Fertility and intelligence

Last updated

The relationship between fertility and intelligence has been investigated in many demographic studies. There is evidence that, on a population level, measures of intelligence such as educational attainment and literacy are negatively correlated with fertility rate in some contexts. [1] However, genetic studies have shown no evidence for dysgenic effects in human populations. [2] [3] [4] [5] Theories about dysgenic and eugenic effects in human populations have historically been associated with scientific racism. [6] [7]

Contents

Early views and research

The negative correlation between fertility and intelligence (as measured by IQ) has been argued to have existed in many parts of the world. Early studies, however, were "superficial and illusory" and not clearly supported by the limited data they collected. [1]

Some of the first studies into the subject were carried out on individuals living before the advent of IQ testing, in the late 19th century, by looking at the fertility of men listed in Who's Who, these individuals being presumably of high intelligence. These men, taken as a whole, had few children, implying a correlation. [8] [9]

More rigorous studies carried out on Americans alive after the Second World War returned different results suggesting a slight positive correlation with respect to intelligence. The findings from these investigations were consistent enough for Osborn and Bajema, writing as late as 1972, to conclude that fertility patterns were eugenic, and that "the reproductive trend toward an increase in the frequency of genes associated with higher IQ... will probably continue in the foreseeable future in the United States and will be found also in other industrial welfare-state democracies." [10]

Several reviewers considered the findings premature, arguing that the samples were nationally unrepresentative, generally being confined to white people born between 1910 and 1940 in the Great Lakes States. [11] [12] Other researchers began to report a negative correlation in the 1960s after two decades of neutral or positive fertility. [13]

In 1982, Daniel R. Vining, Jr. sought to address these issues in a large study on the fertility of over 10,000 individuals throughout the United States, who were then aged 25 to 34. The average fertility in his study was correlated at −0.031 with IQ for white women and −0.086 for black women. Vining argued that this indicated a drop in the genotypic average IQ of 1.6 points per generation for the white population, and 2.4 points per generation for the black population. [14] Critics note Vining's involvement with the white supremacist journal Mankind Quarterly and his acceptance of grants from the Pioneer Fund. [15] [16] [17]

Later research

In a 1988 study, Retherford and Sewell examined the association between the measured intelligence and fertility of over 9,000 high school graduates in Wisconsin in 1957, and confirmed the inverse relationship between IQ and fertility for both sexes, but much more so for females. If children had, on average, the same IQ as their parents, IQ would decline by .81 points per generation. Taking .71 for the additive heritability of IQ as given by Jinks and Fulker, [18] they calculated a dysgenic decline of .57 IQ points per generation. [19]

Another way of checking the negative relationship between IQ and fertility is to consider the relationship which educational attainment has to fertility, since education is known to be a reasonable proxy for IQ, correlating with IQ at .55; [20] in a 1999 study examining the relationship between IQ and education in a large national sample, David Rowe and others found not only that achieved education had a high heritability (.68) and that half of the variance in education was explained by an underlying genetic component shared by IQ, education, and SES. [21] One study investigating fertility and education carried out in 1991 found that high school dropouts in the United States had the most children (2.5 on average), with high school graduates having fewer children, and college graduates having the fewest children (1.56 on average). [22]

The Bell Curve (1994) argued that the average genotypic IQ of the United States was declining due to both dysgenetic fertility and large scale immigration of groups with low average IQ.[ citation needed ]

Controversial psychologist Richard Lynn has been a strong advocate of dysgenic theories. In a 1999 study Richard Lynn examined the relationship between the intelligence of adults aged 40 and above and their numbers of children and their siblings. Data was collected from a 1994 National Opinion Research Center survey among a representative sample of 2992 English-speaking individuals aged 18 years. He found negative correlations between the intelligence of American adults and the number of children and siblings that they had, but only for females. He also reported that there was virtually no correlation between women's intelligence and the number of children they considered ideal. [23] In 2004 Lynn and Marian Van Court attempted a straightforward replication of Vining's work. Their study returned similar results, with the genotypic decline measuring at 0.9 IQ points per generation for the total sample and 0.75 IQ points for whites only. [24]

