Genetic and Environmental Influences on Personality: A Study of Twins Reared Together Using the Self- and Peer Report NEO-FFI Scales

Genetic and Environmental Influences on Personality: A Study of Twins Reared Together Using the Self- and Peer Report NEO-FFI Scales
Rainer Riemann, Alois Angleitner, and Jan Strelau;
Journal of Personality, September 1997 


Abstract

Previous behavior-genetic research on personality has been almost exclusively based on self-report questionnaire measures. The purpose of this research was to measure personality constructs via self- and peer reports on the items of the NEO Five-Factor Inventory (Costa & McCrae, 1989). The sample included 660 monozygotic and 200 same sex and 104 opposite sex dizygotic twin pairs. We collected self- and two independent peer reports for each of the twins. Our analysis of self-report data replicates earlier findings of a substantial genetic influence on the Big Five (h²= .42 to .56). We also found this influence for peer reports. Our results validate findings based solely on self-reports. However, estimates of genetic contributions to phenotypic variance were substantially higher when based on peer reports (h²= .51 to .81) or self- and peer reports (h²= .66 to .79) because these data allowed us to separate error variance from variance due to nonshared environmental in-fluences. Correlations between self- and peer reports reflected the same genetic influences to a much higher extent than identical environmental effects.


[Thanks @ Staffan -> "Studies that have managed to minimize measurement error typically yield heritabilities for personality traits and similar characteristics around 70 percent." ]

The g factor and the "w" factor:

>The distinctness of g from many other valued personal characteristics was clearly recognized within ten years after Spearman discovered it. In 1915, one of Spearman’s doctoral students, E. Webb, published a factor analysis of a ma­trix of correlations including a number of highly g-loaded tests and a number of ratings of character, or personality. The particular personality traits chosen for study and obtained from ratings by students’ teachers and associates were actually selected because they were expected to be related to g, and hence to show significant loadings on the g factor. This expectation, however, was com­pletely contradicted by Webb’s analysis, which yielded two wholly distinct fac­tors— g and a general “character” factor, which Webb labeled w and characterized as “will” and “persistence of motives.” The types of items most highly loaded on the w factor were described as: perseverance, as opposed to willful changeability; perseverance in the face of obstacles; kindness on prin­ciple; trustworthiness; and conscientiousness. It seemed puzzling that this cluster of traits would emerge independent of g. Teachers’ and other people’s subjective impressions of any given person’s level of intelligence create a “halo effect” which biases the observers’ ratings of that person’s personality traits. Despite this bias of the personality ratings by halo effects, Webb’s factor analysis, be­cause it included objective tests of g, gave a clean-cut separation of the two domains. What Webb’s study and subsequent studies seemed to indicate was that g, even as fallibly measured by psychometric tests, is an entirely cognitive variable.

Later studies of the relationship between personality factors and g have fully substantiated this conclusion.<

The g factor, 1998

Arthur Jensen

Diffusion rate of selected household appliances in the US and Britain

Household appliances and the use of time: the United States and Britain since the 1920s
Sue Bowden and Avner Offer; 1994

full size: click at the image

The Scientific Study of General Intelligence: Tribute to Arthur Jensen

The Scientific Study of General Intelligence: Tribute to Arthur Jensen
Helmuth Nyborg (Editor) ; 2003

Sex Differences in Reading Achievement

Sex Differences in Reading Achievement
Richard Lynn and Jaan Mikk; 2009


Abstract

In the last century many studies have revealed the advantages of girls in reading and superiority of boys in science. However, the international tests detected no difference in science test results in the 21st century. The aim of the study was to find the sex effect size and variances in reading achievement in recent international studies. The analysis of PISA 2000, 2003, and 2006 data and the PIRLS 2001 and 2006 data revealed that the advantages in reading achievement of ten-year old girls was 0.23d and that of 15-year old girls was 0.42d. One explanation of girls’ higher achievement in reading is in their deeper engagement in language related activities. Comparisons with other studies and possible implications are shown.

