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How Cognitive Genetic Factors Influence Fertility Outcomes: A Mediational SEM Analysis
Abstract
Utilizing a newly released cognitive Polygenic Score (PGS) from Wave IV of Add Health ( n = 1,886), structural equation models (SEMs) examining the relationship between PGS and fertility (which is approximately 50% complete in the present sample), employing measures of verbal IQ and educational attainment as potential mediators, were estimated. The results of indirect pathway models revealed that verbal IQ mediates the positive relationship between PGS and educational attainment, and educational attainment in turn mediates the negative relationship between verbal IQ and a latent fertility measure. The direct path from PGS to fertility was non-significant. The model was robust to controlling for age, sex, and race; furthermore, the results of a multigroup SEM revealed no significant differences in the estimated path coeficients across sex. These results indicate that those predisposed towards higher verbal IQ by virtue of higher PGS values are also predisposed towards trading fertility against time spent in education, which contributes to those with higher PGS values producing fewer offspring at this stage in their life course.
... One of the most strongly associated markers, SNP rs4851266-T, has been described as raising verbal IQ by 2.8 points in comparisons between those homozygous for the high-IQ versus the low-IQ allele (Gunnarsson et al., 2016). Evidence from AddHealth, using a polygenic score based on Rietveld et al. (2013), found that this particular polygenic score is more closely related to scores on intelligence tests than to educational outcomes (Woodley of Menie, Schwartz & Beaver, 2016). This shows that there is broad overlap between genetic variants affecting intelligence and those affecting educational outcomes. ...
... There is direct evidence that in the United States today, those with higher polygenic scores on "educational attainment" have fewer children on average than those with lower polygenic scores (Beauchamp, 2016;Conley et al., 2016;Sanjak et al., 2018;Woodley of Menie, Schwartz & Beaver, 2016). Therefore, the next generation will be less well equipped than the parental generation with alleles that are not only statistically but also causally associated with higher educational attainment. ...
... As shared family environment is only a minor contributor to individual differences in cognitive test scores during adult life (Haworth et al., 2010;Kaplan, 2012), the effect of differential fertility is mainly genetic. This has been confirmed in recent studies which showed that fertility is predicted by polygenic scores, computed from genetic variants that are statistically associated with higher educational attainment (Beauchamp, 2016;Conley et al., 2016;Kong et al., 2017;Sanjak et al., 2018;Woodley of Menie, Schwartz & Beaver, 2016). Most of these genetic polymorphisms are thought to be related to intelligence, because they predict intelligence as well as or better than educational attainment (Woodley of Menie, Schwartz & Beaver, 2016). ...
Although the relationship between social dominance status and reproductive success is universally positive in those species in which the relationship has been studied, in human societies today the relationship is more often negative. The present study uses detailed information from the General Social Survey in the United States to address this apparent paradox. Results show that education and intelligence had negative relationships with number of children across birth cohorts during most or all of the 20th century. Family income has only minor effects, especially when marital fertility rather than total cohort fertility is considered. The results do not support sociobiological predictions that modern humans turn material resources into reproductive success. Religion, ideology and income are identified as factors that influence the relationship between intelligence and fertility. Results are discussed in the broader context of emerging knowledge in demographics and molecular genetics, especially with respect to the direction of biological and cultural evolution in the modern United States and in modern societies more generally.
... These processes plausibly undergird the precipitous fall of per capita rates of eminent intellectual figures (Murray, 2003) and rates of macro-innovation around the end of the British industrial revolution (Huebner, 2005;Murray, 2003), since both altruism and high g.h are components of eminence and eminent individuals are chiefly responsible for the provision of macro-innovations . Though some may find reassurance in the fact that these trends have not arrested economic growth -owing largely to epigenetic 8 shifts fostering the cultivation of slower life histories 9 coupled with increasing cognitive ability specialization latent in the Flynn effect (Pietschnig & Voracek, 2015;Woodley, 2012a;Woodley of Menie et al., 2016) -it must be noted that they probably have slowed it substantially and threaten its long-run future (Meisenberg, 2014). ...
... Congruently, the direct correlations between intelligence and indicators of individual-level fitness such as completed fertility and sibship size have been consistently negative in the US and UK among cohorts born as far back as the 1880s (Lynn, 2011;Lynn & van Court, 2004). Recently, polygenic scores predictive of g and educational attainment have been found to negatively predict fertility, indicating that the negative phenotypic correlation is associated with genetic selection (Beauchamp, 2016a;Kong et al., 2017;Woodley of Menie, Schwartz & Beaver, 2016). ...
... Consonant with predictions from the multi-level selection model, apparent selection on intelligence -as indicated by the inverse correlation between fertility and IQ scores as well as proxies for IQ such as educational attainment and socioeconomic status -appears to have favored lower levels of the trait over the last century and a half (Lynn, 2011;Lynn & Van Court, 2004;Skirbekk, 2008). This has recently been corroborated via the finding of negative associations between fertility and genomic enrichment with respect to molecular genetic markers of g.h (Beauchamp, 2016a;Kong et al., 2017;Woodley of Menie, Schwartz & Beaver, 2016). Despite the presence of this dysgenic pressure, when the scores of different cohorts on psychometric IQ tests are compared in cross-sectional analyses, the tendency has been towards rising scores: the aforementioned Flynn effect (Flynn, 1987;Pietschnig & Voracek, 2015). ...
... One of the most strongly associated markers, SNP rs4851266-T, has been described as raising verbal IQ by 2.8 points in comparisons between those homozygous for the high-IQ versus the low-IQ allele (Gunnarsson et al., 2016). Evidence from AddHealth, using a polygenic score based on Rietveld et al. (2013), found that this particular polygenic score is more closely related to scores on intelligence tests than to educational outcomes (Woodley of Menie, Schwartz & Beaver, 2016). This shows that there is broad overlap between genetic variants affecting intelligence and those affecting educational outcomes. ...
