Ubiquity of same-sex couplings in nature.

A student has pointed out to me an interesting article in Science American Mind on unorthodox sex in the animal kingdom:

As many as 1,500 species of wild and captive animals have been observed engaging in homosexual activity. Speculations seeking an evolutionary rationale are that animals may engage in same-sex couplings to diffuse social tensions, to better protect their young or to maintain fecundity when opposite-sex partners are unavailable—or simply because it is fun. Bisexuality is a natural state among animals, perhaps Homo sapiens included, despite the sexual-orientation boundaries most people take for granted. In humans the categories of gay and straight are socially constructed.

...homosexuality among some species, including penguins, appears to be far more common in captivity than in the wild. Captivity, scientists say, may bring out gay behaviors in part because of a scarcity of opposite-sex mates. In addition, an enclosed environment boosts an animal’s stress levels, leading to a greater urge to relieve the stress. Some of the same influences may encourage what some researchers call “situational homosexuality” in humans in same-sex settings such as prisons or sports teams.

Driscoll's article continues to describe a number of studies of same-sex partners in wild and captive animals.

A population genetic analysis of male homosexuality

As a companion to the previous post, I pass along this article by Ciani et al. arguing that only a two-locus genetic model for male homosexuality with at least one locus on the X chromosome, in which gene expression is sexually antagonistic (increasing female fitness but decreasing male fitness), accounts for all the known empirical data. That data is interesting (as described in this account in Slate):

It starts with four curious patterns. First, male homosexuality occurs at a low but stable frequency in a wide range of societies. Second, the female relatives of gay men produce children at a higher rate than other women do. Third, among these female relatives, those related to the gay man's mother produce children at a higher rate than do those related to his father. Fourth, among the man's male relatives, homosexuality is more common in those related to his mother than in those related to his father.

More on gay and straight brains.

A recent study notes that in several measures of brain symmetry, straight men and gay women were similar, and gay men and straight women were similar. MindHacks points out a further interesting feature: that amygdala reactivity to simply breathing unscented air (thus having nothing obvious to do with sexual preference or activity per se) is different in gay and straight men and women. This is yet more evidence that sexual preference is not determined solely by individual developmental experience. Here is the complete abstract of the Savic and Per Lindström article, followed by the PET scan amygdala data, which speaks for itself, and finally a clip from the discussion. PDF of article here.

Cerebral responses to putative pheromones and objects of sexual attraction were recently found to differ between homo- and heterosexual subjects. Although this observation may merely mirror perceptional differences, it raises the intriguingquestion as to whether certain sexually dimorphic features in the brain may differ between individuals of the same sex but different sexual orientation. We addressed this issue by studying hemispheric asymmetry and functional connectivity, two parameters that in previous publications have shown specific sex differences. Ninety subjects [25 heterosexual men (HeM) and women (HeW), and 20 homosexual men (HoM) and women (HoW)] were investigated with magnetic resonance volumetry of cerebral and cerebellar hemispheres. Fifty of them also participated in PET measurements of cerebral blood flow, used for analyses of functional connections from the right and left amygdalae. HeM and HoW showed a rightward cerebral asymmetry, whereas volumes of the cerebral hemispheres were symmetrical in HoM and HeW. No cerebellar asymmetries were found. Homosexual subjects also showed sex-atypical amygdala connections. In HoM, as in HeW, the connections were more widespread from the left amygdala; in HoW and HeM, on the other hand, from the right amygdala. Furthermore, in HoM and HeW the connections were primarily displayed with the contralateral amygdala and the anterior cingulate, in HeM and HoW with the caudate, putamen, and the prefrontal cortex. The present study shows sex-atypical cerebral asymmetry and functional connections in homosexual subjects. The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.