The General Factor of Personality and general intelligence: Testing hypotheses from Differential-K, Life History Theory, and strategic differentiation–integration effort

The General Factor of Personality and general intelligence: Testing hypotheses from Differential-K, Life History Theory, and strategic differentiation–integration effort
C.S. Dunkel, T.C. De Baca, M.A. Woodley, and H.B.F. Fernandes
Personality and Individual Differences (In Press - Available online 20 January 2014)


Highlights:

o The association between the GFP and g across racial groups was examined.

o The strength of the association varied across racial groups.

o The results support strategic differentiation–integration effort.

Abstract

Life history as applied to human psychology has progressed on different levels of analysis including between racial groups (Differential-K) and between individuals (Life History Theory). While the approaches at each level have garnered significant research support, some findings at the level of individual differences are inconsistent with findings from the level of group differences. The association between the General Factor of Personality and general intelligence was examined across and within racial groups to investigate the inconsistency. The results were in line with predictions derived from strategic differentiation–integration effort (SD–IE), the proposition that aggregation amongst variables decreases as life history strategy slows. The results suggest SD–IE may be a useful tool in reconciling the apparent contradictions across the levels of analysis.

General and specific ability profiles of students earning terminal degrees in various disciplines:

Neglected Aspects and Truncated Appraisals in Vocational Counseling: Interpreting the Interest–Efficacy Association From a Broader Perspective: Comment on Armstrong and Vogel (2009)
David Lubinski, 2010
Journal of Counseling Psychology

full size: click at the image

Figure 1. Average z scores of participants on verbal, spatial, and mathematical ability for terminal bachelor’s degrees, terminal master’s degrees, and doctoral degrees are plotted by field. The groups are plotted in rank order of their normative standing on g (verbal [V] + spatial [S] + mathematical [M]) along the x-axis, and the line with the arrows from each field pointing to it indicates on the continuous scale where they are in general mental ability in z-score units. This figure is standardized in relation to all participants with complete ability data at the time of initial testing. Respective Ns for each group (men + women) were as follows for bachelor’s, master’s, and doctorates, respectively: engineering (1,143, 339, 71), physical science (633, 182, 202), math/computer science (877, 266, 57), biological science (740, 182, 79), humanities (3,226, 695, 82), social science (2,609, 484, 158), arts (615, 171 [master’s only]), business (2,386, 191 [master’s + doctorate]), and education (3,403, 1,505 [master’s  + doctorate]). * For education and business, master’s degrees and doctorates were combined because the doctorate samples for these groups were too small to obtain stability (N < 30). For the specific N for each degree by sex that composed the major groupings see Appendix A in Wai et al. (2009).

Vocabulary & IQ:

Bias in Mental Testing; (p 145-147)

Arthur Jensen; 1980

Vocabulary.    Word knowledge figures prominently in standard tests. The scores on the vocabulary subtest are usually the most highly correlated with total IQ of any of the other subtests. This fact would seem to contradict Spearman’s important generalization that intelligence is revealed most strongly by tasks calling for the eduction of relations and correlates. Does not the vocabulary test merely show what the subject has learned prior to taking the test? How does this involve reasoning or eduction? 

In fact, vocabulary tests are among the best measures of intelligence, because the acquisition of word meanings is highly dependent on the eduction of meaning from the contexts in which the words are encountered. Vocabulary for the most part is not acquired by rote memorization or through formal instruction. The meaning of a word most usually is acquired by encountering the word in some context that permits at least some partial inference as to its meaning. By hearing or reading the word in a number of different contexts, one acquires, through the mental processes of generalization and discrimination and eduction, the essence of the word’s meaning, and one is then able to recall the word precisely when it is appropriate in a new context. Thus the acquisition of vocabulary is not as much a matter of learning and memory as it is of generalization, discrimination, eduction, and inference. Children of high intelligence acquire vocabulary at a faster rate than children of low intelligence, and as adults they have a much larger than average vocabulary, not primarily because they have spent more time in study or have been more exposed to words, but because they are capable of educing more meaning from single encounters with words and are capable of discriminating subtle differences in meaning between similar words. Words also fill conceptual needs, and for a new word to be easily learned the need must precede one’s encounter with the word. It is remarkable how quickly one forgets the definition of a word he does not need. I do not mean “need” in a practical sense, as something one must use, say, in one’s occupation; I mean a conceptual need, as when one discovers a word for something he has experienced but at the time did not know there was a word for it. Then when the appropriate word is encountered, it “sticks” and becomes a part of one’s vocabulary. Without the cognitive “need,” the word may be just as likely to be encountered, but the word and its context do not elicit the mental processes that will make it “stick.”

