How fragile is our intellect? Estimating losses in general intelligence due to both selection and mutation accumulation

Two dysgenic models of declining general intelligence have been proposed. The first posits that since the Industrial Revolution those with low g have had a reproductive advantage over those with high g. The second posits that relaxed purifying selection against deleterious mutations in modern populations has led to g declining due to mutation accumulation. Here, a meta-analytic estimate of the decline due to selection is computed across nine US and UK studies, revealing a loss of .39 points per decade (combined N = 202,924). By combining findings from a high-precision study of the effects of paternal age on offspring g with a study of paternal age and offspring de novo mutation numbers, it is proposed that, 70 de novo mutations per familial generation should reduce offspring g by 2.94 points, or .84 points per decade. Combining the selection and mutation accumulation losses yields a potential overall dysgenic loss of 1.23 points per decade, with upper and lower bound values ranging from 1.92 to .53 points per decade. This estimate is close to those from studies employing the secular slowing of simple reaction time as a potential indicator of declining g, consistent with predictions that mutation accumulation may play a role in these findings.     

Testing the hypothesized effect of dysgenic fertility on intelligence with existing reaction time data: A comment on Woodley,te Nijenhuis,and Murphy (2013)

Dysgenic fertility has supposedly resulted in a decline in general intelligence (g) over time. In light of evidence that simple visual reaction time (RT) is inversely related to IQ, Woodley et al. (2013) tested the hypothesized dysgenic effect by subjecting to a meta-regression simple visual RT data collected over 100 years in 15 studies. This analysis found that RT had significantly increased according to a linear function over this time period. Woodley et al. then used this result to estimate the rate at which g had declined over the same period. The present comment points out that there are large gaps in the distribution of RTs analyzed by Woodley et al. with respect to year tested, and that RT in males did not vary as a function of year in the 13 studies published from 1941 on. It is concluded that although existing data are consistent with the idea that g has been adversely affected by dysgenic fertility, it cannot be determined at what rate g has fallen over time.     

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.     

A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal Survey of Youth

In this study we attempt to determine whether dysgenic fertility is associated with the Jensen effect. This is investigated with respect to a US population representative sample of 8110 individuals from the National Longitudinal Survey of Youth for whom there exists complete data on IQ and fertility. In addition to the general sample, the sample was also broken out by race and sex so as to examine whether or not the Jensen effect manifested amongst different sub-populations. The method of correlated vectors revealed significant Jensen effects in five of the seven samples, and in all cases the effect was in a direction indicating that subtests with higher g-loadings were associated with larger dysgenic fertility gradients. The magnitude of the difference between Spearman’s ρ and Pearson’s r was non-significant in all cases, suggesting that biasing factors were minimally influencing the result. This finding suggests that dysgenesis occurs on the ‘genetic g’ at the heart of the Jensen effect nexus, unlike the Flynn effect, which is ‘hollow’ with respect to g. Finally, the finding is discussed in the context of two converging lines of evidence indicating that genotypic IQ or ‘genetic g’ really has been declining over the last century.     

A smarter brain is associated with stronger neural interaction in healthy young females: A resting EEG coherence study

General intelligence, the g factor, is a major issue in psychology and neuroscience. However, the neural mechanism of the g factor is still not clear. It is suggested that the g factor should be non-modular (a property across the brain) and show good colinearity with various cognitive tests. This study examines the hypothesis that functional connectivity may be a good candidate for the g factor. We recorded resting state eyes-closed EEG signals in 184 healthy young females. Coherence values of 38 selected channel pairs across delta, theta, alpha, beta and gamma frequencies were correlated with six intelligence quotient (IQ) subtests, including symbol search, block design, object assembly, digit span, similarity and arithmetic. A three-stage analytic flow was constructed to delineate common (g factor) and unique neural components of intelligence. It is noticed that the coherence pattern demonstrates good correlation with five of the IQ subtests (except symbol search) and non-modularity in the brain. Our commonality analyses support connectivity strength in the brain as a good indicator of the g factor. For the digit span and arithmetic tests, the uniqueness analyses provide left-lateralized topography relevant to the operation of working memory. Performance on the arithmetic test is further correlated with strengths at left temporo-parietal and bilateral temporal connections. All the significant correlations are positive, indicating that the stronger the connectivity strengths, the higher the intelligence. Our analyses conclude that a smarter brain is associated with stronger interaction in the central nervous system. The implication and why the symbol search does not show parallel results are discussed.     

