Progress Daily

Viewing curvaceous women has an effect on straight men’s brains similar to that of alcohol and other drugs.

Steven Platek’s researchers asked 14 men (average age of 25) to rate women’s attractiveness before and after plastic surgery that moved fat from their waist to buttocks, changing their waist-to-hip-ratio (WHR).

FMRI showed activation in the subjects’ brain reward centers in response to naked female bodies when surgically altered to express an optimal (~0.7) WHR with redistributed body fat, but relatively little activation when body mass index (BMI) was altered.

“Optimal Waist-to-Hip Ratios in Women Activate Neural Reward Centers in Men”

“Watching curvaceous women feels like drugs to men: study, goodnews

Sexual selected traits come in two main forms: weapons, which are used to fight off competitors; and ornaments, which are used to advertise genetic fitness to the opposite sex.

According to David Puts, human masculine traits — big muscles, facial hair, square jaws, deep voices and a propensity to violence — evolved for their usefulness in fighting with or indimidating other men (”Beauty and the beast: mechanisms of sexual selection in humans“).

In species whose males do not fight for access to females, males are generally the same size as, or smaller than, females. Human males have 40% more fat-free mass than women, which to the difference in gorillas, a species in which males unquestionably compete with other males for exclusive sexual access to females.

“To get the girl,” The Economist

In the past year, nearly 4,800 women participated in an experiment at Faceresearch.org. They were young women, mostly in their early- to mid-twenties, and all identified their ethnicity as white.

The female subjects were presented with two male faces & asked to choose the face they considered more attractive and indicate how much they preferred it to the other one.

The faces were actually two copies of the same photo, each manipulated by software that masculinizes or feminizes a person’s features.

In countries where poor health is particularly a threat to survival, women leaned toward “manlier” men — those with shorter, broader faces and stronger eyebrows, cheekbones and jaw lines.

Women with the weakest masculinity preferences tended to live in some of the healthiest countries: Sweden, Finland, Denmark and Austria and (number one) Belgium. Other countries in the study with low masculinity preferences are Romania, Greece and New Zealand.

Women with the strongest masculinity preferences tended to hail from the countries with higher disease and mortality rates and some of the poorest scores on the health-care index: Mexico, Brazil, Bulgaria and Argentina. (The researcher included only white subjects; Asian and African nations were not included.)

The US had the 5th highest masculinity preference out of the 30 countries, and was 20th in healthiness.

“Why Women Don’t Want Macho Men,” by Jena Pincott

Girls who grow up without their fathers at home reach sexual maturity earlier than girls whose fathers live with them (and early-bloomers are more likely to suffer depression, hate their bodies, engage in risky sex and get pregnant in their teen years).

Research by Jane Mendle (”Associations Between Father Absence and Age of First Sexual Intercourse“) suggests heredity is the cause: the genes that make a dad more likely to leave his family also cause early sexual development.

The researchers analyzed data American National Longitudinal Survey of Youth data on 1,400 boys and girls, each of whom was related to at least one other subject through their mother. Most of the mothers were pairs of sisters, but some were identical twins or first cousins raised as sisters.

The more closely related the cousins were — by having mothers who were identical twins, for instance, versus cousins — the closer their age at first sexual experience, regardless of whether or not a father lived in the home.

“Daddy’s girl,” The Economist

In a study just published in Evolution and Human Behavior (”Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity“), Steven Gaulin analyzes muscularity.

The data came from the NHNES, which followed 12,000 American men and women over the course of 6 years. The researchers found that men require 50% more calories than women do, even after adjusting for activity levels, and that their muscle mass is the strongest predictor of their intake of calories — stronger than their occupation or their body-mass index. Men’s immune systems are less effective than those of women (which was known before), and become worse the more muscular the men are (which was not).

The more muscular a man, the more sexual partners he reported, both in the past year and over his lifetime, and the earlier his first sexual experience was likely to have been.

Gaulin speculates that an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.

“Mr Muscle,” The Economist

According to research by Hasse Walum (”Genetic variation in the vasopressin receptor 1a gene associates with pair-bonding behavior in humans“), men with a particular variant of a gene that influences brain activity (specifically, an allele that regulates the activity of the hormone vasopressin) are less likely to be devoted and loyal husbands.