During childhood and throughout life nearly everyone is bombarded by more dif­ferent words than ever become a part of the person’s vocabulary. Yet some persons acquire much larger vocabularies than others. This is true even among siblings in the same family, who share very similar experiences and are exposed to the same parental vocabu­lary.

Vocabulary tests are made up of words that range widely in difficulty (percentage passing); this is achieved by selecting words that differ in frequency of usage in the language, from relatively common to relatively rare words. (The frequency of occurrence of each of 30,000 different words per 1 million words of printed material—books, magazines, and newspapers—has been tabulated by Thorndike and Lorge, 1944.) Techni­cal, scientific, and specialized words associated with particular occupations or localities are avoided. Also, words with an extremely wide scatter of “ passes” are usually elimi­nated, because high scatter is one indication of unequal exposure to a word among persons in the population because of marked cultural, educational, occupational, or regional differences in the probability of encountering a particular word. Scatter shows up in item  analysis as a lower than average correlation between a given word and the total score on the vocabulary test as a whole. To understand the meaning of scatter, imagine that we had a perfect count of the total number of words in the vocabulary of every person in the population. We could also determine what percentage of all persons know the meaning of each word known by anyone in the population. The best vocabulary test limited to, say, one hundred items would be that selection of words the knowledge of which would best predict the total vocabulary of each person. A word with wide scatter would be one that is almost as likely to be known by persons with a small total vocabulary as by persons with a large total vocabulary, even though the word may be known by less than 50 percent of the total population. Such a wide-scatter word, with about equal probability of being known by persons of every vocabulary size, would be a poor predictor of total vocabulary. It is such words that test constructors, by statistical analyses, try to detect and eliminate.

It is instructive to study the errors made on the words that are failed in a vocabulary test. When there are multiple-choice alternatives for the definition of each word, from which the subject must discriminate the correct answer among the several distractors, we see that failed items do not show a random choice among the distractors. The systematic and reliable differences in choice of distractors indicate that most subjects have been exposed to the word in some context, but have inferred the wrong meaning. Also, the fact that changing the distractors in a vocabulary item can markedly change the percentage passing further indicates that the vocabulary test does not discriminate simply between those persons who have and those who have not been exposed to the words in context. For example, the vocabulary test item ERUDITE has a higher percentage of errors if the word polite is included among the distractors; the same is true for MERCENARY when the words stingy and charity are among the distractors; and STOICAL - sad, DROLL- eerie, FECUND - odor, FATUOUS - large.

Another interesting point about vocabulary tests is that persons recognize many more of the words than they actually know the meaning of. In individual testing they often express dismay at not being able to say what a word means, when they know they have previously heard it or read it any number of times. The crucial variable in vocabulary size is not exposure per se, but conceptual need and inference of meaning from context, which are forms of eduction. Hence, vocabulary is a good index of intelligence.

Picture vocabulary tests are often used with children and nonreaders. The most popular is the Peabody Picture Vocabulary Test. It consists of 150 large cards, each containing four pictures. With the presentation of each card, the tester says one word (a common noun, adjective, or verb) that is best represented by one of the four pictures, and the subject merely has to point to the appropriate picture. Several other standard picture vocabulary tests are highly similar. All are said to measure recognition vocabulary, as contrasted to expressive vocabulary, which requires the subject to state definitions in his or her own words. The distinction between recognition and expressive vocabulary is more formal than psychological, as the correlation between the two is close to perfect when corrected for errors of measurement.

Misjudgments about individual IQ-levels:

Bias in Mental Testing; (p 107)

