On the possibility of the reemergence of a dysgenic trend with respect to intelligence in American fertility differentials

This paper examines the relationship between IQ and fertility in a sample of men and women aged 25–34 as of the late 1970s. This sample is of unusual interest for two reasons: (1) it is a national probability sample, representative of the non-institutional civilian population of the U.S. as a whole, and (2) it is for a post-World War II cohort. Most previous studies of the IQ/fertility relationship have employed nationally unrepresentative samples of cohorts born in the pre-war period, 1910–1940. The bias, in both time and place, of the samples used in these studies has not been adequately grasped by those who cite them as evidence of a eugenic trend with respect to intelligence.The major finding of these previous studies was that the IQ/fertility relationship is slightly positive, contrary to expectations though confirmatory of the so-called Eugenic Hypothesis. My working hypothesis is that this finding is special to the cohort chosen for study, i.e., one whose child-bearing took place during a period of rising birth rates (cohorts born between 1910 and 1940 were largely responsible for the baby boom after World War II). That is, in periods of rising birth rates, persons with higher intelligence tend to have fertility equal to, if not exceeding, that of the population as a whole. In periods of falling birth rates, the opposite is the case, according to my thesis.This thesis is generally supported by the data set described above. Fertility differentials to date within the post-World War II cohort, which entered its reproductive years during a period of falling birth rates, show a negative relationship between intelligence and fertility. The relationship is less negative for white men than for white women and for white women than for black women (black men are omitted from this study due to deficiencies in the data). The stated intentions of this cohort with respect to future fertility, if realized, will moderate the degree of this relationship, particularly for whites, but not change its sign.     

Intelligence and fertility in the United States: 1912-1982

Results are presented for the 1st analysis of the relationship between IQ and completed fertility using a large, representative sample of the US population. Correlations are predominantly negative for cohorts born between 1894 and 1964 but are significantly more positive for cohorts whose fertility was concentrated in the baby boom years. Previous studies reporting slightly positive correlations appear to have been biased in their restriction of samples to atypical cohorts. The National Opinion Research Center (NORC), a nonprofit research organization affiliated with the University of Chicago, conducted the General Social Survey (GSS) in the US each year from 1972 to 1982, except for 1979. A combination of block quota and full probability sampling was employed. Hour-long interviews were completed with 12,120 respondents who were English-speaking, noninstitutionalized adults (18 years or older) living within the continental US. Such questions as age, place of birth, income and occupation, were asked in each interview. Other questions about attitudes on various social, political, and moral issues were rotated in different years. The unique opportunity this data set affords is an overview of the relationship between intelligence and fertility for a nationally representative sample of Americans whose major reproductive years fell between 1912 and 1982. Data were consolidated from the 4 surveys in which the vocabulary test was given (1974, 1976, 1978, and 1982). Respondents were divided into 15 birth cohorts of 5-year intervals ranging from before 1894 to 1964. Correlations between vocabulary scores and number of siblings are markedly negative across all 15 cohorts. Vocabulary sibling correlations are more negative in every cohort than vocabulary offspring correlations. Previous reports of a neutral or slightly eugenic relationship appear to be due to the nature of the samples used, in part because the cohorts chosen were atypical, and in part because they did not include nonwhites. Childless respondents averaged slightly higher scores than did those with 1 or more children, indicating that the automatic exclusion of the childless from sibling-IQ studies has not spuriously inflated negative correlations.     

