009 August 13 Thursday
Women Demand Higher Attractiveness For One Night Stands

We live in an era where science has to prove basic obvious truths about human nature. No, we aren't simply a product of our social environment. The sexes have innate differences that show up time and again. Here's the latest shocker: women demand much higher physical attraction before having a one night stand. Given that women must invest more in reproduction this result is explainable with evolutionary theory.

Men are far more interested in casual sex than women. While men need to be exceptionally at-tractive to tempt women to consider casual sex, men are far less choosy. These findings1 by Dr Achim Schützwohl, from the Department of Psychology at Brunel University in the UK, and his team are published online in Springer’s journal Human Nature.

The research shows that men are more likely than women to report having had casual sex and they express a greater desire for it than do women. It is also thought that women but not men raise their standards of attractiveness for a casual sex partner.

Dr Schützwohl and his colleagues looked at the influence of an imagined requestor’s physical attractiveness on men’s and women’s willingness to accept three distinct offers: go out, go to their apartment and go to bed with them. A total of 427 male and 433 female students from the US, Germany and Italy answered a questionnaire. They were asked to imagine being approached by a member of the opposite sex, described as either “slightly unattractive”, “moderately attractive” or “exceptionally attractive”. They then rated how likely they would be to accept each of the three offers.

The authors found that the requestor’s looks affected men and women differently. Across all three levels of requestor attractiveness, men were more likely to go out, go to their apartment and go to bed with them than were women. German men were less likely to go out with the requestor and go to their apartment than American and Italian men. Italian men were more likely to go to bed with the requestor than were American men. German men were even less likely than American men to go to bed with the requestor. These differences highlight cultural differences in sexual morals and preferences.

For each of the three offers, men were more likely to accept when the hypothetical woman was moderately or exceptionally attractive than when she was slightly unattractive, but whether she was moderately or exceptionally attractive made no difference. Women however placed more importance on the requestor’s good looks. They were more likely to accept the apartment and bed requests from an exceptionally attractive man than from either a moderately attractive or slightly unattractive man.

Women also go for more muscular men and prefer the most muscular men for one night stands and slightly less muscular men for longer term relationships.

By Randall Parker    2009 August 13 08:13 AM   Entry Permalink | Comments (7)
2009 July 15 Wednesday
Brain Development Of Adolescent Girls Different Than Boys

Here's a big non-shocker: science shows once again that in adolescence girls become different than boys in how they think.

The study, by researchers at the National Institute of Mental Health (NIMH) and Georgia State University, appears in the July/August 2009 issue of the journal Child Development.

The researchers looked at mostly White psychiatrically healthy Americans ages 9 to 17 to determine what happens in the brains of preteens and teens at a time of significant change in social behavior. The youths looked at photos of peers and rated their interest in interacting with each one. Then they underwent a brain scan while reviewing the pictures and rated how much each young person in the picture might want to interact with them in return. The youths were told they would be matched with a peer for a chat after the scan.

The study found that in older girls (as compared to younger girls), brain regions (the nucleus accumbens, insula, hypothalamus, hippocampus, and amygdala) associated with social rewards and motivation, processing emotions, hormonal changes, and social memory responded differently when they thought about being judged by their peers, especially peers with whom they wanted to interact. These differences were not evident between younger and older boys.

What type of cognitive ability changes more in male adolescents? I would expect spatial reasoning to take a big leap in developing males.

The mind areas for thinking about other people are developing in preschoolers.

The study, in the July/August 2009 issue of the journal Child Development, was conducted by researchers at Queen's University at Kingston in Ontario, Canada.

In the preschool years, children develop social skills by learning how to understand others' thoughts and feelings, or their theory of mind. In most children, theory of mind changes over time so they come to understand that others' thoughts are representations of the world that may or may not match the way the world actually is. In their study of EEGs of 29 4-year-olds, the researchers found that these changes are related to the functional development of two parts of the brain—the dorsal medial prefrontal cortex and the temporal-parietal juncture—that govern similar understanding in adults.

"For a while now, we have known that specific brain areas are used when adults think about others' thoughts," according to Mark A. Sabbagh, associate professor of psychology at Queen's University at Kingston and the study's lead author. "Our findings are the first to show that these specialized neural circuits may be there as early as the preschool years, and that maturational changes in these areas are associated with preschoolers' abilities to think about their social world in increasingly sophisticated ways.

I wonder whether brain scans of 5 year olds can show which ones will grow up by be highly skilled at handling other people and which will do poorly at relating to others.