However, Lynn's research has been widely criticized as pseudo-scientific and having poor research practices, as well as for promoting scientific racism and white supremacy, [25] [26] particularly with regards to Lynn's status as editor-in-chief of the journal Mankind Quarterly culminating in the revocation of his title as professor emeritus of Psychology at Ulster University in 2018. [27]

Boutwell et al. (2013) reported a strong negative association between county-level IQ and county-level fertility rates in the United States. [28]

A 2014 study by Satoshi Kanazawa using data from the National Child Development Study found that more intelligent women and men were more likely to want to be childless, but that only more intelligent women – not men – were more likely to actually be childless. [29]

Possible causes

Income

A theory to explain the fertility-intelligence relationship is that while income and IQ are positively correlated, [30] income is also in itself a fertility factor that correlates inversely with fertility, that is, the higher the incomes, the lower the fertility rates and vice versa. [31] [32] There is thus an inverse correlation between income and fertility within and between nations. The higher the level of education and GDP per capita of a human population, sub-population or social stratum, the fewer children are born. In a 1974 UN population conference in Bucharest, Karan Singh, a former minister of population in India, encapsulated this relationship by stating "Development is the best contraceptive". [33]

Education

In most countries, education is inversely correlated to childbearing. People often delay childbearing in order to spend more time getting education, and thus have fewer children. Conversely, early childbearing can interfere with education, so people with early or frequent childbearing are likely to be less educated. While education and childbearing place competing demands on a person's resources, education is positively correlated with IQ.

While there is less research into men's fertility and education, in developed countries evidence suggests that highly-educated men display higher levels of childbearing compared to less-educated men. [34] [35]

As a country becomes more developed, education rates increase and fertility rates decrease for both men and women. Fertility has fallen faster for both less-educated men and women than it has for highly-educated men and women. In the Nordic countries of Denmark, Norway, and Sweden, fertility for less-educated women has now fallen enough that childlessness is now highest among the least educated women just as it is for men. [36]

A study analyzing genealogical records of 36,456 men from six Chinese lineages between 1350 and 1920 found that the literati (degree and office holders) had more than double the number of surviving sons compared to non-degree holders. [37]

Birth control and intelligence

Among a sample of women using birth control methods of comparable theoretical effectiveness, success rates were related to IQ, with the percentages of high, medium and low IQ women having unwanted births during a three-year interval being 3%, 8% and 11%, respectively. [38] Since the effectiveness of many methods of birth control is directly correlated with proper usage, an alternative interpretation of the data would indicate lower IQ women were less likely to use birth control consistently and correctly. Another study found that after an unwanted pregnancy has occurred, higher IQ couples are more likely to obtain abortions; [39] and unmarried teenage girls who become pregnant are found to be more likely to carry their babies to term if they are doing poorly in school. [40]

Conversely, while desired family size in the United States is apparently the same for women of all IQ levels, [14] [ dubious ] highly educated women are found to be more likely to say that they desire more children than they have, indicating a "deficit fertility" in the highly intelligent. [41] In her review of reproductive trends in the United States, Van Court argues that "each factor – from initially employing some form of contraception, to successful implementation of the method, to termination of an accidental pregnancy when it occurs – involves selection against intelligence." [42]

Criticisms

Preston and Campbell (1993) argued that it is a mathematical fallacy that such differences in fertility would result in a progressive change of IQ, and applies only when looking at closed subpopulations. In their mathematical model, with constant differences in fertility, since children's IQ can be more or less than that of their parents, a steady-state equilibrium is argued to be established between different subpopulations with different IQ. The mean IQ will not change in the absence of a change of the fertility differences. The steady-state IQ distribution will be lower for negative differential fertility than for positive, but these differences are small. For the extreme and unrealistic assumption of endogamous mating in IQ subgroups, a differential fertility change of 2.5/1.5 to 1.5/2.5 (high IQ/low IQ) causes a maximum shift of four IQ points. For random mating, the shift is less than one IQ point. [43] James S. Coleman, however, argues that Preston and Campbell's model depends on assumptions which are unlikely to be true. [44] [45]

The general increase in IQ test scores, the Flynn effect, has been argued to be evidence against dysgenic arguments. Geneticist Steve Connor wrote that Lynn, writing in Dysgenics: Genetic Deterioration in Modern Populations, "misunderstood modern ideas of genetics." "A flaw in his argument of genetic deterioration in intelligence was the widely accepted fact that intelligence as measured by IQ tests has actually increased over the past 50 years." If the genes causing IQ have been adversely affected, IQ scores should reasonably be expected to change in the same direction, yet the reverse has occurred. [46]