Associations between cortical thickness and general intelligence in children,adolescents and young adults

Neuroimaging research indicates that human intellectual ability is related to brain structure including the thickness of the cerebral cortex. Most studies indicate that general intelligence is positively associated with cortical thickness in areas of association cortex distributed throughout both brain hemispheres. In this study, we performed a cortical thickness mapping analysis on data from 182 healthy typically developing males and females ages 9 to 24 years to identify correlates of general intelligence (g) scores. To determine if these correlates also mediate associations of specific cognitive abilities with cortical thickness, we regressed specific cognitive test scores on g scores and analyzed the residuals with respect to cortical thickness. The effect of age on the association between cortical thickness and intelligence was examined. We found a widely distributed pattern of positive associations between cortical thickness and g scores, as derived from the first unrotated principal factor of a factor analysis of Wechsler Abbreviated Scale of Intelligence (WASI) subtest scores. After WASI specific cognitive subtest scores were regressed on g factor scores, the residual score variances did not correlate significantly with cortical thickness in the full sample with age covaried. When participants were grouped at the age median, significant positive associations of cortical thickness were obtained in the older group for g-residualized scores on Block Design (a measure of visual-motor integrative processing) while significant negative associations of cortical thickness were observed in the younger group for g-residualized Vocabulary scores. These results regarding correlates of general intelligence are concordant with the existing literature, while the findings from younger versus older subgroups have implications for future research on brain structural correlates of specific cognitive abilities, as well as the cognitive domain specificity of behavioral performance correlates of normative gray matter thinning during adolescence.     

The Flynn effect,group differences,and g loadings

Flynn effect gains are predominantly driven by environmental factors. Might these factors also be responsible for group differences in intelligence? Group differences in intelligence have been clearly shown to strongly correlate with g loadings. The empirical studies on whether the pattern of Flynn effect gains is the same as the pattern of group differences yield conflicting findings. We present new evidence on the topic using a number of datasets from the US and the Netherlands. Score gains and g loadings showed a small negative average correlation. The general picture is now that there is a small, negative correlation between g loadings and Flynn effect gains. It appears that the Flynn effect and group differences have different causes.     

Expanding the g-nexus: Further evidence regarding the relations among national IQ, religiosity and national health outcomes

The current study seeks to better understand how religiosity and health are positioned within the g-nexus. Specifically, the degree to which differences in average IQ across nations is associated with differences in national religiosity (i.e., belief rate) and national health statistics independent of differences in national wealth is examined. Consistent with expectations, results show that, independent of national wealth and belief rate, IQ has a positive influence on national health as indicated by fertility rate, infant mortality rate, maternal mortality rate, and deaths due to HIV/AIDS, and life expectancy. Additionally, as hypothesized, IQ and belief rate interacted to influence reproductive health (i.e., fertility rate, infant- and maternal mortality). Specifically, high IQ acts as a buffer against the negative effects of belief rate; when IQ is high belief rate has no effect, but when IQ is low belief rate has a strong negative effect. The pattern of findings from this study, combined with previous research, serve to confirm that general cognitive ability (i.e., the g-factor) is an important and central node within a larger nexus of psychological and social variables. Theoretical and epidemiological implications are discussed.     

The forest and the trees: Examining the association of self-compassion and its positive and negative components with psychological functioning

ABSTRACT

This paper presents two studies focusing on the link between psychological functioning and self-compassion as measured by the Self-Compassion Scale (SCS), especially in terms of SCS components that represent increased compassionate and reduced uncompassionate behavior. Study One examined this association in seven domains – psychopathology, positive psychological health, emotional intelligence, self-concept, body image, motivation, and interpersonal functioning – and found that while reduced negative self-responding had a stronger link to negative emotionality and self-evaluation than positive self-responding, they were roughly equivalent predictors in other domains. Study Two examined the association of compassionate and reduced uncompassionate behavior with sympathetic nervous system and inflammatory activity after stress, and found they equally predicted salivary alpha amylase and interleukin-6 levels in individuals after a stressful situation. Overall, results suggest that both compassionate and reduced uncompassionate self-responding are central to self-compassion and that both help to explain its link to healthy psychological functioning.     

Intelligence and emotional disorders: Is the worrying and ruminating mind a more intelligent mind?

Previous research has shown that anxiety and depression symptoms are negatively associated with measures of intelligence. However, this research has often not taken state distress and test anxiety into account, and recent findings indicate possible positive relationships between generalized anxiety disorder (GAD), worry, and intelligence. The present study examined the relationships between GAD, depression, and social anxiety symptoms, as well as their underlying cognitive processes of worry, rumination, and post-event processing, with verbal and non-verbal intelligence in an undergraduate sample (N = 126). While the results indicate that verbal intelligence has positive relationships with GAD and depression symptoms when test anxiety and state negative affect were taken into account, these relationships became non-significant when overlapping variance was controlled for. However, verbal intelligence was a unique positive predictor of worry and rumination severity. Non-verbal intelligence was a unique negative predictor of post-event processing. The possible connections between intelligence and the cognitive processes that underlie emotional disorders are discussed.     