By Randall Parker    2009 July 15 10:33 PM   Entry Permalink | Comments (2)
2009 June 29 Monday
Men In Closer Agreement Than Women On Attractiveness

Guys know what they want and they pretty much agree with each other on who is hot.

There is much more consensus among men about whom they find attractive than there is among women, according to a new study by Wake Forest University psychologist Dustin Wood.

The study, co-authored by Claudia Brumbaugh of Queens College, appears in the June issue of the Journal of Personality and Social Psychology.

"Men agree a lot more about who they find attractive and unattractive than women agree about who they find attractive and unattractive," says Wood, assistant professor of psychology. "This study shows we can quantify the extent to which men agree about which women are attractive and vice versa."

Unfortunately the press release does not provide any quantitative results. Here is the abstract which also doesn't provide much details. You can buy the article at that link.

The pictures of men and women were only between the ages 18 and 25. I would like to see a study using a wider age range. My expectation is that female attractiveness will be seen as dropping off with age a lot faster than male attractiveness. Also, I'd like to see a study that uses psychometrics to compare attractiveness of women and men based on both the IQ of the viewer and the viewee. Do smart people find smart people more attractive? Do dumb people find smart or dumb people more attractive? Also, I'd like to know how the physical traits and character traits of men and women affect what they see as attractive. For example, does a guy with more masculine physical features and dominant personality feel greater attraction to the most feminine-looking women or to less feminine-looking women?

More than 4,000 participants in the study rated photographs of men and women (ages 18-25) for attractiveness on a 10-point scale ranging from "not at all" to "very." In exchange for their participation, raters were told what characteristics they found attractive compared with the average person. The raters ranged in age from 18 to more than 70.

Before the participants judged the photographs for attractiveness, the members of the research team rated the images for how seductive, confident, thin, sensitive, stylish, curvaceous (women), muscular (men), traditional, masculine/feminine, classy, well-groomed, or upbeat the people looked.

Breaking out these factors helped the researchers figure out what common characteristics appealed most to women and men.

Men's judgments of women's attractiveness were based primarily around physical features and they rated highly those who looked thin and seductive. Most of the men in the study also rated photographs of women who looked confident as more attractive.

As a group, the women rating men showed some preference for thin, muscular subjects, but disagreed on how attractive many men in the study were. Some women gave high attractiveness ratings to the men other women said were not attractive at all.

The press release doesn't indicate whether the pictures were full body or just face. Do ratings of just faces predict ratings of full bodies? I'd expect fat distribution to have a big impact on that. A buxom woman will pick up points in a full body shot while a pot belly will decrease attraction.

So why are men more consistent in their judgments? Do women differ from each other more than men do in their mating strategies? Or is the study picking up on greater variation over time in terms of what women want in men? In particular, how much of the female difference was due to the women being at different stages of their menstrual cycles? See my post Ovulating Women Prefer Smell Of Dominant Men and also my post Nursing Women More Attracted To Higher Pitch Male Voices. Monthly hormonal variations are going to cause women to feel more attraction to alpha men with more masculine features when the women are ovulating and then toward beta men to help raise the kids.

Another possible cause of the greater female difference might be due to age of the females. Does a 35 year old woman on average want different physical features (perhaps less masculinity) than a 20 year old woman? Maybe the full article gets into this. If anyone reads it post in the comments.

Update: Following up on comments made by bbartlog and David Friedman: If the pictures of men showed clearer signs of status (e.g. wearing a medical uniform with an MD on the name tag versus clothing for a lumberjack) would the female choices line up more closely? Or maybe in the pictures used some of the pictures showed status indicators which only some of the women noticed? How consistent are women in their status rankings?

By Randall Parker    2009 June 29 10:18 AM   Entry Permalink | Comments (15)
2009 January 12 Monday
Mental Rotation Sex Differences Due To Brain Parietal Lobe

Brain greater parietal lobe surface area is connected to one's ability to rotate objects in one's mind.

Men consistently outperform women on spatial tasks, including mental rotation, which is the ability to identify how a 3-D object would appear if rotated in space. Now, a University of Iowa study shows a connection between this sex-linked ability and the structure of the parietal lobe, the brain region that controls this type of skill.

The parietal lobe was already known to differ between men and women, with women's parietal lobes having proportionally thicker cortexes or "grey matter." But this difference was never linked back to actual performance differences on the mental rotation test.

