The Science of Sex Differences in Science and Mathematics

Sex differences and science: the etiology of science excellence

BACKGROUND

Are there sex differences in the etiology of high performance in science in childhood that could contribute to the under-representation of women in scientific careers? In this study the relative contributions of genetic and environmental influences on high performance in science in both boys and girls were assessed using standard twin analyses.

METHODS

The sample included 3000 twin pairs from the UK Twins Early Development Study (TEDS). Science performance ratings based on the UK National Curriculum were collected from teachers when the twins were 9, 10 and 12 years old. Science excellence was defined as performing above the 85th percentile. Sex-limitation liability threshold models were used to assess sex differences in etiology.

RESULTS

We found no evidence for quantitative or qualitative sex differences in the etiology of science excellence, which was moderately heritable (30-50%), and influenced by both shared (40-56%) and non-shared (10-13%) environmental influences.

CONCLUSIONS

Although boys and girls do not differ genetically in relation to school science performance per se, the under-representation of women in scientific careers may be due to attitudes rather than aptitudes.

Gender differences in the functional and structural neuroanatomy of mathematical cognition

Despite ongoing debate about the nature of gender differences in mathematics achievement, little is known about gender similarities and differences in mathematical cognition at the neural level. We used fMRI to compare brain responses in 25 females and 24 males during a mental arithmetic task involving 3-operand addition and subtraction. We also used voxel-based morphometry (VBM) to examine gender differences in brain structure. Although females and males did not differ in accuracy or response times (effect size d<0.3), significant gender differences in functional brain activation were observed in the right dorsal and ventral visuospatial information processing streams (d>1.1). Males showed greater dorsal stream activation in the right intra-parietal sulcus areas important for numerical cognition, and angular gyrus regions of the default mode network that are typically deactivated during complex cognitive tasks, as well as greater ventral stream activation in the right lingual and parahippocampal gyri. VBM revealed an opposite pattern of gender differences-compared to males, females had greater regional density and greater regional volume in dorsal and ventral stream regions where males showed greater fMRI activation. There were no brain areas where females showed greater functional activation than males, and no brain areas where males showed greater structural density or volume than females. Our findings provide evidence for gender differences in the functional and structural organization of the right hemisphere brain areas involved in mathematical cognition. Together with the lack of behavioral differences, our results point to more efficient use of neural processing resources in females.

Paracingulate asymmetry in anterior and midcingulate cortex: sex differences and the effect of measurement technique

Many structural brain asymmetries accompany left hemisphere language dominance. For example, the cingulate sulcus is larger in the medial cortex of the right hemisphere, while the more dorsal paracingulate sulcus is larger on the left. The functional significance of these asymmetries is unknown because fMRI studies rarely attempt to localize activation to specific sulci, possibly due to difficulties in consistent sulcal identification. In medial cortex, for example, there are many regions of partial sulcal overlap where MRI images do not provide sufficient information to unambiguously distinguish a paracingulate sulcus from a displaced anterior cingulate segment. As large samples of postmortem material are rarely available for cytoarchitectural studies of sulcal variation, we have investigated the effect of variation in boundary and sulcal definition on paracingulate asymmetry in the MRI scans of 200 healthy adults (100 men, 100 women). Although women displayed a reliable asymmetry in the size of the paracingulate sulcus, regardless of boundary definition or technique, asymmetry was greatest when (1) the measurement was limited to the midcingulate region between the genu and the anterior commissure; and (2) the more dorsal of two overlapping sulci was always classified as a paracingulate sulcus (rather than as a displaced cingulate segment). The fact that paracingulate asymmetry is maximal in the midcingulate region suggests that this region may play a particular role in hemispheric specialization for language. Future work should investigate the structural and functional correlates of sulcal variation in this region.

National differences in gender-science stereotypes predict national sex differences in science and math achievement

About 70% of more than half a million Implicit Association Tests completed by citizens of 34 countries revealed expected implicit stereotypes associating science with males more than with females. We discovered that nation-level implicit stereotypes predicted nation-level sex differences in 8th-grade science and mathematics achievement. Self-reported stereotypes did not provide additional predictive validity of the achievement gap. We suggest that implicit stereotypes and sex differences in science participation and performance are mutually reinforcing, contributing to the persistent gender gap in science engagement.