... There is direct evidence that in the United States today, those with higher polygenic scores on "educational attainment" have fewer children on average than those with lower polygenic scores (Beauchamp, 2016;Conley et al., 2016;Sanjak et al., 2018;Woodley of Menie, Schwartz & Beaver, 2016). Therefore, the next generation will be less well equipped than the parental generation with alleles that are not only statistically but also causally associated with higher educational attainment. ...
... As shared family environment is only a minor contributor to individual differences in cognitive test scores during adult life ( Haworth et al., 2010;Kaplan, 2012), the effect of differential fertility is mainly genetic. This has been confirmed in recent studies which showed that fertility is predicted by polygenic scores, computed from genetic variants that are statistically associated with higher educational attainment (Beauchamp, 2016;Conley et al., 2016;Kong et al., 2017;Sanjak et al., 2018;Woodley of Menie, Schwartz & Beaver, 2016). Most of these genetic polymorphisms are thought to be related to intelligence, because they predict intelligence as well as or better than educational attainment (Woodley of Menie, Schwartz & Beaver, 2016). ...
... Genetic drift based models would make the assumption that the variants comprising POLY COG are selectively neutral, and that their distributions should therefore correspond to the action of genetic diffusion and population bottlenecks. It is unclear however why this would lead to modern genomes being higher in POLY COG relative to ancient ones, and is furthermore at odds with the observation from studies utilizing various alternative POLY COG that these do not appear to be selectively neutral in contemporary human populations (21,22,23,23,25,26). This leaves selection pressure acting on standing genetic variation and population expansion, replacement and admixture. ...
... (32), largely in response to factors such as the asymmetric use of birth control and prolonged exposure to education among those with high GCA (33). Consistent with this, it has been found that various POLY COG negatively predict fertility in contemporary Western populations (23,24,25,26). It is important to note that this microevolutionary process (working in the opposite direction) has likely attenuated the difference in POLY COG between the modern and ancient genomes noted in the present study. ...
Human populations living in Eurasia during the Holocene experienced considerable microevolutionary change. It has been predicted that the transition of Holocene populations into agrarianism and urbanization brought about culture-gene coevolution that favoured via directional selection genetic variants associated with higher general cognitive ability (GCA). To examine whether GCA might have risen during the Holocene, we compare a sample of 99 ancient Eurasian genomes (ranging from 4.56 to 1.21 kyr BP) with a sample of 503 modern European genomes, using three different cognitive polygenic scores. Significant differences favouring the modern genomes were found for all three polygenic scores (Odds Ratios=0.92, p =0.037; 0.81, p =0.001 and 0.81, p =0.02). Furthermore, a significant increase in positive allele count over 3.25 kyr was found using a subsample of 66 ancient genomes ( r =0.217, p one-taiied =0.04). These observations are consistent with the expectation that GCA rose during the Holocene.
... Finally, a study utilizing PGSs in a sample at approximately 50% completed fertility sourced from the US AddHealth dataset found substantial evidence of mediation, with the direct effect of the cognitive ability PGS on fertility being reduced to effectively zero after the indirect paths via cognitive ability and educational attainment were modeled (Woodley of Menie et al., 2016). This latter study discussed the need for genetically informed studies involving samples at completed fertility in order to replicate this mediation. ...
... It was found that number of children mediated the effect of age at first birth on the number of grandchildren. These results are consistent with the findings of Woodley of Menie et al. (2016), in that the impact of the PGS can be modeled as having mediated effects on the sample's fitness characteristics, via the cognitive phenotype, and in particular educational attainment (when this is modeled separately). This is consistent with the 'tradeoff' model (Lynn, 1996), whereby high-IQ individuals select for higher levels of educational attainment, which causes delayed fertility, and consequently lower numbers of both children and grandchildren. ...
Using newly available polygenic scores for educational attainment and cognitive ability, this paper investigates the possible presence and causes of a negative association between IQ and fertility in the Wisconsin Longitudinal Study sample, an issue that Retherford and Sewell first addressed 30 years ago. The effect of the polygenic score on the sample’s reproductive characteristics was indirect: a latent cognitive ability measure, comprised of both educational attainment and IQ, wholly mediated the relationship. Age at first birth mediated the negative effect of cognitive ability on sample fertility, which had a direct (positive) effect on the number of grandchildren. Significantly greater impacts of cognitive ability on the sample’s fertility characteristics were found among the female subsample. This indicates that, in this sample, having a genetic disposition toward higher cognitive ability does not directly reduce number of offspring; instead, higher cognitive ability is a risk factor for prolonging reproductive debut, which, especially for women, reduces the fertility window and, thus, the number of children and grandchildren that can be produced. By estimating the effect of the sample’s reproductive characteristics on the strength of polygenic selection, it was found that the genetic variance component of IQ should be declining at a rate between −.208 (95% CI [−.020, −.383]) and −.424 (95% CI [−.041, −.766]) points per decade, depending on whether GCTA-GREML or classical behavior genetic estimates of IQ heritability are used to correct for ‘missing’ heritability.
... Another prediction was that despite the increase in "phenotypic IQ", there should nevertheless be a decrease in "genotypic IQ". Moreover, this latter prediction has been confirmed several times over by empirical work showing both direct negative associations between polygenic scores predictive of cognitive ability (and proxies such as educational attainment) and fertility (Beauchamp, 2016a;Conley et al., 2016;Hugh-Jones & Abdellaoui, 2021;Kong et al., 2017;Woodley of Menie, Rindermann, Pallesen, & Sarraf, 2019;Woodley of Menie, Schwartz, & Beaver, 2016), and also a reduction in the frequency of alleles associated with cognitive ability over a span of multiple decades (Abdellaoui et al., 2019;Kong et al., 2017). ...