UI researchers found that a thicker cortex in the parietal lobe in women is associated with poorer mental rotation ability, and in a new structural discovery, that the surface area of the parietal lobe is increased in men, compared to women. Moreover, in men, the greater parietal lobe surface area is directly related to better performance on mental rotation tasks. The study results were published online Nov. 5 by the journal Brain and Cognition.

If you want to be able to rotate objects in 3D you need to have more parietal lobe surface area.

The study was based on tests of 76 healthy Caucasian volunteers -- 38 women and 38 men, all right-handed except for two men. The groups were matched for age, education, IQ and socioeconomic upbringing. When tested on mental rotation tasks, men averaged 66 percent correct compared to 53 percent correct for women. Magnetic resonance imaging (MRI) revealed an approximately 10 percent difference between men and women in the overall amount of parietal lobe surface area: 43 square centimeters for men and 40 square centimeters for women.

What selective pressure(s) gave an advantage to men for mental object rotation? Ability to model prey movement? Or tools building? Or what exactly?

By Randall Parker    2009 January 12 09:59 PM   Entry Permalink | Comments (0)
2009 January 10 Saturday
Brain Difference For Pain Between Males And Females

Women need more morphine to relieve pain and the reason might be fewer mu-opioid receptors in female brains.

"Opioid-based narcotics (such as morphine) are the most widely prescribed therapeutic agents for the alleviation of persistent pain; however, it is becoming increasingly clear that morphine is significantly less potent in women compared with men. Until now, the mechanism driving the phenomenon was unknown," said Anne Murphy, Ph.D., a Georgia State Professor of Neuroscience and member of the Center for Behavioral Neuroscience, who conducted the research with Dayna Loyd, Ph.D.

Murphy recently solved the mystery with findings printed in the December issue of The Journal of Neuroscience that show that previously reported differences in morphine's ability to block pain in male versus female rats are most likely due to sex differences in mu-opioid receptor expression in a region of the brain called the periaqueductal gray area (PAG).

Located in the midbrain area, the PAG plays a major role in the modulation of pain by housing a large population of mu-opioid receptor expressing neurons. Morphine and similar drugs bind to these mu-opioid receptors analogous to a 'lock and key' and, ultimately, tell the brain to stop responding to pain signals to the nerve cells resulting in the reduced sensation of pain.

Using a series of anatomical and behavioral tests, Murphy and Loyd were able to determine that male rats have a significantly higher level of mu-opioid receptors in the PAG region of the brain compared with females. This higher level of receptors is what makes morphine more potent in males because less drug is required to activate enough receptors to reduce the experience of pain. Interestingly, when they used a plant-derived toxin to remove the mu-opioid receptor from the PAG, morphine no longer worked, suggesting that this brain region is required for opiate-mediated pain relief.

I wonder what behavioral difference this causes in the daily lives of men and women and why this was selected for.

By Randall Parker    2009 January 10 03:17 PM   Entry Permalink | Comments (5)
2005 July 21 Thursday
Hallucinated Voices Male Because Male Voices Easier To Imagine

Female voices are more complex and hence people who hallucinate voices tend to hallucinate male voices more often than not.

Dr Michael Hunter's research at the University of Sheffield says that male voices are less complex to produce than female.

As such, when the brain spontaneously produces its own "voices", a male voice is more likely to have been generated.

Among both men and women, 71% of such "false" voices are male.

Since male voice hallucinations are harder for the mind to make does average type of voice heard differ as a function of intelligence level? When smarter people hallucinate do they hear female voices at higher rates than dumber people who hallunicate voices? Also. do people with perfect pitch or other musical abilities hear female voices more often? After all, they have more developed abilities for imagining complex voices.

By Randall Parker    2005 July 21 11:06 PM   Entry Permalink | Comments (5)
2004 May 05 Wednesday
Women With Hourglass Bodies Have More Reproductive Hormones

Who are we to question the wisdom of our genes?

Large-breasted, narrow-waisted women have the highest reproductive potential, according to a new study, suggesting western men's penchant for women with an hourglass shape may have some biological justification.

Women with a relatively low waist-to-hip ratio and large breasts had about 30 per cent higher levels of the female reproductive hormone estradiol than women with other combinations of body shapes, found Grazyna Jasienska, at Jagiellonian University in Krakow, Poland and colleagues.

Barbie is now defended by science.

Writing in Proceedings B, the researchers led by Dr Grazyna Jasienska of Harvard University, said the hourglass figure was popular in Western cultures, but not in others across the world.