Some of the studies looking at relation between IQ and fertility cover the fertility of individuals who have attained a particular age, thereby ignoring positive correlation between IQ and survival. To make conclusions about effects on IQ of future populations, such effects would have to be taken into account.[ citation needed ]

Recent research has shown that education and socioeconomic status are better indicators of fertility and suggests that the relationship between intelligence and number of children may be spurious. When controlling for education and socioeconomic status, the relationship between intelligence and number of children, intelligence and number of siblings, and intelligence and ideal number of children reduces to statistical insignificance. Among women, a post-hoc analysis revealed that the lowest and highest intelligence scores did not differ significantly by number of children. [47]

Other research suggest that siblings born further apart achieve higher educational outcomes. Therefore, sibling density, not number of siblings, may explain the negative association between IQ and number of siblings. [47]

See also

Related Research Articles

<span class="mw-page-title-main">Intelligence quotient</span> Score from a test designed to assess intelligence

An intelligence quotient (IQ) is a total score derived from a set of standardised tests or subtests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests at University of Breslau he advocated in a 1912 book.

Discussions of race and intelligence – specifically regarding claims of differences in intelligence along racial lines – have appeared in both popular science and academic research since the modern concept of race was first introduced. With the inception of IQ testing in the early 20th century, differences in average test performance between racial groups were observed, though these differences have fluctuated and in many cases steadily decreased over time. Complicating the issue, modern science has concluded that race is a socially constructed phenomenon rather than a biological reality, and there exist various conflicting definitions of intelligence. In particular, the validity of IQ testing as a metric for human intelligence is disputed. Today, the scientific consensus is that genetics does not explain differences in IQ test performance between groups, and that observed differences are environmental in origin.

Human intelligence is the intellectual capability of humans, which is marked by complex cognitive feats and high levels of motivation and self-awareness. Using their intelligence, humans are able to learn, form concepts, understand, and apply logic and reason. Human intelligence is also thought to encompass our capacities to recognize patterns, plan, innovate, solve problems, make decisions, retain information, and use language to communicate.

The g factor is a construct developed in psychometric investigations of cognitive abilities and human intelligence. It is a variable that summarizes positive correlations among different cognitive tasks, reflecting the fact that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks. The g factor typically accounts for 40 to 50 percent of the between-individual performance differences on a given cognitive test, and composite scores based on many tests are frequently regarded as estimates of individuals' standing on the g factor. The terms IQ, general intelligence, general cognitive ability, general mental ability, and simply intelligence are often used interchangeably to refer to this common core shared by cognitive tests. However, the g factor itself is a mathematical construct indicating the level of observed correlation between cognitive tasks. The measured value of this construct depends on the cognitive tasks that are used, and little is known about the underlying causes of the observed correlations.

<i>IQ and the Wealth of Nations</i> Book by Richard Lynn

IQ and the Wealth of Nations is a 2002 book by psychologist Richard Lynn and political scientist Tatu Vanhanen. The authors argue that differences in national income are correlated with differences in the average national intelligence quotient (IQ). They further argue that differences in average national IQs constitute one important factor, but not the only one, contributing to differences in national wealth and rates of economic growth.

<span class="mw-page-title-main">Richard Lynn</span> British psychologist noted for his views on race and intelligence (1930–2023)

Richard Lynn was a controversial English psychologist and self-described "scientific racist" who advocated for a genetic relationship between race and intelligence. He was a professor emeritus of psychology at Ulster University, but had the title withdrawn by the university in 2018. He was the editor-in-chief of Mankind Quarterly, which is commonly described as a white supremacist journal. Lynn was lecturer in psychology at the University of Exeter and professor of psychology at the Economic and Social Research Institute, Dublin, and at the University of Ulster at Coleraine.

Neuroscience and intelligence refers to the various neurological factors that are partly responsible for the variation of intelligence within species or between different species. A large amount of research in this area has been focused on the neural basis of human intelligence. Historic approaches to studying the neuroscience of intelligence consisted of correlating external head parameters, for example head circumference, to intelligence. Post-mortem measures of brain weight and brain volume have also been used. More recent methodologies focus on examining correlates of intelligence within the living brain using techniques such as magnetic resonance imaging (MRI), functional MRI (fMRI), electroencephalography (EEG), positron emission tomography and other non-invasive measures of brain structure and activity.