Positive and negative characteristics of marital interaction and their association with marital satisfaction in middle-aged and older couples

The study examined age differences in positive (e.g., warm) and negative (e.g., hostile) characteristics of marital interactions between middle-aged and older couples and whether these characteristics were differentially associated with marital satisfaction by age. Spouses' perception of partners' positive and negative behavior during marital interaction was assessed in general and following disagreement and collaborative tasks. Trained observers coded spouses' positive and negative behavior during interactions. Older individuals reported higher marital satisfaction and perceived their spouse's behavior as less negative in general and more positive across all contexts than middle-aged individuals. Spouses' perceptions of their partners' positive and negative behavior independently predicted marital satisfaction for both age groups across contexts. Perceptions of partners' negative behavior in general and of both positive and negative behavior in the disagreement task were more closely associated with marital satisfaction for older spouses than for middle-aged spouses. Results point to the importance of positive and negative characteristics in marital functioning across age cohorts and indicate that such characteristics may be context dependent. Findings suggest that, in some contexts, both positive and negative characteristics are more salient for older adults.     

On the interpretation of the CHC factor Gc

On the one hand, the factors Gf and Gc in the Cattell-Horn-Carroll (CHC) model of intelligence are hypothesized to represent individual differences in unique psychological or biological capacities. On the other hand, they are interpreted as representing the theoretical variables fluid and crystallized intelligence in investment theory. With respect to Gc, this leads to a theoretical conflict because in investment theory crystallized intelligence is not a capacity but purely a statistical entity. We contend that if CHC factor Gc represents a capacity, it cannot represent crystallized intelligence, and if Gc represents crystallized intelligence, it does not represent a capacity. In addition, from our discussion of Gc, we conclude that in investment theory the factors Gf and g represent one and the same capacity. In support of our theoretical conclusions, we implemented the CHC model in a confirmatory factor analysis of a HCA (Human Cognitive Abilities project) data set. As expected, Gf and g were statistically indistinguishable. Gc was effectively absent, because it was statistically equivalent to verbal comprehension. Factors Gc and g could be removed from the model without any reduction in model fit. We argue that in the CHC taxonomy the factors Gc and g are redundant as explanatory variables.     

Social status,cognitive ability,and educational attainment as predictors of liberal social attitudes and political trust

We examined the prospective associations between family socio-economic background, childhood intelligence (g) at age 11, educational and occupational attainment, and social attitudes at age 33 in a large (N = 8804), representative sample of the British population born in 1958. Structural equation Modeling identified a latent trait of ‘liberal social attitudes’ underlying attitude factors that are antiracist, socially liberal, and in support of gender equality. Another attitude factor—‘political trust’—was relatively independent from the latent attitude trait and has somewhat different pathways in relation to the other variables included in the analysis. There was a direct association between higher g at age 11 and more liberal social attitudes and political trust at age 33. For both men and women the association between g and liberal social attitudes was partly mediated via educational qualifications, and to a much lesser extent via adult occupational attainment. For women the association between g and political trust was partly mediated through both educational qualification and occupational attainment, and for men it was mediated mainly via occupational attainment. Men and women who had higher educational qualifications and higher occupational status tend to be more socially liberal and more trusting of the democratic political system. In terms of socio-economic background, people from less privileged families showed less political trust, but did not differ much in liberal social attitudes from those born into relatively more privileged circumstances. This study shows that social background, cognitive ability, education, and own social status influence perceptions of society.     

Parents’ Intelligence Mindsets Relate to Child Internalizing Problems: Moderation Through Child Gender

Parental belief systems can strongly influence children’s affect, behavior, and mental health. However, associations between specific kinds of parental beliefs and children’s mental health have not been thoroughly explored. One relevant belief system is parental intelligence mindset: beliefs about the malleability of intelligence. Children of parents who view intelligence as static (known as a fixed intelligence mindset), rather than malleable through effort (known as a growth intelligence mindset), experience more academic, self-regulatory, and motivational difficulty. However, associations between parental intelligence mindset and child mental health problems are unclear. Accordingly, we tested whether parents’ intelligence mindsets related to internalizing problems in their children (N?=?131, ages 5–8). Overall, parents with stronger fixed intelligence mindsets had children with greater internalizing problems, particularly social anxiety (characterized by fear of negative evaluation). Results further revealed that parents’ fixed intelligence mindsets were associated with overall internalizing problems and depressive symptoms in boys, but not girls. Results are the first to suggest and parse direct links between parents’ intelligence mindsets and youth internalizing problems.     