She said men in non-Western societies did not seem to favour women with hourglass figures, and broader figures, indicating good nutritional status, were considered most attractive.

However, in Western societies, the cultural icon of Barbie as a symbol of female beauty seems to have some biological grounding," added Dr Jasienska.

In Europeans it may well be that the hourglass body shape for women is more highly correlated with fecundity than is the case with other groups and that this is due to average genetic differences. There may have been co-evolution of the hourglass body shape as more fecund along with genetic changes that increased the attraction to that body shape.

The higher level of estradiol translates into 3 times higher likelihood to get pregnant.

"If there are 30 per cent higher levels, it means they are roughly three times more likely to get pregnant," Jasienska, a human biologist, told New Scientist.

By Randall Parker    2004 May 05 11:15 AM   Entry Permalink | Comments (66)
2004 April 27 Tuesday
Women Remember Physical Appearances Better Than Men Do

Women remember physical appearances better than men do and both men and women remember the appearances women more than they remember the appearances of men.

The gender difference in appearance memory was not great, but it shows another area where women are superior to men in interpersonal sensitivity, said Terrence Horgan, lead author of the study and research fellow in psychology at Ohio State University.

“Women have an advantage when it comes to remembering things like the physical features, clothing and postures of other people,” Horgan said. “This advantage might be due to women being slightly more people-oriented than men are.”

The study also found that both men and women did better at remembering the appearance of women than they did remembering how men looked.

The appearance of women may be more memorable because women try to look different from each other.

Women in general may be more memorable than men because their hair and clothing styles and use of jewelry tends to be more varied than that of men. For example, in many offices men may look similar in their suits and ties. But women may be wearing necklaces and earrings, or have other jewelry or clothing that makes their appearance stand out more, Horgan said.

However, the results suggest women aren’t more memorable because people spend more time looking at them. The researchers measured how long participants in the last three studies looked directly at their partners. Overall, the participants didn’t look at women any longer than they looked at men.

Women are known to be better at reading body language and facial expressions. So they tend to focus more on visible qualities of a person.

For example, other studies have shown women have an advantage at using nonverbal cues to understand how others are feeling, and how they are likely to behave. Women also appear to be better at using nonverbal cues to understand someone’s personality traits.

Another reason that women may do a better job at remembering the appearance of other women than men do of remembering the appearance of other men is that heterosexual women are more sexually aroused by the sight of other women than heterosexual men are at the sight of other men. It would be interesting to see these researchers repeat their study using homosexuals and heterosexuals split out separately. It would also be interesting to see whether more variation in the men's clothing and less variation in the women's clothing would influence the outcome.

By Randall Parker    2004 April 27 12:13 PM   Entry Permalink | Comments (2)
2003 June 20 Friday
Study on Differences in Female, Male Sexuality

While heterosexual males are chiefly aroused by females heterosexual females are aroused by males and females.

June 12, 2003

Study on Differences in Female, Male Sexuality

EVANSTON, Ill. --- Three decades of research on men’s sexual arousal show patterns that clearly track sexual orientation -- gay men overwhelmingly become sexually aroused by images of men and heterosexual men by images of women. In other words, men’s sexual arousal patterns seem obvious.

But a new Northwestern University study boosts the relatively limited research on women’s sexuality with a surprisingly different finding regarding women’s sexual arousal.

In contrast to men, both heterosexual and lesbian women tend to become sexually aroused by both male and female erotica, and, thus, have a bisexual arousal pattern.

“These findings likely represent a fundamental difference between men’s and women’s brains and have important implications for understanding how sexual orientation development differs between men and women,” said J. Michael Bailey, professor and chair of psychology at Northwestern and senior researcher of the study “A Sex Difference in the Specificity of Sexual Arousal.” The study is forthcoming in the journal Psychological Science.

Bailey’s main research focus has been on the genetics and environment of sexual orientation, and he is one of the principal investigators of a widely cited study that concludes that genes influence male homosexuality.

As in many areas of sexuality, research on women’s sexual arousal patterns has lagged far behind men’s, but the scant research on the subject does hint that, compared with men, women’s sexual arousal patterns may be less tightly connected to their sexual orientation.

The Northwestern study strongly suggests this is true. The Northwestern researchers measured the psychological and physiological sexual arousal in homosexual and heterosexual men and women as they watched erotic films. There were three types of erotic films: those featuring only men, those featuring only women and those featuring male and female couples. As with previous research, the researchers found that men responded consistent with their sexual orientations. In contrast, both homosexual and heterosexual women showed a bisexual pattern of psychological as well as genital arousal. That is, heterosexual women were just as sexually aroused by watching female stimuli as by watching male stimuli, even though they prefer having sex with men rather than women.

