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Research on human sex differences investigates cognitive and behavioral differences between men and women. This research employs experimental tests of cognition, which take a variety of forms. Tests focus on possible differences in areas such as IQ, spatial reasoning, aggression, emotion, and brain structure and function.
Most IQ tests are constructed so that there are no differences between the average (mean) scores of females and males. Areas where differences in mean scores have been found include verbal and mathematical ability. The variability of male scores is greater than that of females, however, resulting in substantially more males than females in the top and bottom of the IQ distribution.
Because social and environmental factors affect brain activity and behavior, where differences are found, it can be difficult for researchers to assess whether or not the differences are innate. Studies on this topic explore the possibility of social influences on how both sexes perform in cognitive and behavioral tests. Stereotypes about differences between men and women have been shown to affect a person's behavior.
A gender difference is a disparity between male and female humans. This article focuses on quantitative differences which are based on a gradient and involve different averages. For example, men are taller than women on average, but an individual woman may be taller than an individual man.
Other articles describe differences which clearly represent a binary male/female spilt, such as human reproduction. Women give birth to babies; men never do.
In Western countries in the 18th, 19th and 20th centuries, many people believed that inequality between the sexes could be attributed to biological differences. Thomas Gisborne argued that women were naturally suited to domestic work and not spheres suited to men such as politics, science, or business. He argued that this was because women did not possess the same level of rational thinking that men did and had naturally superior abilities in skills related to family support.
Nicolas Malebranche argued that abstraction was impossible for women, because of the "delicacy of the brain fibers." In 1875, Herbert Spencer similarly argued that women were incapable of abstract thought and could not understand issues of justice, and only had the ability to understand issues of care. In 1925, Sigmund Freud also concluded that women were less morally developed in the concept of justice, and, unlike men, were more influenced by feeling than rational thought. Early brain studies comparing mass and volumes between the sexes concluded that women were intellectually inferior because they had smaller and lighter brains. Later studies with better equipment have confirmed this brain size difference. Many believed that the size difference caused women to be excitable, emotional, sensitive, and therefore not suited for political participation. Today, others argue that brain size correlates with intelligence and/or personality. The correlation is around 0.44 for brain size and IQ. This together with the brain size difference between sexes have caused some scholars to propose a sex difference in IQ/intelligence.
In the nineteenth century, whether men and women had equal intelligence was seen by many as a prerequisite for the granting of suffrage. Leta Hollingworth argues that women were not permitted to realize their full potential, as they were confined to the roles of child-rearing and housekeeping. From the late twentieth century onwards, researchers have investigated the possibility of environmental factors in perceived sex differences. Possible biological sex differences in intelligence have been discussed to determine whether disproportionate employment or payment favoring men is a manifestation of sexism or instead a reflection of innate aptitudes.
During the early twentieth century, the scientific consensus held that gender plays no role in intelligence. In his research, psychologist Lewis Terman found "rather marked" differences on a minority of tests. For example, he found boys were "decidedly better" in arithmetical reasoning, while girls were "superior" at answering comprehension questions, though he concluded that sex plays no role in general intelligence. He also proposed that discrimination, denied opportunities, women's responsibilities in motherhood, or emotional factors may have accounted for the fact that few women had careers in intellectual fields.
Possible causes: some theories
The existence of a gender difference does not necessarily identify whether the trait is due to nature or environment. Some traits are obviously innate (for example, reproductive organs), others obviously environmental (for example, given names), while for others the relationship is either multi-cause or unknown.
From the viewpoint of evolutionary psychology, modern humans have inherited natural traits that were adaptive in a prehistoric environment, including traits that had different advantages for males versus females (see Sexual selection). Gender role theory claims that boys and girls learn the appropriate behaviour and attitudes from the family and overall culture they grow up with, and so non-physical gender differences are a product of socialization. These are not all mutually exclusive theories: it is possible that gender differences are partially innate but are then reinforced and exaggerated by the environment.
Some feminists see gender differences as caused by patriarchy or discrimination, although difference feminism argues for an acceptance of natural differences between men and women. Traditional masculists tend to see gender differences as inherent in human nature, while liberal masculists may challenge traditional roles.
Traditional Abrahamic religion sees gender differences as created by God: "He made them in his image: man and woman He made them." (Genesis 1:27) (see Role of women in Judaism, Christian views of women, Gender roles in Islam).
According to Diane F. Halpern, some combination of social and biological factors may be at work in psychological sex differences. She wrote in the preface of her 2000 book Sex Differences In Cognitive Abilities, "Socialization practices are undoubtedly important, but there is also good evidence that biological sex differences play a role in establishing and maintaining cognitive sex differences, a conclusion I wasn't prepared to make when I began reviewing the relevant literature."
Cordelia Fine has argued that there is currently no scientific evidence for innate biological differences between men and women's minds, and that cultural and societal beliefs contribute to commonly perceived sex differences. She states that many studies of psychological gender differences are controversial and subject to error. Observing that many results from smaller scale studies are not repeated in larger studies and that self-report questionnaires are vulnerable to bias.
One study argues that a division of labor between sexes developed relatively late, 45,000-10,000 years ago. It may have given humans an important advantage over Neanderthals who likely did not have a similar division of labor and who had similarly robust skeletons for both sexes. The paper also argues that gender roles varied across early human cultures and that the division of labor is not only due to innate differences between sexes but that much of it was learned.
- Main article: Physical sex differences in humans
- On average, men are taller than women, by about half a foot (~15 cm) (See sexual dimorphism).
- On average, men have a larger waist in comparison to their hips (see waist-hip ratio) than women.
- On average, men have longer canine teeth than women.
- On average, men have a greater capacity for cardiovascular endurance[How to reference and link to summary or text]. This is due to the enlargement of the lungs of boys during puberty, characterized by a more prominent chest.
- On average, men are stronger than women. This is due to a greater capacity for muscular hypertrophy as a result of men's higher levels of testosterone.
- On average, men have more body hair than women.
- Men’s skin is thicker (more collagen) and oilier (more sebum) than women’s skin.
- Women's skin is warmer on average than men's.
- In men, the second digit (index finger) tends to be shorter than the fourth digit (ring finger), while in women the second digit tends to be longer than the fourth (see digit ratio).
- Women have a larger hip section than men, an adaptation for giving birth to infants with large skulls.