About 40% of men have one or two copies of the allele. Men with two copies of the allele had a greater risk of marital discord than men with one copy, and men with one copy of the allele were at more risk of such discord than men with no copies.

In a sample of more than 1,000 heterosexual couples, about 15% of the men without the allele reported serious marital discord in the past year, compared with 34% of men with two copies of the allele.

17% of the men without the allele were living with women without being married to them, compared with 32% of men with two alleles.

“Study Links Gene Variant in Men to Marital Discord” by Shankar Vedantam

Wen Zhou & Denise Chen speculated that if humans produce and respond to sweat pheromones, then a woman should respond to a guy’s sweat when sexually aroused differently than she does to his normal sweat.

The researchers asked 20 heterosexual guys to put pads in their armpits as they watched pornographic videos and became aroused (verified by electrodes). Later, they collected the sweat they produced when they weren’t aroused. (See “Encoding Human Sexual Chemosensory Cues in the Orbitofrontal and Fusiform Cortices“)

The researchers then recruited 19 women to smell the men’s pads while undergoing (fMRI) brain scans. The sexual sweat, but not the normal sweat, activated the right orbitofrontal cortex and the right fusiform cortex, brain areas that help us recognize emotions and perceive things, respectively. Both regions are in the right hemisphere, which is generally involved in smell, social response, and emotion.

“Women Can Smell a Man’s Intentions,” Melinda Wenner

 Genes that make some people gay may make their siblings fecund.

Homosexuality is at least partly genetic. Studies of identical twins, for example, show that if one of a pair (regardless of sex) is homosexual, the other has a 50% chance of being so, too. How could a trait so at odds with reproductive success survive natural selection?

Brendan Zietsch, of the QIMR, thinks that genes which cause men to be more feminine in appearance, outlook and behavior and those that make women more masculine in those attributes, confer reproductive advantages as long as they do not push the individual possessing them all the way to homosexuality.

Gay men tend to rank higher than straight men in standardised tests for agreeableness, expressiveness, conscientiousness, openness to experience and neuroticism. Lesbians tend to be more assertive and less neurotic than straight women.

Though women prefer traditionally macho men at the time in their menstrual cycles when they are most fertile, at other times they are more attracted to those with feminine traits such as tenderness, considerateness and kindness, as well as those with feminised faces. This suggests that women prefer macho men for breeding but the more feminised phenotype for carers and providers (husbands). And husbands father most of the world’s children.

Zietsch’s researchers asked 4,900 individual twins, not all of them identical, to fill out anonymous questionnaires about their sexual orientation, their gender self-identification and the number of opposite-sex partners they had had during the course of their lives.

They found that the more feminine a man, the more masculine a woman, the higher the hit rate with the opposite sex — though women of all gender identities reported fewer partners than men did (which may reflect male boasting &/or female bashfulness).

Heterosexuals with a homosexual twin tend to have more sexual partners than heterosexuals with a heterosexual twin. The researchers then analyzed the relationships between twins (all genes in common for identical twins; a 50% overlap for the non-identical) and calculated that genes explain 27% of an individual’s gender identity and 59% of the variation in the number of sexual partners. (They also calculated that the genetic component of sexual orientation was 47% — similar to previous studies

“Gender bending,” The Economist

As human societies grow richer, people have fewer children. In most species, such an increase in available resources leads in the opposite reproductive direction. What makes the “demographic transition” even more paradoxical is that in less developed times and places, the rich do not have smaller families than the poor.

Most explanations of the demographic transition are social, and none is really satisfactory.

A study by Agnar Helgason, of deCODE Genetics, has recently provided a new explanation: that the mixing-up of people caused by the urbanisation which normally accompanies development is, itself, partly responsible — because it breaks up optimal mating patterns.

Iceland’s records since its founding by a few Vikings are so good that the antecedents of today’s inhabitants (apart from a handful of recent immigrants) are known with precision. Its medical records are also good, and most Icelanders have given genetic samples to deCode.

