Progress Daily

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

Steve Cole and John Cacioppo, used a “gene chip” to look at the DNA of isolated people and found that people who described themselves as chronically lonely have distinct patterns of genetic activity, almost all of it involving the immune system.

The study does not show which came first — the loneliness or the physical traits.

Many studies of large populations have shown that people who describe themselves as lonely or as having little social support are more likely to die prematurely and to have infections, high blood pressure, insomnia and cancer.

When the researchers studied and compared all 22,000 human genes, 209 stood out in the loneliest people.

Many of the these genes seemed to be involved in the basic immune response to tissue damage and others were involved in the production of antibodies (the tag the body uses to mark microbes or damaged cells for removal), suggesting that the loneliest people had unhealthy levels of chronic inflammation, which has been associated with heart and artery disease, arthritis, Alzheimer’s, etc.

“Sick? Lonely? Genes tell the tale,” Reuters

According to “Where is the Wealth of Nations?,” a 2005 World Bank study by Kirk Hamilton, solid goods amount to only about 20% of the wealth of rich nations and 40% of the wealth of poor countries.

Worldwide, natural capital (cropland, pastureland, forested areas, protected areas, and nonrenewable resources, such as oil, natural gas, coal, and minerals) accounts for 5% of total wealth, produced capital (machinery, equipment, structures, infrastructure, and urban land) for 18%, and intangible capital (raw labor; human capital, which includes the sum of a population’s knowledge and skills; and the level of trust in a society and the quality of its formal and informal institutions) 77%.

The World Bank has devised a rule of law index that measures the extent to which people have confidence in and abide by the rules of their society. An economy with a very efficient judicial system, clear and enforceable property rights, and an effective and uncorrupt government will produce higher total wealth. For example, Switzerland scores 99.5 out of 100 on the rule of law index and the U.S. hits 92. Nigeria gets a score of just 5.8, while the Democratic Republic of the Congo scores 1. The members of the Organisation for Economic Co-operation and Development — 30 wealthy developed countries — have an average score of 90, while sub-Saharan Africa’s is 28. According to Hamilton’s figures, the rule of law explains 57% of countries’ intangible capital. Education accounts for 36%.

The rule of law index was created using several hundred individual variables measuring perceptions of governance, drawn from 25 separate data sources constructed by 18 different organizations. The latter include civil society groups, political and business risk-rating agencies, and think tanks.

The Ugandan government reports that it spends 2 or 3% of GDP on education but one study found that approximately 13% of that money made it to the schools. In the U.S. the figure is about 60 to 65%.

As countries get richer they’re using smaller and smaller amounts of natural capital — minerals, energy, soils, forests, fish, etc. Richer countries are increasing their efficiency faster than they use up natural resources, so development does not necessarily entail the depletion of the environment and natural resources.

“Our Intangible Riches,” by Ronald Bailey

A recent study by Amanda Rose found that teenage girls who vented to each other about their problems were more likely to develop depression and anxiety.

(Rose found that guys don’t tend to analyze their problems as deeply as women. That might be because relationship issues tend to spark the most obsessive discussions, and that’s a subject women are more likely to dwell on.)

Girls who vented to each other reported feeling closer to their friends.

“Quit complaining — it may make you feel worse,” by Melissa Dahl

When the Nurses’ Health Study first published its observations on estrogen and heart disease in 1985, it showed that women taking estrogen therapy had only 1/3 the risk of having a heart attack as had women who had never taken it. Only 90 heart attacks had been reported among the 32,000 postmenopausal nurses in the study.

In 1987, Diana Petitti reported that she, too, had detected a reduced risk of heart-disease deaths among women taking HRT in the Walnut Creek Study, a population of 16,500 women. However, she “found an even more dramatic reduction in death from homicide, suicide and accidents.” “Healthy-user bias” appeared to be “confounding” the association.

People who faithfully engage in activities that are good for them are fundamentally different from those who don’t. Women who take HRT differ from those who don’t: they’re thinner; they have fewer risk factors for heart disease to begin with; they tend to be more educated and wealthier; to exercise more; and to be more health conscious.

In a large population studied by Elizabeth Barrett-Connor, having gone to college was associated with a 50% lower risk of heart disease.

According to George Davey Smith, the poor are less educated than the wealthy; they smoke more and weigh more; they’re more likely to have hypertension and other heart-disease risk factors, to eat what’s affordable rather than what the experts tell them is healthful, to have poor medical care and to live in environments with more pollutants, noise and stress.