- Men have a more pronounced 'Adam's Apple' or thyroid cartilage due to larger vocal cords (and deeper voices).
General differences in physical brain parameters
Studies have found many similarities but also differences in brain structure, neurotransmitters, and function. However, some argue that innate differences in the neurobiology of men and women have not been conclusively identified. The relationship between sex differences in the brain and human behavior is a subject of controversy in psychology and society at large.
A 2004 review in Nature Reviews Neuroscience stated that the brain's sexual dimorphism is probably determined by genes on the sex chromosomes. They likely do so by genes in cells in the gonads causing the gonads to produce sex hormones that travel to the brain which affect brain cells and also by genes in brain cells directly affecting these brain cells. In the human brain, a difference between sexes has been observed in regarding the PCDH11X/Y gene pair which is unique to Homo sapiens.
In adults, men's brains are an average of 11–12% heavier than women's brains. However, men's bodies are also larger and heavier than women's bodies. In the United States, for example, adult men are an average of 18% heavier than adult women. Some researchers propose that the brain-to-body mass ratio does not differ between the sexes. However, some argue that the brain-to-body mass ratio tends to decrease as body size increases, and a sex difference in brain size still exists between men and women of the same size. A 1992 study of 6,325 Army personnel found that men's brains had an average volume of 1442 cm3, while the women averaged 1332 cm3. These differences were shown to be smaller but to persist even when adjusted for body size measured as body height or body surface, such that women averaged 100g less brain mass than men of equal size.
Though statistically there are sex differences in white matter and gray matter percentage, this ratio is directly related to brain size, and some argue these sex differences in gray and white matter percentage are caused by the average size difference between men and women. Others argue that these differences remain after controlling for brain volume.
Biological factors involved in gender identity
An ongoing debate in psychology is the extent to which gender identity and gender-specific behavior is due to socialization as opposed to genetic factors. The mainstream view is that both factors play a role, but the relative importance of each is contentious.[How to reference and link to summary or text]
Because of the wide acceptance of gender roles, it is difficult to execute a study which controls for the influence of such socialization. Individuals who are sex reassigned at birth offer an opportunity to see what happens when a child who is genetically one sex is raised as the other. The largest study of such individuals was conducted by Reiner & Gearhart on 14 children born with cloacal exstrophy and reassigned female at birth. Upon follow-up between the ages of 5 to 12, 8 of them identified as boys, and all of the subjects had at least moderately male-typical attitudes and interests, however these tests were not double blind as the parents (and often the subjects) knew the biological sex of children they were raising. The procedure of sex reassignment and vaginoplasty on intersex children assigned to be females also changes their experiences in ways not analogous to typically developed females, including vaginal dilatation by parents on toddlers (routine widening of the vagina through insertion of a device), and testing of clitoral scar tissue for sensation by doctors.
One study showed that at birth girls gaze longer at a face, whereas suspended mechanical mobiles, rather than a face, keep boys' attention for longer, though this study has been criticized as having methodological flaws.
In one large scale study, most cognitive abilities and psychological traits showed little or no average difference between the sexes . Where sex differences exist, there is often considerable overlap between the sexes; in addition, it is unclear how many of these differences hold true across different cultures. Nevertheless, certain trends can be found:
- Men are more physically aggressive. Although women were once held to be less aggressive and competitive overall, modern experts such as Rachel Simmons have suggested that women simply tend to express aggression and competition in less physical ways.
- In many situations, men are more prone to taking risks .
- Women express their emotions more readily and report feeling a greater intensity of emotion.
- In the big five personality traits, women score higher in Agreeableness (tendency to be compassionate and cooperative) and Neuroticism (tendency to feel anxiety, anger, and depression).
- Demographics of MBTI surveys indicate that 60-75% of women prefer feeling and 55-80% of men prefer thinking.
- Main article: Sex and intelligence
|Abilities, traits and constructs|
|Models and theories|
|Fields of study|
According to the 1994 report "Intelligence: Knowns and Unknowns" by the American Psychological Association, "Most standard tests of intelligence have been constructed so that there are no overall score differences between females and males." Differences have been found, however, in specific areas such as mathematics and verbal measures.
When standardized IQ tests were first developed in the early 20th century, girls typically scored higher than boys until age 14, at which time the curve for girls dropped below that for boys. As testing methodology was revised, efforts were made to equalize gender performance.
Several meta-studies by Richard Lynn between 1994 and 2005 found mean IQ of men exceeding that of women by a range of 3-5 points. Lynn's findings were debated in a series of articles for Nature. Jackson and Rushton found males aged 17–18 years had average of 3.63 IQ points in excess of their female equivalents. A 2005 study by Helmuth Nyborg found an average advantage for males of 3.8 IQ points. One study concluded that after controlling for sociodemographic and health variables, "gender differences tended to disappear on tests for which there was a male advantage and to magnify on tests for which there was a female advantage." A study from 2007 found a 2-4 IQ point advantage for females in later life. One study investigated the differences in IQ between the sexes in relation to age, finding that girls do better at younger ages but that their performance declines relative to boys with age. Colom et al. (2002) found 3.16 higher IQ points for males but no difference on the general intelligence factor (g) and therefore explained the differences as due to non-g factors such as specific group factors and test specificity. A study conducted by James Flynn and Lilia Rossi-Case (2011) found that men and women achieved roughly equal IQ scores on Raven's Progressive Matrices after reviewing recent standardization samples in five modernized nations. Irwing (2012) found a 3 point IQ advantage for males in g from subjects aged 16–89 in the United States.
Differences in brain physiology between sexes do not necessarily relate to differences in intellect. Haier et al. found in a 2004 study that: "Men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance. For men, the gray matter volume in the frontal and parietal lobes correlates with IQ; for women, the gray matter volume in the frontal lobe and Broca's area (which is used in language processing) correlates with IQ.
Some studies have identified the degree of IQ variance as a difference between males and females. Males tend to show greater variability on many traits including tests of cognitive abilities, though this may differ between countries. A 2005 study by Ian Deary, Paul Irwing, Geoff Der, and Timothy Bates, focusing on the ASVAB showed a significantly higher variance in male scores, resulting in more than twice as many men as women scoring in the top 2%. The study also found a very small (d' ≈ 0.07, less than 7%, of a standard deviation) average male advantage in g. A 2006 study by Rosalind Arden and Robert Plomin focused on children aged 2, 3, 4, 7, 9 and 10 and stated that there was greater 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."