Cohort Differences in Personal Goals and Life Satisfaction in Young Adulthood: Evidence for Historical Shifts in Developmental Tasks

This study investigated the influence of changing socio-historical conditions on personal goals in young adulthood. It was hypothesized that socio-historical changes related to individualization have resulted in shifts in goal pursuit. Participants from three birth cohorts reconstructed their important goals when they were 20 years old. Members of the oldest cohort were born between 1920 and 1925. Members of the middle cohort were born between 1945 and 1950. Members of the youngest cohort were born between 1970 and 1975. Goal content, the degree to which goals were perceived as being shared by members of the same cohort (social sharedness), perceived control over goal attainment, success in attainment, and life satisfaction at age 25 were measured in a retrospective study. Results show consistent shifts over time. Whereas members of older cohorts mentioned goals related to classical developmental tasks, members of younger cohorts mentioned more individualistic, self-related goals and goals related to education. The processes through which goal pursuit influenced life satisfaction also changed. Perceived social sharedness of goals was a direct predictor of life satisfaction for the oldest cohort. For the younger cohorts, perceived control over goal attainment influenced success which in turn influenced life satisfaction. These changes support the contention that developmental tasks and processes are historically variant.     

Mitochondrial DNA marker EST00083 is not associated with high vs. average IQ in a German sample

In a recent report in this journal (Plomin & Petrill, 1997), a mitochondrial DNA marker (EST00083) yielded significant associations with high vs. low IQ in two population-based samples of children in the U.S. The present study tested this allelic association for German adults with high vs. average IQ scores. The high IQ adults (N=47) were members of Mensa, an organization whose membership criterion is an IQ score above 130. Their EST00083 allelic frequencies were compared to the allelic frequencies for a control group of adults (N=77) whose IQ scores were less than 110 as estimated from short-term memory and speed-of information-processing tests. Although the differences between the two studies are considerable, the present results do not provide support for the hypothesis that EST00083 is associated with high IQ.     

Were the Victorians cleverer than us? The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time

The Victorian era was marked by an explosion of innovation and genius, per capita rates of which appear to have declined subsequently. The presence of dysgenic fertility for IQ amongst Western nations, starting in the 19th century, suggests that these trends might be related to declining IQ. This is because high-IQ people are more productive and more creative. We tested the hypothesis that the Victorians were cleverer than modern populations, using high-quality instruments, namely measures of simple visual reaction time in a meta-analytic study. Simple reaction time measures correlate substantially with measures of general intelligence (g) and are considered elementary measures of cognition. In this study we used the data on the secular slowing of simple reaction time described in a meta-analysis of 14 age-matched studies from Western countries conducted between 1889 and 2004 to estimate the decline in g that may have resulted from the presence of dysgenic fertility. Using psychometric meta-analysis we computed the true correlation between simple reaction time and g, yielding a decline of − 1.16 IQ points per decade or − 13.35 IQ points since Victorian times. These findings strongly indicate that with respect to g the Victorians were substantially cleverer than modern Western populations.     

Young male violent death trends in the general population during the Vietnam era.

Suicide and homicide rates significantly increased throughout the Vietnam War among young American civilian males who constituted the principal manpower pool for the war. Ironically, men who reached military age after the war were at greatest risk. Years of high combat intensity were not associated with higher suicide or homicide rates than years of low combat intensity. Suicide and homicide rates were correlated at .95, suggesting a common source of pathogenesis. No similar trend was found for motor vehicle death. Broad social forces, not the Vietnam War itself, were responsible for the changes in violent mortality trends that we observed among the birth cohorts of men in our study.     

The association of childhood intelligence with mortality risk from adolescence to middle age: Findings from the Aberdeen Children of the 1950s cohort study

There is growing evidence that childhood IQ is inversely associated with mortality in later life. However, the specificity of this association in terms of causes of death, whether it is continuous over the whole range of IQ scores and whether it is the same according to age and sex is not clear. In a large cohort (N = 11,603) of a complete population of children born in one city in the UK in the early 1950s, IQ measured at age 7 years (using a routinely administered picture test) was found to be inversely associated with mortality between the ages of 15 and 57 years. For every 1 SD increase in IQ at 7, the all cause mortality hazard ratio was 0.79 (95% CI 0.73, 0.85). On adjustment for a range of perinatal factors, father's social class at birth, number of sibs in the household and childhood height and weight, this was attenuated slightly to 0.81 (0.74, 0.88). Almost identical associations of IQ with mortality were seen for men and women as well as at younger (15–39) and older (40+) ages. These associations were across the entire IQ range, although some of the high mortality in the lowest category of IQ (< 70) was accounted for by causes associated with congenital disorders. Overall, external causes of death showed the strongest association, with weaker associations being seen for cancer. Further work is required to understand the mechanisms whereby childhood IQ has such a robust association with mortality in later life.     