This paper discusses the co-occurrence model and its associated research program, and it argues that the model provides the best supported theory of secular changes in cognitive ability. The co-occurrence model offers a better solution to Cattell's paradox (relative to the alternatives in the literature), and it is able to accommodate Flynn's four major paradoxes also. A review of empirical work conducted in order to test the model's predictions demonstrates that many populations in which selection favors lower intelligence have experienced a decline in g or some cognitive ability variable that correlates with g, at the same time that average phenotypic IQ has increased. Moreover, since the co-occurrence model makes predictions about variables that are not directly concerned with cognitive ability testing, its research program can be extended to other domains of research.
... The studies included in this analysis range from the early 20th century (Willoughby, 1928) to current day (Wang, Fuerst, & Ren, 2016;Woodley of Menie, Schwartz, & Beaver, 2016). This provides us with two alternative approaches to exploring the g-fertility gradient over time. ...
The purpose of this study is to conduct a systematic review of the literature on the relationship between general cognitive ability and fertility among modern humans. Our goals were to (a) evaluate the state of the extant literature, and (b) provide a quantitative summary of effect sizes to the extent possible (given the limitations of the literature). A thorough search identified 17 unique datasets that passed the inclusion criteria. Using a Random Effects Model to evaluate the data, the overall weighted effect was r = −0.11, although the data also indicated a sex effect (stronger correlations among females than males), and a race effect (stronger correlations among Black and Hispanic populations compared to Whites). Importantly, the data suggest the correlation has been increasing in strength throughout the 20th century (and early 21st). Finally, we discovered several notable limitations of the extant literature; limitations that currently prohibit a psychometric meta-analysis. We discuss these issues with emphasis on improving future primary studies to allow for more effective meta-analytic investigations.
... This rapid increase in population-level IQ was subsequently termed the Flynn effect (Herrnstein and Murray 1994), after James Flynn, who Matthew A. Sarraf and Mateo Peñaherrera-Aguirre: Joint second authors demonstrated that these gains are ubiquitous across modernized and modernizing countries and are found on many cognitive ability measures (Flynn 1987;Pietschnig and Voracek 2015). Recent molecular research has confirmed that selection is acting directly against genetic variants associated with cognitive ability and related phenotypes, such as educational attainment, in certain populations (Beauchamp 2016;Conley et al. 2016;Kong et al. 2017;Woodley of Menie et al. 2016). Of particular note is a large study of the population of Iceland, which found evidence that an educational attainment polygenic score (a normally distributed genetic index comprised of multiple single nucleotide polymorphisms which collectively significantly predict phenotypic variance in a trait of interest) has declined over time across cohorts, at a rate consistent with the strength of selection acting against variants captured by this score in this population (Kong et al. 2017). ...
Several converging lines of evidence indicate that general intelligence (g) has declined in Western populations. The causes of these declines are debated. Here, two hypotheses are tested: (1) selection acting against genetic variants that promote g causes the decline and (2) the presence of neurotoxic pollution in the environment causes the decline. A linear mixed model was devised to test (1) and (2), in which the secular decline in a “heritable g” (g.h) chronometric factor (comprised of convergent indicators of simple reaction time, working memory, utilization frequencies of high difficulty and also social-intelligence-indicating vocabulary items and per capita macro-innovation rates) was predicted using a neurotoxin chronometric factor (comprised of convergent secular trends among measures of lead, mercury and dioxin + furan pollution, in addition to alcohol consumption) and a polygenic score chronometric factor (comprised of polygenic score means for genetic variants predictive of g, sourced from US and Icelandic age-stratified cohorts). Bivariate correlations revealed that (other than time) only the polygenic score factor was significantly associated with declining g.h (r = .393, p < .05 vs. .033, ns for the neurotoxin factor). Using a hierarchical linear mixed model approach incorporating 25 year lags between the predictors and g.h, time period, operationalized categorically as fifths of a century, accounted for the majority of the variance in the decline in g.h (partial η2 = .584, p < .05). Net of time period and neurotoxins, changing levels of polygenic scores also significantly predicted variance in the decline in g.h (partial η2 = .253, p < .05); however, changing levels of neurotoxins did not significantly predict variance in g.h net of time (partial η2 = .027 ns). Within-period analysis indicates that the independent significant positive effect of the polygenic score factor on g.h was restricted to the third fifth of a century period (β = .202, p < .05).
... The millennia-long microevolutionary trend favoring higher GCA not only ceased, but likely went into reverse among European-derived populations living in the 19th century (Lynn, 1996;Lynn & Van Court, 2004), largely in response to factors such as the asymmetric use of birth control and prolonged exposure to education among those with high GCA (Lynn, 1996). Consistent with this, it has been found that various POLY COG negatively predict reproductive success in contemporary Western populations (Beauchamp, 2016;Conley et al., 2016;Kong et al., 2017;Woodley of Menie, Schwartz et al., 2016). It is important to note that this recent microevolutionary trend (working in the opposite direction) has likely attenuated the difference in POLY COG between the modern and ancient genomes noted in the present study. ...
Human populations living during the Holocene underwent considerable microevolutionary change. It has been theorized that the transition of Holocene populations into agrarianism and urbanization brought about culture-gene co-evolution that favored via directional selection genetic variants associated with higher general cognitive ability (GCA). To examine whether GCA might have risen during the Holocene, we compare a sample of 99 ancient Eurasian genomes (ranging from 4.56 to 1.21 kyr BP) with a sample of 503 modern European genomes ( F st = 0.013), using three different cognitive polygenic scores (130 SNP, 9 SNP and 11 SNP). Significant differences favoring the modern genomes were found for all three polygenic scores (odds ratios = 0.92, p = 001; .81, p = 037; and .81, p = .02 respectively). These polygenic scores also outperformed the majority of scores assembled from random SNPs generated via a Monte Carlo model (between 76.4% and 84.6%). Furthermore, an indication of increasing positive allele count over 3.25 kyr was found using a subsample of 66 ancient genomes ( r = 0.22, p one-tailed = .04). These observations are consistent with the expectation that GCA rose during the Holocene.
