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IQ and fertility: A cross-national study
Abstract
Many studies have found a small to moderate negative correlation between IQ and fertility rates. However, these studies have been limited to the United States and some European countries. The present study was a between-nation study using national IQ scores and national fertility rates. There were strong negative correlations found between national IQ and three national indicators of fertility.
... Thus, dysgenic fertility might continue to be a pertinent concern for future populations. Shatz (2008) examined the IQ-fertility relationship at a broader aggregate level. Instead of comparing individual IQ scores to individual fertility rates, national IQ scores were compared to national fertility rates for 113 countries around the world. ...
... Based on the results found in Shatz's (2008) study it is predicted that there will be a statistically significant, small to moderate negative correlation between state IQ scores and fertility rates between states in the USA. ...
... The correlations found between SAT-derived state IQ scores and state fertility indicators support the hypothesis that they would be negatively correlated. The correlations are larger than those typically found in studies that relate individuals' IQs to their fertility, but smaller than those found in Shatz (2008) for IQ and fertility rates between nations. This is not at all unexpected. ...
Results are reported for intelligence in Tunisia based on a standardization sample of adults on the Standard Progressive Matrices and in Libya for a standardization sample of 6- to 11-year-olds on the Colored Progressive Matrices. In relation to a British IQ of 100, the mean IQ of the Tunisian sample is 84, and the mean IQ of the Libyan sample is 86.5. In the Libyan sample younger children performed better than older children. There was no difference between girls and boys in either means or variability.
... Research frequently shows that intelligence is negatively related to fertility, measured by the number of children (e.g. Reeve, Lyerly, & Peach, 2013;Shatz, 2008). If individuals with heightened cognitive abilities have lower number of children, it may lead to a decrease in genetic potential for intelligence across generations in a process called dysgenic fertility (Lynn & Harvey, 2008). ...
... Previous research also found a positive link between education and the number of children (Goodman & Koupil, 2010). Since intelligence is related to a higher age at first birth, it is not surprising that previous studies found negative relations between intellectual abilities and fertility (Reeve et al., 2013;Shatz, 2008). Because of the slow life history strategy of individuals with higher cognitive abilities, lifetime reproductive success is potentially a more valid indicator of fitness. ...
The evolutionary status of intelligence is not clear: It is positively related to various indicators of fitness but negatively to reproductive success as the most important fitness marker. In the present research, we explored the links between intelligence and three fitness indicators: number of children (short-term reproductive success), number of grandchildren (long-term reproductive success), and age at first birth. Participants were individuals in a postreproductive stage (N = 191; mean age = 66.5 years). Intelligence had a positive correlation with short-term reproductive success and age at first birth but a negative correlation with long-term reproductive success. Participants’ education turned out to be a significant mediator of the link between intelligence and criterion measures. The results showed that intelligence can elevate short-term reproductive success. Furthermore, individuals with higher intellectual abilities tended to delay reproduction, which negatively affected their long-term reproductive success. Education was revealed as a very important resource which affects the link between cognitive abilities and fitness, thus proving its evolutionary role in contemporary populations.
... Baru-baru ini hasil tes intelegensi (IQ) sudah mulai dilaporkan untuk mewakili kapasitas kecerdasan suatu kelompok. Salah satunya adalah IQ Nasional (Shatz, 2007). IQ nasional menggambarkan variasi nilai intelegensi antar Negara, dimana IQ nasional ini digunakan untuk melihat kapasitas IQ rata-rata populasi pada suatu Negara. ...
... IQ nasional merupakan nilai intelegensi yang didapatkan melalui pengukuran yang seringkali diukur dengan Raven's Progressive Matrices, tes penalaran non-verbal atau diukur dengan berbagai variasi alat ukur non-verbal lainnya, termasuk The Cattell Culture Fair dan the Goodenough Draw-a-Person test (Shatz, 2007). ...