Dysgenics is the decrease in prevalence of traits deemed to be either socially desirable or well adapted to their environment due to selective pressure disfavoring the reproduction of those traits.

Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors.

The study of height and intelligence examines correlations between human height and human intelligence. Some epidemiological research on the subject has shown that there is a small but statistically significant positive correlation between height and intelligence after controlling for socioeconomic class and parental education. The cited study, however, does not draw any conclusions about height and intelligence, but rather suggests "a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years." This correlation arises in both the developed and developing world and persists across age groups. An individual's taller stature has been attributed to higher economic status, which often translates to a higher quality of nutrition. This correlation, however, can be inverted to characterize one's socioeconomic status as a consequence of stature, where shorter stature can attract discrimination that affects many factors, among them employment, and treatment by educators. One such theory argues that since height strongly correlates with white and gray matter volume, it may act as a biomarker for cerebral development which itself mediates intelligence. Competing explanations include that certain genetic factors may influence both height and intelligence, or that both height and intelligence may be affected in similar ways by adverse environmental exposures during development. Measurements of the total surface area and mean thickness of the cortical grey matter using a magnetic resonance imaging (MRI) revealed that the height of individuals had a positive correlation with the total cortical surface area. This supports the idea that genes that influence height also influence total surface area of the brain, which in turn influences intelligence, resulting in the correlation. Other explanations further qualify the positive correlation between height and intelligence, suggesting that because the correlation becomes weaker with higher socioeconomic class and education level, environmental factors could partially override any genetic factors affecting both characteristics.

<span class="mw-page-title-main">Income and fertility</span>

Income and fertility is the association between monetary gain on one hand, and the tendency to produce offspring on the other. There is generally an inverse correlation between income and the total fertility rate within and between nations. The higher the degree of education and GDP per capita of a human population, subpopulation or social stratum, the fewer children are born in any developed country. In a 1974 United Nations population conference in Bucharest, Karan Singh, a former minister of population in India, illustrated this trend by stating "Development is the best contraceptive." In 2015, this thesis was supported by Vogl, T.S., who concluded that increasing the cumulative educational attainment of a generation of parents was by far the most important predictor of the inverse correlation between income and fertility based on a sample of 48 developing countries.

<i>IQ and Global Inequality</i> 2006 book by Richard Lynn and Tatu Vanhanen

IQ and Global Inequality is a 2006 book by psychologist Richard Lynn and political scientist Tatu Vanhanen. IQ and Global Inequality is follow-up to their 2002 book IQ and the Wealth of Nations, an expansion of the argument that international differences in current economic development are due in part to differences in average national intelligence as indicated by national IQ estimates, and a response to critics. The book was published by Washington Summit Publishers, a white nationalist and eugenicist publishing group.

Environment and intelligence research investigates the impact of environment on intelligence. This is one of the most important factors in understanding human group differences in IQ test scores and other measures of cognitive ability. It is estimated that genes contribute about 20–40% of the variance in intelligence in childhood and about 80% in adulthood. Thus the environment and its interaction with genes account for a high proportion of the variation in intelligence seen in groups of young children, and for a small proportion of the variation observed in groups of mature adults. Historically, there has been great interest in the field of intelligence research to determine environmental influences on the development of cognitive functioning, in particular, fluid intelligence, as defined by its stabilization at 16 years of age. Despite the fact that intelligence stabilizes in early adulthood it is thought that genetic factors come to play more of a role in our intelligence during middle and old age and that the importance of the environment dissipates.

Cognitive epidemiology is a field of research that examines the associations between intelligence test scores and health, more specifically morbidity and mortality. Typically, test scores are obtained at an early age, and compared to later morbidity and mortality. In addition to exploring and establishing these associations, cognitive epidemiology seeks to understand causal relationships between intelligence and health outcomes. Researchers in the field argue that intelligence measured at an early age is an important predictor of later health and mortality differences.

