Progress Daily

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

According to new research by Bruce T. Lahn and Sarah Tishkoff, microcephalin and ASPM, two genes involved in determining the size of the human brain, have undergone substantial evolution in the last 60,000 years.

The researchers studied the worldwide distribution of the two genes’ alleles by decoding the DNA of the microcephalin and ASPM in many different populations.

With microcephalin, a new allele arose about 37,000 years ago, although it could have appeared as early as 60,000 or as late as 14,000 years ago. About 70% of people in most European and East Asian populations carry this allele of the gene, but it is much rarer in most sub-Saharan Africans.

With ASPM, a new allele emerged about 5,800 years ago (14,000 to 500 years ago). The allele has attained a frequency of about 50% in populations of the Middle East and Europe, is less common in East Asia, and is found at low frequency in some sub-Saharan Africa peoples.

The ASPM allele emerged about the same time as the spread of agriculture in the Middle East 10,000 years ago and the emergence of the civilizations of the Middle East some 5,000 years ago.

Dr Tishkoff said the statistical signature of selection on the two genes was “one of the strongest that I’ve seen.”

“Brain May Still Be Evolving, Studies Hint,” by Nicholas Wade

Place a rat in a cage with an electrified floor and subject it to repeated shocks; it will show many signs of stress, at first flinging itself against the walls with each shock. But after a while, it just sits there apathetically, showing no inclination to escape from its painful prison. When autopsied, it will be found to have oversized adrenal glands and, frequently, stomach ulcers, both indicating serious stress.

Now repeat the experiment, but with a wooden stick in the cage alongside the rat. When shocked, the rat chews on the stick, and as a result, it can endure its experience much longer without burnout. At autopsy, its adrenal glands are smaller, stomach ulcers fewer.

Put 2 rats in the electrified cage. Shock them both. They snarl and fight. At autopsy, their adrenal glands are normal, and, even though they have experienced numerous shocks, they have no ulcers.

Recently physiologists have uncovered the hormonal basis for such behavior. Animals and people subjected to attack or threat experience “subordination stress,” as a result of which their adrenal hormones go up, along with blood pressure and the probability of developing ulcers. But when given the opportunity to “take it out” on someone else, victims show no sign of stress.

“The Targets of Aggression,” by David P. Barash

If the decision to vote is based in part on genetics, James H. Fowler reasoned, identical twins should behave more alike than fraternal twins, because identical twins share all of their DNA, whereas fraternal twins share only half on average.

The researchers matched data from the Southern California Twin Registry with publicly accessible electronic voter registration and turnout records from Los Angeles County. Their analysis of voting histories for 326 identical and 196 fraternal twins suggests that genetics was responsible for 60% of differences in voting turnout between twin types.

Fowler also investigated a larger, more nationally representative database from the National Longitudinal Study of Adolescent Health, or Add Health. This study not only asked if participants voted but also inquired about participation in other political activities, such as whether they contributed to campaigns or attended political rallies or marches. The researchers’ data on 442 identical and 364 fraternal Add Health twins indicate that genetics underlies 72% of differences in voting turnout and roughly 60% of differences in other political activity. Preliminary results from the Twins Days festival in Twinsburg, Ohio, also support the findings.

Fowler hypothesizes that the drive to vote or participate in politics may be linked with genes underlying more ancient behaviors, such as innate dispositions toward cooperation.

Robert Plomin analyzed Fowler’s data, and concluded that genetics was responsible for 40%, not 60%, of differences in voting turnout between twin types. 40% is also the average estimate of heritability seen in twin studies of personality.

Evan Balaban cautions that about two thirds of identical twins share the same bloodstream while fetuses, so greater similarities between twins could be attributable not only to sharing genes but to sharing more similar levels of hormones and other compounds each fetus produces during development.

“The Genetics of Politics,” Scientific American

Studies have shown that the IQs of breastfed children are, on average, about 6 points higher than those given baby formulas.

Terrie Moffitt and Avshalom Caspi suspected the involvement of a gene called FADS2, which regulates the metabolism of long-chain polyunsaturated fatty acids — which are important for the growth of nerve cells and are abundant in human milk. FADS2 comes in two varieties, known as C and G, and the researchers wondered if these two varieties interacted differently with breast milk.

To find out (see “Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism“), they drew on data from two groups of people, one in New Zealand (born in 1972 and 1973) and one in Britain (born in 1994 and 1995).

The researchers found that the increase in intelligence associated with breastfeeding only happened to people who had inherited at least one copy of the C version of FADS2. (Most genes are present as two copies, one inherited from the mother and one from the father.) The effect did not depend on parental social class or IQ, nor on birthweight (low birthweight has been linked to lower IQ). And the difference in IQ was preserved into adulthood.

