The Greater Male Variability Hypothesis (GMVH)

In a wide variety of traits, males are more variable than females: The male distribution is slightly flatter and stretches out somewhat further on both sides of the mean

Men, Women, and Science: Why the Differences and What Should Be Done?

Abstract

It is a well-known and widely lamented fact that men outnumber women in a number of fields in STEM, including physics, mathematics, and computer science. The most common explanations for the gender gaps are discrimination and social norms, and the most common policy prescriptions are targeted at these ostensible causes. However, a great deal of evidence in the behavioral sciences suggests that discrimination and social norms are only part of the story. Other plausible contributors include relatively large mean sex differences in career and lifestyle preferences, and relatively small mean differences in cognitive aptitudes – some favoring males, others favoring females – which are associated with progressively larger differences the further above the mean one looks. A more complete picture of the causes of the unequal sex ratios in STEM may productively inform policy debates, and is likely to improve women’s situation across the STEM fields.

GMVH1

This is the case for various physical traits, including birth weight, adult weight, adult height, BMI, running speed, and various aspects of brain structure.

https://onlinelibrary.wiley.com/doi/abs/10.1002/dev.20358

Greater intrasex phenotype variability in males than in females is a fundamental aspect of the gender differences in humans

Abstract

Human studies of intrasex variability have shown that males are intellectually more variable. Here we have performed retrospective statistical analysis of human intrasex variability in several different properties and performances that are unrelated or indirectly related to intelligence: (a) birth weights of nearly 48,000 babies (Medical Birth Registry of Norway); (b) adult weight, height, body mass index and blood parameters of more than 2,700 adults aged 18–90 (NORIP); (c) physical performance in the 60 meter dash event of 575 junior high school students; and (d) psychological performance reflected by the results of more than 222,000 undergraduate university examination grades (LIST). For all characteristics, the data were analyzed using cumulative distribution functions and the resultant intrasex variability for males was compared with that for females. The principal finding is that human intrasex variability is significantly higher in males, and consequently constitutes a fundamental sex difference. © 2008 Wiley Periodicals, Inc. Dev Psychobiol 51: 198–206, 2009

https://academic.oup.com/cercor/article/28/8/2959/4996558

Sex Differences in the Adult Human Brain: Evidence from 5216 UK Biobank Participants

Abstract

Sex differences in the human brain are of interest for many reasons: for example, there are sex differences in the observed prevalence of psychiatric disorders and in some psychological traits that brain differences might help to explain. We report the largest single-sample study of structural and functional sex differences in the human brain (2750 female, 2466 male participants; mean age 61.7 years, range 44–77 years). Males had higher raw volumes, raw surface areas, and white matter fractional anisotropy; females had higher raw cortical thickness and higher white matter tract complexity. There was considerable distributional overlap between the sexes. Subregional differences were not fully attributable to differences in total volume, total surface area, mean cortical thickness, or height. There was generally greater male variance across the raw structural measures. Functional connectome organization showed stronger connectivity for males in unimodal sensorimotor cortices, and stronger connectivity for females in the default mode network. This large-scale study provides a foundation for attempts to understand the causes and consequences of sex differences in adult brain structure and function.

sex phys1sex phys2

It also appears to be the case for a range of psychological traits, including creativity , aggression , and at least four of the Big 5 personality traits.

Greater male variability in creativity: A latent variables approach

Abstract

Although gender differences do not usually exist when it comes to creative potential, males do exhibit a higher variability of creative ability: the effect that may result in more males than females having both very low and very high creative potential. Two studies examined the greater male variability in creativity hypothesis (GMVC): a cross-sequential investigation conducted on a sample of children (4–7 years old; N = 351) over the span of two years and a cross-sectional study conducted on a sample diverse in age (6–46 years old; N = 3594). In both studies, the Test of Creative Thinking-Drawing Production (TCT-DP; Urban & Jellen, 1996) was used, but unlike previous research, data were analyzed using the latent variables approach: latent growth curve modeling (Study 1) and exploratory and confirmatory factor analyses (Study 2). Greater male variability of creative ability was found across studies and age groups, but while this pattern was characteristic for some aspects of creative ability (originality and unconventionality), higher female variability was observed in the case of the other aspects (adaptiveness).