Saat ini, hasil tes kecerdasan (IQ) tidak hanya digunakan untuk melihat variasi kecerdasan secara invidual, tapi mulai digunakan untuk melihat variasi kecerdasan secara kelompok bahkan negara. Richard Lynn dan Tatu Vanhanen’s merupakan peneliti pertama yang menggunakan IQ nasional sebagai variabel penelitian, yang kemudian berkembang dan banyak di teliti. Peneliti tertarik mencoba melihat keterkaitan variasi IQ nasional, Gross Domestic Product (GDP), dan Indeks Persepsi Korupsi antara beberapa negara di Asia Tenggara. Hasil penelitian yang dilakukan pada tujuh negara Asia Tenggara didapatkan korelasi yang singnifikan antara IQ nasional dengan GDP dan IQ nasional dengan Indeks Persepsi Korupsi.
... While the Sękowski and Siekańska (2008) and studies examined adults at or under the age of 35, which could account for the low numbers of children, in general, the reproduction rates of individuals with a high IQ are lower than those of average ability and lower ability adults (Shatz, 2008). Among the 1964-1968 Presidential Scholars, at around the age of 60 years, 81% of the Scholars were married (or in marriage-like relationships, such as domestic partnerships and civil unions). ...
... By their 60s, gifted adults are likely to be married, but still have small families (either no children or one to two children; Kaufmann & Matthews, 2012). Research repeatedly shows a negative correlation between IQ and fertility rates, both in the United States and European countries (Lynn, 1996;Lynn & Van Court, 2004;Rodgers, Cleveland, van den Oord, & Rowe, 2000) and between nations using national IQ scores and national fertility rates (Shatz, 2008). It is not surprising, then, that gifted adults are not having children at the same rates as average and lower ability adults. ...
What happens when a gifted child grows up? Despite a slew of provocative book titles regarding gifted adults in the mainstream media, and the inclusion of the notion of giftedness among adults in the definition of giftedness proposed by Subotnik, Olszewski-Kubilius, and Worrell, there is a limited amount of research that has examined the gifted adult. In this systematic review of the literature, we categorized the available research literature into nine thematic areas: (a) whether or not gifted children become gifted adults; (b) family of origin; (c) effects of early educational experiences; (d) characteristics of gifted adults; (e) career; (f) family of procreation; (g) career and family interaction; (h) life goals, satisfaction, and well-being; and (i) counseling. Implications for gifted adults and the field of gifted education are discussed.
... While it is quite plausible to hypothesize that cognitive abilities evolved as an adaptation, there is an ongoing debate whether intelligence is adaptive in contemporary humans, due to a mismatch between adaptations and environment. This debate is reflected in empirical data as well: both negative (Reeve et al., 2013;Shatz, 2008) and positive (Kolk & Barclay, 2021;Međedović, 2017) associations were detected between the phenotypic scores of intellectual performance and fitness. Hence, examining the current evolution of intelligence remains an intriguing and exciting task. ...
The phenotypic gambit is one of the crucial assumptions in evolutionary behavioral ecology: it asserts that a phenotypic variation of a trait represents a reasonably adequate estimation of its genetic variation. This is particularly important since one of the main goals of behavioral ecology is to analyze the patterns of natural selection on phenotypic traits—the phenotypic gambit allows only the measurement of phenotypic variance of a trait, without exploring its genetic variance. The phenotypic gambit is crucially dependent on heritability itself—if there are systematic factors that decrease heritability, there is elevated chance for phenotypic gambit to fail. We argue that there is at least one ecological condition, harsh environment, which is related to markedly lower heritability of life history and behavioral traits in humans. Hence, the measurement of phenotypic variance of a trait may generate invalid results, at least for participants who originated from harsh environmental conditions. As a solution we propose the integration of behavioral ecological and behavioral genetic research designs: this integrative design allows researchers to partition the genetic and environmental variances of an examined trait and to obtain genetic correlations between the trait and fitness proxies. Furthermore, it enables that ecological conditions can be analyzed as a moderator in this link. Due to the strengths of integrated design, we believe that this research approach may be highly fruitful for the future studies in evolutionary human sciences.
... While some of these are in fringe journals, such as Mankind Quarterly (e.g. Kirkegaard 2013; Koljevic 2020), research using the data set has also appeared in journals published by mainstream academic publishers, for example in Intelligence (Barber 2005;Shatz 2008) and Personality and Individual Differences (Meisenberg 2012), both Elsevier journals, and in Evolutionary Psychological Science (Figueredo et al. 2020), a Springer journal, as well as in mainstream journals which demographers may have published in, such as the Journal of Biosocial Science (Kanazawa 2009). The data set was also used in a Harvard PhD thesis to argue for restricted immigration into the US from countries with a 'low IQ' (Richwine 2009), by a researcher who was appointed to a US government post in 2018 (Mervis 2020). ...