The history of the race and intelligence controversy concerns the historical development of a debate about possible explanations of group differences encountered in the study of race and intelligence. Since the beginning of IQ testing around the time of World War I, there have been observed differences between the average scores of different population groups, and there have been debates over whether this is mainly due to environmental and cultural factors, or mainly due to some as yet undiscovered genetic factor, or whether such a dichotomy between environmental and genetic factors is the appropriate framing of the debate. Today, the scientific consensus is that genetics does not explain differences in IQ test performance between racial groups.

The relationship between nations and IQ is a controversial area of study concerning differences between nations in average intelligence test scores, their possible causes, and their correlation with measures of social well-being and economic prosperity.

<span class="mw-page-title-main">Correlates of crime</span> Things associated with unlawful behavior

The correlates of crime explore the associations of specific non-criminal factors with specific crimes.

Fertility factors are determinants of the number of children that an individual is likely to have. Fertility factors are mostly positive or negative correlations without certain causations.

Neuroimaging intelligence testing concerns the use of neuroimaging techniques to evaluate human intelligence. Neuroimaging technology has advanced such that scientists hope to use neuroimaging increasingly for investigations of brain function related to IQ.

Intelligence and personality have traditionally been studied as separate entities in psychology, but more recent work has increasingly challenged this view. An increasing number of studies have recently explored the relationship between intelligence and personality, in particular the Big Five personality traits.