http://psycnet.apa.org/buy/2003-99845-001

Abstract

Greater male than female variability is found in behavioral and morphological traits in animals. A theory that greater male variability is associated with variability in parental investment is described and contrasted with sexual strategies theory, which posits no sex differences in variability. Predictions from the theories were tested through meta-analyses of variance ratios for data sets involving sexually selected characteristics analyses (physical aggression and 5 aspects of mate choice) and 2 unlikely to have resulted from sexual selection (anger and self-esteem). Variation was significantly greater among men than women in 5 of the 6 former data sets and was similar for men and women in the latter 2 data sets, broadly supporting the predictions. A further analysis extends the theory to intellectual abilities. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Do men vary more than women in personality? A study in 51 cultures

Abstract

Do men vary more than women in personality? Evolutionary, genetic, and cultural arguments suggest that hypothesis. In this study we tested it using 12,156 college student raters from 51 cultures who described a person they knew well on the 3rd-person version of the Revised NEO Personality Inventory. In most cultures, male targets varied more than female targets, and ratings by female informants varied more than ratings by male informants, which may explain why higher variances for men are not found in self-reports. Variances were higher in more developed, and effects of target sex were stronger in more individualistic societies. It seems that individualistic cultures enable a less restricted expression of personality, resulting in larger variances and particularly so among men.

More controversially, males appear to be somewhat more variable in a number of cognitive traits. This includes various specific cognitive capacities, such as verbal, mathematical, and spatial ability.

https://www.annualreviews.org/doi/abs/10.1146/annurev-psych-010213-115057?journalCode=psych

Gender Similarities and Differences

Abstract

Whether men and women are fundamentally different or similar has been debated for more than a century. This review summarizes major theories designed to explain gender differences: evolutionary theories, cognitive social learning theory, sociocultural theory, and expectancy-value theory. The gender similarities hypothesis raises the possibility of theorizing gender similarities. Statistical methods for the analysis of gender differences and similarities are reviewed, including effect sizes, meta-analysis, taxometric analysis, and equivalence testing. Then, relying mainly on evidence from meta-analyses, gender differences are reviewed in cognitive performance (e.g., math performance), personality and social behaviors (e.g., temperament, emotions, aggression, and leadership), and psychological well-being. The evidence on gender differences in variance is summarized. The final sections explore applications of intersectionality and directions for future research.

variability in personality vs sex

It also includes general cognitive ability or IQ: Males seem to somewhat outnumber females among the minority at the top, and among the minority at the bottom

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.880.6529&rep=rep1&type=pdf

Sex Differences in Variability in
General Intelligence

ABSTRACT—The idea that general intelligence may be more
variable in males than in females has a long history. In
recent years it has been presented as a reason that there
is little, if any, mean sex difference in general intelligence,
yet males tend to be overrepresented at both the top
and bottom ends of its overall, presumably normal, distribution.
Clear analysis of the actual distribution of
general intelligence based on large and appropriately
population-representative samples is rare, however. Using
two population-wide surveys of general intelligence in
11-year-olds in Scotland, we showed that there were substantial
departures from normality in the distribution,
with less variability in the higher range than in the lower.
Despite mean IQ-scale scores of 100, modal scores were
about 105. Even above modal level, males showed more
variability than females. This is consistent with a model
of the population distribution of general intelligence as a
mixture of two essentially normal distributions, one reflecting
normal variation in general intelligence and one
reflecting normal variation in effects of genetic and environmental
conditions involving mental retardation.
Though present at the high end of the distribution, sex
differences in variability did not appear to account for sex
differences in high-level achievement.

iq differences

although see for a recent failure to replicate this pattern in a large, nationally representative Romanian sample

iq differences2

What might account for sex differences in within-sex variability? At this stage, we don’t know for sure. But we do have at least some reason to think that biological factors are an important part of the story