Demography was heavily involved in the eugenics movement of the early twentieth century but, along with most other social science disciplines, largely rejected eugenic thinking in the decades after the Second World War. Eugenic ideology never entirely deserted academia, however, and in the twenty-first century, it is re-emerging into mainstream academic discussion. This paper aims, first, to provide a reminder of demography’s early links with eugenics and, second, to raise awareness of this academic resurgence of eugenic ideology. The final aim of the paper is to recommend ways to counter this resurgence: these include more active discussion of demography’s eugenic past, especially when training students; greater emphasis on critical approaches in demography; and greater engagement of demographers (and other social scientists) with biologists and geneticists, in order to ensure that research which combines the biological and social sciences is rigorous.
... Previous research has shown both state and national IQs to be related to numerous variables including years of education (Tulsky & Ledbetter, 2000), birth rate (Shatz, 2008), and violent crime rates (McDaniel, 2006a;Bartels, Ryan, Urban, & Glass, 2010). Research further suggests that IQ at the national level may be associated with climate differences. ...
Relations between average temperature of each of the 48 contiguous states and estimates of state IQ were inspected. Additional state variables were controlled in the correlational analyses, namely gross state product, percent Hispanic, Black, and Asian in the state population, and the pupil-to-teacher ratio for each state. A significant correlation between average temperature and state IQ was found (r = -.70, p<.001). Possible explanations are discussed.
... Generally, it has been found that fertility has a slight negative correlation with GI and s factor indicators at the individual level (Lynn, 2011). It has also been found that internationally, GI has a strong negative relationship, -.5 to -.7 depending on measure, to fertility (Lynn & Harvey, 2008;Shatz, 2008). I have also previously reported a group-level correlation of about -.50 among Danish immigrant groups (Kirkegaard, 2014). ...
I analyze the S factor in Italian states by reanalyzing data published by Lynn (2010) as well as new data compiled from the Italian statistics agency (7 and 10 socioeconomic variables, respectively). The S factors from the datasets are highly correlated (.92) and both are strongly correlated with a G factor from PISA scores (.93 and .88).
... This estimate features prominently in several evolutionary theories of intelligence (Kanazawa, 2004;Lynn, 2006;Rushton, 2000). Moreover, Vanhanen's (2002, 2006) estimates of national IQ have featured in over twenty scientific studies (Barber, 2005;Dickerson, 2006;Gelade, 2008a,b;Jones & Schneider, 2006;Kanazawa, 2006Kanazawa, , 2008Kirkcaldy, Furnham, & Siefen, 2004;Lynn, Harvey, & Nyborg, 2009;Meisenberg, 2004;Morse, 2006;Ram, 2007;Rindermann, 2006Rindermann, , 2007Rindermann, , 2008aRindermann & Meisenberg, in press;Rushton & Templer, in press;Shatz, 2008;Templer, 2008;Templer & Arikawa, 2006a,b;Voracek, 2004;Weede & Kampf, 2002;Whetzel & McDaniel, 2006;Woodley, 2009). ...
On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit Publishers.] concluded that the average IQ of the Black population of sub-Saharan Africa lies below 70. In this paper, the authors systematically review published empirical data on the performance of Africans on the following IQ tests: Draw-A-Man (DAM) test, Kaufman-Assessment Battery for Children (K-ABC), the Wechsler scales (WAIS & WISC), and several other IQ tests (but not the Raven's tests). Inclusion and exclusion criteria are explicitly discussed. Results show that average IQ of Africans on these tests is approximately 82 when compared to UK norms. We provide estimates of the average IQ per country and estimates on the basis of alternative inclusion criteria. Our estimate of average IQ converges with the finding that national IQs of sub-Saharan African countries as predicted from several international studies of student achievement are around 82. It is suggested that this estimate should be considered in light of the Flynn Effect. It is concluded that more psychometric studies are needed to address the issue of measurement bias of western IQ tests for Africans.