Arthur Jensen; 1980

Misjudgments of an individual’s general intelligence are usually a result of basing judgment on an atypical aspect of the person’s behavior. Almost everyone may do or say something that is particularly clever or bright or sagacious now and then, or may behave quite stupidly on occasion. If we give too much weight to these atypical occurrences in our subjective judgment of a person’s mental capacity, we are apt to take exception to his or her tested IQ. Parents seem especially prone to judge their own children by their atypical performances. Each person’s abilities vary about his own mean, and we usually notice the deviations more than the mean. Prejudices and the like may cause us consistently to give greater weight to the positive deviations than to the negative for some persons and vice versa for others. School teachers, who observe large numbers of children of similar age over a wide range of ability, are usually better judges of intelligence than parents are. I once had occasion to interview independently the mothers and the classroom teachers of a number of children to whom I had given individual IQ tests. I found that the teachers had a much better estimate than the mothers of a given child’s rank in the total distribution of IQs. In giving their reasons for their estimate of a particular child’s IQ, the teachers usually noted the child’s typical behavior in cognitively demanding situations, whereas mothers more often pointed out exceptional instances of clever behavior. On this basis, low-IQ children especially are often rated average or above by their parents. Very-high-IQ children, on the other hand, are often underrated by their parents, who are usually surprised to learn that their child is quite exceptional. Parental judgments of children’s intelligence tend to cluster more closely around the mean (or slightly above) than do the children’s IQs. Personality factors affect subjective judgments, too, for both parents and teachers. The socially outgoing, extraverted child tends to be overrated as compared with the more shy, quiet, or introverted child.

Distribution of Achievement:

Distribution of Achievement

Bias in Mental Testing; (p 95-98)

Arthur Jensen; 1980

As we have seen, there are a number of reasons for believing that mental ability is normally distributed in the population. But this generalization most likely does not extend to manifestations of ability in individual achievements, output, acquired knowledge, developed skills, occupational success, earnings, and the like. There is good reason to believe that achievement, in contrast to more elemental traits and abilities, is not normally distributed in the general population but that it has a markedly skewed distribution, like that in Figure 4.20.

When frequency distributions are plotted for accomplishments that can be counted, and thus are measurable on an absolute scale, the distributions are found to be markedly skewed. Examples are number of patents held by inventors, number of publications of research scientists and university professors, amount of music written by composers, and yearly earnings.

The skewness of the distribution of accomplishments also accords with subjective impressions of the absolute differences between persons lying at various percentile points on the scale of accomplishments in any field. The difference in chess skill between world champions and the average chess player certainly seems greater than the difference be­tween the average player and the chess duffer. An Olympics champion is much farther above the average person in his particular athletic skill than the average person is above those who are just barely capable of displaying the particular skill at all.

A similar skewness is found for scholastic achievement and measures of general knowledge. Most scholastic achievement tests, however, are constructed in such a way as not to reveal the skewed distribution of achievement. In the first place, the usual achieve­ment tests given in any grade in school have too little “ top,” that is, too few hard items, thereby cutting off the long upper tail of the skewed curve. The reason for this is that the usual achievement tests are intended to measure the achievement of a particular grade and do not include information and skills that are a part of the curriculum of higher grades. The eighth-grader who has mastered calculus could never show it on the usual math achievement tests given to eighth-graders. In the second place, most scholastic achieve­ment tests today are in a sense double-duty tests; they are designed to measure not only what the child has learned in a given grade in school, but to test his intelligence as well.

Figure 4.20. Theoretical distribution of achievement as measured on a scale of equal intervals. Notice that, even with this marked positive skewness of the distribution, the median and mean are quite close together but that the mean is pulled in the direction of the skew.

Knowledge acquisition is substantially correlated with intelligence, but not to the ex­tremely high degree suggested by the correlation between the usual group verbal IQ test and the usual achievement test. A large number of the items in achievement tests requires the subject to use his or her acquired knowledge to solve novel problems, to reason, compare, generalize, and figure out answers to questions that may be unlike anything he or she has been taught in school, except that the information required to solve the problems has been taught. The ability to use information in reasoning and problem solving is more a matter of intelligence than of how much information the child has acquired in class, and so a larger proportion of the variance in achievement will represent intelligence variance than variance in how much children have actually learned from their lessons. Thus, when achievement tests are made to resemble intelligence tests in this way, and also are made to restrict the range of informational content sampled by the test, it should not be surprising that the distribution of achievement scores on such tests is much like the distribution of intelligence test scores. Because their informational content is so restricted, the usual grade-level achievement tests can be made difficult enough to spread students out into a normal distribution only by increasing the level of reasoning and problem­ solving ability required by some of the items, making them very much like intelligence test items.