“In fact, the large majority of women in contemporary Western societies have sex exclusively with men,” said Meredith Chivers, a Ph.D. candidate in clinical psychology at Northwestern University and a psychology intern at the Centre for Addiction and Mental Health and the study’s first author. “But I have long suspected that women’s sexuality is very different from men’s, and this study scientifically demonstrates one way this is so.”

The study’s results mesh with current research showing that women’s sexuality demonstrates increased flexibility relative to men in other areas besides sexual orientation, according to Chivers.

“Taken together, these results suggest that women’s sexuality differs from men and emphasize the need for researchers to develop a model of the development and organization of female sexuality independent from models of male sexuality,” she said.

The study’s four authors include Bailey and three graduate students in Northwestern’s psychology department, Chivers, Gerulf Rieger and Elizabeth Latty.

“Since most women seem capable of sexual arousal to both sexes, why do they choose one or the other?” Bailey asked. “Probably for reasons other than sexual arousal.”

Sexual arousal is the emotional and physical response to sexual stimuli, including erotica or actual people. It has been known since the early 1960s that homosexual and heterosexual men respond in specific but opposite ways to sexual stimuli depicting men and women. Films provoke the greatest sexual response, and films of men having sex with men or of women having sex with women provoke the largest differences between homosexual and heterosexual men. That is because the same-sex films offer clear-cut results, whereas watching heterosexual sex could be exciting to both homosexual and heterosexual men, but for different reasons.

Typically, men experience genital arousal and psychological sexual arousal when they watch films depicting their preferred sex, but not when they watch films depicting the other sex. Men’s specific pattern of sexual arousal is such a reliable fact that genital arousal can be used to assess men’s sexual preferences. Even gay men who deny their own homosexuality will become more sexually aroused by male sexual stimuli than by female stimuli.

“The fact that women’s sexual arousal patterns are not all predicted by their sexual orientations suggests that men’s and women’s minds and brains are very different,” Bailey said.

To rule out the possibility that the differences between men’s and women’s genital sexual arousal patterns might be due to the different ways that genital arousal is measured in men and women, the Northwestern researchers identified a subset of subjects: postoperative transsexuals who began life as men but had surgery to construct artificial vaginas.

In a sense, those transsexuals have the brains of men but the genitals of women. Their psychological and genital arousal patterns matched those of men -- those who like men were more aroused by male stimuli and those who like women were more aroused by the female stimuli -- even though their genital arousal was measured in the same way women’s was.

“This shows that the sex difference that we found is real and almost certainly due to a sex difference in the brain,” said Bailey.

You can download the full paper A Sex Difference in the Specificity of Sexual Arousal as a 494 kb PDF. From the full paper:

The sex difference reported here has important implications for future conceptualizations of women’s sexuality. Sexual arousal, especially genital sexual arousal, is likely to play a much smaller role in women’s sexual orientation development than it does in men’s. Female sexuality, in general, may be more motivated by extrinsic factors, such as the desire to create or maintain a romantic relationship, than intrinsic factors, such as genital sexual arousal (Baumeister, Catanese, & Vohs, 2001). This basic sex difference in the role of sexual arousal processes highlights the need to use distinct models when investigating the development and expression of female or male sexuality.

Bailey has information about his areas of research interest. Also, he has a book out that, by reports from people whose judgement I trust, is an excellent examination of the types of transsexuality: The Man Who Would Be Queen: The Science of Gender-Bending and Transsexualism.

You might be wonder what does all this have to do with the future? I think a great deal. Some day 2 or 3 or, at the very most, 4 decades from now it will become possible to do large scale germ line genetic engineering to give offspring different genetic endowments that change how their minds will develop. The extent to which various aspects of human behavior are found to have a firm biological basis is a strong indicator of how much changes in genetic endowments will be able to change mental qualities in human offspring.

In my opinion, this latest result is more evidence that differences in how genes are regulated during embryonic and early life development probably cause male and female brains to develop in such a way to cause them to have different sexual natures and likely causes different forms of male and female heterosexuality, bisexuality, homosexuality, and transsexuality.

Update: There is an on-going blogosphere discussion of various aspects of Bailey's research on sexuality. See Charles Murtaugh's post as a good starting point.