Effects of Recent and Past Stress on Mental Health: Coping with Unemployment Among Vietnam Veterans and Nonveterans1

To determine the additive as well as interactive effects of pre-war stresses (adolescence), Vietnam war stresses (combat experiences) and post-war stresses (job loss, other life events), interview data were collected from a sample of 486 males who were eligible for service during the Vietnam war era. Of these respondents, 297 had recently lost their job and thus became subjected to the stress of unemployment. Our findings, like those of others (Egendorf, Kadushin, Laufer, Rothbart, & Sloan, 1981; Boulanger, 1981), suggest that exposure to war produces long-lasting effects on emotional well-being. Similarly, stressful childhood and adolescence experiences also appear to be long-lasting. In contrast to the long-lasting effects of these past stresses, the harmful effects of unemployment on mental health are reversed when employment is regained. All of the past pre-war and war stresses, and the recent unemployment and other stressful life events that were investigated had independent, adverse, main effects on mental health. Social support and internal control orientation had independent, positive, main effects on mental health. Of the various recent and past stresses, only the recent ones, unemployment and later unpleasant life events, had an additional exacerbating (interactive) effect on mental health.     

Genetic and environmental transactions underlying educational attainment

This report used a population-representative longitudinal twin study with two birth cohorts to explore the association between intelligence and education by understanding how genetic and environmental influences on intelligence moderate genetic and environmental influences on school grades and educational attainment. Nonshared environmental influences on grades were strong when IQ was low, but decreased across the range of IQ. Shared environmental influences common to age 24 educational attainment and age 17 IQ were strong when IQ was low, but genetic influences common to IQ and education were strong when IQ was high. These results suggest that the causal mechanisms linking educational variables with intelligence differ for people with different levels of intelligence.     

IQ/fertility relationships in Japan and Sweden

This study explores the relationship between intelligence and family size in Japan and Sweden. In Japan, there is no relationship, once father's education is controlled for. However, if father's education is not controlled for, then there is a negative relationship between IQ and number of siblings. In Sweden, there is a positive relationship between IQ and fertility only for the male cohort born between 1915 and 1924. The remaining relationships, for both females and males, are neither negative nor positive.     

Philosophy of medicine in the Netherlands

This report explores the relationship between philosophy and medicine in the Netherlands. In Section 1 we outline the ups and downs of medico-philosophical research in our country: pre-war flourishing, post-war decline, and modern renaissance. In Section 2 we review recent Dutch literature in the philosophy of medicine. The topics dealt with include methodology of medical science, alternative medicine, the basic concepts of medicine, anthropological medicine, medicalization, medicine and culture, and health care ethics.     

Cohort differences in cognitive aging and terminal decline in the Seattle Longitudinal Study

Life span researchers have long been interested in how and why fundamental aspects of human ontogeny differ between cohorts of people who have lived through different historical epochs. When examined at the same age, later born cohorts are often cognitively and physically fitter than earlier born cohorts. Less is known, however, about cohort differences in the rate of cognitive aging and if, at the very end of life, pervasive mortality-related processes overshadow and minimize cohort differences. We used data on 5 primary mental abilities from the Seattle Longitudinal Study (Schaie, 2005) to compare both age-related and mortality-related changes between earlier born cohorts (1886-1913) and later born cohorts (1914-1948). Our models covary for several individual and cohort differences in central indicators of life expectancy, education, health, and gender. Age-related growth models corroborate and extend earlier findings by documenting level differences at age 70 of up to 0.50 SD and less steep rates of cognitive aging on all abilities between 50 and 80 years of age favoring the later born cohort. In contrast, mortality-related models provide limited support for positive cohort differences. The later born cohort showed steeper mortality-related declines. We discuss possible reasons why often reported positive secular trends in age-related processes may not generalize to the vulnerable segment of the population that is close to death and suggest routes for further inquiry.     