From the discussion:

HeW and HoM displayed more pronounced between-amygdala connections and greater connections with the anterior cingulate, the subcallosum, and the hypothalamus. This connectivity pattern provides a strong substrate for processing of external stimuli that are relayed by the two amygdalae and represents a possible pathway for their functional interconnection in HeW and HoM. The remarkable similarity between HeW and HoM in the connectivity pattern deserves special attention. The amygdala has a key role in emotional reactions to external stimuli, including stress; the subcallosum and the anterior cingulate, on the other hand, are highly involved in mediation of mood and anxiety-related processes. Affective disorders are 2–3 times more common in women than men, and the tight functional connections between the amygdala and cingulate in women is currently discussed as a possible neurobiological substrate for their higher vulnerability, in addition to the effects of estrogen and testosterone. Interestingly, the incidence of depression and suicide attempts is elevated in homosexual subjects, and HoM in particular. Although the underlying mechanisms are likely to be multifactorial and include social pressure, the presently observed similarity with HeW vis-a`-vis the amygdala connectivity motivates further evaluations.

Sex differences in judging attractiveness - brain correlates

When selecting mates, men place greater importance on attractiveness than do women, whereas women favor status and resources more so than men. The reasons behind these differences can be rationalized from both evolutionary and sociocultural perspectives. Cloutier et al use fMRI to examine the possibility that attractive faces of the opposite sex simply have different reward value for men and women. They show that brain reward circuits (nucleus accumbens [NAcc], orbito-frontal cortex [OFC]) exhibit a linear increase in activation with increased judgments of attractiveness. Their analysis further reveals sex differences in the recruitment of OFC, which distinguished attractive and unattractive faces only for male participants. In short, brain regions involved in identifying the potential reward value of a stimulus are more active when men view attractive women than when women view attractive men.


Figure - Axial sections display the left NAcc (top) and right NAcc (middle) and a sagittal section displays mOFC (bottom) spherical regions of interest superimposed on normalized anatomic images. Graphs to the right of each image display signal change (parameter estimates) for attractive and unattractive faces across female and male participants relative to the baseline fixation. Error bars indicate standard error of the mean. Activity in the left and right NAcc was greater for attractive than unattractive faces irrespective or the participants' sex. Activity in the mOFC exhibited an interaction between facial attractiveness and participant sex displaying greater activity for attractive than unattractive faces only for male participants.

Another reason for being gay?

Ever alert for the latest speculation on a possible biological basis for why I might be gay, I come across this little gem on fruitflies: genetic manipulation that enhances dopamine levels in males makes them more likely to court with other males.

Your sexy voice and your hormones.

I'm passing this on to you, despite the fact that this gem went straight from the NY Times to the maw of the John Stuart Daily News/Colbert Report machine within one day... a women's voice becomes more seductive during ovulation, possibly because the larynx changes both its shape and size in response to reproductive hormones.

...The researchers recorded voice samples from about 50 undergraduate women at four times in their menstrual cycle. Then they asked 34 men and 32 women to listen to the recordings and rate them in terms of attractiveness...On the surface, the recordings were not terribly sexy. The women were asked to count from 1 to 10. But they must have been doing something different when they were closest to ovulating, because that was when they received the highest ratings, the researchers said.

So, I wonder if something similar happens in guys who are juiced when their testosterone levels increase?

In Most Species, Faithfulness Is a Fantasy

This post has the title of a great article by Natalie Angier in the NYTimes Science section. Elliot Spitzer was doing nothing that hasn't been done by males and females of thousands of other species - representatives of every taxonomic twig on the great tree of life.

Even the “oldest profession” that figured so prominently in Mr. Spitzer’s demise is old news. Nonhuman beings have been shown to pay for sex, too. Reporting in the journal Animal Behaviour, researchers from Adam Mickiewicz University and the University of South Bohemia described transactions among great grey shrikes, elegant raptorlike birds with silver capes, white bellies and black tails that, like 90 percent of bird species, form pair bonds to breed. A male shrike provisions his mate with so-called nuptial gifts: rodents, lizards, small birds or large insects that he impales on sticks. But when the male shrike hankers after extracurricular sex, he will offer a would-be mistress an even bigger kebab than the ones he gives to his wife — for the richer the offering, the researchers found, the greater the chance that the female will agree to a fly-by-night fling.

In another recent report from the lubricious annals of Animal Behaviour entitled “Payment for sex in a macaque mating market,” Michael D. Gumert of Hiram College described his two-year study of a group of longtailed macaques that live near the Rimba ecotourist lodge in the Tanjung Puting National Park of Indonesia. Dr. Gumert determined that male macaques pay for sex with that all-important, multipurpose primate currency, grooming. He saw that, whereas females groomed males and other females for social and political reasons — to affirm a friendship or make nice to a dominant — and mothers groomed their young to soothe and clean them, when an adult male spent time picking parasites from an adult female’s hide, he expected compensation in the form of copulation, or at the very least a close genital inspection. About 89 percent of the male-grooming-female episodes observed, Dr. Gumert said in an interview from Singapore, where he is on the faculty of Nanyang Technological University, “were directed toward sexually active females” with whom the males had a chance of mating.