... Previous research has shown both state and national IQs to be related to numerous variables including years of education (Tulsky & Ledbetter, 2000), birth rate (Shatz, 2008), and violent crime rates (McDaniel, 2006a;Bartels, Ryan, Urban, & Glass, 2010). Research further suggests that IQ at the national level may be associated with climate differences. ...
Relations between average temperature of each of the 48 contiguous states and estimates of state IQ were inspected. Additional state variables were controlled in the correlational analyses, namely gross state product, percent Hispanic, Black, and Asian in the state population, and the pupil-to-teacher ratio for each state. A significant correlation between average temperature and state IQ was found (r = -.70, p < .001). Possible explanations are discussed.
The Cambridge Handbook of Creativity is a comprehensive scholarly handbook on creativity from the most respected psychologists, researchers and educators. This handbook serves both as a thorough introduction to the field of creativity and as an invaluable reference and current source of important information. It covers such diverse topics as the brain, education, business, and world cultures. The first section, 'Basic Concepts', is designed to introduce readers to both the history of and key concepts in the field of creativity. The next section, 'Diverse Perspectives of Creativity', contains chapters on the many ways of approaching creativity. Several of these approaches, such as the functional, evolutionary, and neuroscientific approaches, have been invented or greatly reconceptualized in the last decade. The third section, 'Contemporary Debates', highlights ongoing topics that still inspire discussion. Finally, the editors summarize and discuss important concepts from the book and look to what lies ahead.
Cambridge Core - Cognition - The Nature of Human Intelligence - edited by Robert J. Sternberg
The relationship between IQ and fertility was examined at the state level within the USA. As predicted, SAT-derived state IQ scores were negatively correlated with three different indicators of state fertility rates. The IQ-fertility relationship remained relatively unchanged when demographic and educational characteristics of the states were controlled for. Limitations and possible causal hypotheses are discussed.
The purpose of this study is to replicate recent findings demonstrating that the dysgenic fertility trend is a Jensen effect. Data were drawn from Project TALENT. Present analyses included data from a total sample of 79,734 participants with complete data regarding number of biological children at the 11 year follow up, and analyses were further split by sex and race to examine possible differential trends among subgroups. Correlated vectors analyses revealed strong Jensen effects such that subtests with higher g-saturation were associated with larger dysgenic fertility gradients. This effect was evident in the total sample, and within all race/gender subgroups except for Asian males. Such findings yield further confirmation that g is in fact the principal factor by which the dysgenic fertility gradient operates.
Across 177 countries around the world, the Failed State Index, a measure of state vulnerability, was reliably negatively associated with the estimates of national intelligence. Psychometric analysis of the Failed State Index, compounded of 12 social, economic, and political indicators, suggested factorial unidimensionality of this index. The observed correspondence of higher national intelligence figures to lower state vulnerability might arise through these two macro-level variables possibly being proxies of even more pervasive historical and societal background variables that affect both.
This paper summarizes the results of 244 correlates of national IQs that have been published from 2002 through 2012 and include educational attainment, cognitive output, educational input, per capita income, economic growth, other economic variables, crime, political institutions, health, fertility, sociological variables, and geographic and climatic variables.
Counter-intuitively, sociobiological and evolutionary theories predict a negative relationship between g and reproduction when applied to modern humans. Although existing research has documented this dysgenic trend, the association between g and socio-economic factors presents a confound that has not systematically been addressed in prior research. Based on a sample of 325,252 individuals drawn from the nationally representative Project Talent database, we examined the unique effects of g and socio-economic wealth, assessed in adolescence, on marital and reproductive behavior over the next 11 years. Results show that both g and socio-economic wealth have unique, independent negative effects on marital and reproductive behavior such that individuals of higher intelligence and higher wealth delay marriage and reproductive longer than those of lower intelligence and wealth. The effect of g was slightly stronger than that of wealth, though for both variables much of their influence was mediated by educational attainment. Consistent with sociobiological theory, these dysgenic effects were stronger among females than males.