Only about 10% of the population is double-G.

“The nature of nurture,” The Economist

From the Stone Age to 1800, there was no gain in average living conditions. Now incomes rise steadily.

The average Briton in 1788 ate only as many calories a day as hunter-gatherers (2,300). And the British diet was more monotonous. Life expectancy was only slightly above that of hunter-gatherers (38 years). Height is a good guide to nutrition and health: men in England averaged 5ft 6in, the same as males in the Stone Age. Men then worked 60 hours a week. Compared to hunter-gatherers’ 35 hours.

Englishmen who were economically successful, from the Middle Ages to 1800, left 4 or 5 surviving children at their deaths. In contrast, landless labourers left fewer than 2 children.

Preindustrial England was thus a world of constant downward mobility. Given the static nature of the preindustrial economy, the superabundant children of the rich had to, on average, move down the social hierarchy to find work. Attributes that ensured later economic dynamism – hard work, ingenuity, innovativeness, education – were thus spread throughout the population.

From 1200 to 1800 interest rates fell, murder rates declined, work hours increased, the taste for violence declined, and numeracy and literacy spread to even the lower reaches of society.

In both preindustrial Japan and China the rich had more children than the poor, but in a more modest way. The samurai in Japan in the Tokugawa era (1603-1868), for example, produced on average little more than one son per father.

In modern affluent societies, the higher income a person has, on average, the less leisure he has. The source of our compulsion to work may lie in our ancestors’ passage through a preindustrial world that rewarded a compulsion to work and accumulate with reproductive success.

“England’s success may be in our genes,” Gregory Clark

In the ultimatum game, 2 players, a proposer and a responder, divide a reward. The responder can either accept the proposer’s division or reject it. If he rejects it, both players receive nothing.

Scores of studies have run the ultimatum game across cultures and ages. Universally, people reject any share lower than 20% — apparently to punish the greed of the proposer.

A study by Björn Wallace, et al (”Heritability of ultimatum game responder behavior“), suggests that the sense of fairness is rooted in genetics.

Wallace played the ultimatum game with twins. He neutralized the effect of upbringing and exposed that of genetics by comparing identical twins (who share all their genes) with fraternal twins (who share half).

Each twin of a pair played the ultimatum game, both as proposer and as responder. In the case of identical twins, there was a striking correlation between the average division that each member of a pair proposed and also between what they were willing to accept. In other words, their senses of what was fair were similar. No such correlations were seen in the behaviour of fraternal twins.

“Patience, fairness and the human condition,” The Economist

An experiment by Joshua New tested a theory developed by Leda Cosmides and John Tooby (”C&T”), with whom he collaborated on the experiment. C&T suggested that some tasks are so important and so universal that you would expect to find specially evolved “modules” to handle them.

(They found evidence to support the existence of such modules in areas of human relations such as the perception of fairness.)

Dr New showed volunteers pairs of photographs. The photos in each pair were identical except that one object had changed its orientation or had been removed altogether, and the volunteers had to work out what had changed.

Changes concerning animals were significantly easier to detect than those concerning cars. 100% of volunteers noticed the movement of an elephant in the African bush. Only 72% noticed the movement of a minivan in a similar piece of bush. And that was despite the fact that the image of the van was somewhat larger in the photograph than the image of the elephant, and that the minivan was red, not grey.

This highly honed ability to notice animal activity (it also applies to small familiar animals, such as pigeons) argues that an animal-monitoring module is innate in the brain.

“More news from the savannah,” The Economist

Babies are born with distinctive characteristics that make certain developmental outcomes more likely. Parental behavior is, in part, a reaction to the child’s behavior (See “Parent, child, and reciprocal influences,” and “How people make their own environments“) and physical appearance (”Infant attractiveness predicts maternal behaviors and attitudes“). Every published report of a correlation between parental behavior and child outcome now contains a disclaimer admitting that the direction of effects is uncertain and that the correlation could be due in part to a child-to-parent effect (The Nurture Assumption, p. 27), a type of evocative gene–environment correlation.

Children share 50% of their genes with each of their biological parents, which means that for genetic reasons alone, children born with a predisposition to be timid (Galen’s Prophecy) are more likely to be raised by timid parents, and children born with a predisposition to be aggressive are more likely to be reared by aggressive parents.

Genetic influences can produce change as well as stability. An individual may have blond hair at age 5, brown hair at age 25, and no hair at age 75, and these changes are ordained by the genes. As we get older we become more like our parents because our parents, too, went through these changes. Longitudinal studies using genetically informative designs (”Genetic change and continuity from fourteen to twenty months“) have shown that genetic influences that affect behavior or adjustment at one age are not necessarily the same genetic influences that affect these variables at another age. There are genes that kick in early and genes that bide their time.