Adolescent outbursts related to prefrontal and amygdala sizes

Whittle et al. have done fMRI experiments on adolescents that focused on three key brain regions which are known to represent critical nodes in neural networks supporting affective regulation: the amygdala, anterior cingulate cortex (ACC), and orbitofrontal cortex (OFC). Increased amygdala volume and a relative decrease of left versus right paralimbic ACC volumes were associated with increased duration of aggressive behaviors during parent-child interactions, with the latter association being apparent in males but not females. Decreased relative volume of left vs. right OFC was associated with greater reciprocity of dysphoric behaviors, the association also being specific to males. An absence of mean gender differences in affective behaviors suggests that the neural circuits underlying affective behaviors may differ for male and female adolescents during this age period. Here are some (slightly edited) comments by the authors:

The maturation of the prefrontal cortex and its inhibitory connections with the subcortex are key outcomes of the adolescent neurodevelopment that underlies the development of emotional and behavioral regulatory abilities. The associations of increased amygdala volume and decreased left frontal asymmetries with more negative affective behaviors may represent a delay in brain maturation. Longitudinal research would be needed to examine whether these findings have implications for the development of affective and behavioral dysregulation later in life.

The male specificity of this finding adds to a growing body of evidence that the neural mechanisms underlying affective processing differ between males and females. Males have been found to exhibit structural and functional brain asymmetries to a greater extent than females in a number of prefrontal areas, including the cingulate region. It has been suggested that these asymmetries may render males more vulnerable to certain disorders involving dysfunction of the frontal lobes such as ADHD, autism, and dyslexia. Although males in the present study did not display more aggressive behavior than females, the more pronounced relationship between ACCP asymmetry and aggressive affective behaviors in males suggests that aggressive affect in male adolescents may function as a mechanism by which their brain asymmetry is implicated in their risk for psychopathology.

Here is a useful figure that shows you the locations and variations in the anatomy of the cingulate structures being discussed:

Figure-Example of changes in the location and extent of the limbic (ACCL; highlighted in green) and paralimbic (ACCP; highlighted in blue) anterior cingulate cortices as a function of variations in the cingulate sulcus (CS; green arrow, Upper row) and paracingulate sulcus (PCS; blue arrow, Upper row). A PCS is absent in the left-hand case and present in the right-hand case. The Upper row presents parasagittal slices through an individual's T1-weighted image. The coronal section illustrates the distinction between absent (left-hand side) and present (right-hand side) cases. Notice that the ACCP is buried in the depths of the CS when the PCS is absent and extends over the paracingulate gyrus when the PCS is present. The same principle applies throughout consecutive coronal sections.

The Best Men Are (Not Always) Already Taken

Bressan1 and Stranieri take a (dubious) evolutionary psychological approach to the question of female preference for single versus attached males. The outcome is interesting. Here is their abstract:

Because men of higher genetic quality tend to be poorer partners and parents than men of lower genetic quality, women may profit from securing a stable investment from the latter, while obtaining good genes via extrapair mating with the former. Only if conception occurs, however, do the evolutionary benefits of such a strategy overcome its costs. Accordingly, we predicted that (a) partnered women should prefer attached men, because such men are more likely than single men to have pair-bonding qualities, and hence to be good replacement partners, and (b) this inclination should reverse when fertility rises, because attached men are less available for impromptu sex than single men. In this study, 208 women rated the attractiveness of men described as single or attached. As predicted, partnered women favored attached men at the low-fertility phases of the menstrual cycle, but preferred single men (if masculine, i.e., advertising good genetic quality) when conception risk was high.

The algorithms of love...

John Tierney writes an interesting article on internet match finding services in the Jan 29 New York Times.

