Sex differences in intellectual functioning: How much of a difference do genes make?

An X-linkage theory of inheritance of genes controlling sex differences in major intellectual traits is critically examined. A review of the research suggests that the mechanism of inheritance of differences in spatial visualization ability is X-linked recessive and its expression is probably testosterone-limited. However, the evidence concerning inheritance of differences in IQ does not support an X-linkage theory. Several characteristics of heritability estimates are discussed, including their specificity to a particular population at a certain point in time, their fluctuation with changes in amount of environmental variation, and the necessity of unconfounding sex and treatment in order to better determine the relationship between heritability and changeability of sex differences in specific intellectual trait expression.Parts of this paper were presented at the Western Psychological Association Convention, 1974.     

On the Empirical Relation Between Spatial Ability and Sex Differences in Other Aspects of Cognitive Performance

The hypothesis that sex differences in field independence and mental arithmetic can be accounted for by sex differences in spatial ability was supported for a group of 46 female and 35 male undergraduates. Sex-typing does not appear to be strongly related to spatial ability for either sex. There is a possibility of the existence of a field-independence trait independent of spatial ability, particularly among females; however, if such a trait does exist there do not appear to be significant sex differences with respect to it. Factor analysis indicates that tests of spatial ability, field independence, and mental arithmetic emerge together in a spatial ability factor. Sex differences in the factor structure of nine measures, most of which typically display sex differences (spatial ability, field independence, mental arithmetic, vocabulary, verbal and nonverbal creativity, femininity, and achievement motivation) were largely the result of differences with respect to a spatial factor.     

Distribution of Spatial Visualization and Mathematical Problem Solving Scores: A Test of Stafford's X-linked Hypotheses

This study investigated distribution of spatial visualization scores (Space Relations test of the Differential Aptitude Test) and mathematical problem solving scores (Mental Arithmetic Problems) obtained by 161 male and 152 female, 9th grade, white students for fit to the distributions predicted by the X-linked hypotheses of recessive inheritance of these skills. Data did not support the X-linked hypotheses. No significant sex-related differences were found between mean scores of tests of spatial visualization or mathematical problem solving.     

The role of experience in spatial test performance: A meta-analysis

The hypothesis that spatial ability is, in part, experientially determined, and that sex differences in spatial ability can be explained by sex differences in spatial experience, can be studied in a correlational manner by examining the relationship between spatial activity participation and spatial ability test performance for males and females. Alternatively, an experimental training situation, comparing male and female susceptibility to training, has been proposed to test the hypothesis that environment has an impact on spatial skills and sex differences in ability. Both lines of research are reviewed here, through the use of meta-analytic techniques. The first meta-analysis reveals a weak but reliable relationship between spatial activity participation and spatial ability. This relationship appears similar for males and females. The second meta-analysis reveals that spatial ability test performance can be improved by training for both sexes. This improvement does not appear different for males and females, however, contrary to a predominant hypothesis in the literature. Training to asymptote may be a better test of the relevance of differential experience to sex differences. Content and duration of training are also discussed as important factors in the effectiveness of training.This research was supported by Grant No. MH39671 from the National Institute of Mental Health. A version of this paper was presented at the biennial meetings of the Society for Research in Child Development, Baltimore, Maryland, April 1987. We are grateful to Margaret Signorella and Susan Resnick for providing data. We would also like to thank Judith Dubas, Susan Resnick, Ralph Rosnow, Carolyn Spies, Lance Weinmann, and Marsha Weinraub for helpful comments on earlier drafts of this article.     

