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load file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia hypothesis that human males have more variance in certain traits compared to females two distribution curves with identical means but different variabilities the curve with the greater variability green yields higher values in both the lowest and highest ends of the range the variability hypothesis also known as the greater male variability hypothesis is the hypothesis that human males generally display greater variability in traits than human females do it has often been discussed in relation to human cognitive ability where some studies appear to show that males are more likely than females to have either very high or very low iq test scores in this context there is controversy over whether such sex based differences in the variability of intelligence exist and if so whether they are caused by genetic differences environmental conditioning or a combination of both early history edit the notion of greater male variability at least in respect to physical characteristics can be traced back to the writings of charles darwin 1 when he expounded his theory of sexual selection in the descent of man and selection in relation to sex darwin cites some observations made by his contemporaries for example he highlights findings from the novara expedition of 1861 1867 where a vast number of measurements of various parts of the body in different races were made and the men were found in almost every case to present a greater range of variation than the women p 275 to darwin the evidence from the medical community at the time which suggested a greater prevalence of physical abnormalities among men than women was also indicative of men s greater physical variability although darwin was curious about sex differences in variability throughout the animal kingdom variability in humans was not a chief concern of his research the first scholar to carry out a detailed empirical investigation on the question of human sex differences in variability in both physical and mental faculties was the sexologist and eugenecist havelock ellis in his 1894 publication man and woman a study of human secondary sexual characters ellis dedicated an entire chapter to the subject entitled the variational tendency of men 2 in this chapter he posits that both the physical and mental characters of men show wider limits of variation than do the physical and mental characters of women p 358 ellis documents several studies that support this assertion see pp 360 367 and by the 1890s several studies had been conducted to demonstrate that variability was indeed more characteristic of males the biological evidence overwhelmingly favored males as the more variable sex 3 early controversies in the 20th century edit the publication of ellis s man and woman led to an intellectual dispute about the variability hypothesis between ellis and the statistician karl pearson whose critique of ellis s work was both theoretical and methodological after pearson dismissed ellis s conclusions he then presented his own data to show that it was the female who was more variable than the male 3 ellis wrote a letter to pearson thanking him for the criticisms which would allow him to present his arguments more clearly precisely than before but did not yield his position regarding greater male variability 3 support for the greater male variability hypothesis grew during the early part of the 20th century 1 during this period the attention of researchers shifted towards studying variability in mental abilities partly due to the advent of standardised mental tests see the history of the intelligence quotient which made it possible to examine intelligence with greater objectivity and precision one advocate of greater male variability during this time was the american psychologist edward thorndike one of the leading exponents of mental testing who played an instrumental role in the development of today s armed services vocational aptitude battery asvab in his 1906 publication sex in education thorndike argued that while mean level sex differences in intellectual ability appeared to be negligible sex differences in variability were clear 1 other influential proponents of the hypothesis at this time were psychologists g stanley hall and james mckeen cattell 4 5 6 thorndike believed that variability in intelligence could have a biological basis and suggested that this could have important implications for achievement and pedagogy for example he postulated that greater male variation could mean eminence and leadership of the world s affairs of whatever sort will inevitably belong oftener to men 7 in addition since the number of women that fall within the extreme top end of the intelligence distribution would be inherently smaller he suggested that educational resources should be invested in preparing women for roles and occupations that require only a mediocre level of cognitive ability 8 leta hollingworth s studies edit see also leta hollingworth by examining the case records of 1 000 patients at the clearing house for mental defectives leta hollingworth determined that although men outnumbered women in the clearing house the ratio of men to women decreased with age hollingworth explained this to be the result of men facing greater societal expectations than women consequently deficiencies in men were often detected at an earlier age while similar deficiencies in women might not be detected because less was expected of them therefore deficiencies in women would be required to be more pronounced than those in men in order to be detected at similar ages 4 5 8 9 6 hollingworth also attacked the variability hypothesis theoretically criticizing the underlying logic of the hypothesis 4 5 8 10 hollingworth argued that the variability hypothesis was flawed because 1 it had not been empirically established that men were more anatomically variable than women 2 even if greater anatomical variability in men were established this would not necessarily mean that men were also more variable in mental traits 3 even if it were established that men were more variable in mental traits this would not automatically mean that men were innately more variable 4 variability is not significant in and of itself but rather depends on what the variability consists of and 5 that any possible differences in variability between men and women must also be understood with reference to the fact that women lack the opportunity to achieve eminence because of their prescribed societal and cultural roles at the time 4 5 8 additionally the argument that great variability automatically meant greater range was criticized by hollingworth 8 11 how in an attempt to examine the validity of the variability hypothesis while avoiding intervening social and cultural factors hollingworth gathered data on birth weight and length of 1 000 male and 1 000 female newborns this research found virtually no difference in the variability of male and female infants birth weight and it was concluded that if variability favored any sex it was the female sex 4 5 8 9 the general consensus today is that boys have a higher birth weight than girls and are more responsive to their mother s diet while in the womb thus causing an even greater variation if nutritional needs are met 12 modern studies edit the 21st century has witnessed