But achievement tests can be constructed to measure knowledge of things taught in school, rather than reasoning ability; the items sample knowledge at all levels over a wide range of fields, so that the test has virtually no ceiling and few if any subjects at any age could obtain a perfect score. An example of such a test is the General Culture Test (Learned & Wood, 1938), which was originally devised to assess all-around scholastic achievement in the high schools and colleges of Pennsylvania. The test contains some 1,200 questions involving information on all the fine arts, all periods of history, social studies, natural sciences, and world literature. The test has plenty of bottom and plenty of top for high school and college students. The total range of scores in a group of 1,503 high school seniors was from 25 to 615. The highest score found in a sample of 5,747 college sophomores was 755; the highest among 3,720 college seniors was 805, which is only about two-thirds of the maximum possible score. The distribution of scores in a large sample of high school seniors was quite skewed (10 percent less skew than in Figure 4.20).

If achievement depends on other normally distributed factors in addition to ability, such as motivation, interest, energy, and persistence, and if all these factors act multi­plicatively, then theoretically we should expect achievement to show a positively skewed distribution. The greater the number of factors (each normally distributed), the more skewed is the distribution of their products. The products of normally distributed variables are distributed in a skewed way such that the distribution of products can be normalized by a logarithmic transformation. A logarithmic transformation of achievement scores in effect makes the component elements of achievement additive rather than multiplicative. Theoretically a multiplicative effect of ability and motivation (or other traits involved in achievement) makes sense. Imagine the limiting case of zero ability; then regardless of the amount of motivation, achievement would equal zero. Also, with zero motivation, regard­less of the amount of ability, achievement would equal zero. Great achievers in any field are always high in a number of relevant traits, the multiplicative interaction of which places their accomplishments far beyond those of the average person—much farther than their standing on any single trait or a mere additive combination of several traits. A superior talent alone does not produce the achievements of a Michelangelo, a Beethoven, or an Einstein. The same can be said of Olympics-level athletic performance, which depends on years of concentrated effort and training as well as certain inborn physical advantages. Thus it is probably more correct to say that a person’s achievements are a product, rather than a summation, of his or her abilities, disposition, and training.

In God's Image - The Natural History of Intelligence and Ethics

In God's Image - The Natural History of Intelligence and Ethics
Gerhard Meisenberg; 2007

Secularization and Desecularization in Our Time

Secularization and Desecularization in Our Time (full download)

Gerhard Meisenberg; 2011

Journal of Social, Political, and Economic Studies

Abstract

Using data from the World Values Survey covering the period from 1981 to 2008, this study examines trends in the strength of religious belief worldwide. At the country level, the most important predictors of current religiosity are high intelligence and a history of communist rule, both of which reduce religious belief. However, religiosity has been rising vigorously in the communist and ex-communist countries during the surveyed period although religion is declining in most countries of non-communist Europe and East Asia. In addition to a history of communist rule, other factors associated with rising religiosity include high religiosity of young people relative to older people, high female relative to male religiosity, and a positive relationship between religiosity and fertility. In addition, religion tends to grow in countries in which less educated people are far more religious than those with higher education. Aside from the rebound of religion in the (ex)communist countries, the religiosity gap between the most advanced and the most backward nations has widened worldwide. The implications of these findings for the future of religion are discussed.

-----------------------------------------------------------------------------------------------------------

Sex differences in religiosity:

"In countries with high average religiosity, both men and women are highly religious and the gender difference is small. Gender differences are larger in low-religiosity countries, and are largest in advanced nations with Christian tradition. Gender differences are smallest in the Muslim countries of North Africa and the Middle East. This region has high average religiosity, and it is quite possible that Islam is intrinsically more attractive for men whereas Christianity is more attractive for women. The appendix shows that Mali and Saudi Arabia are the only countries in the World Values Survey in which men are (marginally) more religious than women."

The Contingent Smile: A Meta-Analysis of Sex Differences in Smiling

The Contingent Smile: A Meta-Analysis of Sex Differences in Smiling
M. LaFrance, E. L. Paluck, and M. A. Hecht; 2003


Abstract

The authors present a meta-analysis of sex differences in smiling based on 448 effect sizes derived from 162 research reports. There was a statistically significant tendency for women and adolescent girls to smile more than men and adolescent boys (d = 0.41). The authors hypothesized that sex differences in smiling would be larger when concerns about gender-appropriate behavior were made more conspicuous, situational constraints were absent or ambiguous, or emotion (especially negative) was salient. It was also predicted that the size of the sex difference in smiling would vary by culture and age. Moderator analysis supported these predictions. Although men tend to smile less than women, the degree to which this is so is contingent on rules and roles.