Sex differences in emotion recognition ability: The mediating role of trait emotional awareness

Although previous research on emotion recognition ability (ERA) has found consistent evidence for a female advantage, the explanation for this sex difference remains incompletely understood. This study compared males and females on four emotion recognition tasks, using a community sample of 379 adults drawn from two regions of the United States (stratified with respect to age, sex, and socioeconomic status). Participants also completed the Levels of Emotional Awareness Scale (LEAS), a measure of trait emotional awareness (EA) thought to primarily reflect individual differences in emotion concept learning. We observed that individual differences in LEAS scores mediated the relationship between sex and ERA; in addition, we observed that ERA distributions were noticeably non-normal, and that—similar to findings with other cognitive performance measures—males had more variability in ERA than females. These results further characterize sex differences in ERA and suggest that these differences may be explained by differences in EA—a trait variable linked primarily to early learning.     

Assessing the role of different spatial frequencies in word perception by good and poor readers

Numerous studies indicate that dyslexic and nondyslexic individuals exhibit different patterns of sensitivity to spatial frequency. However, the extension of this effect to normal (nondyslexic) adults of good and poor reading abilities and the role played by different spatial frequencies in word perception have yet to be determined. In this study, using normal (nondyslexic) adults, we assessed reading ability, spatial frequency sensitivity, and perception of spatially filtered words and nonwords (using a two-alternative forced choice paradigm to avoid artifactual influences of nonperceptual guesswork). Good and poor readers showed different patterns of spatial frequency sensitivity. However, no differences in accuracy of word and nonword perception were found between good and poor readers, despite their differences in spatial frequency sensitivity. Indeed, both reading abilities showed the same superior perceptibility for spatially filtered words over nonwords across different spatial frequency bands. These findings indicate that spatial frequency sensitivity differences extend to normal (nondyslexic) adult readers and that a range of spatial frequencies can be used for word perception by good and poor readers. However, spatial frequency sensitivity may not accurately reveal an individual's ability to perceive words.     

Sex differences in the lateralization of spatial abilities: a spatial component analysis of extreme group scores

Sex differences in the cerebral lateralization of two discrete components of spatial processing were investigated in high and low ability males and females using the dual-task paradigm. In the first phase of the experiment, the results indicated a pattern of right hemispheric control for a spatial visualization component, regardless of sex and ability level. In the processing of the spatial orientation component of spatial ability, high ability males and females showed left hemispheric lateralization, whereas low ability males and females displayed right hemispheric control. In the second phase of this study, it was observed that high ability females and low ability males may use a verbal mediation strategy in processing spatial visualization tasks. No verbal mediation effects were found for the spatial orientation component.     

Spatial visualization and sex differences in quantitative ability

The hypothesis that sex differences in spatial visualization ability might account for sex differences in mathematical ability was supported for a group of 183 male and 81 female college students. With spatial visualization statistically controlled, no significant sex differences in Quantitative Scholastic Aptitude Test (QSAT) scores was found; including sex as a predictor variable increased the variance explained by less than 1%. Although the slope of the regression of mathematics on spatial visualization did not differ as a function of sex, males were somewhat more predictable than females. As the OSAT of both males and females high on spatial visualization was more predictable than the QSAT of those scoring less well, it appears that the sex difference in predictability is due to males having higher spatial ability than females.     

Solution strategies as possible explanations of individual and sex differences in a dynamic spatial task

When individuals perform spatial tasks, individual differences emerge in accuracy and speed as well as in the response patterns used to cope with the task. The purpose of this study is to identify, through empirical criteria, the different response patterns or strategies used by individuals when performing the dynamic spatial task presented in the Spatial Orientation Dynamic Test-Revised (SODT-R). Results show that participants can be classified according to their response patterns. Three different ways of solving a task are described, and their relation to (a) performance factors (response latency, response frequency, and invested time) and (b) ability tests (analytical reasoning, verbal reasoning, and spatial estimation) are investigated. Sex differences in response patterns and performance are also analyzed. It is found that the frequency with which men and women employ each one of the strategies described here, is different and statistically significant. Thus, employed strategy plays an important role when interpreting sex differences on dynamic spatial tasks.     