Online matchmaking has become a boom industry as rival scientists test their algorithms for finding love...The leading yenta is eHarmony, which pioneered the don’t-try-this-yourself approach eight years ago by refusing to let its online customers browse for their own dates. It requires them to answer a 258-question personality test and then picks potential partners...Another company, Perfectmatch.com, is using an algorithm designed by Pepper Schwartz, a sociologist at the University of Washington at Seattle. Match.com, which became the largest online dating service by letting people find their own partners, set up a new matchmaking service, Chemistry.com, using an algorithm created by Helen E. Fisher, an anthropologist at Rutgers who has studied the neural chemistry of people in love.

As the matchmakers compete for customers — and denigrate each other’s methodology — the battle has intrigued academic researchers who study the mating game. On the one hand, they are skeptical, because the algorithms and the results have not been published for peer review. But they also realize that these online companies give scientists a remarkable opportunity to gather enormous amounts of data and test their theories in the field. EHarmony says more than 19 million people have filled out its questionnaire...In the battle of the matchmakers, Chemistry.com has been running commercials faulting eHarmony for refusing to match gay couples (eHarmony says it can’t because its algorithm is based on data from heterosexuals), and eHarmony asked the Better Business Bureau to stop Chemistry.com from claiming its algorithm had been scientifically validated. The bureau concurred that there was not enough evidence, and Chemistry.com agreed to stop advertising that Dr. Fisher’s method was based on “the latest science of attraction.”

Dr. Fisher now says the ruling against her last year made sense because her algorithm at that time was still a work in progress as she correlated sociological and psychological measures, as well as indicators linked to chemical systems in the brain. But now, she said, she has the evidence from Chemistry.com users to validate the method, and she plans to publish it along with the details of the algorithm...“I believe in transparency,” she said, taking a dig at eHarmony. “I want to share my data so that I will get peer review.”

On reading that Chemistry.com didn't discriminate against gay match making, I naturally decided to give it a spin and went through their series of questions (including one on the relative lengths of one's index and ringer finger). It included psychological profile questions and some interesting tests of susceptibility to visual illusions. Alas, the list of prospective mates for a 65 yr. old retired professor was rather lean, and I ended my experiment by withdrawing my chemistry.com profile after one day.

The fruits of promiscuity...more dancing and food

From the research highlights section of the Jan. 24 issue of Nature, summarizing work by Matilla et al:

A honeybee colony led by a promiscuous queen does better than one led by a faithful queen: the colony forages more, stores more food and grows faster. Heather Mattila and her colleagues at Cornell University in Ithaca, New York, think this happens because genetically diverse colonies dance more....Honeybees 'waggle dance' to tell each other where to fly to find food. Mattila's team compared colonies in which the queen always bred with the same male to colonies ruled by a queen that had been inseminated by 15 drones. On average, worker bees from the latter category performed 36% more dances daily, kept waggling for 62% longer and communicated about food discoveries farther from the nest than did workers from single-father colonies.

Why men are at the top.

Helena Cronin presents an interesting idea about why men walk off with most of the top positions and prizes that sidesteps the usual assumption of average differences between men and women in innate talents, tastes and temperaments. She notes that there not only more Nobels, but also more dumbbells among men, and suggests that it is a fourth "T" that most decisively shapes the distinctive structure of male — female differences. Some clips from her essay:

That T is Tails — the tails of these statistical distributions. Females are much of a muchness, clustering round the mean. But, among males, the variance — the difference between the most and the least, the best and the worst — can be vast. So males are almost bound to be over-represented both at the bottom and at the top...Consider the mathematics sections in the USA's National Academy of Sciences: 95% male. Which contributes most to this predominance — higher means or larger variance? One calculation yields the following answer. If the sex difference between the means was obliterated but the variance was left intact, male membership would drop modestly to 91%. But if the means were left intact but the difference in the variance was obliterated, male membership would plummet to 64%. The overwhelming male predominance stems largely from greater variance...Similarly, consider the most intellectually gifted of the USA population, an elite 1%. The difference between their bottom and top quartiles is so wide that it encompasses one-third of the entire ability range in the American population, from IQs above 137 to IQs beyond 200. And who's overwhelmingly in the top quartile? Males. Look, for instance, at the boy:girl ratios among adolescents for scores in mathematical-reasoning tests: scores of at least 500, 2:1; scores of at least 600, 4:1; scores of at least 700, 13.1.