People who comply with their doctors’ orders when given a prescription are different and healthier than people who don’t.

The Coronary Drug Project set out in the 1970s to test whether clofibrate might prevent heart attacks. The subjects were some 8,500 middle-aged men with established heart problems. Two-thirds of them were randomly assigned to take one of the 5 drugs and the other 1/3 a placebo.

After 5 years, those men who said they took more than 80% of the pills prescribed fared substantially better than those who didn’t. Only 15% of these faithful “adherers” died, compared with almost 25% of the “poor adherers.” This might have been taken as reason to believe that clofibrate actually did cut heart-disease deaths almost by 1/2, but then the researchers looked at those men who faithfully took their placebos. Only 15% of them died compared with 28% who were less conscientious.

“Do We Really Know What Makes Us Healthy?” by Gary Taubes

“Peer effects” are hard to measure. Girls’ schools produce good academic results, for example, but that could be because particular types of parent favour such schools, because those schools have a strong historical record, or because of selection.

A new working paper (”Mechanisms and Impacts of Gender Peer Effects at School”; .pdf file here) from Victor Lavy and Analia Schlosser attempts to unpick the peer effects associated with gender, using data on nearly half a million students passing through Israel’s school system in the 1990s. They compared consecutive year groups passing through the same school, figuring that if one year group was 55% boys and the next year was 55%, that difference was likely to be random.

Boys, it turns out, benefit from being in a classroom with girls, but girls do not benefit from being taught with boys. Boys wear down teachers, disrupt classes and ruin the atmosphere for everyone

“Miss match,” by Tim Harford

According to the ILO’s Key Indicators of the Labour Market, agriculture has recently lost its place as the main sector of world employment and has been replaced by the services sector.

Agriculture is still the main sector of employment in the world’s poorest regions, comprising 2/3rds of workers in sub-Saharan Africa and almost 1/2 of workers in South Asia and South-East Asia & the Pacific.

Modernization of large economies is largely bypassing industrialization and going straight to the service sectors - in the western economies the service sector was about 2/3rds of the economy, and has grown further (to 71%). Worldwide, in 1996 agriculture employed 42%, industry 21%, and services 37%. In 2006, the numbers are 36%, 22%, and 42%.

“For the first time in 10,000 years, farming is not the dominating industry“

Ian Spence tested people’s ability to spot unusual objects that appear in their field of vision. Success at spatial tasks like this often differs between the sexes (men are better at remembering and locating general landmarks; women are better at remembering and locating food). The test asked people to identify an “odd man out” object in a briefly displayed field of 24 otherwise identical objects. Men had a 68% success rate. Women had a 55% success rate.

Spence then asked some of the volunteers to spend 10 hours playing an action-packed, shoot-’em-up video game, called “Medal of Honour: Pacific Assault.” Other volunteers were asked to play a decidedly non-action-packed puzzle game, called “Ballance,” for a similar time. Both sets then re-took the odd-man-out test.

Among the Ballancers, there was no change in ability. Among those who had played “Medal of Honour,” both sexes improved their performances.

The women’s improvement was greater than the men’s — so much so that there was no longer a significant difference between the two. When the volunteers were tested again after 5 months, the improvement remained.

Apparently, playing violent computer games can have beneficial effects. They might provide a way of rapidly improving spatial ability in people.

“Nurture strikes back,” The Economist

The CDC recently issued a flier to combat myths about the flu vaccine. It recited various commonly held views and labeled them either “true” or “false.” Among those identified as false were statements such as “The side effects are worse than the flu” and “Only older people need flu vaccine.”

When Norbert Schwarz had volunteers read the CDC flier, he found that within 30 minutes, older people misremembered 28% of the false statements as true. Three days later, they remembered 40% of the myths as factual.

Younger people did better at first, but 3 days later they made as many errors as older people did after 30 minutes. People of all ages now felt that the source of their false beliefs was the respected CDC.

The new psychological studies show that denials and clarifications can paradoxically contribute to the resiliency of popular myths.

An experiment by Kimberlee Weaver (”Inferring the popularity of an opinion from its familiarity: A repetitive voice can sound like a chorus“) shows that hearing the same thing over and over again from one source can have the same effect as hearing that thing from many different people — the brain gets tricked into thinking it has heard a piece of information from multiple, independent sources, even when it has not.

“Persistence of Myths Could Alter Public Policy Approach,” by “Shankar Vedantam