A psychological study was conducted where about 1200 high school graduates were recruited to take tests looking at each of their verbal, reasoning, spatial abilities, and general scholastic knowledge. Male and female performances were compared through these tests. As a result of this testing, it was discovered that males had a higher mean score on all four tests than the mean score of the females who participated in the study. In 1995, it was suggested by Charles Lewis and Warren W. Willingham that patterns of gender differences on IQ scores can change because of the selectivity of the sample itself. They argued two factors played in giving the males an advantage: the greater male variability and the sampling of a greater proportion of women.
Another study on intelligence came up with similar findings. Young adolescents were asked to volunteer in this study and completed various assessments including ones looking at language, math, and sciences skills as well as the Toulous-Pieron test of attention and the Dominoes test. While one sample of children completed these assessments, another sample completed these plus another handful. The tests results from both samples show a null sex difference in general intelligence in young adolescents. Researchers concluded that since g does not differ through academic and cognitive abilities in young adolescents, male or female, and that some other factor must be responsible for the variance between the sexes.
It was believed at one point that Gf, or fluid intelligence, can be used to be systematically detect sex differences in general intelligence if there are any. The PMA Inductive Reasoning Test, Cattell’s Culture-Fair Intelligence Test, and the Advanced Progressive Matrices were used to test a group of about 4000 high school graduates. Through the results of these tests, researchers discovered that females perform better in the PMA Inductive Reasoning Test and males perform better in the Advanced Progressive Matrices assessment. There was no sex difference noted from the results of the Culture-Fair Test. Sex difference in fluid intelligence was proven to be non-existent in this study.
While research has shown that males and females do indeed each excel in different abilities, math and science might be an exception to this.
While some think that IQ scores are the best way to reach conclusions about cognitive sex differences, this theory is not used consistently to measure intelligence. These tests have been complied over the years so there is no sex difference. This was done in order to keep one sex from gaining an unfair advantage over the other in performance. Although this would imply that males and females have about the same IQ scores on average and most researchers maintain this view, some researchers have concluded that men have slightly higher IQ scores than women.
Large, representative studies of US students show that no sex differences in mathematics performance exist before secondary school. During and after secondary school, historic sex differences in mathematics enrollment account for nearly all of the sex differences in mathematics performance. However, a performance difference in mathematics on the SAT exists favoring males, though differences in mathematics course performance measures favor females. In 1983, Benbow concluded that the study showed a large sex difference by age 13 and that it was especially pronounced at the high end of the distribution. However, Gallagher and Kaufman criticized Benbow's and other reports finding males overrepresented in the highest percentages as not ensuring representative sampling.
In a 2008 study paid for by the National Science Foundation in the United States, researchers found that "girls perform as well as boys on standardized math tests. Although 20 years ago, high school boys performed better than girls in math, the researchers found that is no longer the case. The reason, they said, is simple: Girls used to take fewer advanced math courses than boys, but now they are taking just as many." However, the study indicated that, while on average boys and girls performed similarly, boys were overrepresented among the very best performers as well as among the very worst.
Kiefer and Sekaquaptewa proposed that a source of some women's underperformance and lowered perseverance in mathematical fields is these women's underlying "implicit" sex-based stereotypes regarding mathematical ability and association, as well as their identification with their gender. Some psychologists believe that many historical and current sex differences in mathematics performance may be related to boy's higher likelihood of receiving math encouragement than girls. Parents were, and sometimes still are, more likely to consider a son's mathematical achievement as being a natural skill while a daughter's mathematical achievement is more likely to be seen as something she studied hard for. This difference in attitude may contribute to girls and women being discouraged from further involvement in mathematics-related subjects and careers. Stereotype threat has been shown to affect performance and confidence in mathematics of both males and females. However, a review of stereotype threat literature found most studies couldn't be replicated or suffered methodological problems and concluded "that although stereotype threat may affect some women, the existing state of knowledge does not support the current level of enthusiasm for this as a mechanism underlying the gender gap in mathematics."
Two cross-country comparisons have found great variation in the gender differences regarding the degree of variance in mathematical ability. In most nations males have greater variance. In a few females have greater variance. Hyde and Mertz argue that boys and girls differ in the variance of their ability due to sociocultural factors.
Some studies investigating the spatial abilities of men and women have found no significant differences, though metastudies show a male advantage in mental rotation and assessing horizontality and verticality, and a female advantage in spatial memory.
A proposed hypothesis is that men and women evolved different mental abilities to adapt to their different roles in society. This explanation suggests that men may have evolved greater spatial abilities as a result of certain behaviors, such as navigating during a hunt. Similarly, this hypothesis suggests that women may have evolved to devote more mental resources to remembering locations of food sources in relation to objects and other features in order to gather food.
A number of studies have shown that women tend to rely more on visual information than men in a number of spatial tasks related to perceived orientation,. However, 'visual dependence' has been found to be task specific and not a general characteristic of spatial processing that differs between the sexes. Here an alternative hypothesis suggests that heightened visual dependence in females does not generalize to all aspects of spatial processing but is probably attributable to task-specific differences in how male and females brains process multisensory spatial information.
Results from studies conducted in the physical environment are not conclusive about sex differences, with various studies on the same task showing no differences. For example, there are studies that show no difference in 'wayfinding'. One study found men more likely to report having a good sense of direction and are more confident about finding their way in a new environment, but evidence does not support men having better map reading skills. Women have been found to use landmarks more often when giving directions and when describing routes. Additionally, a study concludes that women are better at recalling where objects are located in a physical environment. Women show greater proficiency and reliance on distinctive landmarks for navigation while males rely on an overall mental map.
Performance in mental rotation and similar spatial tasks is affected by gender expectations. For example, studies show that being told before the test that men typically perform better, or that the task is linked with jobs like aviation engineering typically associated with men versus jobs like fashion design typically associated with women, will negatively affect female performance on spatial rotation and positively influence it when subjects are told the opposite. Experiences such as playing video games also increase a person's mental rotation ability. A study from the University of Toronto showed that differences in ability get reduced after playing video games requiring complex mental rotation. The experiment showed that playing such games creates larger gains in spatial cognition in females than males.