Survey researchers often administer batteries of questions to measure respondents' abilities, but these batteries are not always designed in keeping with the principles of optimal test construction. This paper illustrates one instance in which following these principles can improve a measurement tool used widely in the social and behavioral sciences: the GSS's vocabulary test called "Wordsum". This ten-item test is composed of very difficult items and very easy items, and item response theory (IRT) suggests that the omission of moderately difficult items is likely to have handicapped Wordsum's effectiveness. Analyses of data from national samples of thousands of American adults show that after adding four moderately difficult items to create a 14-item battery, "Wordsumplus" (1) outperformed the original battery in terms of quality indicators suggested by classical test theory; (2) reduced the standard error of IRT ability estimates in the middle of the latent ability dimension; and (3) exhibited higher concurrent validity. These findings show how to improve Wordsum and suggest that analysts should use a score based on all 14 items instead of using the summary score provided by the GSS, which is based on only the original 10 items. These results also show more generally how surveys measuring abilities (and other constructs) can benefit from careful application of insights from the contemporary educational testing literature.
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.
Hundreds of research articles have addressed the relationship between birth order and intelligence. Virtually all have used cross-sectional data, which are fundamentally flawed in the assessment of within-family (including birth order) processes. Although within-family models have been based on patterns in cross-sectional data, a number of equally plausible between-family explanations also exist. Within-family (preferably intact-family) data are prerequisite for separating within- and between-family causal processes. This observation reframes an old issue in a way that can be easily addressed by studying graphical patterns. Sibling data from the National Longitudinal Survey of Youth are evaluated, and the results are compared with those from other studies using within-family data. It appears that although low-IQ parents have been making large families, large families do not make low-IQ children in modern U.S. society. The apparent relation between birth order and intelligence has been a methodological illusion.
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.
Data from the General Social Survey (GSS) collected in the years 1990–1996 are examined for the relationship between fertility and intelligence as measured by vocabulary. The results show that the relation between fertility and intelligence has been consistently negative for successive birth cohorts from to 1900 to 1979, indicating the presence of dysgenic fertility for all of the 20th century studied thus far. The most recent cohort for which fertility can be regarded as complete is that born in the years 1940–1949. In this cohort, the decline of genotypic intelligence arising from the negative association between intelligence and fertility is estimated at .90 IQ points per generation. The decline of genotypic intelligence of Whites is estimated at 0.75 IQ points a generation.
The new paradigm of evolutionary social science suggests that humans adjust rapidly to changing economic conditions, including cognitive changes in response to the economic significance of education. This research tested the predictions that cross-national differences in IQ scores would be positively correlated with education and negatively correlated with an agricultural way of life. Regression analysis found that much of the variance in IQ scores of 81 countries (derived from [Lynn, R., & Vanhanen, T. (2002). IQ and the wealth of nations. Westport, CT: Praeger]) was explained by enrollment in secondary education, illiteracy rates, and by the proportion of agricultural workers. Cross-national IQ scores were also related to low birth weights. These effects remained with national wealth, infant mortality, and geographic continent controlled (exception secondary education) and were largely due to variation within continents. Cross-national differences in IQ scores thus suggest that increasing cognitive demands in developed countries promote an adaptive increase in cognitive ability.
First, I describe why intelligence (Spearman's g) can only be fully understood through r–K theory, which places it into an evolutionary framework along with brain size, longevity, maturation speed, and several other life-history traits. The r–K formulation explains why IQ predicts longevity and also why the gap in mortality rates between rich and poor has increased with greater access to health care. Next, I illustrate the power of this approach by analyzing a large data set of life-history variables on 234 mammalian species and find that brain size correlates r=.70 with longevity (.59, after controlling for body weight and body length). A principal component analysis reveals a single r–K life-history factor with loadings such as: brain weight (.85), longevity (.91), gestation time (.86), birth weight (.62), litter size (−.54), age at first mating (.73), duration of lactation (.67), body weight (.61), and body length (.63). The factor loadings remain high when body weight and length are covaried. Finally, I demonstrate the theoretical importance of this approach in restoring the concept of “progress” to its proper place in evolutionary biology showing why, over the last 575 million years of evolutionary competition of finding and filling new niches, there has always been (and likely always will be) “room at the top.”
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).
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.
IQ and global inequality
- R Lynn
- T Vanhanen
Lynn, R., & Vanhanen, T. (2006). IQ and global inequality. Atlanta, GA: Washington Summit Publishers.