Associative learning predicts intelligence above and beyond working memory and processing speed

Recent evidence suggests the existence of multiple cognitive mechanisms that support the general cognitive ability factor (g). Working memory and processing speed are the two best established candidate mechanisms. Relatively little attention has been given to the possibility that associative learning is an additional mechanism contributing to g. The present study tested the hypothesis that associative learning ability, as assessed by psychometrically sound associative learning tasks, would predict variance in g above and beyond the variance predicted by working memory capacity and processing speed. This hypothesis was confirmed in a sample of 169 adolescents, using structural equation modeling. Associative learning, working memory, and processing speed all contributed significant unique variance to g, indicating not only that multiple elementary cognitive processes underlie intelligence, but also the novel finding that associative learning is one such process.     

An examination of the differential relationship of marital discord to parents' discipline strategies for boys and girls

Previous research has tentatively indicated that coercive, ineffective parenting might have a mediating role in the differential impact of marital discord on boys and girls. To further explore this role, we examined the relationship between children's perceptions of marital discord and their evaluations of parental discipline techniques. Ninety-one children aged 8 to 13 years (mean age: 11 years 4 months) were split into high, moderate, and low perceived marital discord on the basis of their responses to the Children's Perceptions Questionnaire (Emery & O'Leary, 1982). The children rated how coercive they believed both mothers and fathers would and should be in three discipline situations. Children with high marital discord indicated that both mothers and fathers would and should use more coercive behavior than did children with low marital discord. The effects of marital discord were stronger for boys than for girls. All children also believed that fathers would and should be more coercive than mothers. Results are discussed in relation to the effects of marital discord on children's social development with regard to sex of the child.Thanks are due to Mike Siegal and Pat Noller for their helpful comments on previous drafts.     

Social comparison and the drive upward revisited: Affiliation as a response to marital stress

To test theoretical ideas derived from classic and recent social comparison theory, two studies examined affiliative tendencies as a response to marital problems among individuals varying in marital dissatisfaction. Study 1 (n. = 632) showed that the higher the degree of marital dissatisfaction and the higher the uncertainty about how things are going in one's marriage, the stronger was the desire for affiliation (operationalized as the desire to talk with others about one's marriage). Moreover, among individuals high in marital dissatisfaction, a preference for upward affiliation was found, i.e. for contact with others having better marriages. Individuals with lower levels of dissatisfaction preferred affiliation with similar others. Women experienced more uncertainty and a stronger affiliative tendency than men. In Study 2 (n = 233), these findings were largely replicated. Moreover, it was shown that the desire to affiliate when facing marital stress was particularly strong among individuals high in interpersonal orientation.     

Sex differences in brain volume are related to specific skills, not to general intelligence

It has been proposed that males would show higher mean scores than females in general intelligence (g) because (1) men have, on average, larger brains than women, and (2) brain volume correlates with g. Here we report a failure to support the conclusion derived from these premises. High resolution MRIs were acquired in a sample of one hundred healthy young participants for estimating total, gray, and white matter volumes. Participants also completed an intelligence battery - comprising tests measuring abstract, verbal, and spatial abilities - that allowed the extraction of g scores. Results showed consistent relations between sex differences in brain volumes and non-g spatial and verbal skills but not for g.     

The reproduction of intelligence

Although a negative relationship between fertility and education has been described consistently in most countries of the world, less is known about the relationship between intelligence and reproductive outcomes. Also the paths through which intelligence influences reproductive outcomes are uncertain. The present study uses the NLSY79 to analyze the relationship of intelligence measured in 1980 with the number of children reported in 2004, when the respondents were between 39 and 47 years old. Intelligence is negatively related to the number of children, with partial correlations (age controlled) of ?.156, ?.069, ?.235 and ?.028 for White females, White males, Black females and Black males, respectively. This effect is related mainly to the g-factor. It is mediated in part by education and income, and to a lesser extent by the more “liberal” gender attitudes of more intelligent people. In the absence of migration and with constant environment, genetic selection would reduce the average IQ of the US population by about .8 points per generation.     

Average intelligence predicts atheism rates across 137 nations

Evidence is reviewed pointing to a negative relationship between intelligence and religious belief in the United States and Europe. It is shown that intelligence measured as psychometric g is negatively related to religious belief. We also examine whether this negative relationship between intelligence and religious belief is present between nations. We find that in a sample of 137 countries the correlation between national IQ and disbelief in God is 0.60.