The possibility of testosterone and other androgens as a cause of sex differences in psychology has been a subject of study. Adult women who were exposed to unusually high levels of androgens in the womb due to congenital adrenal hyperplasia score significantly higher on tests of spatial ability. Many studies find positive correlations between testosterone levels in normal males and measures of spatial ability. However, the relationship is complex.
A study was done to compare the relationship between mental rotation ability and gender difference specifically with the SAT-Math. Cognitive gender differences are apparent and findings of a male advantage in certain mathematical domains have been demonstrated cross-culturally. These gender differences found are largely in geometry and word problems and tend to be in countries with the highest achieving students and with the largest gender gap in experience. Smaller differences were noted in countries with lower achieving students in mathematics which includes the United States. Moore and Smith state that within the United States, poorly educated female students outperform their male peers, but as the level of education increases, the male advantage in mathematics emerges.
Spatial ability may be responsible in part for facilitating gender differences in math aptitude. Casey et al. (1995) looked at the relationship of mental rotation ability and the SAT-M among four samples. The four samples were: (1) undergraduates at two liberal arts colleges in the Northeast that were tested on their mental rotation ability in groups of 10-20, (2) a group of mathematically talented preadolescents participating in a summer math and science training in the Midwest which included seventh to nigh graders who were either recruited from a national talent search program or statewide teacher selection program, (3) a high ability group of college bound students who were enrolled in a middle-income suburban high school in the Northeast and elected to take the SAT, and (4) a low ability group of college bound students who were enrolled in a middle-income suburban high school in the Northeast and elected to take the SAT. The data used were SAT math and verbal scores and mental rotation scores. Mental rotation was assessed using the Vandenberg Test of Mental Rotation. Students were asked to match two out of four choices to a standard figure.
The study found that that when mental rotation is used as a predictor of Math aptitude for female students, the correlations between mental rotation and SAT-Math scores ranged from 0.35 to 0.38 whereas males showed no consistent pattern. Male correlations ranged from -0.03 to 0.54. However, an interesting finding was that in the three high ability samples, there was a significant gender difference in SAT-Math scores alone. This difference favored males. In the three high ability samples, males scored higher than females in mental rotation ability. Interesting enough, for the verbal aptitude test on SAT, there was a significant difference in verbal ability for the low ability college bound sample favoring girls.
Dyslexia is a learning disability that impairs a person’s fluency or comprehension accuracy in being able to read.  The cause of this disability is associated with abnormal brain anatomy and function. Gray matter deficits have been demonstrated in dyslexics using structural magnetic resonance imaging. This deficit has been found in specific regions within the left hemisphere involved in language.
There is higher prevalence of dyslexia in males than in females. However, different abnormalities are found in female brains as opposed to male brains. In a study that examined gray matter volume in dyslexic females, it was found that there was less gray matter volume in the right precuneus and paracentral lobule/medial frontal gyrus. In males, there was less gray matter volume in the left inferior parietal cortex. This study shows that dyslexia in females does not involve the left hemisphere regions involved in language as it does in males. Instead, it affects the sensory and motor cortices such as the motor and premotor cortex and primary visual cortex).
The results from research on sex differences in memory are mixed and inconsistent, with some studies showing no difference, and others showing a female or male advantage. Most studies have found no sex differences in short term memory, the rate of memory decline due to aging, or memory of visual stimuli. Females have been found to have an advantage in recalling auditory and olfactory stimuli, experiences, faces, names, and the location of objects in space. However, males show an advantage in recalling "masculine" events. A study examining sex differences in performance on the California Verbal Learning Test found that males performed better on Digit Span Backwards and on reaction time, while females were better on short-term memory recall and Symbol-Digit Modalities Test.
A study was conducted to explore regions within the brain that are activated during working memory tasks in males versus females. Four different tasks of increasing difficulty were given to 9 males and 8 females. Functional magnetic resonance imaging was used to measure brain activity. The lateral prefrontal cortices, the parietal cortices and caudates were activated in both genders. With more difficult tasks, more brain tissue was activated. The left hemisphere was predominantly activated in females’ brains, whereas there was bilateral activation in males’ brains. This suggests some sort of gender difference in the brain organization involved in working memory.
Although research on sex differences in aggression show that males are generally more likely to display aggression than females, how much of this is due to social factors and gender expectations is unclear. Aggression is closely linked with cultural definitions of "masculine" and "feminine." In some situations women show equal or more aggression than men; for example, women are more likely to use direct aggression in private, where other people cannot see them, and are more likely to use indirect aggression in public. Eagly and Steffen suggested in their meta-analysis of data on sex and aggression that beliefs about the negative consequences of violating gender expectations affect how both genders behave regarding aggression. Men are more likely to be the targets of displays of aggression and provocation than females. Studies by Bettencourt and Miller show that when provocation is controlled for, sex differences in aggression are greatly reduced. They argue that this shows that gender-role norms play a large part in the differences in aggressive behavior between men and women. Psychologist Anne Campbell argues that females are more likely to use indirect aggression, and that "cultural interpretations have 'enhanced' evolutionarily based sex differences by a process of imposition which stigmatises the expression of aggression by females and causes women to offer exculpatory (rather than justificatory) accounts of their own aggression."
The relationship between testosterone and aggression is unclear, and a causal link has not been conclusively shown. Some studies indicate that testosterone levels may be affected by environmental and social influences. The relationship is difficult to study since the only reliable measure of brain testosterone is from a lumbar puncture which is not done for research purposes and many studies have instead used less reliable measures such as blood testosterone. In humans, males engage in crime and especially violent crime more than females. The involvement in crime usually rises in the early teens to mid teens which happen at the same time as testosterone levels rise. Most studies support a link between adult criminality and testosterone although the relationship is modest if examined separately for each sex. However, nearly all studies of juvenile delinquency and testosterone are not significant. Most studies have also found testosterone to be associated with behaviors or personality traits linked with criminality such as antisocial behavior and alcoholism.