Form of day care and respiratory infections among Finnish children.

Form of day care and respiratory infections among Finnish children.
Louhiala PJ, Jaakkola N, Ruotsalainen R, and Jaakkola JJ; 1995
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1615809/


Abstract

The relationship between respiratory infectious diseases and form of day care was assessed in a retrospective cohort study of 2568 randomly selected children aged 1 through 7 years in Espoo, Finland. Day-care center children had an increased risk for the common cold, acute otitis media, and pneumonia. The risk concentrated in 1-year-old children, for whom the adjusted relative risks (incidence density ratios) for the common cold, otitis media, and pneumonia were 1.69 (95% confidence interval [CI] = 1.43, 2.01), 1.99 (95% CI = 1.57, 2.52), and 9.69 (95% CI = 2.31, 40.55), respectively. Among 1-year-old children, the proportion of infections attributable to care at day-care centers were 41% (95% CI = 30, 50) for colds, 50% (95% CI = 36, 60) for otitis media, and 85% (95% CI = 57, 98) for pneumonia. The results provide evidence that care in day-care centers is a determinant of acute respiratory infections in children under 2, whereas family day care does not essentially increase risk.

Processing Speed Mediates the Development of General Intelligence (g) in Adolescence

Processing Speed Mediates the Development of General Intelligence (g) in Adolescence
Thomas R. Coyle, David R. Pillow, Anissa C. Snyder, and Peter Kochunov; 2011
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3725745/


Abstract

In the research reported here, we examined whether processing speed mediates the development of general intelligence (g) in adolescence. Using the Armed Services Vocational Aptitude Battery, a battery of 12 diverse cognitive tests, we assessed processing speed and g in a large sample of 13- to 17-year-olds obtained from the National Longitudinal Survey of Youth (N = 6,969). The direct effect of age on g was small compared with the total effect of age on g, which was almost fully mediated through speed. The results suggest that increases in g in adolescence can be attributed to increases in mental speed.


See also: 
Clocking the mind: Mental chronometry and individual differences; A. R. Jensen; 2006

Fatherhood & Health:

Fatherhood - Evolution and Human Paternal Behavior
P B Gray & K G Anderson; 2012

Fatherhood appears to have both protective and deleterious impacts on men's health. The parenting of young children tends to negatively impact marital quality, meaning that men lose some of the beneficial effects of affiliative pair-bonds. Male mental health may suffer, especially if his partner is also struggling with mental health difficulties. Sleep and sexual challenges may exacerbate these difficulties. Young children, particularly those in daycare, can also serve as disease vectors (for example, Hillis et al. 1992), presenting a father with greater exposure to transmissible diseases. The outcome of these types of issues is that fathers of young children may have compromised health.

Yet as those children age, men's health may rebound. The strains of caring for young children wane. Those children may provide social and material support to aging parents. Perhaps an older father, living somewhere without a Social Security check to cash, is supported partly by the sons or daughters he raised to adulthood. Put all of these health and fatherhood variables together, and maybe observations like the following make sense. As shown in a U.S. study of approximately five thousand adults, the effects of fatherhood altered across a man's life and his children's ages (see E. E. Bartlett 2004). In this large U.S. study, among married men aged forty years or younger, 8.9% of fathers but only 1.1% of married men without children rated their health as fair or poor. In the same study, among married men aged forty-one to sixty-four, 16.5% of married fathers with children but 22.7% of married men without children rated their health as fair or poor. Similarly, in an Australian study, fathers of preschool-aged children reported worse health than fathers did of older children (Hewitt, Baxter, and Western 2006). These data suggests that earlier in life fatherhood may be a drain on a man's health, but that same relationship may have later, beneficial effects. This pattern appears to be the overarching perspective on fatherhood and health.

[This excerpt doesn't seem to be based on very hard data, but I think it makes some interesting points.]