The outcome of many years of research on parent-training interventions by Rex Forehand: Parents found the training to be effective in improving their children’s behavior at home but not at school. Similar conclusions have been reached in regard to programs designed to improve the school adjustment and academic performance of children living in poverty: There is little evidence that parenting programs produce the hoped-for linkage between changed parent behaviors and improved child outcomes (”Does research support claims about the benefits of involving parents in early intervention programs?“).

Behavioral genetic studies estimate genetic and environmental influences on developmental outcomes by measuring pairs of siblings. The results of these studies are monotonously consistent, regardless of the outcome measure used and the kinds of sibling pairs who participate — twins or ordinary siblings, reared together or apart, biologically related or not. Genetic effects generally account for 35% to 65% of the variance among the participants, the effects of being reared in the same home account for 0 to 10%, and the balance remains unaccounted for (”Where is the child’s environment?“). With few exceptions, being reared in the same home does not make siblings of any kind more alike.

These results show not only that siblings are different but that the home environment has had little or no net effect on the measured outcomes. If being reared by conscientious parents, for example, tended to make children more conscientious, then 2 children reared by conscientious parents should, on average, both be more conscientious than 2 reared by careless parents. Therefore, 2 children reared in the same home should be significantly more alike in conscientiousness than 2 reared in different homes, which is exactly what the studies do not find (”Genes, environment, and personality“). The same results also rule out the possibility that being reared by conscientious parents makes children less conscientious on average. The bottom-line effect of the shared home environment on conscientiousness is not noticeably different from zero.

For alcoholism (”The behavioral genetics of alcoholism“) and criminal behavior, the evidence strongly suggests that the operative environmental influences are in the neighborhood, not in the home.

A major study was launched in 1987; its results are described in The Relationship Code. David Reiss studied 720 pairs of same-sex adolescent siblings (identical and fraternal twins and full, half and stepsiblings) over a 3-year period, from early to mid-adolescence. The adolescents’ behavior and adjustment, and the behavior of their parents, were judged by observers, the parents, and the adolescents themselves; these multiple sources of information were combined to produce measures of unusual reliability.

Virtually all correlations between parental behaviors and child outcomes were accounted for by genetic factors. The parents treated their children differently but they were reacting to genetic differences among the children, rather than causing the differences. The environment not shared by siblings was by far the largest (in many cases, the sole) nongenetic contributor to the adolescents’ behavior and adjustment, and the study eliminated all of the following as possible sources of nonshared environmental influence: “differential marital conflict about the adolescent versus the sib, differential parenting toward siblings, and asymmetrical relationships the sibs construct with each other.” Ruling out the last factor indicates that differences in age — that is, birth order — cannot account for the differences between siblings.

Developmentalists and behavioral geneticists alike have so far been unable to identify the important environmental influences on development, the sources of the nongenetic variation in personality and behavior.

Birth order effects are real, but they are tied to the context of the family. We ordinarily know the birth order only of people we are close to, and these are the people we are most likely to see with their parents and siblings. Birth order studies in which parents are asked to rate their children’s personalities, or adults are asked to compare themselves with their siblings, generally do yield significant birth order effects; studies that use other methods generally do not (”Context-specific learning, personality, and birth order“). In a study in which pairs of siblings were rated both by parents and by teachers, parents judged the older sibling to be more aggressive than the younger one, but teachers judged them to be about the same (”An adoption study of the etiology of teacher and parent reports of externalizing behavior problems in middle childhood“).

Family misfortunes have repercussions on children’s lives outside the home. A divorce, for example, often involves moving to a different residence, and moving disrupts the child’s life outside the family. Even when other demographic differences are controlled, children who have experienced frequent residential moves have higher rates of social, behavioral, and academic problems (”Mobility as a mediator of the effects of child maltreatment on academic performance” & “Impact of family relocation on children’s growth, development, school function, and behavior“). McLanahan and Sandefur (Growing up with a Single Parent) found that controlling for 2 factors — number of residential moves and differences in family income — can erase most of the differences in outcome between children reared in single-parent and two-parent families.

Because developed societies require very different behaviors in the home and in public (”Growing up in the post-modern age”), and people everywhere make distinctions between kin and nonkin (How the Mind Works), children behave differently in different contexts (”Studying temperament via construction of the Toddler Behavior Assessment Questionnaire“).

Children bring with them to adulthood the language and accent of their peers, not those of their parents. Evidence comes from studies of hearing children reared by deaf parents and of deaf children reared by hearing parents and from studies of the children of immigrants.