In species that have high levels of male physical competition and aggression over females, males tend to be larger and stronger than females. Humans have modest general body sexual dimorphism on characteristics such as height and body mass. However, this may understate the sexual dimorphism regarding characteristics related to aggression since females have large fat stores. The sex differences are greater for muscle mass and especially for upper body muscle mass. Men's skeleton, especially in the vulnerable face, is more robust. Another possible explanation, instead of intra-species aggression, for this sexual dimorphism may be that it is an adaption for a sexual division of labor with males doing the hunting. However, the hunting theory may have difficulty explaining differences regarding features such as stronger protective skeleton, beards (not helpful in hunting but they increase the perceived size of the jaws and perceived dominance which may helpful in intra-species male competition), and greater male ability at interception (greater targeting ability can be explained by hunting).
There are evolutionary theories regarding male aggression in specific areas such as sociobiological theories of rape and theories regarding the high degree of abuse against stepchildren (the Cinderella effect).
Cross-cultural research has shown gender differences on the domains and facets of the Big Five personality traits. For example, women consistently report higher Neuroticism, Agreeableness, warmth (an extraversion facet) and openness to feelings, and men often report higher assertiveness (a facet of extraversion) and openness to ideas as assessed by the NEO-PI-R. Gender differences in personality traits are largest in prosperous, healthy, and egalitarian cultures in which women have more opportunities that are equal to those of men. Differences in the magnitude of sex differences between more or less developed world regions were due to differences between men not women in these respective regions. That is, men in highly developed world regions were less neurotic, extraverted, conscientious and agreeable compared to men in less developed world regions. Women, on the other hand tended not to differ in personality traits across regions. Researchers have speculated that resource poor environments (that is, countries with low levels of development) may inhibit the development of gender differences, whereas resource rich environments facilitate them. This may be because males require more resources than females in order to reach their full developmental potential. The authors argued that due to different evolutionary pressures, men may have evolved to be more risk taking and socially dominant, whereas women evolved to be more cautious and nurturant. Hunter-gatherer societies in which humans originally evolved may have been more egalitarian than later agriculturally oriented societies. Hence, the development of gender inequalities may have acted to constrain the development of gender differences in personality that originally evolved in hunter-gatherer societies. As modern societies have become more egalitarian again it may be that innate sex differences are no longer constrained and hence manifest more fully than in less developed cultures. Currently, this hypothesis remains untested, as gender differences in modern societies have not been compared with those in hunter-gatherer societies.
A personality trait directly linked to emotion and empathy where gender differences exist (see below) is Machiavellianism. Individuals who score high on this dimension are emotionally cool; this allows them to detach from others as well as values, and act strategically rather than driven by affect, empathy or morality. In large samples of US college students males are on average more Machiavellian than females; in particular, males are over-represented among very high Machiavellians, while females are overrepresented among low Machiavellians.
Some studies argue that this is related to the subject's perceived gender identity and gender expectations. Additionally, culture impacts gender differences in the expression of emotions. This may be explained by the different social roles men and women have in different cultures, and by the status and power men and women hold in different societies, as well as the different cultural values various societies hold. Some studies have found no differences in empathy between men and women, and suggest that perceived gender differences are the result of motivational differences. Some researchers argue that because differences in empathy disappear on tests where it is not clear that empathy is being studied, men and women do not differ in ability, but instead in how empathetic they would like to appear to themselves and others.
An evolutionary explanation for the difference is that understanding and tracking relationships and reading others' emotional states was particularly important for women in prehistoric societies for tasks such as caring for children and social networking.
When measured with an affect intensity measure, women reported greater intensity of both positive and negative affect than men. Women also reported a more intense and more frequent experience of affect, joy, and love but also experienced more embarrassment, guilt, shame, sadness, anger, fear, and distress. Experiencing pride was more frequent and intense for men than for women. In imagined frightening situations, such as being home alone and witnessing a stranger walking towards your house, women reported greater fear. Women also reported more fear in situations that involved "a male's hostile and aggressive behavior" (281) In anger-eliciting situations, women communicated more intense feelings of anger than men. Women also reported more intense feelings of anger in relation to terrifying situations, especially situations involving a male protagonist. Emotional contagion refers to the phenomenon of a person’s emotions becoming similar to those of surrounding people. Women have been reported to be more responsive to this.
Women are stereotypically more emotional and men are stereotypically angrier. When lacking substantial emotion information they can base judgments on, people tend to rely more on gender stereotypes. Results from a study conducted by Robinson and colleagues implied that gender stereotypes are more influential when judging others' emotions in a hypothetical situation.
There are documented differences in socialization that could contribute to sex differences in emotion and to differences in patterns of brain activity. An American Psychological Association article states that, "boys are generally expected to suppress emotions and to express anger through violence, rather than constructively". A child development researcher at Harvard University argues that boys are taught to shut down their feelings, such as empathy, sympathy and other key components of what is deemed to be pro-social behavior. According to this view, differences in emotionality between the sexes are theoretically only socially-constructed, rather than biological.
Context also determines a man or woman's emotional behavior. Context-based emotion norms, such as feeling rules or display rules, "prescribe emotional experience and expressions in specific situations like a wedding or a funeral," independent of the person's gender. In situations like a wedding or a funeral, the activated emotion norms apply to and constrain every person in the situation. Gender differences are more pronounced when situational demands are very small or non-existent as well as in ambiguous situations. During these situations, gender norms "are the default option that prescribes emotional behavior." (290-1)
Scientists in the field distinguish between emotionality and the expression of emotion: Associate Professor of Psychology Ann Kring said, "It is incorrect to make a blanket statement that women are more emotional than men, it is correct to say that women show their emotions more than men." In two studies by Kring, women were found to be more facially expressive than men when it came to both positive and negative emotions. These researchers concluded that men and women experience the same amount of emotion, but that women are more likely to express their emotions.
Women are known to have anatomically differently shaped tear glands than men as well as having more of the hormone prolactin, which is present in tear glands, as adults. While girls and boys cry at roughly the same amount at age 12, by age 18, women generally cry four times more than men, which could be explained by higher levels of prolactin.
In a study where researchers wanted to concentrate on nonverbal expressions by just looking at the eyebrows, lips, and the eyes, participants read certain cue cards that were either negative or positive and recorded the responses. In the results of this experiment it is shown that feminine emotions happen more frequently and have a higher intensity in women than men. In relation to the masculine emotions, such as anger, the results are flipped and the women’s frequency and intensity is lower than the men’s. Studies that measure facial expression by the use of electromyography recordings show that women are more adequately able to manipulate their facial expressions than men. Men, however can inhibit their expressions better than females when cued to do so. In the observer ratings women’s facial expressions are easier to read as opposed to men’s except for the expression of anger.