On the Real Magnitude of Psychological Sex Differences

A comprehensive evolutionary theory of sex differences will benefit from an accurate assessment of their magnitude across different psychological domains. This article shows that mainstream research has severely underestimated the magnitude of psychological sex differences; the reason lies in the common practice of measuring multidimensional differences one dimension at a time, without integrating them into a proper multivariate effect size (ES). Employing the Mahalanobis distance D (the multivariate generalization of Cohen's d) results in more accurate, and predictably larger, estimates of overall sex differences in multidimensional constructs. Two real-world examples are presented: (1) In a published dataset on Big Five personality traits, sex differences on individual scales averaged d = .27, a typical ES conventionally regarded as “small.” However, the overall difference was D = .84 (disattenuated D = .98), implying considerable statistical separation between male and female distributions. (2) In a recent meta-analytic summary of sex differences in aggression, the individual ESs averaged d = .34. However, the overall difference was estimated at D = .75 – .80 (disattenuated D = .89–1.01). In many psychological domains, sex differences may be substantially larger than previously acknowledged.

A large-scale investigation of lateralization in cortical anatomy and word reading: are there sex differences?

The authors report findings of a large-scale, multitask investigation of sex differences in both structural asymmetries and lateralization of word reading. Two hundred participants were tested in eight divided visual field lexical tasks, and each received a structural magnetic resonance imaging scan. The authors examined whether there was evidence for sex differences in overall measures of neuroanatomical and behavioral lateralization, in specific language tasks and brain regions, and in variation in asymmetry within and across tasks and brain regions. There was very little evidence for sex differences on any behavioral measure. The few indications of sex differences in the current report accounted for 2% or less of the individual variation in asymmetry and could not be replicated in independent subsamples. No sex differences were observed in the asymmetry of structures in Broca's and Wernicke's areas such as pars triangularis, pars opercularis, the planum temporale, planum parietale, or Heschl's gyrus. There were also no sex differences in the variability of neuroanatomical asymmetries within or between brain regions. However, a significant relationship between planum temporale and behavioral asymmetry was restricted to men.

Size matters: cerebral volume influences sex differences in neuroanatomy

Biological and behavioral differences between the sexes range from obvious to subtle or nonexistent. Neuroanatomical differences are particularly controversial, perhaps due to the implication that they might account for behavioral differences. In this sample of 200 men and women, large effect sizes (Cohen's d > 0.8) were found for sex differences in total cerebral gray and white matter, cerebellum, and gray matter proportion (women had a higher proportion of gray matter). The only one of these sex differences that survived adjustment for the effect of cerebral volume was gray matter proportion. Individual differences in cerebral volume accounted for 21% of the difference in gray matter proportion, while sex accounted for an additional 4%. The relative size of the corpus callosum was 5% larger in women, but this difference was completely explained by a negative relationship between relative callosal size and cerebral volume. In agreement with Jancke et al., individuals with higher cerebral volume tended to have smaller corpora callosa. There were few sex differences in the size of structures in Broca's and Wernicke's area. We conclude that individual differences in brain volume, in both men and women, account for apparent sex differences in relative size.

Changes in brain activation induced by the training of hypothesis generation skills: an fMRI study

The aim of the present study is to investigate the learning-related changes in brain activation induced by the training of hypothesis generation skills regarding biological phenomena. Eighteen undergraduate participants were scanned twice with functional magnetic resonance imaging (fMRI) before and after training over a period of 2 months. The experimental group underwent eight biological hypothesis generation training programs, but the control group was not given any during the 2-month period. The results showed that the left frontal gyri, the cingulate gyrus, and the cuneus were activated during hypothesis generation. In addition, the brain activation of the trained group increased in the left inferior and the superior frontal gyri, which are related to working memory load and higher-order inferential processes. However, the activation after training decreased in the occipito-parietal route, which is associated with the perception and the analysis processes of visual information. Furthermore, the results have suggested that the dorsolateral prefrontal cortex (DLPFC) region is the critical area in the training of hypothesis generation skills.