... For nearly a century, studies of the relationship between cognitive ability measures and fertility have revealed negative relationships-indicating the existence of a selection pressure disfavoring high general intelligence (Woodley of Menie 2015). This has recently been substantiated utilizing genetic markers of general intelligence, which also negatively predict fertility outcomes (Beauchamp 2016;Woodley of Menie et al. 2016). Much trepidation has accompanied these findingsrevolving around the idea that the "dumbing down" of society will have severely negative consequences for future generations (Galton 1869;Lynn 1996). ...
Nothing is presently known about the relationship between individual differences in fertility and life history (LH) speed, as measured by the K-Factor. To examine this relationship, the correlation between LH speed and the number of children was examined in two, large samples (MIDUS II and the Swedish STAGE dataset). Their association was positive and statistically significant in both cross-national samples. The association was robust with respect to statistically controlling for participant age. Nested model comparison of a Model looking only at linear effects with a second Model incorporating a quadratic term did not improve model fit in any instance, suggesting directional selection for slower LH, The heritability of the indicators comprising the K-Factor positively moderated the strength of selection, while K-Factor loading weakly negatively moderated selection strength, suggesting that K-Factor variance, as a multivariate latent construct, is not the primary target of selection. These results are consistent with fertility intentions data indicating positive correlations between slower LH and desired numbers of children. In modern environments, higher mating effort does not appear to result in more offspring, likely because of strategic interference suppressing the fertility of those with fast LH, stemming from influences that may be either endogenous (i.e., contraceptive usage) or exogenous (i.e., the presence of laws, such as alimony) to the individual.
Prior research suggests a relationship between number of sons and maternal long-term health outcomes, including dementia. We assessed the relationship between having sons and parental cognitive aging. Specifically, we investigated the relationship between having at least 1 son and parental baseline cognition level and rate of cognitive decline, accounting for life course sociodemographic characteristics in a cohort of 13 222 adults aged ≥50 years from the US Health and Retirement Study. We included only participants with at least one child. We further explored whether this relationship varies by parental sex and whether the magnitude of the relationship increases with each additional son. Cognition was assessed biennially for a maximum of nine times as a sum of scores from immediate and delayed 10-noun free recall tests, a serial 7s subtraction test, and a backwards counting test. Associations were evaluated using linear mixed-effects models, stepwise adjusting for sociodemographic and health-related factors. In our analytic sample of parents, a total of 82.3% of respondents had at least 1 son and 61.6% of respondents were female. Parents of at least 1 son had a faster rate of cognitive decline in comparison to parents without any son. Our results also suggest that cognitive decline was faster among parents of multiple sons, compared to parents with only daughters. Thus, the results support the theory that having sons might have a long-term negative effect on parental cognition.
We argue that it is highly doubtful that humans, especially given their current limitations, could devise an artificial selection regime able to promote the subtle and complex array of desirable traits most auspicious for traditional civilization, and so critique eugenics. We further argue that transhumanism presents grave dangers, in that it could deface all of humankind in an irrevocable way insofar as it may amplify the effects of pathological human qualities that modernity has engendered. Absent the guidance of what has typically been called virtue (i.e. group-selected moral values and behavioral dispositions), the outcomes of transhuman “augmentation” could be highly undesirable. We then conclude the book on a pessimistic note regarding the prospects of human life in particular and, more generally, intelligent life in the universe.
Molecular Psychiatry publishes work aimed at elucidating biological mechanisms underlying psychiatric disorders and their treatment
Beauchamp (1) presents a paradox: There is genetic selection favoring reduced time spent in education, or educational attainment, among the contemporary population of the United States, amounting to an expected decline of 1.5 mo per generation. Despite this finding, the average time spent in education among this population has increased by 24 mo per generation (1). This paradox is analogous to the one that confronted psychologists when it was discovered that the total-scores obtained from intelligence tests (IQ) were rising sharply (this being the Flynn effect), rather than falling over generations, as predicted by negative associations between IQ and fertility (2).
A genome-wide polygenic score (GPS), derived from a 2013 genome-wide association study (N=127,000), explained 2% of the variance in total years of education (EduYears). In a follow-up study (N=329,000), a new EduYears GPS explains up to 4%. Here, we tested the association between this latest EduYears GPS and educational achievement scores at ages 7, 12 and 16 in an independent sample of 5825 UK individuals. We found that EduYears GPS explained greater amounts of variance in educational achievement over time, up to 9% at age 16, accounting for 15% of the heritable variance. This is the strongest GPS prediction to date for quantitative behavioral traits. Individuals in the highest and lowest GPS septiles differed by a whole school grade at age 16. Furthermore, EduYears GPS was associated with general cognitive ability (~3.5%) and family socioeconomic status (~7%). There was no evidence of an interaction between EduYears GPS and family socioeconomic status on educational achievement or on general cognitive ability. These results are a harbinger of future widespread use of GPS to predict genetic risk and resilience in the social and behavioral sciences.Molecular Psychiatry advance online publication, 19 July 2016; doi:10.1038/mp.2016.107.