The study’s principal finding is that the most fecund marriages are between distant cousins. The optimum degree of outbreeding (measured in terms of the number of children and grandchildren produced) lay somewhere between cousins of the third and fourth degrees.

(”Kissing cousins, missing children,” The Economist)

Icelandic women born between 1800 and 1824 who mated with a third cousin had significantly more children and grandchildren (4.0 and 9.2, respectively) than women who hooked up with someone no closer than an eighth cousin (3.3 and 7.3). Those proportions held up among women born more than a century later when couples were, on average, having fewer children.

Despite the general pattern for reproductive success favoring close kinship, couples that were second cousins or more closely related did not have as many children.

With close inbreeding — between first cousins — there is a significant increase in the probability that both partners will share one or more detrimental recessive genes, leading to a 25 percent chance that these genes will be expressed in each pregnancy.

Mating with a relative might reduce a woman’s chance of having a miscarriage caused by immunological incompatibility between a mother and her child. Some individuals have an antigen (a protein that can launch an immune response) on the surface of their red blood cells called a rhesus factor. In some cases — typically during a second pregnancy — when a woman gets pregnant, she and her fetus may have incompatible blood cells, which could trigger the mother’s immune system to treat the fetus as a foreign intruder, causing a miscarriage. This occurrence is less probable if the parents are closely related, because their blood makeup is more likely to match.

It may be that the enhanced reproductive success at the level of third and fourth cousins (who on average would be expected to have inherited 0.8 percent to 0.2 percent of their genes from a common ancestor) represents a point of balance between the competing advantages and disadvantages of inbreeding and outbreeding.

(”When Incest Is Best,” by Nikhil Swaminathan)

Dr Randy Thornhill manipulated pictures to make people’s faces appear more and less symmetrical, then asked volunteers of the opposite sex rank them for attractiveness. Symetery and attractiveness correlated. His later experiments have shown that all aspects of bodily symmetry contribute, down to the lengths of corresponding fingers, and that the assessment also applies to those of the same sex.

Perfect symmetry is hard for a developing embryo to maintain, so one that can maintain it must have good genes (and luck).

Other aspects of beauty, too, are indicators of health. Skin and hair condition are sensitive to illness and malnutrition.

Leslie Zebrowitz and Gillian Rhodes found 9 past studies on attractiveness and IQ, and subjected them to a “meta-analysis.”

The studies’ researchers had photographed people and asked them to do IQ tests, then showed the photographs to other people and asked them to rank the intelligence of the first lot. The results suggested that people get such judgments right often enough to be significant.

Dr Daniel Hamermesh presided over a series of surveys in the USA and Canada that showed that when all other things are taken into account, ugly people earn less than average incomes, while beautiful people earn more than the average. The ugliness “penalty” for men was -9% while the beauty premium was +5%. For women, the ugliness penalty was -6% while the beauty premium was +4%.

He found the figures for men in Shanghai are –25% and +3%; for women they are –31% and +10%. In Britain, ugly men do worse than ugly women (-18% as against -11%) but the beauty premium is the same for both (+1%).

Dr Hamermesh found that those members of a particular (anonymous) US law school rated attractive on the basis of their graduation photographs went on to earn higher salaries. Moreover, lawyers in private practice tended to be better looking than those working in government departments.

Hamermesh’s study of Dutch advertising firms showed that those with the most beautiful executives had the largest size-adjusted revenues — a difference that exceeded the salary differentials of the firms in question. Finally, he found that attractive candidates were more successful in elections for office in the American Economic Association.

Working in Shanghai, where his research indicated the difference between the ugliness penalty and the beauty bonus was greatest, Dr Hamermesh looked at how women’s spending on their cosmetics and clothes affected their income.

The beauty premium generated by such primping was worth only about 15% of the money expended.

Niclas Berggren’s research team looked at almost 2,000 candidates in Finnish elections. They asked foreigners (mainly Americans and Swedes) to examine the candidates’ campaign photographs and rank them for beauty. The more beautiful candidates, as ranked by people who knew nothing of Finland’s internal politics, tended to have been the more successful — the effect was larger for women than for men.

“To those that have, shall be given,” The Economist