Sex Differences in Mathematical Reasoning Ability at Age 13: Their Status 20 Years Later

Sex Differences in Mathematical Reasoning Ability at Age 13: Their Status 20 Years Later
Camilla P. Benbow, David Lubinski, Daniel L. Shea, and Hossain Eftekhari-Sanjani; 2000


Abstract

Reported is the 20-year follow-up of 1,975 mathematically gifted adolescents (top 1%) whose assessments at age 12 to 14 revealed robust gender differences in mathematical reasoning ability. Both sexes became exceptional achievers and perceived themselves as such; they reported uniformly high levels of degree attainment and satisfaction with both their career direction and their overall success. The earlier sex differences in mathematical reasoning ability did predict differential educational and occupational outcomes. The observed differences also appeared to be a function of sex differences in preferences for (a) inorganic versus organic disciplines and (b) a career-focused versus more balanced life. Because profile differences in abilities and preferences are longitudinally stable, males probably will remain more represented in some disciplines, whereas females are likely to remain more represented in others. These data have policy implications for higher education and the world of work.

The Inequality Taboo

The Inequality Taboo
Charles Murray; September 2005

Spatial Ability for STEM Domains: Aligning Over 50 Years of Cumulative Psychological Knowledge Solidifies Its Importance

Spatial Ability for STEM Domains: Aligning Over 50 Years of Cumulative Psychological Knowledge Solidifies Its Importance
Jonathan Wai, David Lubinski, and Camilla P. Benbow; 2009
https://my.vanderbilt.edu/smpy/files/2013/02/Wai2009SpatialAbility1.pdf


Abstract

The importance of spatial ability in educational pursuits and the world of work was examined, with particular attention devoted to STEM (science, technology, engineering, and mathematics) domains. Participants were drawn from a stratified random sample of U.S. high schools (Grades 9 –12, N = 400,000) and were tracked for 11+ years; their longitudinal findings were aligned with pre-1957 findings and with contemporary data from the Graduate Record Examination and the Study of Mathematically Precocious Youth. For decades, spatial ability assessed during adolescence has surfaced as a salient psychological attribute among those adolescents who subsequently go on to achieve advanced educational credentials and occupations in STEM. Results solidify the generalization that spatial ability plays a critical role in developing expertise in STEM and suggest, among other things, that including spatial ability in modern talent searches would identify many adolescents with potential for STEM who are currently being missed.



[Siehe auch den Beitrag / das lesenswerte Kommentar von Christian Schmidt: Räumliches Denken als Voraussetzung für die Naturwissenschaften]

Nurturant Females

Sex, Evolution, and Behavior
Martin Daly & Margo Wilson; 1983

In animals such as ourselves, where parental care is an immense undertaking, the energetic cost of the initial gamete is a negligible proportion of total parental investment. The ovum-sperm disparity seems trivial. Yet nurturance is predominantly a female enterprise in many animals including almost all mammals, and the dimorphism of those little gametes is ultimately to blame. This is because the gamete size distinction has set the stage for some other evolutionary developments that have greatly amplified the initial difference in the parental investment of female and male.

Large ova bias organisms toward female nurture wherever fertilization takes place inside one parent's body because the relative immobility of the ovum assures that, whenever internal fertilization occurs, it takes place within the female. Internal fertilization protects the young from perils like desiccation and predation, thereby greatly increasing each individual ovum's prospects for fertilization and survival. But it also has a cost. By increasing her nurture for each ovum, the female can no longer invest in so many. In one season a ten-year-old cod may release as many as 5 million eggs for external fertilization. No fish with internal fertilization can match the cod's fecundity. But neither will an internal fertilizer suffer the same massive destruction from early deaths and fertilization failures as unparented cod eggs. There are trade-offs between fecundity and nurture.

Once the female is harboring zygotes within her, any further investment in nurturant or protective devices that may then evolve tends most often to be paid by the female, although both parents reap the fitness benefits. Birds and reptiles, for example, construct a protective eggshell at considerable material expense. In several types of animals, mechanisms have evolved to feed the infant while it grows within the maternal body; the mammalian placenta is perhaps the most sophisticated such device. In fact, we mammals have attained a pinnacle of concentrated maternal investment. First there is pregnancy: Prolonged internal gestation and placental nurture are enormous commitments of female's resources that pay off in greatly reduced offspring mortality during the early stages of development. And then, at birth, the mammalian female doesn't even take a recuperative break, for we mammals have invented another major maternal investment - milk.