References

  1. 1 2 Graff HJ (March 1979). "Literacy, education, and fertility, past and present: A critical review". Population and Development Review. 5 (1): 105–40. doi:10.2307/1972320. JSTOR   1972320.
  2. Fischbach, Karl-Friedrich; Niggeschmidt, Martin (2021). "Do the Dumb Get Dumber and the Smart Get Smarter?". Heritability of Intelligence. Essentials. Springer. pp. 37–39. doi:10.1007/978-3-658-35321-6_9. ISBN   978-3-658-35321-6. S2CID   244640696. Since the nineteenth century, a 'race deterioration' has been repeatedly predicted as a result of the excessive multiplication of less gifted people (Galton 1869; see also Fig. 9.1). Nevertheless, the educational and qualification level of people in the industrialized countries has risen strongly. The fact that the 'test intelligence' has also significantly increased (Flynn 2013), is difficult to explain for supporters of the dysgenic thesis: they suspect that the 'phenotypic intelligence' has increased for environmental reasons, while the 'genotypic quality' secretly decreases (Lynn 1996, p. 111). There is neither evidence nor proof for this theory.
  3. Conley, Dalton; Laidley, Thomas; Belsky, Daniel W.; Fletcher, Jason M.; Boardman, Jason D.; Domingue, Benjamin W. (14 June 2016). "Assortative mating and differential fertility by phenotype and genotype across the 20th century". Proceedings of the National Academy of Sciences. 113 (24): 6647–6652. doi: 10.1073/pnas.1523592113 . PMC   4914190 . PMID   27247411.
  4. Bratsberg, Bernt; Rogeberg, Ole (26 June 2018). "Flynn effect and its reversal are both environmentally caused". Proceedings of the National Academy of Sciences. 115 (26): 6674–6678. doi: 10.1073/pnas.1718793115 . PMC   6042097 . PMID   29891660.
  5. Neisser, Ulric (1998). The Rising Curve: Long-Term Gains in IQ and Related Measures. American Psychological Association. pp. xiii–xiv. ISBN   978-1557985033. There is no convincing evidence that any dysgenic trend exists. . . . It turns out, counterintuitively, that differential birth rates (for groups scoring high and low on a trait) do not necessarily produces changes in the population mean.
  6. Carlson, Elof Axel (2001). The unfit : a history of a bad idea. Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press. ISBN   0-87969-658-3. OCLC   46959597.
  7. Devlin, Bernie (1997). Intelligence, genes, and success: scientists respond to The bell curve. New York: Springer. ISBN   0-387-98234-5. OCLC   36590694.
  8. Huntington E, Whitney L (1927). The Builders of America. New York: Morrow.
  9. Kirk D (1957). "The fertility of a gifted group: A study of the number of children of men in WHO'S WHO.". The Nature and Transmission of the Genetic and Cultural Characteristics of Human Populations. New York: Milbank Memorial Fund. pp. 78–98.
  10. Osborn F, Bajema CJ (December 1972). "The eugenic hypothesis". Social Biology. 19 (4): 337–45. doi:10.1080/19485565.1972.9988006. PMID   4664670. S2CID   5348999.
  11. Osborne RT (December 1975). "Fertility, IQ and school achievement". Psychological Reports. 37 (3 PT 2): 1067–73. doi:10.2466/pr0.1975.37.3f.1067. PMID   1208722. S2CID   31954683.
  12. Cattell RB (1974). "Differential fertility and normal selection for IQ: some required conditions in their investigation". Social Biology. 21 (2): 168–77. doi:10.1080/19485565.1974.9988103. PMID   4439031.
  13. Kirk D (November 1969). "The biological effects of family planning. B. The genetic implications of family planning". Journal of Medical Education. 44 (11): Suppl 2:80–3. doi: 10.1097/00001888-196911000-00031 . PMID   5357924.
  14. 1 2 Vining Jr DR (1982). "On the possibility of the reemergence of a dysgenic trend with respect to intelligence in American fertility differentials". Intelligence. 6 (3): 241–64. doi:10.1016/0160-2896(82)90002-2. PMID   12265416.
  15. Miller, Adam (1994). "The Pioneer Fund: Bankrolling the Professors of Hate". The Journal of Blacks in Higher Education (6): 58–61. doi:10.2307/2962466. JSTOR   2962466.
  16. "Pioneer Fund". Southern Poverty Law Center. Retrieved 2022-04-29.
  17. Lane, Charles. "The Tainted Sources of 'The Bell Curve' | Charles Lane". New York Review of Books. ISSN   0028-7504 . Retrieved 2022-04-29.
  18. Jinks JL, Fulker DW (May 1970). "Comparison of the biometrical genetical, MAVA, and classical approaches to the analysis of human behavior". Psychological Bulletin. 73 (5): 311–49. doi:10.1037/h0029135. PMID   5528333. S2CID   319948. Closed Access logo transparent.svg
  19. Retherford RD, Sewell WH (1988). "Intelligence and family size reconsidered" (PDF). Social Biology. 35 (1–2): 1–40. doi:10.1080/19485565.1988.9988685. PMID   3217809.
  20. Neisser U, Boodoo G, Bouchard Jr TJ, Boykin AW, Brody N, Ceci SJ, et al. (1996). "Intelligence: Knowns and unknowns". American Psychologist. 51 (2): 77–101. doi:10.1037/0003-066X.51.2.77. S2CID   20957095.
  21. Rowe D (1998). "Herrnstein's syllogism: genetic and shared environmental influences on IQ, education, and income". Intelligence. 26 (4): 405–423. doi:10.1016/S0160-2896(99)00008-2.