Larry Cahill argues that neurobiological differences between men and women exist in brain lateralization and emotional processing. Fine criticizes his conclusions as failing to account for size differences and failing to consider the possibility of environmental influences on brain activity, and in some cases relying on research about rats instead of humans.
Women show a significantly greater activity in the left amygdala when encoding and remembering emotionally arousing pictures (such as mutilated bodies.) Men and women tend to use different neural pathways to encode stimuli into memory. While highly emotional pictures were remembered best by all participants in one study, as compared to emotionally neutral images, women remembered the pictures better than men. This study also found greater activation of the right amygdala in men and the left amygdala in women. On average, women use more of the left cerebral hemisphere when shown emotionally arousing images, while men use more of their right hemisphere. Women also show more consistency between individuals for the areas of the brain activated by emotionally disturbing images. One study of 12 men and 12 women found that more areas in the brains of women were highly activated by emotional imagery, though the differences may have been due to the upbringing of the test participants. When women are asked to think about past events that made them angry, they show activity in the septum in the limbic system; this activity is absent in males. In contrast, men's brains show more activity in the limbic system when asked to identify happy or sad male and female faces. Men and women also differ in their ability to recognize sad female faces: in one study, men recognized 70%, while women recognized 90%. Responses to pain also reveal sex differences. In women, the limbic system, which is involved in the processing of emotions, shows greater activity in response to pain. In men, cognitive areas of the brain, which are involved in analytical processing, show higher activity in response to pain. This indicates a connection between pain-responsive brain regions and emotional regions in women.
Avoidance or approach to moderately negative stimuli
- Further information: News values#Evolutionary perspectives
Men and women differ on average how they respond to moderately negative stimuli which may have evolutionary causes as well as implications regarding (negative) news consumption and knowledge of public affairs.
- Men tend to talk more than women in public situations, but women tend to talk more than men at home.
- Females are more inclined to face each other and make eye contact when talking, while males are more likely to look away from each other.
- Girls and women tend to talk at length about one topic, but boys and men tend to jump from topic to topic.
- When listening, women make more noises such as “mhm” and “uhuh”, while men are more likely to listen silently.
- Women are inclined to express agreement and support, while men are more inclined to debate.
However, not all research supports these claims. One study by Erina MacGeorge found only a 2% difference in the conversational styles of men and women, and reported that in general both sexes communicated in similar ways . Critics, including Suzette Haden Elgin, have suggested that Tannen's findings may apply more to women of certain specific cultural and economic groups than to women in general. There is no evidence to support the belief that women speak far more words than men. 
- Overall, women are happier than men with their lives, and reported more often that they had made personal progress in the last five years.
- Women show greater concern about family and home life issues, while men express more concern about political issues. Men are happier with their family life and more optimistic about their personal future and that of their children.
- Women generally have a higher body fat percentage than men. 
- Women usually have lower blood pressure than men, and women's hearts beat faster, even when they are asleep. 
- On average, men are stronger than women, particularly in the upper body.
- Female fertility declines after age 35 and ends with the menopause. Men are capable of fathering children into old age.
- Men and women have different levels of certain hormones. Men have a higher concentration of androgens while women have a higher concentration of estrogens.
- On average, girls begin puberty approximately two years before boys.
Women live longer than men in most countries (notable exceptions are Afghanistan and Pakistan). One possible explanation is that more men die young because of war, criminal activity, accidents, and heart disease. The gender gap is decreasing in many developed countries as more women take up unhealthy practices that were once considered masculine like smoking and drinking, and more men practice healthier living. In Russia, however, the gender gap has been increasing as male life expectancy declines .
- Overall rates of mental illness are similar for men and women. There is no significant gender difference in rates of schizophrenia and bipolar depression. Women are more likely to suffer from unipolar depression, anxiety, eating disorders, and post-traumatic stress disorder. Men are more likely to suffer from alcoholism and antisocial personality disorder.
- Worldwide, more men than women are infected with HIV. The exception is sub-Saharan Africa, where more women than men are infected.
- Adult males are more likely to be diagnosed with tuberculosis.
- Before menopause, women are less likely to suffer from cardiovascular disease. However, after age 60, the risk for both men and women is the same.
- Overall, men are more likely to suffer from cancer, with much of this driven by lung cancer. In most countries, more men than women smoke, although this gap is narrowing especially among young women.
- Women are twice as likely to be blind than men. In developed countries, this may be linked to higher life expectancy and age-related conditions. In developing countries, women are less likely to get timely treatments for conditions that lead to blindness such as cataracts and trachoma.
- Women are more likely to suffer from osteoarthritis and osteoporosis.
- Worldwide, 2.7 times as many men as women die in traffic accidents.
Certain conditions are X-linked recessive, in that the gene is carried on the X chromosome. Genetic females (XX) will have the disease only if both their X chromosomes are defective with a similar deficiency, whereas genetic males (XY) will have the disease if their only X chromosome is defective. For this reason, such conditions are far more common in males than in females. Examples of X-linked recessive conditions are hemophilia and Duchenne muscular dystrophy.
Problems with research
Studies of psychological gender differences are controversial and subject to error. Many small-scale studies report differences that are not repeated in larger studies. Self-report questionnaires are subject to bias, particularly if the subjects are told that the questionnaire is testing for gender roles. It is also possible that commentators may exaggerate or downplay differences for ideological reasons.
- Main article: Income disparity
In many countries, there is a gender income gap which favors males in the labor market. For example, the median salary for U.S. women is 76% of that of U.S. men; however, studies find that U.S. women earn 98% of what men do when controlled for experience, education, and number of years on the job. The income gap in other countries ranges from 53% in Botswana to 92% in Malta. There is a debate to what extent this is the result of gender differences, lifestyle choices, or because of discrimination.
According to a 2004 report by the US department of labor :
- 52.9% of American women are in the labor force versus 73.3% of men.
- 70.7% of women with children under 18 are in the workforce (up from 47% in 1975), compared with 94% of men with children under 18.
- Approximately 26 percent of employed women usually work part time, compared with about 11 percent of employed men.