In 1994, the publication of Herrnstein’s and Murray’s The Bell Curve resulted in a social science maelstrom of responses. In the present study, we argue that Herrnstein’s and Murray’s assertions were made prematurely, on their own terms, given the lack of data available to test the role of genotype in the dynamics of achievement and attainment in U.S. society. Today, however, the scientific community has access to at least one dataset that is nationally representative and has genome-wide molecular markers. We deploy those data from the Health and Retirement Study in order to test the core series of propositions offered by Herrnstein and Murray in 1994. First, we ask whether the effect of genotype is increasing in predictive power across birth cohorts in the middle twentieth century. Second, we ask whether assortative mating on relevant genotypes is increasing across the same time period. Finally, we ask whether educational genotypes are increasingly predictive of fertility (number ever born [NEB]) in tandem with the rising (negative) association of educational outcomes and NEB. The answers to these questions are mostly no; while molecular genetic markers can predict educational attainment, we find little evidence for the proposition that we are becoming increasingly genetically stratified.
The most commonly used method to test an indirect effect is to divide the estimate of the indirect effect by its standard error and compare the resulting z statistic with a critical value from the standard normal distribution. Confidence limits for the indirect effect are also typically based on critical values from the standard normal distribution. This article uses a simulation study to demonstrate that confidence limits are imbalanced because the distribution of the indirect effect is normal only in special cases. Two alternatives for improving the performance of confidence limits for the indirect effect are evaluated: (a) a method based on the distribution of the product of two normal random variables, and (b) resampling methods. In Study 1, confidence limits based on the distribution of the product are more accurate than methods based on an assumed normal distribution but confidence limits are still imbalanced. Study 2 demonstrates that more accurate confidence limits are obtained using resampling methods, with the bias-corrected bootstrap the best method overall.
A Monte Carlo study compared 14 methods to test the statistical significance of the intervening variable effect. An intervening variable (mediator) transmits the effect of an independent variable to a dependent variable. The commonly used R. M. Baron and D. A. Kenny (1986) approach has low statistical power. Two methods based on the distribution of the product and 2 difference-in-coefficients methods have the most accurate Type I error rates and greatest statistical power except in 1 important case in which Type I error rates are too high. The best balance of Type I error and statistical power across all cases is the test of the joint significance of the two effects comprising the intervening variable effect.
Recent studies have begun to uncover the genetic architecture of educational attainment. We build on this work using genome-wide data from siblings in the National Longitudinal Study of Adolescent to Adult Health (Add Health). We measure the genetic predisposition of siblings to educational attainment using polygenic scores. We then test how polygenic scores are related to social environments and educational outcomes. In Add Health, genetic predisposition to educational attainment is patterned across the social environment. Participants with higher polygenic scores were more likely to grow up in socially advantaged families. Even so, the previously published genetic associations appear to be causal. Among pairs of siblings, the sibling with the higher polygenic score typically went on to complete more years of schooling as compared to their lower-scored co-sibling. We found subtle differences between sibling fixed-effect estimates of the genetic effect versus those based on unrelated individuals.
Research has shown that genes play an important role in educational achievement. A key question is the extent to which the same genes affect different academic subjects before and after controlling for general intelligence. The present study investigated genetic and environmental influences on, and links between, the various subjects of the age-16 UK-wide standardized GCSE (General Certificate of Secondary Education) examination results for 12,632 twins. Using the twin method that compares identical and non-identical twins, we found that all GCSE subjects were substantially heritable, and that various academic subjects correlated substantially both phenotypically and genetically, even after controlling for intelligence. Further evidence for pleiotropy in academic achievement was found using a method based directly on DNA from unrelated individuals. We conclude that performance differences for all subjects are highly heritable at the end of compulsory education and that many of the same genes affect different subjects independent of intelligence.
Research on genetic influences on human fertility outcomes such as number of children ever born (NEB) or the age at first childbirth (AFB) has been solely based on twin and family-designs that suffer from problematic assumptions and practical limitations. The current study exploits recent advances in the field of molecular genetics by applying the genomic-relationship-matrix based restricted maximum likelihood (GREML) methods to quantify for the first time the extent to which common genetic variants influence the NEB and the AFB of women. Using data from the UK and the Netherlands (N = 6,758), results show significant additive genetic effects on both traits explaining 10% (SE = 5) of the variance in the NEB and 15% (SE = 4) in the AFB. We further find a significant negative genetic correlation between AFB and NEB in the pooled sample of -0.62 (SE = 0.27, p-value = 0.02). This finding implies that individuals with genetic predispositions for an earlier AFB had a reproductive advantage and that natural selection operated not only in historical, but also in contemporary populations. The observed postponement in the AFB across the past century in Europe contrasts with these findings, suggesting an evolutionary override by environmental effects and underscoring that evolutionary predictions in modern human societies are not straight forward. It emphasizes the necessity for an integrative research design from the fields of genetics and social sciences in order to understand and predict fertility outcomes. Finally, our results suggest that we may be able to find genetic variants associated with human fertility when conducting GWAS-meta analyses with sufficient sample size.
Previous research has indicated that education influences cognitive development, but it is unclear what, precisely, is being improved. Here, we tested whether education is associated with cognitive test score improvements via domain-general effects on general cognitive ability (g), or via domain-specific effects on particular cognitive skills. We conducted structural equation modeling on data from a large (n = 1,091), longitudinal sample, with a measure of intelligence at age 11 years and 10 tests covering a diverse range of cognitive abilities taken at age 70. Results indicated that the association of education with improved cognitive test scores is not mediated by g, but consists of direct effects on specific cognitive skills. These results suggest a decoupling of educational gains from increases in general intellectual capacity. (PsycINFO Database Record
(c) 2015 APA, all rights reserved).
