Psychology Module 33 Study-Guide Definitions: Heritability- the proportion of variation among individuals that we can attribute to genes. The heritability of a trait may vary, depending on the range of populations and environments studied. Stereotype threat- a self-confirming concern that one will be evaluated based on negative stereotype. Genetic and Environmental Influences on Intelligence Intelligence runs in families. Few issues arouse such passion or have such serious political implications. People who share the same genes also share comparable mental abilities. Across studies of 10,000 twins, the intelligence test scores of identical twins reared together are virtually as similar as those of the same person taking the same test twice. The scores of fraternal twins, who typically share only half their genes, are much less similar. Likewise, the test scores of identical twins reared separately are similar enough to lead twin researcher Thomas Bouchard to estimate that about 70 percent of intelligence score variation can be attributed to genetic variation. Brain scans reveal that identical twins have very similar gray matter volume. Moreover, unlike fraternal twins, their brains are virtually the same in areas associated with verbal and spatial intelligence. Comparisons of the genes of people of high versus average intelligence have produced slow progress in identifying the many genes that contribute to cognitive ability. By inserting an extra gene into fertilized mouse eggs, researchers have, however, produced smarter mice- mice that excel at learning and remembering the location of a hidden underwater platform or at recognizing cues that signal impending shock. The genes help create a neural receptor involved in memory. But there is also some evidence pointing to an effect of environment. Fraternal twins, who are genetically no more alike than any other siblings- but who are treated more alike because they are the same age- tend to score more alike than other siblings. Seeking to disentangle genes and environment, researchers have also asked whether adopted children and their siblings, thanks to their shared environment, share similar aptitudes. During childhood, the intelligence test scores of adoptive siblings correlate modestly. Researchers have also compared the intelligence test scores of adopted children to their biological parents, and their adoptive parents. Over time, adopted children accumulate experience in their differing adoptive families. With age, mental similarities between adopted children and their adoptive families disappear as parental influence wanes; by adulthood, the correlation is roughly zero. As we accumulate life experience, genetic influences- not environmental ones- become more apparent. Adopted children?s intelligence scores become more like those of their biological parents, and identical twins? similarities continue to increase into their eighties. Given such studies, one might be tempted to make statements about the heritability of intelligence. But be very careful how you use the word heritability. To say that the heritability of intelligence- the variation in intelligence test scores attributable to genetic factors- is 50 percent (or a tad more) does not mean that your genes account for 50 percent of your intelligence and your environment for the rest. It means that we can attribute to heredity 50 percent of the variation in intelligence (among those studied). This point is so often misunderstood. We can never say what percentage of an individual?s intelligence is inherited. Heritability refers instead to the extent to which differences among people are attributable to genes. Heritability never pertains to an individual, only to why people differ. Even this conclusion might be qualified, because heritability can vary from study to study. For example, environmental differences are more predictive of intelligence scores among children of less-educated parents- among whom family environments may vary widely. Mark Twain once proposed that boys should be raised and fed through a hole until they were 12 years old. Given the boys? equal environments, differences in their individual intelligence test scores at age 12 could be explained only by their heredity. Thus, heritability for their differences would be nearly 100 percent. But if we raise people with similar heredities in drastically different environments (barrels versus advantaged homes), the environment effect will be greater, and heritability- differences due to genes- will therefore be lower. In a world of clones, heritability would be zero. Genes and environment correlate. If you are just slightly taller and quicker than others, notes James Flynn, you will more likely be picked for a basketball team, will play more, and will get more coaching. The same would be true for your separated identical twin- who might, not just for genetic reasons, also come to excel at basketball. Likewise, students with a natural aptitude for mathematics are more likely to select math courses in high school and later to score well on math aptitude tests- thanks both to their natural math aptitude and to their math experience. If you have a slight genetically disposed intelligence edge, you will more likely stay in school, read books, and ask questions- all of which will amplify your cognitive brain power. Thanks to such gene-environment correlation, modest genetic advantages can be socially multiplied into big performance advantages. Our genes shape the experiences that shape us. Genes make a difference. Even if we were all raised in the same intellectually stimulating environment, we would have differing aptitudes. But when we consider the similarities of identical twins, heredity does not tell the whole story. In ways sometimes predisposed by our genes, our life experiences matter. Human environments are rarely as impoverished as the dark and barren cages inhabited by deprived rats that develop thinner-than-normal brain cortexes. Yet severe life experiences do leave footprints on the brain. In a destitute Iranian orphanage, J. McVicker Hunt observed the dramatic effects of early experiences and demonstrated the impact of early intervention. The typical child Hunt observed there could not sit up unassisted at age 2 or walk at age 4. The little care the infants received was not in response to their