- 5.6% of employed women and 8% of men are self-employed.
- Women in nonagricultural industries work 35.9 hours per week versus 41.6 hours for men.
- Women account for more than half of all workers in the following industries: financial activities, education services, healthcare, leisure and hospitality, and office and administrative support. Women are far more likely than men to be social workers, paralegals and legal assistants, teachers, nurses, speech pathologists, dental hygienists, maids and housekeeping cleaners, and childcare workers.
- More men than women work in the following industries: mining, construction, transportation and utilities, farming, computer and mathematical occupations, engineering, and architecture. Men are far more likely than women to be chief executives, firefighters, police and patrol officers, electricians, dentists, and surgeons.
These figures will be different for other parts of the world.
The majority of occupational deaths occur among men. In one U.S. study, 93% of deaths on the job involved men, with a death rate approximately 11 times higher than women. The industries with the highest death rates are mining, agriculture/forestry/fishing, and construction, all of which tend to employ more men than women .
Many countries, including Mexico, India, Germany, Brazil, and Australia require companies to grant 12-week maternity leave for working women at full pay. Paternity leave is not available to the same extent, although some countries such as Sweden are trying to close this disparity.
Worldwide, men are more likely to be literate, with 100 men considered literate for every 88 women. In some countries the difference is even greater; for example, in Bangladesh only 62 women are literate for every 100 men .
In an OECD study of 43 developed countries, 15-year-old girls were ahead of boys in literacy skills and were more confident than boys about getting high-income jobs .
As of October 2005, women made up 57% of all college students in the United States. This is repeated in other countries; for example, women make up 58% of admissions in the UK  and 60% in Iran .
The Sexual Strategies Theory by David Buss and David P. Schmitt is a comprehensive evolutionary psychology theory regarding female and male short-term and long-term mating strategies which are argued to be dependent on several different goals and vary depending on the environment. Men and women are predicted to have both similar and different strategies depending on the circumstances. The theory included many predictions that could be empirically tested. The theory is argued to have received extensive empirical support in subsequent research. It has also been developed further. Terri D. Conley et al. has argued that other empirical evidence support smaller or non-existing gender differences and social theories such as stigma, socialization, and double standards.
- Main article: Epidemiology and methodology of suicide
In western countries, males are much more likely to die by suicide than females (usually by a factor of 3–4:1); while 69 out of 74 non-western countries found an excess male mortality from suicide.
While there are more completed male suicides than female, females are more likely to attempt suicide. One possible explanation is that males tend to use more violent, immediately lethal methods than females. Another theory is that females are more likely to use self-harm as a cry for help or attention while males are more likely to genuinely want to end their lives.
- Main article: Sex and crime
Men are more likely to commit violent crime and to be incarcerated. However, this gender gap is decreasing.
With the exception of rape, men are more likely to be victims of violent crime.
In a honesty study conducted in the American city of Belleville Illinois - 100 identical wallets containing money and valuables were intentionally 'lost' in front of hidden cameras. In that particular study, the dishonesty rate for men was higher then that of women: Of the 51 females tested - 7 (14%) were dishonest and kept the wallets. Of the 49 males tested - 19 (39%) were dishonest and kept the wallets.
In an American study, the percentage of men using the Internet was ahead of the percentage of women, although this difference disappeared in the under 30s. Men log on more often, spend more time online, and are more likely to be broadband users. Women are more likely to e-mail friends and family about a variety of topics. Men are more likely to use the Internet to pay bills, participate in auctions, and for recreation such as downloading music and videos. Men and women are equally likely to use the Internet for shopping and banking.
Marriage and sexuality
Dating and marriage customs are dependent on culture and differ greatly across countries and even in subcultures within the same country. For example, many marriages in India are arranged, whereas in the Western World most people choose their own partners. In most societies, men are generally expected to play the more active role in the early stages of courtship, for example in asking the woman for a date.
Age at first marriage
- Main article: Age at first marriage
Men are older, on average, when they marry.
The demographics of sexual orientation in any population is difficult to establish with reasonable accuracy. However, most surveys find that a greater proportion of men than women report that they are exclusively homosexual, whereas more women than men report being bisexual. In most societies, homosexual and bisexual women are more widely accepted than their male counterparts.
Numbers of unmarried people
In the USA, single men are greatly outnumbered by single women at a ratio of 100 single women to every 86 single men . This very much depends on age group, with 118 single men per 100 single women in their 20s, versus 33 single men to 100 single women over 65 .
The numbers are different in other countries. For example, China has many more young men than young women, and this disparity is expected to increase. In regions with recent conflict such as Chechnya, women may greatly outnumber men.
There are still more men than women in online dating websites. According to a November 2003 study by Jupiter Research, men are four times more likely than women to subscribe to an online dating site and twice as likely to browse, post, or respond to a profile .
Choosing a partner
In a cross-cultural study by David Buss, men and women were asked to rank certain traits in order of importance in a long-term partner. Both men and women ranked "kindness" and "intelligence" as the two most important factors. Men valued beauty and youth more highly than women, while women valued financial and social status more highly than men.
- Men's orgasm is essential for reproduction whereas female orgasm is not. The female orgasm has thus no obvious function other than to be pleasurable.
- Typical male orgasmic contractions lasts no more than a couple of seconds, while in women, such contractions lasting up to a minute are known.
- According to Kinsey, for about 75% of all males, orgasm is possible to be attained within the first two minutes after initiation of sexual intercourse. For women the average time to reach orgasm is between 10 and 20 minutes. The swiftness of the male system virtually guarantees climactic orgasms for males but is usually too quick to give the female a penetration-induced orgasm. However, the average time to female orgasm via masturbation is significantly less at four minutes  .
- Male circumcision (removal of the foreskin) does not prevent the ability to orgasm, but female genital cutting usually does. However, the two procedures are not directly comparable; in particular, the phrase "female genital cutting" is used to refer to a wide variety of different practices, from minor ritual cuts to the labia (which are much less likely to impede orgasm) to complete excision of the clitoris.
In most cultures, different sorts of clothing are considered appropriate for men and women.