Mental rotation and real-world wayfinding

Sex differences in mental rotation skills are a robust finding in small-scale laboratory-based studies of spatial cognition. There is almost no evidence in the literature, however, relating these skills to performance on spatial tasks in large-scale, real-world activities such as navigating in a new city or in the woods. This study investigates the connections between mental rotation skills as measured by the Vandenburg-Kuse Mental Rotations test and the performance of college students (n=211) navigating a 6-km orienteering course. The results indicate that mental rotation skills are significantly correlated with wayfinding performance on an orienteering task. The findings also replicate sex differences in spatial ability as found in laboratory-scale studies. However, the findings complicate the discussion of mental rotation skills and sex because women often performed as well as men despite having lower mean test scores. This suggests that mental rotation ability may not be as necessary for some women's wayfinding as it is for men's navigation.     

Trait anxiety focuses spatial attention

Some findings suggest that trait anxiety impairs selective attention (e.g., Fox, 1993) while others suggest the opposite (e.g., Murray & Janelle, 2003). Both views may hold some truth if trait anxiety affects different levels of selective attention in opposite directions: trait anxiety might improve spatial attention, or perceptual selection, but weaken postperceptual selection. We used an adaptation of the flanker task (Eriksen & Hoffman, 1973) which distinguishes between spatial attention and postperceptual selection (Caparos & Linnell, 2010) to test this hypothesis. Trait anxiety was found to improve spatial attention but not to affect post-perceptual selection. The latter null effect may have resulted from the relatively high perceptual load used in this study. The focusing effect of trait anxiety suggests that anxiety reduces perceptual resources or increases cognitive engagement.     

A test of the X-linked genetic hypothesis for sex differences on Piaget's water-level task

Data from seven studies involving 849 high school and college students were used to test the recessive X-linked genetic model prediction that the square of the proportion of men who perform accurately on the water-level task is equal to the proportion of women who perform accurately. Goodness-of-fit tests showed that this prediction was confirmed for each sample. A model with a single estimate of gene frequency accounted for all the data when a classification error parameter was incorporated into the X-linked model. In both models the gene frequency parameter was about $\text{2}\text{3}$.     

Predicting preferences for sex acts: Which traits matter most, and why?

Several dispositional traits have been examined in mating contexts by evolutionary psychologists. Such traits include life history strategy, sociosexuality, and the Big Five. Recently, scholars have examined the validity and predictive utility of mating intelligence, a new construct designed to capture the cognitive processes that underlie mating psychology. The current research employed a battery of dispositional traits that include all these constructs in an effort to predict preferences for different kinds of sex acts. Sexual acts vary wildly, and the ability to predict this variability may well hold an important key to underlying sexual strategies. A sample of 607 young adults (144 males and 463 females) completed measures of each of these traits as well as a measure of preference for specific sex acts (along with providing information on their sexual orientation). The traits predicted variability in preference for sex acts - with mating intelligence being the most predictive (for instance, mating intelligence was positively related to preference for vaginal intercourse across the sexes). Sex differences emerged (e.g., males show a stronger preference for anal sex than do females). Discussion focuses on (a) sex differences in preference for sex acts along with (b) why the trait variables predicted preferences in sex acts.     

Personality, intelligence, and spatial visualization: correlates of mental rotations test performance

In the context of a longitudinal study of cognitive and personality development, I examined various correlates of spatial visualization ability, as measured by Vandenberg's Mental Rotations Test, in order to elaborate the meaning of the known sex difference on this factor. Spatial visualization ability in females was correlated with verbal IQ and various aspects of personality. These relations were absent in males. Within each sex, measures of cognitive abilities obtained in childhood predicted spatial visualization ability at age 18. Hypotheses designed to explain the sex difference in spatial visualization must be sensitive to the different implications of this factor in males and females.     