crying, cooing, or other behaviors, so the children developed little sense of personal control over their environment. They were instead becoming passive ?glum lumps.? Extreme deprivation was bludgeoning native intelligence. Aware of the benefits of responsive caregiving, Hunt began a program of ?tutored human enrichment.? He trained caregivers to play vocal games with the infants. They first imitated the babies? babbling. Then they led the babies in vocal follow-the-leader by shifting from one familiar sound to another. Then they began to teach sounds from the Persian language. The results were dramatic. By 22 months of age, all 11 infants who received these language-fostering experiences could name more than 50 objects and body parts. So charming had the infants become that most were adopted- an unprecedented success for the orphanage. Hunt?s findings testify to the importance of environment. Severe disadvantage takes a toll. Unlike children of affluence, siblings within impoverished families have more similar intelligence scores. This indicates that among the poor, environmental conditions can override genetic differences. Ones study of 1450 Virginia schools found that schools with lots of poverty-level children often had less-qualified teachers. And even after controlling for poverty, less-qualified teachers predicted lower achievement scores. Malnutrition can also influence cognitive development. When the infant malnutrition associated with severe poverty is relieved with nutritional supplements, poverty?s effect on physical and cognitive development lessons. And improving nutrition helps explain the rising intelligence scores across generations. Some popular books claim that with intensive preschool training, your child can get a superior intellect. But most experts are doubtful. Although malnutrition, sensory deprivation, and social isolation can retard normal brain development, the difference between normal and ?enriched? environments matters less. There is no environmental recipe for superbabies, beyond normal exposure to sights, sounds, and speech. Extra instruction has little effect on the intellectual development of children from stimulating environments. Hunt was optimistic when it came to children form from disadvantaged environments. Indeed in his 1961 book, Intelligence and Experience, helped launch Project Head Start in 165. Head Start serves more than 900,000 children, most of whom come from families below the poverty level. It aims to enhance children?s chances for success in school and beyond by boosting their cognitive and social skills. Quality programs, offering individual attention, increase children?s school readiness, which decreases their likelihood of repeating a grade or being placed in special education. Generally, the aptitude benefits dissipate over time. Psychologist Edward Zigler, the program?s first director, nevertheless believes there are long-term benefits. High quality preschool programs can provide at least a small boost to emotional intelligence- creating better attitudes toward learning and reducing school dropout and criminality. Schooling itself is an intervention that pays dividends reflected in intelligence scores. Stephen Ceci and Wendy Williams have amassed evidence that schooling and intelligence contribute to each other (and that both enhance later income). High intelligence is conductive to prolonged schooling. But intelligence scores tend to rise during the school year and drop over the summer months and when schooling is discontinued. Completing high school elevates intelligence scores over those obtained by comparable children who leave school early. The worldwide rise in intelligence tests scores since the 1920?s, known as the Flynn effect, is probably partly due to increasing years of schooling over the last half-century- and to the more stimulating home environments provided by today?s better-educated parents. If there were no group differences in aptitude scores, psychologists would politely debate hereditary and environmental influences in their ivory towers. But there are group differences. Fueling this discussion are two disturbing but agreed-upon facts: Racial groups differ in their average scores on intelligence tests. High-scoring people (and groups) are more likely to attain high levels of education and income. A statement by 52 intelligence researchers explained: the bell curve for Whites is centered roughly around IQ 100; the bell curve for America Blacks roughly around 85; and those for different subgroups of Hispanics roughly midway between those for Whites and Blacks. Comparable results come from other academic aptitude tests, such as the SAT. In recent years, the Black-White difference has diminished somewhat, and among children has dropped to 10 points in some studies. Yet the test score gap stubbornly persists. There are differences among other groups as well. European New Zealanders outscore native Maori New Zealanders. Israeli Jews outscore Israeli Arabs. Most Japanese outscore the Burakumin. And those who can hear outscore those born deaf. Everyone further agrees that such group differences provide little basis for judging individuals. Women outlive men by six years, but knowing someone?s sex doesn?t tell us with any precision how long that person will live. Millions of blacks have higher IQ?s than the average White. Swedes and Bantus differ in complexion and language. That first factor is genetic, the second environmental. So what about intelligence scores? As we have seen, heredity contributes to individual differences in intelligence. Some psychologists believe that heredity contributes to group differences, perhaps because of the world?s differing climates and survival challenges. But we have also seen that group differences in a heritable trait may be entirely environmental, as in our earlier barrel-versus-home-reared boys example. Consider one of nature?s experiments: Allow some children to grow up hearing their culture?s dominant language, while others, born deaf, do not. Then give them an intelligence test, rooted in that language, and (no surprise) those with expertise in the test?s language will score highest. Although individual performance differences may be substantially genetic, the group difference is not. Consider: If each identical twin were exactly as tall as his or her co-twin, heritability