- In Western societies, skirts and dresses and high-heeled shoes are seen as women's clothing, while neckties are generally worn by men. Trousers were once seen as exclusively male clothing but nowadays are worn by both sexes. Male clothes are often more practical, but a wider range of clothing styles is available for females. Males are typically allowed to bare their chests in a greater variety of public places. It is generally acceptable, to some degree, for a woman to wear traditionally male clothing, but not the other way around.
- In India, saris are commonly worn by women and dhotis (less commonly) by men.
- Traditional Islam requires both sexes to wear hijab, or modest clothing. What qualifies as "modest" varies in different Muslim societies; however, women are usually required to cover more of their bodies than men are. Articles of clothing worn by Muslim women for purposes of modesty range from the headscarf to the burka.
- Scottish men may wear kilts on ceremonial occasions.
- The sex ratio of males to females at birth is 105 boys to 100 girls. In some countries, such as China and India, this ratio is skewed, probably due to sex-selective abortion and infanticide.
- Men have more responsibilities and presence in many religions or religious organizations. For example, the Roman Catholic church forbids women to become priests. Men have more rights under Sharia (Islamic law).
- Some societies place restrictions on women during their menstrual cycle.
- Men play in more sports.
- In the United States, women are more likely to vote disproportionately for the Democratic Party. Women were more likely to oppose the 2003 invasion of Iraq. Men are disproportionately likely to vote Republican and support the invasion of Iraq. Both sexes are equally likely to vote for independent candidates.
- Women take longer to use the bathroom (see potty parity).
- Typically, women spend more time than men doing childcare and household chores (see homemaker).
- Gender HCI
- Fertility and intelligence
- Height and intelligence
- Individual differences
- Neuroscience and intelligence
- Psychology of men
- Psychology of women
- Sex linked developmental differences
- Sexual dimorphism
- Sex recognition
- Single sex environments
- Species differences
- Variability hypothesis
- ^ Gender-related features of skin Procter & Gamble Haircare Research Centre 1997
- ^ Wilson, Tracy V. How Women Work howstuffworks.com
- ^ Bren, Linda (2005) Does Sex Make a Difference? FDA Consumer magazine, July-August 2005 Issue
- ^ Marano, Hara Estroff (2003) The New Sex Scorecard Psychology Today Magazine, Publication Date: Jul/Aug 2003, Last Reviewed: 9 Sep 2005
- ^ Harasty J, Double KL, Halliday GM, Kril JJ, McRitchie DA. (1997) Language-associated cortical regions are proportionally larger in the female brain Archives of Neurology 1997 Feb;54(2):171-6.
- ^ Frederikse ME, Lu A, Aylward E, Barta P, Pearlson G. (1999) Sex differences in the inferior parietal lobe Cerebral Cortex. 1999 Dec;9(8):896-901
- ^ WHO Countries A list that provides links to statistics on various countries, including life expectancy.
- ^ Lifestyle 'hits life length gap' BBC September 16, 2005
- ^ A Country of Widows Viktor Perevedentsev, New Times, May 2006
- ^ Gender, women, and health Reports from WHO 2002-2005
- ^ Hyde, J. S. (2005) The Gender Similarities Hypothesis American Psychologist, Vol. 60, No. 6, pp. 581-592. See also: Men and Women: No Big Difference on the APA-sponsored website, www.psychologymatters.org.
- ^ Young, Cathy (1999) Sex and Sensibility Reason, March 1999
- ^ Larkin, Judith E. (2003) Gender and risk in public performance Sex Roles: A Journal of Research
- ^ Goleman, D. (1995). Emotional Intelligence: why it can matter more than IQ. New York: Bantam Books. (ISBN 0-553-37506-7)
- ^ Estimated Frequencies of the Types in the United States Population
- ^ Gender differences in the distribution of types in Australia
- ^ Baron-Cohen, Simon (2003) 'They just can't help it' The Guardian April 17, 2003
- ^ Tannen, Deborah (1990) Sex, Lies and Conversation; Why Is It So Hard for Men and Women to Talk to Each Other? The Washington Post, June 24, 1990
- ^ MacGeorge, Erina (2004) Purdue study shows men, women share same planet Purdue News, February 17, 2004
- ^ Liberman, Mark (2006) Sex-Linked Lexical Budgets Language Log, August 06, 2006
- ^ Hyde, Janet Shibley and Linn, Marcia C. (1988) "Gender Differences in Verbal Ability: A Meta-Analysis", Psychological Bulletin, 104:1 53-69
- ^ James, Deborah and Drakich, Janice (1993) "Understanding Gender Differences in Amount of Talk: A Critical Review of Research", in D. Tannen, (ed.) Gender and Conversational Interaction. Oxford University Press: New York and Oxford.
- ^ Global Gender Gaps: Women Like Their Lives Better Pew Research Center October 29, 2003
- ^ Women in the Labor Force: A Databook US Dept of Labor 2005
- ^ Are Teens in Low-Income and Welfare Families Working Too Much? Robert I. Lerman, Urban Institute, November 01, 2000
- ^ Fatal Occupational Injuries - United States, 1980-1997 MMWR Weekly, April 27, 2001
- ^ Popcorn, Faith and Hyperion, Lys Marigold (2000) EVEolution – The Eight Truths of Marketing to Women New York. (ISBN 0-7868-6523-7)
- ^ Illiteracy 'hinders world's poor' BBC November 09, 2005
- ^ 'Girls top of the class worldwide' BBC September 16, 2003
- ^ College gender gap USA Today October 19, 2005
- ^ 'Where have all the young men gone? ' The Guardian May 18, 2004
- ^ 'In Iran, More Women Leaving Nest for University' The New York Times July 22, 2000
- ^ How men and women use the Internet Pew Research Center December 28, 2005
- ^ 'Men hold the edge on gender gap odds' Oakland Tribune October 21, 2003
- ^ Facts for features: Valentine’s Day U.S. Census Bureau Report February 7, 2006
- ^ '40m Bachelors And No Women' The Guardian March 09, 2004
- ^ 'Polygamy Proposal for Chechen Men' BBC January 13, 2006
- ^ Scott, Kenneth (2005) 'Why Online Dating is So Tough For Men' solveyourproblem.com February 3, 2005
- ^ Buss, D. M. (2003). The evolution of desire: Strategies of human mating. New York: Basic Books. (ISBN 0-465-02143-3)
- ^ Sexual Averages 1997-2003 Holodyne, Inc.
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