  22. Bachu A (October 1991). "Fertility of American women: June 1990". Current Population Reports. Series P-20, Population Characteristics. U.S. Bureau of the Census. Current Population Report Series. U.S. Government Printing Office (454): i-1–69. PMID   12158801.
  23. Lynn R (1999). "New evidence for dysgenic fertility for intelligence in the United States". Social Biology. 46 (1–2): 146–53. doi:10.1080/19485565.1999.9988992. PMID   10842506.
  24. Lynn R (2004). "New evidence of dysgenic fertility for intelligence in the United States". Intelligence. 32 (2): 193–201. doi:10.1016/j.intell.2003.09.002. PMID   10842506.
  25. Jackson, John P.; Winston, Andrew S. (March 2021). "The Mythical Taboo on Race and Intelligence". Review of General Psychology. 25 (1): 3–26. doi:10.1177/1089268020953622. ISSN   1089-2680. S2CID   225143131.
  26. Leech, Kenneth (2005). Race. Church Pub. p. 14. ISBN   0-89869-495-7. OCLC   61724759.
  27. "Ulster University withdraws status from Prof Richard Lynn". BBC News. 2018-04-14. Retrieved 2022-10-23.
  28. Boutwell BB, Franklin TW, Barnes JC, Beaver KM, Deaton R, Lewis RH, et al. (2013-09-01). "County-level IQ and fertility rates: A partial test of Differential-K theory". Personality and Individual Differences. 55 (5): 547–552. doi:10.1016/j.paid.2013.04.018. ISSN   0191-8869.
  29. Kanazawa S (November 2014). "Intelligence and childlessness". Social Science Research. 48: 157–70. doi:10.1016/j.ssresearch.2014.06.003. PMID   25131282.
  30. Geary DM (2004). The Origin of the Mind: Evolution of Brain, Cognition, and General Intelligence. American Psychological Association (APA). ISBN   978-1-59147-181-3. OCLC   217494183.
  31. "Income as a determinant of declining Russian fertility; Trevitt, Jamie; Public Policy; 18-Apr-2006". Archived from the original on 2009-02-20. Retrieved 2008-07-02.
  32. Freedman DS (1963). "The Relation of Economic Status to Fertility". The American Economic Review. 53 (3): 414–426. JSTOR   1809165.
  33. Weil DN (2004). Economic Growth. Addison-Wesley. p. 111. ISBN   978-0-201-68026-3.
  34. Jalovaara M, Neyer G, Andersson G, Dahlberg J, Dommermuth L, Fallesen P, Lappegård T (July 2019). "Education, Gender, and Cohort Fertility in the Nordic Countries" (PDF). European Journal of Population. 35 (3): 563–586. doi:10.1007/s10680-018-9492-2. PMC   6639448 . PMID   31372105.
  35. Miettinen A, Rotkirch A, Szalma I, Donno A, Tanturri ML. "Increasing childlessness in Europe: time trends and country differences" (PDF). Families and Societies.
  36. Jalovaara M, Neyer G, Andersson G, Dahlberg J, Dommermuth L, Fallesen P, Lappegård T (July 2019). "Education, Gender, and Cohort Fertility in the Nordic Countries". European Journal of Population. 35 (3): 563–586. doi:10.1007/s10680-018-9492-2. PMC   6639448 . PMID   31372105.
  37. Hu, Sijie (2023-06-08). "Survival of the literati: Social status and reproduction in Ming–Qing China". Journal of Population Economics. 36 (4): 2025–2070. doi:10.1007/s00148-023-00960-2. ISSN   1432-1475. S2CID   259614725.
  38. Udry JR (1978). "Differential fertility by intelligence: the role of birth planning". Social Biology. 25 (1): 10–4. doi:10.1080/19485565.1978.9988313. PMID   653365.
  39. Cohen JE (March 1971). "Legal abortions, socioeconomic status, and measured intelligence in the United States". Social Biology. 18 (1): 55–63. doi:10.1080/19485565.1971.9987900. PMID   5580587. S2CID   1843957.
  40. Olson L (July 1980). "Social and psychological correlates of pregnancy resolution among adolescent women: a review". The American Journal of Orthopsychiatry. 50 (3): 432–445. doi:10.1111/j.1939-0025.1980.tb03303.x. PMID   7406028.
  41. Weller RH (1974). "Excess and deficit fertility in the United States, 1965". Social Biology. 21 (1): 77–87. doi:10.1080/19485565.1974.9988091. PMID   4851952.
  42. Van Court M (1983). "Unwanted Births And Dysgenic Reproduction In The United States". Eugenics Bulletin.
  43. Preston SH, Campbell C (March 1993). "Differential Fertility and the Distribution of Traits: The Case of IQ". The American Journal of Sociology. 98 (5): 997–1019. doi:10.1086/230135. JSTOR   2781579. S2CID   143653371.
  44. Coleman JS (1993). "Comment on Preston and Campbell's 'Differential Fertility and the Distribution of Traits'". The American Journal of Sociology. 98 (5): 1020–1032. doi:10.1086/230136. JSTOR   2781580. S2CID   144461577.
  45. Lam D (March 1993). "Comment on Preston and Campbell's "Differential Fertility and the Distribution of Traits"". The American Journal of Sociology. 98 (5): 1033–1039. doi:10.1086/230137. JSTOR   2781581. S2CID   145151340.
  46. Connor S (December 22, 1996). "Stalking the Wild Taboo; Professor predicts genetic decline and fall of man". The Sunday Times. Archived from the original on 2008-07-23. Retrieved 2008-04-15.
  47. 1 2 Parker MP (2004). "Intelligence and dysgenic fertility: Re-specification and reanalysis" (PDF). Chrestomathy: Annual Review of Undergraduate Research at the College of Charleston (3): 167–81. S2CID   39817063. Archived from the original (PDF) on 2018-02-26.