Birth-cohort effects in the association between personality and fertility

The present study investigated whether associations between individuals' personality traits and whether they have children have been modified by birth-cohort effects in the 20th-century United States. Participants were from the Midlife Development in the United States study (n = 6,259) and the Wisconsin Longitudinal Study (n = 3,994) and were born between 1914 and 1974. Data on personality traits of the Five Factor model and fertility history were collected in adulthood. Higher levels of openness to experience in both sexes and higher levels of conscientiousness in women were associated with lower fertility, and these associations strengthened linearly as birth cohorts became younger. In the total sample, high extraversion, low neuroticism, and women's high agreeableness were associated with high fertility rate, but there were no systematic cohort effects. The fertility decisions of people with certain personality traits may be influenced by prevailing societal and cultural circumstances.     

Twin-singleton differences in intelligence: a meta-analysis

Since the emergence of twin studies in the 1920s, time and again the question of possible twin-singleton differences in intelligence has been posed. This study addressed the issue through a meta-analysis of published studies on this theme. Twins on the average seem to have lower IQs than singletons. The best estimate for this group difference is 4.2 IQ points (less than one-third of a standard deviation), with a great divide between study outcomes of less vs more recent birth cohorts (5.1 vs 0.5 IQ points, respectively). The evidence is based on studies from six countries (including population-based ones of entire birth cohorts), a massive database (comparisons of more than 30,000 twins with nearly 1.6 million singletons), a variety of intelligence tests, and birth cohorts spanning most of the 20th century, but, for the most part, on an age range limited to children and adolescents. The effect shows considerable between-study heterogeneity but appears robust (fail-safe N calculations), not due to influential individual studies (sensitivity analysis) or publication bias, was present since the very first published studies (cumulative meta-analysis), and appears generalizable across sex, zygosity, and other intelligence domains beyond the verbal. There are insufficient data as to whether the effect persists over the lifespan, exists as well within families, or has ceased in recent birth cohorts of highly developed countries (Denmark and The Netherlands). Likely causes of the effect appear to be prenatal and perinatal factors (reduced fetal growth and shorter gestation for twins).     

How does the strength of the relationships between cognitive abilities evolve over the life span for low-IQ vs high-IQ adults?

The present study was designed to examine how the correlations between cognitive abilities evolve during adulthood. Data from 1104 participants on the French version of the Wechsler Adult Intelligence Scale-Third Edition were analyzed. The entire sample was divided into four age groups (16–24 years; 25–44 years; 45–69 years and 70–89 years), which were themselves split into two IQ-levels using the mean standard score on Vocabulary and Block Design. For every age group, the mean correlation between subtest scores of low-IQ participants was higher than that of high-IQ participants. There was also no interaction between age and IQ for the strength of subtest relationships. Indeed, the effect sizes of correlation differences between low- and high-IQ participants appeared to be relatively constant across age. A general developmental schema of how the strength of correlations between cognitive abilities of low- and high-IQ individuals evolves during the entire life span is sketched in the discussion.     

Estimating the strength of genetic selection against heritable g in a sample of 3520 Americans,sourced from MIDUS II

The relationship between IQ and completed fertility among a sample of 3520 Americans from MIDUS II (1960's birth cohorts) is examined using a common factor comprised of eight cognitive ability measures, in order to determine the rate of phenotypic IQ loss due to genetic selection. Negative correlations are present in both the male and female subsamples, and are associated with a predicted loss in heritable g (g.h) of − .262 points per decade, increasing to − 1.072 points when the additive effect of mutation accumulation is considered. The ability–fertility associations showed Jensen effects at the level of the whole sample (.167), and also separately for each sex (.185 and .147 for the females and males respectively). The magnitude of the expected g.h loss in this cohort due to selection is comparable to that derived from a meta-analysis of disattenuated decadal g.h declines from eight US studies (− .44 points per decade; N = 127,389). There is a Flynn effect in the US amounting to gains of 3.6 points per decade, which are concentrated on more environmentally plastic and specialized sources of ability variance (s.e) suggesting co-occurrent socio-ecological specialization with respect to narrower cognitive abilities in the present cohort.     