Here we provide a detailed description of the genome-wide information available on the National Longitudinal Study of Adolescent to Adult Health (Add Health) sibling pair subsample (Harris et al. in Twin Res Hum Genet 16:391-398, 2013). A total of 2,020 samples were genotyped (including duplicates) arising from 1946 Add Health individuals from the sibling pairs subsample. After various steps for quality control (QC) and quality assurance (QA), we have high quality genome-wide data available on 1,888 individuals. In this report, we first highlight the QC and QA steps that were taken to prune the data of poorly performing samples and genetic markers. We further estimate the pairwise biological relationships using genome-wide data and compare those estimates to the assumed relationships in Add Health. Additionally, using genome-wide data from known regional reference populations from Europe, West Africa, North and South America, Japan and China, we estimate the relative genetic ancestry of the respondents. Finally, rather than conducting a traditional cross-sectional genome-wide association study (GWAS) of body mass index (BMI), we opted to utilize the extensive publicly available genome-wide information to conduct a weighted GWAS of longitudinal BMI while accounting for both family and ethnic variation.
Significance
We identify several common genetic variants associated with cognitive performance using a two-stage approach: we conduct a genome-wide association study of educational attainment to generate a set of candidates, and then we estimate the association of these variants with cognitive performance. In older Americans, we find that these variants are jointly associated with cognitive health. Bioinformatics analyses implicate a set of genes that is associated with a particular neurotransmitter pathway involved in synaptic plasticity, the main cellular mechanism for learning and memory. In addition to the substantive contribution, this work also serves to show a proxy-phenotype approach to discovering common genetic variants that is likely to be useful for many phenotypes of interest to social scientists (such as personality traits).
A genome-wide association study (GWAS) of educational attainment was conducted in a discovery sample of 101,069 individuals
and a replication sample of 25,490. Three independent single-nucleotide polymorphisms (SNPs) are genome-wide significant (rs9320913,
rs11584700, rs4851266), and all three replicate. Estimated effects sizes are small (coefficient of determination R2 ≈ 0.02%), approximately 1 month of schooling per allele. A linear polygenic score from all measured SNPs accounts for ≈2%
of the variance in both educational attainment and cognitive function. Genes in the region of the loci have previously been
associated with health, cognitive, and central nervous system phenotypes, and bioinformatics analyses suggest the involvement
of the anterior caudate nucleus. These findings provide promising candidate SNPs for follow-up work, and our effect size estimates
can anchor power analyses in social-science genetics.
A negative correlation between education and fertility has been described with great regularity in modern societies. The present investigation examines the strength of this relationship with data from the 1990, 1995 and 2000 waves of the World Values Survey covering 78 countries with a combined sample size of up to 181,728 respondents. The negative correlation is present in nearly all countries, is stronger in females than males, is greater for educational level than for length of schooling, and is not mediated by personal wealth. It is strongest at relatively low levels of economic, social and cognitive development and becomes weaker in the most advanced societies. However, it is also less than maximal in the least developed countries. The relationship is strongest in Latin America and the Middle East, where the typical correlations for cohorts with completed fertility are -.31 for females and -.24 for males, and weakest in Protestant Europe, where average correlations are -.10 for females and -.01 for males. The negative relationship persists in the younger generation of advanced societies, who are reproducing under conditions of sub-replacement fertility.
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.
Human cognitive abilities inter-correlate to form a positive matrix, from which a large first factor, called ‘Spearman's g’ or general intelligence, can be extracted. General intelligence itself is correlated with many important health outcomes including cardio-vascular function and longevity. However, the important evolutionary question of whether intelligence is a fitness-related trait has not been tested directly, let alone answered. If the correlations among cognitive abilities are part of a larger matrix of positive associations among fitness-related traits, then intelligence ought to correlate with seemingly unrelated traits that affect fitness—such as semen quality. We found significant positive correlations between intelligence and 3 key indices of semen quality: log sperm concentration (r = .15, p = .002), log sperm count (r = .19, p < .001), and sperm motility (r = .14, p = .002) in a large sample of US Army Veterans. None was mediated by age, body mass index, days of sexual abstinence, service in Vietnam, or use of alcohol, tobacco, marijuana, or hard drugs. These results suggest that a phenotype-wide fitness factor may contribute to the association between intelligence and health. Clarifying whether a fitness factor exists is important theoretically for understanding the genomic architecture of fitness-related traits, and practically for understanding patterns of human physical and psychological health.
This article discusses how fertility relates to social status with the use of a new dataset, several times larger than the ones used so far. The status-fertility relation is investigated over several centuries, across world regions and by the type of status-measure. The study reveals that as fertility declines, there is a general shift from a positive to a negative or neutral status-fertility relation. Those with high income/wealth or high occupation/social class switch from having relatively many to fewer or the same number of children as others. Education, however, depresses fertility for as long as this relation is observed (from early in the 20th century).
This study presents a multivariate behavioural genetic analysis of the relationship between education, intelligence and age of first birth. Analyses investigated the mediational role of education in explaining the relationship between intelligence and age of first birth at both the phenotypic and behavioural genetic level. The data come from the National Longitudinal Survey of Youth (NLSY), a nationally representative survey that included genetically informative full- and half-sibling pairs (n = 1423 pairs). Respondents were aged 14 to 22 when contacted in 1979. Heritability estimates were 0.32, 0.50 and 0.06 for IQ, education and age of first birth, respectively. Shared environment estimates were 0.35, 0.23 and 0.20 respectively. Common genetic and shared environmental factors were substantial in explaining the relationship between intelligence and education, and also education and age of first birth. Education partially mediated the relationship between intelligence and age of first birth only in the phenotypic analyses. After considering the genetic and shared environmental factors that influence all three variables, evidence for mediation was less convincing. This pattern of results suggests that the apparent mediational role of education at the phenotypic level is in fact the result of underlying genetic and shared environmental influences that affect education, IQ and age of first birth in common.