a resurgence of research on gender differences in variability with most of the emphasis on humans the results vary based on the type of problem but some recent studies have found that the variability hypothesis is true for parts of iq tests with more men falling at the extremes of the distribution 13 14 publications differ as to the extent and distribution of male variability including on whether variability can be shown across various cultural and social factors 15 16 2004 twin chromosome study edit a 2004 study attempted to test for the effects of the averaging of the x chromosomes through a sample of about 1000 female twins and 1000 male twins at each age from 2 to 4 they hypothesized that mzf monozygotic female twins due to x inactivation would have lower correlations with their co twin than males and the opposite would be true for dzf dizygotic female twins due to females sharing an x chromosome from their father they found statistically significant results for prosocial behavior at age 2 for mzf lower and at age 3 for dzf twins higher peer problems for mzf twins data only available for age 4 verbal ability at age 3 for mzf lower and dzf higher twins anxiety at age 4 for mzf higher the inconsistent result with the hypothesis likely means there are no x linked loci for anxiety no statistically significant results were found for mz or dz twins for hyperactivity conduct problems total behavioural problems nonverbal ability or g 17 2007 metanalysis edit a 2007 meta analysis found that males are more variable on most measures of quantitative and visuospatial ability making no conclusions of its causation 18 2008 analyses edit a 2008 analysis of test scores across 41 countries published in science concluded that data shows a higher variance in boys than girls results on mathematics and reading tests in most oecd countries the results implying that gender differences in the variance of test scores are an international phenomenon however it also found that several countries failed to exhibit a gender difference in variance 13 a follow up study of c s loat et al 2004 17 replicated some of their previous findings 2 4 year olds edit sdq prosociality mzf lower dzf higher sdq hyperactivity mzf lower sdq problem behaviour mzf lower 8 year olds edit cast composite dzf higher cast social mzf lower cast communication dzf higher cast non social dzf higher no statistically significant results were found for the cognitive or academic measures 7 year olds sdq conduct sdq peer problems sdq anxiety 8 year olds conners adhd rpq composite the study was done on about 1000 twins for each sex and zygosity like the previous study but the sample was 7 8 years old this time and only different behavioral measures were taken by the 8 year olds unlike the 7 year olds who took cognitive tests too 19 2008 review edit a 2008 study reviewed the history of the hypothesis that general intelligence is more biologically variable in males than in females and presented data which the authors claim in many ways are the most complete that have ever been compiled and which substantially support the hypothesis 1 2009 non cognitive traits study edit a 2009 study in developmental psychology examined non cognitive traits including blood parameters and birth weight as well as certain cognitive traits and concluded that greater intrasex phenotype variability in males than in females is a fundamental aspect of the gender differences in humans 20 2010 metanalysis of math scores edit recent studies indicate that greater male variability in mathematics persists in the u s although the ratio of boys to girls at the top end of the distribution is reversed in asian americans 21 a 2010 meta analysis of 242 studies found that males have an 8 greater variance in mathematical abilities than females which the authors indicate is not meaningfully different from an equal variance additionally they find several datasets indicate no or a reversed variance ratio 22 2010 twin study edit though female students scored slightly higher on average the graph depicts identical standard deviations and therefore identical variability between male and female students the authors of the 2012 study debunking myths about gender and mathematics performance used this as evidence while refuting the greater male variability hypothesis while the male students scored higher on average this graph shows that female students were more variable than male students which the authors of the 2012 study debunking myths about gender and mathematics performance used to refute the greater male variability hypothesis a 2010 study with a similar methodology to c s loat et al 2004 17 with 272 twin pairs taking an iq test and 324 twin pairs were assessed using measure of child behavioural problems and found no evidence of an x linked contribution to greater variance in males and no statistically significant interaction of sex and chorion type 19 2012 study on variance in math performance edit a 2012 study compared male and female variability on math scores using data from the trends in international mathematics and science study timss and the programme for international student assessment pisa in order to draw conclusions about the greater male variability hypothesis it found that sex differences in mathematics performance variability varied drastically by country in some countries such as tunisia indonesia and armenia female students actually demonstrated greater variability than their male peers in terms of mathematics performance while other nations such as the netherlands the czech republic and morocco saw no difference in variability between sexes and the remainder of countries including hong kong spain and the united states showed greater male variability as a result the authors concluded that sex differences in variability are not driven by innate biological mechanics but rather socioeconomic and cultural factors 23 2012 genetic study edit a 2012 study tested for evidence of x linked basis of greater variance of males in cognitive abilities the authors had two hypotheses the within pair variance should be greater in dz dizygotic twins than mz twins if the x chromosome causes greater variation in the cognitive test scores of males although obviously x chromosome differences aren t the only genetic sources of within pair variation greater differences in within pair variation between mz and dz twins for male relative to female mz and dz the evidence supported hypothesis one for both males and females but not hypothesis two thus the authors found no evidence of an averaging effect on the x chromosomes for females results in greater variance for males in cognitive abilities but they do not accept this as conclusive evidence 24 2013 genetic study edit looking for genetic evidence of variability between the sexes a 2013 study used the body sizes of different species that either had heterogametic males mammals and insects or heterogametic females birds and butterflies the study found that heterogametic males had higher variability in body size than homogametic females while heterogametic females had higher variability in body size than homogametic males thus showing a relation between the chromosomes and variability between the sexes in traits 25 2014 review of math and emotion variance edit a 2014 review found that males tend to have higher variance on mathematical and verbal abilities bu...