The legacy of natural selection is twofold: mean differences in the 3 Ts and males generally being more variable; these two features hold for most sex differences in our species and, as Darwin noted, greater male variance is ubiquitous across the entire animal kingdom...The upshot? When we're dealing with evolved sex differences, we should expect that the further out we go along the right curve, the more we will find men predominating. So there we are: whether or not there are more male dumbbells, there will certainly be — both figuratively and actually — more male Nobels.

Unfortunately, however, this is not the prevailing perspective in current debates, particularly where policy is concerned. On the contrary, discussions standardly zoom in on the means and blithely ignore the tails. So sex differences are judged to be small. And thus it seems that there's a gaping discrepancy: if women are as good on average as men, why are men overwhelmingly at the top? The answer must be systematic unfairness — bias and barriers. Therefore, so the argument runs, it is to bias and barriers that policy should be directed. And so the results of straightforward facts of statistical distribution get treated as political problems

Planned Obsolescence? The Four-Year Itch

Helen Fisher, author of "Why We Love" and an anthropology professor at Rutgers, has written a brief essay with the title of this post. She did a cross cultural survey of when divorces occur and found that divorces regularly peaked during and around the fourth year after wedding (no evidence for the commonly assumed seven year itch indicated in the graphic). Divorces peaked among couples in their late twenties. And the more children a couple had, the less likely they were to divorce: some 39% of worldwide divorces occurred among couples with no dependent children; 26% occurred among those with one child; 19% occurred among couples with two children; and 7% of divorces occurred among couples with three young. In trying to figure out so many men and women divorce during and around the 4-year mark; at the height of their reproductive years; and often with a single child, she had an "a ha" moment:

Women in hunting and gathering societies breastfeed around the clock, eat a low-fat diet and get a lot of exercise — habits that tend to inhibit ovulation. As a result, they regularly space their children about four years apart. Thus, the modern duration of many marriages—about four years—conforms to the traditional period of human birth spacing, four years.

Perhaps human parental bonds originally evolved to last only long enough to raise a single child through infancy, about four years, unless a second infant was conceived. By age five, a youngster could be reared by mother and a host of relatives. Equally important, both parents could choose a new partner and bear more varied young.

Her theory fits with data on other species:

Only about three percent of mammals form a pairbond to rear their young. Take foxes. The vixen's milk is low in fat and protein; she must feed her kits constantly; and she will starve unless the dog fox brings her food. So foxes pair in February and rear their young together. But when the kits leave the den in mid summer, the pairbond breaks up. Among foxes, the partnership lasts only through the breeding season. This pattern is common in birds. Among the more than 8,000 avian species, some 90% form a pairbond to rear their young. But most do not pair for life. A male and female robin, for example, form a bond in the early spring and rear one or more broods together. But when the last of the fledgling fly away, the pairbond breaks up... Like pair-bonding in many other creatures, humans have probably inherited a tendency to love and love again—to create more genetic variety in our young.

Drunken flies get hypersexual - and gay

Sound familiar? Reminds me of similar behaviors after University of Wisconsin football games, when drunken guys who could not find an appropriate female object would go ahead with what was available - other guys. This news item by Heidi Ledford in Nature describes experiments by Lee et al. that:

...tested the effects of chronic alcohol exposure on sexual behaviour in the fruitfly Drosophila melanogaster. The researchers noted that male flies repeatedly exposed to ethanol vapour became less discriminate in their mate selection. The buzzed flies often courted fellow males, pursuing them around the cage while serenading with a traditional fruitfly courtship song played on vibrating wings.


[Figure: Love Chain, male fruit flies chase each other in a circle] Eventually, the lusty flies devolve into a courting frenzy. “You get a chain of males chasing each other,” says Heberlein, who was not associated with the study but has observed similar behaviour in her own unpublished work. In contrast, alcohol had little effect on mating in female fruitflies, which normally do not court their mates.

The findings suggest that the flies do not fundamentally change their sexual orientation, but rather get over-sexed. “Multiple alcohol exposures makes them essentially hypersexual,” says Heberlein. The mind-dulling effects of alcohol might also make it more of a challenge for male fruitflies to distinguish the gender of other flies in the crowd.