A Monte Carlo study compared 14 methods to test the statistical significance of the intervening variable effect. An intervening variable (mediator) transmits the effect of an independent variable to a dependent variable. The commonly used R. M. Baron and D. A. Kenny (1986) approach has low statistical power. Two methods based on the distribution of the product and 2 difference-in-coefficients methods have the most accurate Type I error rates and greatest statistical power except in 1 important case in which Type I error rates are too high. The best balance of Type I error and statistical power across all cases is the test of the joint significance of the two effects comprising the intervening variable effect.
This article describes the design and data availability for samples of genetic pairs in the National Longitudinal Study of Adolescent Health (Add Health). Add Health provides unique samples of genetic pairs that are nationally representative and followed longitudinally from early adolescence into young adulthood with 3 in-home interviews and a 4th interview planned for 2007 to 2008. The design of Add Health included an embedded genetic sample of more than 3000 pairs of individuals with varying genetic resemblance, including monozygotic twins, dizygotic twins, full siblings, half siblings, and unrelated siblings who were raised in the same household. Add Health has collected rich longitudinal social, behavioral, and environmental survey data, as well as buccal cell DNA from a subsample of the genetic sample (N = 2612). Add Health has an enlightened dissemination policy and to date has released phenotype and genotype data to more than 3000 researchers in the scientific community.
Three large and nationally representative datasets (NCDS, N = 5225, NLSY′79, N = 7598 and Project Talent, N = 76,150) are here examined in order to determine if models incorporating negative quadratic effects of IQ on fertility (which would indicate the presence of stabilizing phenotypic selection) improve model fit, relative to ones that only consider linear effects (which indicate directional phenotypic selection). Also considered were possible interactions among these terms and sex and race. For two datasets (NCDS and NLSY′79) the best fitting models did not include quadratic terms, however significant sex*IQ and race*IQ interactions were found respectively. Only in Project Talent did the inclusion of a quadratic effect (along with IQ*sex and IQ²* sex interactions) yield the best-fitting model. In this instance a small magnitude, significant negative quadratic term was found in addition to a larger magnitude linear term. Post hoc power analysis revealed that power was lacking in the two smaller samples (NCDS and NLSY′79) to detect the quadratic term, however the best fitting and most parsimonious models selected for these datasets did not include the quadratic term. The quadratic terms were furthermore several times smaller in magnitude than the linear terms in all models incorporating both terms. This indicates that stabilizing phenotypic selection is likely only very weakly present in these datasets. The dominance of linear effects across samples therefore suggests that phenotypic selection on IQ in these datasets is principally directional, although the magnitude of selection is relatively small, with IQ explaining at most 1% of the variance in fertility.
Significance
I leverage recent advances in molecular genetics to test directly whether genetic variants associated with a number of phenotypes have been under natural selection in the contemporary United States. My finding that natural selection has been slowly occurring for genetic variants associated with educational attainment and (suggestively, in females) for variants associated with age at menarche provides additional evidence that humans are still evolving—albeit slowly and at a rate that cannot account for more than a small fraction of the large changes that have occurred over the past few generations.
Significance
We describe dynamics in assortative mating and fertility patterns by polygenic scores associated with anthropometric traits, depression, and educational attainment across birth cohorts from 1920 to 1955. We find that, for example, increases in assortative mating at the phenotypic level for education are not matched at the genotypic level. We also show that genes related to height are positively associated with fertility and that, despite a widening gap between the more and less educated with respect to fertility, there is no evidence that this trend is associated with genes. These findings are important to our understanding of the roots of shifting distributions of health and behavior across generations in US society.
Educational attainment is strongly influenced by social and other environmental factors, but genetic factors are estimated to account for at least 20% of the variation across individuals1. Here we report the results of a genome-wide association study (GWAS) for educational attainment that extends our earlier discovery sample1, 2 of 101,069 individuals to 293,723 individuals, and a replication study in an independent sample of 111,349 individuals from the UK Biobank. We identify 74 genome-wide significant loci associated with the number of years of schooling completed. Single-nucleotide polymorphisms associated with educational attainment are disproportionately found in genomic regions regulating gene expression in the fetal brain. Candidate genes are preferentially expressed in neural tissue, especially during the prenatal period, and enriched for biological pathways involved in neural development. Our findings demonstrate that, even for a behavioural phenotype that is mostly environmentally determined, a well-powered GWAS identifies replicable associated genetic variants that suggest biologically relevant pathways. Because educational attainment is measured in large numbers of individuals, it will continue to be useful as a proxy phenotype in efforts to characterize the genetic influences of related phenotypes, including cognition and neuropsychiatric diseases.
Historical Understanding of the Problem Natural Selection in Preindustrial Societies The Breakdown of Natural Selection The Genetic Deterioration of Health Intelligence and Fertility Sibling Studies Intelligence and Fertility in the United States Intelligence and Fertility in Europe Resolving the Paradox of the Secular Rise of Intelligence Education and Fertility Socioeconomic Status and Fertility Socioeconomic Status Differences in Intelligence Socioeconomic Status Differences in Conscientiousness The Genetic Basis of Socioeconomic Status Differences in Conscientiousness Dysgenic Fertility for Conscientiousness Dysgenic Fertility in Economically Developing National Counterarguments and Rejoinders.
This article describes the design and phenotype and genotype data available for sibling pairs with varying genetic relatedness in the National Longitudinal Study of Adolescent Health (Add Health). Add Health is a nationally representative longitudinal study of over 20,000 adolescents in the United States in 1994-1995 who have been followed for 15 years into adulthood. The Add Health design included oversamples of more than 3,000 pairs of individuals with varying genetic resemblance, ranging from monozygotic twins, dizygotic twins, full siblings, half siblings, and unrelated siblings who were raised in the same household. Add Health sibling pairs are therefore nationally representative and followed longitudinally from early adolescence into adulthood with four in-home interviews during the period 1994-2009. Add Health has collected rich longitudinal social, behavioral, environmental, and biological data, as well as buccal cell DNA from all sample members, including sibling pairs. Add Health has an enlightened dissemination policy and to date has released phenotype and genotype data to more than 10,000 researchers in the scientific community.