would be 100 percent. Imagine that we then separated some young twins and gave only half of them a nutritious diet, and that the well-nourished twins all grew up to be exactly 3 inches taller than their counterparts- an environmental effect comparable to that actually observed in both Britain and America, where adolescents are several inches taller than their counterparts were a half-century ago. Still, the heritability for the well-nourished twins would be 100% because the variation in height within the group would remain entirely predictable from the heights of their malnourished identical siblings. So even perfect heritability within groups would not eliminate the possibility of a strong environmental impact on the group differences. Genetics research reveals that under the skin, the races are remarkably alike. Individual differences within a race are much greater than differences between races. The average genetic difference between two Icelandic villagers or between two Kenyans greatly exceeds the group difference between Icelanders and Kenyans. Moreover, looks can deceive. Light-skinned Europeans and dark-skinned Africans are genetically closer than are dark-skinned Africans and dark-skinned Aboriginal Australians. Race is not a neatly defined biological category. Some scholars argue that there is a reality to race, noting that there are genetic markers for race and that medical risks vary by race. Your vulnerability to skin cancer depends on both sun exposure and who your ancestors were. Behavioral traits may also vary by race. No runner of Asian or European descent has broken 10 seconds in the 100-meter dash, but dozens of West Africans have. Many more social scientists, though, see race primarily as a social construction without well-defined physical boundaries. People with varying ancestry may categorize themselves in the same race. Moreover, with increasingly mixed ancestries, more and more people defy neat racial categorization. Asian students outperform North American students on math achievement and aptitude tests. But this difference appears to be a recent phenomenon and may reflect conscientiousness more than competence. Asian students also attend school 30-percent more days per year and spend much more time in and out of school studying math. The intelligence test performance of today?s better-fed, better-educated, and more test-prepared population exceeds that of the 1930s population. The Flynn effect- by the same margin that the intelligence test score of the average White today exceeds that of the average Black. No one attributes the generational group difference to genetics. White and black infants have scored equally well on an infant intelligence measure (preference for looking at novel stimuli- a crude predictor of future intelligence scores) In different eras, different groups have experienced golden ages- periods of remarkable achievement. Twenty-five-hundred years ago it was the Greeks and the Egyptians, then the Romans; in the eighth and ninth centuries, genius seemed to reside in the Arab world; 500 years ago it was the Aztec Indians and the peoples of Northern Europe. Today, people marvel at Asians? technological genius. Cultures rise and fall over centuries; genes do not. That fact makes it difficult to attribute a natural superiority to any race. From eighth grade through the early high school years, the average aptitude score of the white students increased, while those of the black students decreased- creating a gap that reached its widest point at about the time that high school students take college admissions tests. But during college, the black students? scores increased more than four times as much as those of their white counterparts, thus greatly decreasing the aptitude gap. It is not surprising that as black and white students complete more grades in high school environments that differ in quality, the gap in cognitive test scores widens. At the college level, however, where black and white students are exposed to educational environments of comparable quality, many blacks are able to make remarkable gains, closing the gap in test scores. In science, as in everyday life, differences, not similarities, excite interest. Sex differences are relatively minor in anatomical and physiological factors. The same is true in the psychological domain. Girls are better spellers: at the end of high school in the United States, only 30 percent of males spell better than the average female. Girls are more verbally fluent and more capable of remembering words. Girls have the edge on boys at locating objects. Girls also modestly surpassed boys in memory for picture associations. Girls are more sensitive to touch, taste, and odor. Boys outnumber girls at the low extremes and therefore in special education classes. Boys tend to talk later and to stutter more often. In remedial reading classes, boys outnumber girls three to one. Among U.S. high school underachievers, boys outnumber girls by two to one. In U.S. schools, the average girl?s math scores typically equal or surpass the average boy?s. And on math tests given to more than 3 million representatively sampled people in 100 independent studies, males and females obtained nearly identical average scores. Despite greater diversity within the genders than between them, group differences make the news. Although females have an edge in math computation, males in 20 of 21 countries scored higher in math problem solving. Males average 45 points higher on the math portion of the SAT. The score differences are sharpest at the extremes. Males have an edge in physics and computer science. In Western countries, virtually all math prodigies are men. More female math prodigies have, however, reached the top levels in nonwestern countries such as China. The average male edge seems most reliable in tests of spatial mental rotation. Such spatial ability helps when fitting suitcases into a car trunk, playing chess, or doing certain types of geometry problems. Working from an evolutionary perspective, David Geary and Irwin Silverman and his colleagues speculate that skills in navigating within three-dimensional space helped our ancestral fathers in tracking their prey and making their way home. In contrast, the survival of our ancestral mothers was enhanced by keen memory for the location of edible plants- a legacy that