Because of the genetic tools available, fruitflies might be a good model system for probing the idea, suggested for humans, that the neurotransmitter dopamine is a link between sex and alcohol.

Love hangover - the sex peptide

A male, after copulation, has a particular interest in seeing that the female involved ceases further sexual activity that might dilute his genetic contribution. It turns out that male fruitflies don't have to stand by and guard their transferred genetic material — a sex peptide in their semen will do the job. This peptide leads to increased egg-laying by the mated female and behavioural changes that reduce the likelihood of her re-mating. Yapici et al. have now identified the receptor protein for this peptide. It functions in a subset of neurons implicated in other sex-related behaviors. The receptor is highly conserved across insect species, raising the possibility that it could be targeted to disrupt reproduction in insect pests or host-seeking behaviour in disease vectors. (There appears to be no evidence for such a mechanism in primates and humans!).

Vegansexuality

Jeff Stryker gives us more from the fringe (Dec. 9 NY Times Magazine):

Forget homo-, bi- or even metro-: the latest prefix in sexuality is vegan-, as in “vegansexual.” In a study released in May, Annie Potts, a researcher at the University of Canterbury and a director of the New Zealand Centre for Human-Animal Studies, surveyed 157 vegans and vegetarians (120 of them women) on the topic of cruelty-free living. The questions ranged from attitudes about eating meat to keeping pets to wearing possum fur to, yes, “cruelty-free sex” — that is, “rejecting meat eaters as intimate partners.”

Some of the survey respondents volunteered their reluctance to kiss meat eaters. “I couldn’t think of kissing lips that allow dead animal pieces to pass between them,” a 49-year-old vegan woman from Auckland said. For some, the resistance is the squeamishness factor. “Nonvegetarian bodies smell different to me,” a 41-year-old Christchurch vegan woman said. “They are, after all, literally sustained through carcasses — the murdered flesh of others.” For some, it is a question of finding a like-minded life partner. An Auckland ovo-vegetarian had tried a relationship with a carnivore, but reported that despite the sexual attraction, the gulf in “shared values and moral codes” was just too wide.

Potts, who coined the term vegansexuality, says the “negative response of omnivores” to her study has surprised her. Even some fellow animal lovers question the wisdom of vegansexuality. A blog for People for the Ethical Treatment of Animals noted that sleeping with only fellow vegans means forgoing the opportunity to turn carnivores into vegans by the most powerful recruiting tool available — sex.

PETA’s founder and president, Ingrid Newkirk, agrees that vegans smell fresher. (“There’s science to prove it,” she says.) But Newkirk is all about the recruiting, even if it means one convert at a time. “When my staff members come to me and say: ‘Guess what? My boyfriend, now he’s a vegan,’ I say, half-jokingly: ‘Well, it is time to ditch him and get another. You’ve done your work; move on.’ ”

The male chill-out after sex: role for brain oxytocin

Here is an intriguing account from Waldherr and Neumann:

Sexual activity and mating are accompanied by a high level of arousal, whereas anecdotal and experimental evidence demonstrate that sedation and calmness are common phenomena in the postcoital period in humans. These remarkable behavioral consequences of sexual activity contribute to a general feeling of well being, but underlying neurobiological mechanisms are largely unknown. Here, we demonstrate that sexual activity and mating with a receptive female reduce the level of anxiety and increase risk-taking behavior in male rats for several hours. The neuropeptide oxytocin has been shown to exert multiple functions in male and female reproduction, and to play a key role in the regulation of emotionality after its peripheral and central release, respectively. In the present study, we reveal that oxytocin is released within the brain, specifically within the hypothalamic paraventricular nucleus, of male rats during mating with a receptive female. Furthermore, blockade of the activated brain oxytocin system by central administration of an oxytocin receptor antagonist immediately after mating prevents the anxiolytic effect of mating, while having no effect in nonmated males. These findings provide direct evidence for an essential role of an activated brain oxytocin system mediating the anxiolytic effect of mating in males.