Also, the Chronicle of Higher Education has an article on Bailey and the reactions to his research on sexuality.

But his latest work has created a bigger buzz than most scholars hope to enjoy in their entire careers. Not only does he identify a set of interests and behaviors he says can be used to tell whether a man is gay, he ties homosexuality to transsexualism. The book is receiving praise and damnation in equal measures, and the controversy is quickly making the author one of the most talked-about sex and gender researchers in academe.

By Randall Parker    2003 June 20 03:57 PM   Entry Permalink | Comments (4)
2003 April 13 Sunday
Women Eat Less While Ovulating To Make Time For Sex

Daniel MT Fessler, an anthropologist at UCLA, argues that hormones decrease interest in food in human women and a large variety of other animal species during the period of ovulation.

During this ovulatory period, a California anthropologist now finds, women naturally and unwittingly eat some 5 to 25 percent less than at other times.

The purpose of the decrease in appetite is to cause femals to spend less time searching for and consuming food in order to free up more time for mating.

Women's bodies must be telling them to give less attention to food and more attention to sex during the time each month when they could become pregnant.

Fessler speculates that the mechanism of action is that higher blood estrogen potentiates the effect of the hormone cholecystokinin. Cholecystokinin is believed to play a role in inducing satiety and is released by the small intestine after meals.

You can read the abstract of the paper from The Quarterly Review of Biology.

Fessler is an advocate of evolutionary psychology as an approach for understanding human nature and behavior.

Evolutionary psychology grew out of sociobiology and, like its predecessor, is based on the assumption that human behavior has been importantly shaped by natural and sexual selection. However, evolutionary psychology differs from sociobiology in a number of fundamental ways. While sociobiology is content to treat the mind as a black box, evolutionary psychology asserts that because behavior is a product of mind, in order to shape behavior selective forces must have shaped the mind. Moreover, because selective forces are highly specific, the mind ought to consist of multiple independent systems, each a response to a particular selective force. Lastly, because foraging in small groups probably constituted the principal adaptation throughout most of hominid evolution, selection will have operated to maximize fitness within this social and physical context.

Human minds are thus seen as a package of proclivities and capacities, each of which served a specific function in our foraging past.

Fessler has additional information about his areas of research on his UCLA web site.

By Randall Parker    2003 April 13 05:59 PM   Entry Permalink | Comments (0)
2003 March 17 Monday
Male Sweat Brightens, Soothes Females

If your woman is unhappy you need to work up a sweat more often.

PHILADELPHIA -- Scientists at the University of Pennsylvania and the Monell Chemical Senses Center in Philadelphia have found that exposure to male perspiration has marked psychological and physiological effects on women: It can brighten women's moods, reducing tension and increasing relaxation, and also has a direct effect on the release of luteinizing hormone, which affects the length and timing of the menstrual cycle.

The results will be published in June in the journal Biology of Reproduction and currently appear on the journal's Web site.

"It has long been recognized that female pheromones can affect the menstrual cycles of other women," said George Preti, a member of the Monell Center and adjunct professor of dermatology in Penn's School of Medicine. "These findings are the first to document mood and neuroendocrine effects of male pheromones on females."

In a study led by Preti and colleague Charles J. Wysocki, extracts from the underarms of male volunteers were applied to the upper lip of 18 women ages 25 to 45. During the six hours of exposure to the compound, the women were asked to rate their mood using a fixed scale.

"Much to our surprise, the women reported feeling less tense and more relaxed during exposure to the male extract," said Wysocki, a member of the Monell Center and adjunct professor of animal biology in Penn's School of Veterinary Medicine. "This suggests that there may be much more going on in social settings like singles bars than meets the eye."

After the women's exposure to the underarm extract, further testing revealed a shift in blood levels of luteinizing hormone. Levels of this reproductive hormone, produced in pulses by the pituitary gland, typically surge right before ovulation but also experience hundreds of smaller peaks throughout the menstrual cycle.

Preti and Wysocki found that application of male underarm secretions hastened onset of these smaller pulses. Duration to the next pulse of luteinizing hormone was shortened by an average 20 percent, from 59 to 47 minutes.

Headed for a pick-up bar? How about a work-out or a trip to the sauna first?

The scientists who did this work are currently trying to identify what compound(s)s in sweat cause the reported responses. Cologne and after-shave makers will no doubt rush to incorporate any compound that is found to play a role in causing the reported effects.

By Randall Parker    2003 March 17 11:59 PM   Entry Permalink | Comments (0)
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