lives today in women?s superior memory for objects and their location. Exposure to high levels of male sex hormones during the prenatal period does spatial abilities. Moreover, there do appear to be biological as well as social influences on gender differences in life priorities (women?s greater interest in people versus men?s in money and things), in risk taking, and in math reasoning and spatial abilities. Such differences are observed across cultures, stable over time, observed in genetic boys raised as girls, and influenced by prenatal hormones. Women excel at verbal fluency, men at verbal analogies. Women excel at rapid math calculations, men at rapid math reasoning. Women excel at remembering objects? spatial positions, men at remembering geometric layouts. Social expectations and divergent opportunities do shape boys? and girls? interests and abilities. The male edge in math problem solving grows with age, becoming detectable only after elementary school. Traditionally, math and science have been considered masculine subjects. Many parents send their sons to computer camps and give their daughters more encouragement in English. But as more and more girls are encouraged to develop their abilities in math and science, the gap is narrowing. In some fields, including psychology, women now earn most of the Ph.D.s. Emotional intelligence is the ability to perceive, understand, manage, and use emotions. Thus, one part of emotional intelligence is empathic accuracy in reading others? emotions. Some of us are more sensitive to emotional cues. Some psychologists speculate that women?s ability to detect emotions helped out ancestral mothers read emotions in their infants and would-be lever, which may in turn have fueled cultural tendencies to encourage women?s empathic skills. Such skills may explain women?s somewhat greater responsiveness in both positive and negative situations. Knowing there are group differences in intelligence test scores leads us to wonder whether intelligence tests are biased. The answer depends on which of two very different definitions of bias are used, and on an understanding of stereotypes. If a test detects not only innate differences in intelligence but also performance differences caused by cultural experiences, it may be considered biased. In this popular sense, everyone agrees that intelligence tests are biased. An intelligence test measures your developed abilities, which reflect, your education and experiences. Defenders of aptitude testing note that racial group differences are at least as great on nonverbal items, such as counting digits backward. Moreover, they add, blaming the test for a group?s lower scores is like blaming the measuring stick that reveals stunted growth. If unequal past experiences predict unequal future achievements, a valid aptitude test will detect such inequalities. The scientific meaning of bias is different. It hinges on whether a test is less valid for some groups than for others- whether it predicts future behavior only for some groups of test-takers. The U.S. aptitude tests are not scientifically biased. The predictive validity of the SAT or of a standard intelligence test is roughly the same for women and men, for Blacks and Whites, and for rich and poor. To predict school performance accurately, an aptitude test must mirror any gender or racial bias in school teaching and testing. Among students given a difficult math test, men outperformed equally capable women- except when the women had been led to expect that women usually do as well as men on the test. Otherwise, the women apparently felt apprehensive, which affected their performance. Stereotype threat- a self-confirming concern that one will be evaluated based on a negative stereotype. Stereotype threat also explains why women have scored higher on math tests when no male test-takers were in the group, and why Black have scored higher when tested by Blacks than when tested by Whites. If you tell students they probably won?t succeed, this stereotype will eventually erode their performance both on aptitude tests and in school. Over time, such students may ?disidentify? with school achievement. They may detach their self-esteem elsewhere- which might help explain why minority students tend to underachieve relative to their abilities. Indeed, as African-American boys progress from eighth to twelfth grade, they disconnect between their grades and their self-esteem becomes more pronounced. Minority students in university programs that challenge them to believe in their potential have produced markedly higher grades and had lower dropout rates. The tests do seem biased in one sense- sensitivity to performance differences caused by cultural experience. But they are no biased in the scientific sense of making valid statistical predictions for different groups. In one sense, tests are discriminatory, In another sense, their purpose is to reduce discrimination by reducing reliance on subjective criteria for school and job placement. Civil service aptitude tests were designed to discriminate more fairly and objectively, by reducing the political, racial, and ethnic discrimination that preceded their use. Banning aptitude tests would lead those who decide on jobs and admissions to rely more on other considerations, such as their personal opinions. Perhaps, then, our aim should be threefold. First, we should realize the benefits, which are to enable schools to recognize who might profit most from early intervention. Second, we must remain alert that intelligence test scores may be misinterpreted as literal measures of a person?s worth and fixed potential. Finally, we must remember that intelligence test scores reflect only one aspect of personal competence. Our practical intelligence and emotional intelligence matter, too, as do other forms of talent and character. Almost all the joyful all the joyful things of life are outside the measure of IQ tests. The competence that general intelligence tests sample is important; it helps enable success in some life paths. But it is far from all-important. The carpenter?s spatial ability differs from the programmer?s logical ability, which differs from the poet?s verbal ability. Because there are many ways of being successful, our differences are variations of human adaptability.
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