Playing Action Video Games Reduces Gender Differences in Spatial Cognition

From Feng, Spence, and Pratt (PDF here):

We demonstrate a previously unknown gender difference in the distribution of spatial attention, a basic capacity that supports higher-level spatial cognition. More remarkably, we found that playing an action video game can virtually eliminate this gender difference in spatial attention and simultaneously decrease the gender disparity in mental rotation ability, a higher-level process in spatial cognition. After only 10 hr of training with an action video game, subjects realized substantial gains in both spatial attention and mental rotation, with women benefiting more than men. Control subjects who played a non-action game showed no improvement. Given that superior spatial skills are important in the mathematical and engineering sciences, these findings have practical implications for attracting men and women to these fields.

From their article:

The experimental group was trained using Medal of Honor: Pacific Assault, which was chosen because it is similar to the games typically played by players in Experiment 1 [note: which compared students based on their self reports of game use] and because it has been used before in attention training studies. This game is a 3-D first-person shooter game that requires intense visual monitoring and attentional resources. The control group played Ballance, a 3-D puzzle game that involves steering a ball through a hovering maze of paths and rails with obstacles such as seesaws, suspension bridges, and pendulums.

Different cognitive processes underlying human mate choices and mate preferences

Starting with the assumption that the underlying function of mate choice is reproductive success, evolutionary psychologists have proposed that men should seek young, fertile, faithful women, and women should seek high-status, resourceful, committed men. This evolutionary reasoning predicts what traits people will actually tend to choose, but not necessarily what people say they will (or would like to) choose. Todd et al. suggest that different cognitive processes underlie mate preferences and actual human mate choices. Here is their abstract:

Based on undergraduates' self-reports of mate preferences for various traits and self-perceptions of their own levels on those traits, Buston and Emlen [Buston PM, Emlen ST (2003) Proc Natl Acad Sci USA 100:8805–8810] concluded that modern human mate choices do not reflect predictions of tradeoffs from evolutionary theory but instead follow a "likes-attract" pattern, where people choose mates who match their self-perceptions. However, reported preferences need not correspond to actual mate choices, which are more relevant from an evolutionary perspective. In a study of 46 adults participating in a speed-dating event, we were largely able to replicate Buston and Emlen's self-report results in a pre-event questionnaire, but we found that the stated preferences did not predict actual choices made during the speed-dates. Instead, men chose women based on their physical attractiveness, whereas women, who were generally much more discriminating than men, chose men whose overall desirability as a mate matched the women's self-perceived physical attractiveness. Unlike the cognitive processes that Buston and Emlen inferred from self-reports, this pattern of results from actual mate choices is very much in line with the evolutionary predictions of parental investment theory.

The smell of an alpha male....

Pheromones influence sexual behavior and reproduction in rodents. Mak et al report that:

...the pheromones of dominant (but not subordinate) males stimulate neuronal production in both the olfactory bulb and hippocampus of female mice, which are independently mediated by prolactin and luteinizing hormone, respectively. Neurogenesis induced by dominant-male pheromones correlates with a female preference for dominant males over subordinate males, whereas blocking neurogenesis with the mitotic inhibitor cytosine arabinoside eliminated this preference. These results suggest that male pheromones are involved in regulating neurogenesis in both the olfactory bulb and hippocampus, which may be important for female reproductive success.

I keep wondering if we won't be finding evidence for a version of this effect (perhaps more subtle) in humans... would the cheerleader, like the female rat in the box below, be more likely to hang out with the star quarterback if she had smelled his sweaty jersey a day earlier??

An illustration from the summary review by DiRocco and Xia:

Figure legend: Dominant male pheromones stimulate neurogenesis in females.
(a) Female mice exposed to dominant male pheromones spent more time sniffing the dominant male, whereas females exposed to subordinate male pheromones did not show any preference. (b) Exposing female mice to pheromones from dominant males led to increased neurogenesis in the subventricular zone (SVZ) and dentate gyrus (DG). Pheromones signal the main olfactory epithelium (MOE)–main olfactory bulb (MOB) axis, which relays the signal to the hypothalamus (HYP)–pituitary (PIT) axis, leading to the release of luteinizing hormone (LH) and prolactin (PRL). LH appeared to stimulate neurogenesis in the dentate gyrus of the hippocampus, whereas prolactin induced neurogenesis in the SVZ and MOB. It is hypothesized that pheromone-induced neurogenesis may underlie female mating preference for the dominant male. NC, nasal cavity; RMS, rostral migratory stream; green circles, newborn neurons.