Internal fertilization, gestation, placentation, lactation: Each of these evolutionary developments has had the effect of concentrating female investment in a decreasing number of offspring. In the evolutionary sequence leading to modern mammals, each advance in the effective nurture of young has amplified the sex difference in parental contributions. Among vertebrate animals with external fertilization (most fish and amphibia), things are very different: If there is any postmating parental care at all, it is at least as likely to be performed by males as by females. In birds, internal fertilization is universal, but so is an early externalization of the developing embryo, with the result that both parents can care for it; biparental investment is the rule. But in mammals, and indeed in most animals with internal fertilization, parental nurture is overwhelmingly female-dominated.

Does a fitness factor contribute to the association between intelligence and health outcomes? Evidence from medical abnormality counts among 3654 US Veterans

Does a fitness factor contribute to the association between intelligence and health outcomes? Evidence from medical abnormality counts among 3654 US Veterans
Rosalind Arden , Linda S. Gottfredson, and Geoffrey Miller; 2009


Abstract

We suggest that an over-arching ‘fitness factor’ (an index of general genetic quality that predicts survival and reproductive success) partially explains the observed associations between health outcomes and intelligence. As a proof of concept, we tested this idea in a sample of 3654 US Vietnam veterans aged 31–49 who completed five cognitive tests (from which we extracted a g factor), a detailed medical examination, and self-reports concerning lifestyle health risks (such as smoking and drinking). As indices of physical health, we aggregated ‘abnormality counts’ of physician-assessed neurological, morphological, and physiological abnormalities in eight categories: cranial nerves, motor nerves, peripheral sensory nerves, reflexes, head, body, skin condition, and urine tests. Since each abnormality was rare, the abnormality counts showed highly skewed, Poisson-like distributions. The correlation matrix amongst these eight abnormality counts formed only a weak positive manifold and thus yielded only a weak common factor. However, Poisson regressions showed that intelligence was a significant positive predictor of six of the eight abnormality counts, even controlling for diverse lifestyle covariates (age, obesity, combat and toxin exposure owing to service in Vietnam, and use of tobacco, alcohol, marijuana, and hard drugs). These results give preliminary support for the notion of a superordinate fitness factor above intelligence and physical health, which could be further investigated with direct genetic assessments of mutation load across individuals.

Genetic and Environmental Influences on Human Psychological Differences

Genetic and Environmental Influences on Human Psychological Differences
Thomas J. Bouchard, Jr. & Matt McGue; 2003


Abstract

Psychological researchers typically distinguish five major domains of individual differences in human behavior: cognitive abilities, personality, social attitudes, psychological interests, and psychopathology (Lubinski, 2000). In this article we: discuss a number of methodological errors commonly found in research on human individual differences; introduce a broad framework for interpreting findings from contemporary behavioral genetic studies; briefly outline the basic quantitative methods used in human behavioral genetic research; review the major criticisms of behavior genetic designs, with particular emphasis on the twin and adoption methods; describe the major or dominant theoretical scheme in each domain; and review behavioral genetic findings in all five domains. We conclude that there is now strong evidence that virtually all individual psychological differences, when reliably measured, are moderately to substantially heritable.

An Association Between the Kinship and Fertility of Human Couples

An Association Between the Kinship and Fertility of Human Couples
Agnar Helgason et al.; 2008


Abstract

Previous studies have reported that related human couples tend to produce more children than unrelated couples but have been unable to determine whether this difference is biological or stems from socioeconomic variables. Our results, drawn from all known couples of the Icelandic population born between 1800 and 1965, show a significant positive association between kinship and fertility, with the greatest reproductive success observed for couples related at the level of third and fourth cousins. Owing to the relative socioeconomic homogeneity of Icelanders, and the observation of highly significant differences in the fertility of couples separated by very fine intervals of kinship, we conclude that this association is likely to have a biological basis.


See also: http://www.sciencemag.org/content/322/5908/1634.2.full.pdf 
(Comment on “An Association Between the Kinship and Fertility of Human Couples” - Rodrigo Labouriau and António Amorim; 2008)



[Thanks @ Tomás]