Derek Bickerton interviewed adults whose parents had immigrated to Hawaii around the turn of the last century. Though the parents came from all over the world and spoke a variety of languages, their adult offspring all spoke the same language — a creole, created in their childhood peer groups. No trace of their parents’ language or accent was detectable in their speech; the language of their peers had become their “native language.” The adults in these communities used a pidgin, not the creole, to communicate with each other.

Simon Baron-Cohen (”Do children with autism acquire the phonology of their peers?”) studied the accents of children and young adults with autism. These were the offspring of immigrants; their mothers spoke English with a foreign accent. The nonautistic siblings of these children spoke English without a foreign accent, but 83% of the children and young adults with autism had retained the foreign accent of their mothers. Baron-Cohen attributed this outcome to “a lack of the normal drive to identify with peers.”

Multivariate genetic analysis makes it possible to estimate how much genetic and environmental influences each contribute to the correlations found between behavior in different contexts. For example, children who are shy in one social context are not necessarily shy in others, but some children are shy in every context (”The Consistency and Concomitants of Inhibition“). Multivariate genetic analysis shows that the genetic component of shyness is responsible for the correlation across contexts; differences in shyness from one context to another are due primarily to environmental influences (”Continuity and change in infant shyness from 14 to 20 months“).

Interventions designed to teach parents better ways of dealing with their noncompliant children succeed in reducing the children’s coercive behavior at home but do not produce significant improvements in their behavior in school.

Infants who behave in a somber, subdued fashion in the presence of their depressed mothers behave normally in the presence of nondepressed caregivers; their subdued behavior is “specific to their interactions with their depressed mothers” (”Infants of depressed mothers show less ‘depressed’ behavior with their nursery teachers”). Secure attachments to one caregiver are not good predictors of secure attachments to another (”Prediction of infant-father and infant-mother attachment” & “Quality of infants’ attachments to professional caregivers“). Nor are secure attachments to parents good predictors of successful relationships with peers (”Maternal, teacher, and child care history correlates of children’s relationships with peers“). The quality of sibling relationships does not predict the quality of relationships with peers; sometimes the correlations are negative (”Compensatory patterns of support among children’s peer relationships“).

According to Irenäus Eibl-Eibesfeldt (Human Ethology), once children in hunter–gatherer and tribal societies have been weaned, they spend most of their time in the local play group. “Thus the child’s socialization occurs mainly within the play group.”

When children divide or are divided into two groups, preexisting differences between the groups are widened by contrast effects between groups and assimilation within them.

Thus, putting antisocial youth together for a group intervention is likely to make them more antisocial, a prediction that has recently been confirmed by Thomas J. Dishion (”When interventions harm”).

A boy’s status in his peer group is determined in part by his size. Small, slow-maturing boys generally have lower status (”An ethological study of dominance formation and maintenance in a group of human adolescents“). Studies have shown that children who are small for their age tend to have more than their share of psychological problems (”Academic and emotional difficulties associated with short stature”).

M.C. Jones (”The later careers of boys who were early or late maturing,” 1957) did a longitudinal study comparing males who were slow developers — smaller than most of their peers throughout childhood — with early developers. The two groups ended up almost equal in mean adult height, but there were significant differences in their adult personalities. The early developers were more dominant, relaxed, and poised; the slow developers were more impulsive, attention-seeking, and touchy.

“Socialization, Personality Development, and the Child’s Environments,” by Judith Rich Harris

The average IQs of adult men and women are about the same. But there are more men at the top levels of ability. And more males with very low IQs. The pattern with mental retardation is the same: as you go from mild to medium to extreme, the preponderance of males gets bigger.

The male distribution of height is also flatter, with more very tall and very short men.

Research by Jacquelynne Eccles has repeatedly concluded that the shortage of females in math and science reflects motivation more than ability.

Average gender differences in abilities tend to be extremely small. But there are significant differences in motivation. For example, Roy Baumeister’s survey of published research found that almost every measure and every study has shown higher sex drive in men.

And according to another study, over 80% of the people who work 50-hour weeks are men.

According to recent research using DNA analysis, today’s human population is descended from approximately twice as many women as men. Throughout the entire history of the human race, approximately 80% of women but only 40% of men reproduced.

Since women’s odds of reproducing have been good, the optimal strategy has been to minimize risks.

But most men who ever lived did not have descendants who are alive today.

Also, while few women have had more than a dozen children, some men have had hundreds.

If a group loses 1/2 its men, the next generation can still be full-sized. But if it loses 1/2 its women, the size of the next generation will be severely curtailed. Hence most cultures keep their women out of harm’s way while using men for risky jobs.

The US Department of Labor statistics report that 93% of the people killed on the job are men. Of the first 3,000 Americans killed in Iraq, 2,938 were men, 62 were women.

“Is There Anything Good About Men?,” by Roy F. Baumeister