Cross-national social ecology of intelligence and suicide prevalence: integration, refinement, and update of studies

This study integrates, refines, and updates previous findings pertaining to positive ecologic (population-level) associations between intelligence and suicide prevalence across nations by using corrected and revised national IQ estimates and, further, a quality-of-human-conditions index, both recently published by Lynn and Vanhanen. Across a global 85-nation sample of sex-specific total suicide rates and a Eurasian 48-nation sample of sex-specific elderly suicide rates, these were positively associated with updated national IQ estimates. The associations were stronger for the general population than for elderly persons, independent of the quality of human conditions, and notedly stronger in exponential fitting of suicide rates with national IQ than in linear fitting, thereby indicating that shifts or differences in national IQ correspond to proportional, not absolute, changes in suicide rates. Implications of these findings and the question of generalizability of such associations to the individual level are discussed.     

A state level investigation of the associations among intellectual capital, religiosity and reproductive health

The current study examines the degree to which state intellectual capital, state religiosity and reproductive health form a meaningful nexus of ecological relations. Though the specific magnitude of effects vary across outcomes, results from hierarchical regression analyses were consistent with the hypothesized path model indicating that a state's intellectual capital (as indicated by average state IQ and graduation rates at various levels) has a positive overall effect on state reproductive health statistics, whereas state religiosity generally has a negative impact. Specifically, both IQ and education were positively associated with breastfeeding rates, immunization rates, and rates of mammography screening, and negatively associated with teen fertility rates and infant mortality rates. Additionally, results confirm that education rates partially mediate the influence of IQ onto religiosity, and both education and religiosity partially or fully mediate the relation between IQ and state health (depending on specific outcome measure). The current results are consistent with a growing interdisciplinary literature establishing that individual, state and national well-being is substantially related to general mental ability and its covariates.     

Personality Traits Increasingly Important for Male Fertility: Evidence from Norway

We study the relationship between personality traits and fertility using a survey of Norwegian men and women born from 1927 to 1968 (N = 7017 individuals). We found that personality relates to men's and women's fertility differently; conscientiousness decreases female fertility, openness decreases male fertility and extraversion raises the fertility of both sexes. Neuroticism depresses fertility for men, but only for those born after 1956. The lower male fertility in younger cohorts high in neuroticism cannot be explained by partnership status, income or education. The proportion of childless men (at age 40 years) has increased rapidly for Norwegian male cohorts from 1940 to 1970 (from about 15 to 25 per cent). For women, it has only increased marginally (from 10 to 13 per cent). Our findings suggest that this could be partly explained by the increasing importance of personality characteristics for men's probability of becoming fathers. Men that have certain personality traits may increasingly be avoiding the long‐term commitment of having children, or their female partners are shunning entering this type of commitment with them. Childbearing in contemporary richer countries may be less likely to be influenced by economic necessities and more by individual partner characteristics, such as personality. Copyright © 2013 European Association of Personality Psychology     

ERP and behavioral evidence of individual differences in metaphor comprehension

In two experiments, we examined individual differences in metaphor processing. In Experiment 1, the subjects judged the literal truth of literal, metaphorical, and scrambled sentences. Overall, metaphors were more difficult to judge as false, in comparison with scrambled controls, suggesting that the metaphorical meaning was being processed automatically. However, there were individual differences in that high-IQ subjects showed more interference. These effects were reflected in ERP amplitude differences at the onset of N400 and after the response. In Experiment 2, the subjects completed IQ tests and a series of working memory tests and then rated and interpreted the same set of metaphors. The results showed that IQ was correlated with working memory capacity and that low-IQ subjects had similar ratings but poorer quality interpretations than did high-IQ subjects. The results were most consistent with a constraint satisfaction approach to metaphor comprehension.