First, greater male variability is found not only in psychological traits, but in traits that are largely impervious to socialization and cultural norms, such as height, birth weight, and BMI

https://onlinelibrary.wiley.com/doi/abs/10.1002/dev.20358

Greater intrasex phenotype variability in males than in females is a fundamental aspect of the gender differences in humans

Abstract

Human studies of intrasex variability have shown that males are intellectually more variable. Here we have performed retrospective statistical analysis of human intrasex variability in several different properties and performances that are unrelated or indirectly related to intelligence: (a) birth weights of nearly 48,000 babies (Medical Birth Registry of Norway); (b) adult weight, height, body mass index and blood parameters of more than 2,700 adults aged 18–90 (NORIP); (c) physical performance in the 60 meter dash event of 575 junior high school students; and (d) psychological performance reflected by the results of more than 222,000 undergraduate university examination grades (LIST). For all characteristics, the data were analyzed using cumulative distribution functions and the resultant intrasex variability for males was compared with that for females. The principal finding is that human intrasex variability is significantly higher in males, and consequently constitutes a fundamental sex difference.

phys diffs

Second, sex differences in psychological variability emerge in early childhood. The sex difference in IQ variability, for example, appears before children begin preschool.

https://www.sciencedirect.com/science/article/pii/S0191886906000420

Sex differences in variance of intelligence across childhood

Abstract

Why are males over-represented at the upper extremes of intelligence? One possibility for which there is some empirical support is that variance is greater among adult males. There is little published evidence of the development of that variability – is it manifest in early childhood or does it develop later?

We explored sex differences in phenotypic variance in scores on a general ability factor extracted from several tests of verbal and non-verbal ability at ages 2, 3, 4, 7, 9 and 10 (Ns from > 10,000 to > 2000) in a sample of British children.

We found greater variance, by Levene’s test of homogeneity of variance, among boys at every age except age two despite the girls’ mean advantage from ages two to seven. Girls are significantly over-represented, as measured by chi-square tests, at the high tail and boys at the low tail at ages 2, 3 and 4. By age 10 the boys have a higher mean, greater variance and are over-represented in the high tail. Sex differences in variance emerge early – even before pre-school – suggesting that they are not determined by educational influences.

And third, sex differences in within-sex variability are not unique to humans, but are found in many other species. This suggests, at the very least, that non-biological explanations that apply only to humans are unlikely to tell the whole story.

 

https://psyarxiv.com/ms524

Abstract

It is a well-known and widely lamented fact that men outnumber women in a number of fields in STEM, including physics, mathematics, and computer science. The most common explanations for the gender gaps are discrimination and social norms, and the most common policy prescriptions are targeted at these ostensible causes. However, a great deal of evidence in the behavioral sciences suggests that discrimination and social norms are only part of the story. Other plausible contributors include relatively large mean sex differences in career and lifestyle preferences, and relatively small mean differences in cognitive aptitudes – some favoring males, others favoring females – which are associated with progressively larger differences the further above the mean one looks. A more complete picture of the causes of the unequal sex ratios in STEM may productively inform policy debates, and is likely to improve women’s situation across the STEM fields.

animal diffs

If greater male variability has a biological basis, why might it have evolved? Not sure! One popular theory, though, traces greater male variability in general to another, more fundamental sex difference: greater male variability in reproductive success

male freq

The basic idea is that, in species where males can potentially have more offspring than females, selection favours greater male risk-taking – not just behaviourally but developmentally. As a result, more males win big, but more also crash and burn

https://psyarxiv.com/ms524

Abstract

It is a well-known and widely lamented fact that men outnumber women in a number of fields in STEM, including physics, mathematics, and computer science. The most common explanations for the gender gaps are discrimination and social norms, and the most common policy prescriptions are targeted at these ostensible causes. However, a great deal of evidence in the behavioral sciences suggests that discrimination and social norms are only part of the story. Other plausible contributors include relatively large mean sex differences in career and lifestyle preferences, and relatively small mean differences in cognitive aptitudes – some favoring males, others favoring females – which are associated with progressively larger differences the further above the mean one looks. A more complete picture of the causes of the unequal sex ratios in STEM may productively inform policy debates, and is likely to improve women’s situation across the STEM fields.

male freq2

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