Spatial ability in secondary school students: Intra‐sex differences based on self‐selection for physical education

Past research has demonstrated consistent sex differences with men typically outperforming women on tests of spatial ability. However, less is known about intra‐sex effects. In the present study, two groups of female students (physical education and non‐physical education secondary students) and two corresponding groups of male students explored a large‐scale virtual shopping centre. In a battery of tasks, spatial knowledge of the shopping centre as well as mental rotation ability were tested. Additional variables considered were circulating testosterone levels, the ratio of 2D:4D digit length, and computer experience. The results revealed both sex and intra‐sex differences in spatial ability. Variables related to virtual navigation and computer ability and experience were found to be the most powerful predictors of group membership. Our results suggest that in female and male secondary students, participation in physical education and spatial skill are related.     

Sex Differences in Right Hemisphere Tasks

We tested the hypothesis that sex differences in spatial ability and emotional perception are due to sex differences in intrahemispheric organization of the right hemisphere. If the right hemisphere is differently organized by sex—primarily specialized for spatial ability in men, but primarily specialized for emotional perception in women—then there should be a negative correlation between spatial ability and emotional perception within sex, and the greatest disparity between abilities should be found in people with characteristic arousal of the right hemisphere. Undergraduate men (N= 86) and women (N= 132) completed tests of Mental Rotation, Surface Development, Profile of Nonverbal Sensitivity, Progressive Matrices, and Chimeric Faces. Although the expected pattern of sex differences was observed, there was no evidence for the hypothesized negative correlation between spatial ability and emotional perception, even after statistical control of general intelligence.     

Evolution and the hormonal control of sexually-dimorphic spatial abilities in humans

A number of hypotheses have been proposed for the evolution of sex differences in spatial ability. Two of these hypotheses assume a sex-based division of labor in foraging during human evolutionary history, three propose sexual selection for spatial ability, and two suggest that human life history has imposed sex-specific selection on spatial abilities. We derive predictions from each of these models and test the predictions against recent data on the effects of hormones on spatial ability across the lifespan. Sexual selection for increased range size in males might be the evolutionary origin of the enhancing effects of testosterone on spatial ability, while the benefits of reduced mobility in women at different stages of reproduction could be the origin of the inhibitory effects of oestrogen on spatial ability.     

Moderate Aerobic Exercise, T'ai Chi, and Social Problem-Solving Ability in Relation to Psychological Stress

This study evaluated the importance of exercise mode, social problem-solving ability, gender, and age in relation to anxiety and perceived daily hassles. Adult participants were classified as moderate aerobic exercisers, T'ai Chi exercisers, or sedentary via completion of a questionnaire. Social problem-solving ability, state and trait anxiety, and frequency and severity of daily hassles were measured. As predicted, scores indicating effective social problem-solving ability were associated with fewer reported severe daily hassles and with lower scores on state and trait anxiety. For state and trait anxiety, a main effect of exercise mode emerged after age and gender were controlled. A 3-way interaction involving age, gender, and exercise mode suggested that age and gender moderate the effects of exercise on anxiety, that is, the stress-reducing efficacy of different exercise modes may be dependent on a person's age and/or gender. Implications for theory, research, and practice are discussed.     

A Quantitative Trait Locus Associated With Cognitive Ability in Children

Quantitative trait loci (QTLs) associated with general cognitive ability ( g ) were investigated for several groups of children selected for very high or for average cognitive functioning. A DNA marker in the gene for insulin-like growth factor-2 receptor (IGF2R) on Chromosome 6 yielded a significantly greater frequency of a particular form of the gene (allele) in a high- g group (.303; average IQ = 136, N = 51) than in a control group (.156; average IQ = 103, N = 51). This association was replicated in an extremely-high- g group (all estimated IQs > 160, N = 52) as compared with an independent control group (average IQ = 101, N = 50), with allelic frequencies of .340 and .169, respectively. Moreover, a high-mathematics-ability group ( N = 62) and a high-verbal-ability group ( N = 51) yielded results that were in the same direction but only marginally significant ( p = .06 and .08, respectively).