The intelligence quotients of 4330 pupils, ranging in age from 6 to 20 and in grade from first through high school, were computed from scores on various group tests. As the number of children in the families increases the median I. Q. decreases, with but one exception. The correlation between I. Q. and number of children in a family varies from—.095 in one community to—.41 in another. Since there are a larger number being born of low I. Q. the general trend is toward a lower intelligence. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
This report presents national estimates of the fertility of men and women aged 15-44 years in the United States in 2006-2010 based on the National Survey of Family Growth (NSFG). Data are compared with similar measures for 2002.
Descriptive tables of numbers, percentages, and means are presented and discussed. Data were collected through in-person interviews of a nationally representative sample of the household population aged 15-44 years in the United States between July 2006 and June 2010. The 2006-2010 NSFG sample is comprised of 22,682 respondents including 10,403 men and 12,279 women. The overall response rate for the 2006-2010 NSFG was 77%, 75% for men and 78% for women.
Many of the fertility measures among men and women aged 15-44 based on the 2006-2010 NSFG were generally similar to those reported based on the 2002 NSFG. The mean age at first child's birth for women was 23 and the mean age at first child's birth for men was 25. One-half of first births to women were in their 20s and two-thirds of first births were fathered by men who were in their 20s. On average, women aged 15-44 have 1.3 children as of the time of the interview. By age 40, 85% of women had had a birth, and 76% of men had fathered a child. In 2006-2010, 22% of first births to women occurred within cohabiting unions, up from 12% in 2002. These measures differed by Hispanic origin and race and other demographic characteristics.
This article examines the adequacy of the “rules of thumb” conventional cutoff criteria and several new alternatives for various fit indexes used to evaluate model fit in practice. Using a 2‐index presentation strategy, which includes using the maximum likelihood (ML)‐based standardized root mean squared residual (SRMR) and supplementing it with either Tucker‐Lewis Index (TLI), Bollen's (1989) Fit Index (BL89), Relative Noncentrality Index (RNI), Comparative Fit Index (CFI), Gamma Hat, McDonald's Centrality Index (Mc), or root mean squared error of approximation (RMSEA), various combinations of cutoff values from selected ranges of cutoff criteria for the ML‐based SRMR and a given supplemental fit index were used to calculate rejection rates for various types of true‐population and misspecified models; that is, models with misspecified factor covariance(s) and models with misspecified factor loading(s). The results suggest that, for the ML method, a cutoff value close to .95 for TLI, BL89, CFI, RNI, and Gamma Hat; a cutoff value close to .90 for Mc; a cutoff value close to .08 for SRMR; and a cutoff value close to .06 for RMSEA are needed before we can conclude that there is a relatively good fit between the hypothesized model and the observed data. Furthermore, the 2‐index presentation strategy is required to reject reasonable proportions of various types of true‐population and misspecified models. Finally, using the proposed cutoff criteria, the ML‐based TLI, Mc, and RMSEA tend to overreject true‐population models at small sample size and thus are less preferable when sample size is small.
This paper is simply an update of the author's previous study of this subject (Vining, Intelligence, 6, 241–264, 1982). The previous study examines a cohort of women aged 25–34 yr in 1978. This study examines the same cohort 10 years later, aged 35–44 yr in 1988. An obvious criticism of the previous study is that the women had not completed their child-bearing in 1978. In 1988, they mostly have. The same negative relationship is found between IQ and fertility as is found in Vining (1982). This negative relationship is more pronounced in non-whites than whites. The overall decline in mean IQ implied by these data is less than the one IQ point per generation that is reported in Vining (1982).
Hypotheses involving mediation are common in the behavioral sciences. Mediation exists when a predictor affects a dependent variable indirectly through at least one intervening variable, or mediator. Methods to assess mediation involving multiple simultaneous mediators have received little attention in the methodological literature despite a clear need. We provide an overview of simple and multiple mediation and explore three approaches that can be used to investigate indirect processes, as well as methods for contrasting two or more mediators within a single model. We present an illustrative example, assessing and contrasting potential mediators of the relationship between the helpfulness of socialization agents and job satisfaction. We also provide SAS and SPSS macros, as well as Mplus and LISREL syntax, to facilitate the use of these methods in applications.
The author "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." It is hypothesized that persons with higher intelligence tend to have fertility equal to, if not exceeding, that of the population as a whole in periods of rising birth rates and that the opposite is true in periods of falling birth rates. This hypothesis is generally supported by the data set described above. Variations by sex and race are also examined.
Can assortative mating account for greater genetic variance in IQ with higher SES? Paper presented at the 13th annual conference of the International Society For Intelligence Research
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Can assortative mating account for greater genetic variance
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Assortative mating and differential fertility by phenotype and genotype across the 20th century
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mating and differential fertility by phenotype and genotype across the 20th century. Proceedings of the National
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Common genetic variants associated with cognitive performance identified using the proxy-phenotype method
- C A Rietveld
- T Esko
- G Davies
- T H Pers
- P Turley
- B Benyamin
- P D Koellinger
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Trading off or having it all? Completed fertility and midcareer earnings of Swedish men and women (Working paper)
- A Boschini
- C Håkanson
- Å Rosén
- A Sjögren
Boschini, A., Håkanson, C., Rosén,Å., & Sjögren, A. (2011).
Trading off or having it all? Completed fertility and midcareer earnings of Swedish men and women (Working paper).
Uppsala: IFAU -Institute for Labour Market Policy Evaluation.