Sex differences in psychology
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|Sex differences in humans|
Psychological sex differences are sexually dimorphic adaptations, or specifically their behavioral manifestations. Such differences are hypothesized to be evolved consequences of sexual selection. In contrast, the term "gender differences" refers to traits and behaviors that are presumed to be sexually monomorphic and due to differential socialization (see social construction of gender difference). For further differentiation of these terms see sex and gender distinction.
Numerous factors may influence the development of sex differences including genetics and epigenetics, differences in brain structure and function; hormones, or differences in psychological traits such as emotion, motivation, cognition, and sexuality. Differential socialization of males and females may decrease or increase the magnitude of sex differences. Sex differences may manifest distally as cultural phenomena. Since all behavior is phenotypical (occurs as a result of complex interactions between nature and nurture) researchers are especially interested in investigating how biology and environment interact to produce differences between the sexes.
- 1 History
- 2 Biology
- 3 Psychological traits
- 4 Culture
- 5 Controversies
- 6 See also
- 7 References
- 8 Bibliography
In his 1859 book On the Origin of Species Charles Darwin hypothesized that sexually dimporhic traits were an evolved product of the process he termed sexual selection. Darwin also proposed that, like physical traits, psychological traits evolve:
In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.—Charles Darwin, The Origin of Species, 1859, p. 449.
He explored the evolution of sexually dimorphic psychological traits in two of his later books The Descent of Man, and Selection in Relation to Sex in 1871 and The Expression of the Emotions in Man and Animals in 1872. The The Descent of Man and Selection in Relation to Sex includes 70 pages on sexual selection in human evolution, and 500 pages on sexual selection in other animals.
In 1972 Robert Trivers published an influential paper on sex differences that is now referred to as parental investment theory. The size differences of gametes (anisogamy) is the fundamental, defining difference between males (small gametes—sperm) and females (large gametes—ova). Trivers noted that anisogamy typically results in different levels of parental investment between the sexes, with females initially investing more. Trivers proposed that this difference in parental investment leads to the sexual selection of different reproductive strategies between the sexes and to sexual conflict. For example, he suggested that the sex that invests less in offspring will generally compete for access to the higher-investing sex to increase their inclusive fitness (also see Bateman's principle). Trivers posited that differential parental investment led to the evolution sexual dimorphisms in mate choice, intra- and inter- sexual reproductive competition, and courtship displays. In mammals, including humans, females make a much larger parental investment than males (i.e. gestation followed by childbirth and lactation). Parental investment theory is a branch of life history theory.
Buss and Schmitt's (1993) Sexual Strategies Theory  proposed that, due to differential parental investment, humans have evolved sexually dimorphic adaptations related to "sexual accessibility, fertility assessment, commitment seeking and avoidance, immediate and enduring resource procurement, paternity certainty, assessment of mate value, and parental investment." Their Strategic Interference Theory suggested that conflict between the sexes occurs when the preferred reproductive strategies of one sex interfere with those of the other sex, resulting in the activation of emotional responses such as anger or jealousy.
Sex linkage occurs when phenotypic expression of a trait is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to when both sexes have the same probability of inheritance of the trait. This in turn is due to the expression of one or several alleles present on a sex chromosome as opposed to on a autosomal (non-sex) chromosome.
Sex-linked characteristics, which are controlled by genes on sex chromosomes, can be differentiated from "sex influenced" and "sex-limited" traits. "Sex-influenced" (or sex-conditioned) traits are phenotypes affected by whether they appear in a male or female body. Even in a homozygous dominant or recessive female the condition may not be expressed fully. Example: baldness in humans. "Sex-limited" traits are characteristics only expressed in one sex. They may be caused by genes on either autosomal or sex chromosomes.
Sex-linked genes have been found to differentially affect the brains of males and females. A 2013 study found that "sex differences in gene expression and splicing are widespread in adult human brain, being detectable in all major brain regions and involving 2.5% of all expressed genes."
Epigenetic effects have also been found to cause sex differences in the brain.
Brain structure and function
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, due to relative difference in body size some researchers propose that the brain-to-body mass ratio does not differ between the sexes. Despite this 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, and differences were shown to be smaller but persisting after being 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.
In the cerebral cortex it has been observed that there is greater intra-lobe neural communication in male brains and greater inter-lobe (between the left and right hemispheres of the cerebral cortex) neural communication in female brains.
Testosterone appears to be a major contributing factor to sexual motivation in male primates, including humans. The elimination of testosterone in adulthood has been shown to reduce sexual motivation in both male humans and male primates. Male humans who had their testicular function suppressed with a GnRH anatagonist displayed decreases in sexual desire and masturbation two weeks following the procedure. It is also suggested that levels of testosterone in men are related to the type of relationship in which they are involved. Men involved in polyamorous relationships display higher levels of testosterone than men involved in either a single partner relationship or single men.
Females at different stages of their menstrual cycle have been shown to display differences in sexual attraction. Non-pill using heterosexual females who are ovulating (high levels of estrogens) have a preference for the scent of males with low levels of fluctuating asymmetry. Ovulating heterosexual females also display preferences toward masculine faces and report greater sexual attraction to males other than their current partner. From an evolutionary perspective, increases in estrogens during fertile periods in females may direct sexual motivation toward males with preferential genes (the good genes hypothesis).
Development of gender identity
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.
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.
|This section relies on references to primary sources. (July 2014)|
Differences in intelligence or mental power have long been a hot topic among researchers and scholars. With the advent of the concept of g or general intelligence some form of empiricism was allowed, but results are often inconsistent with studies showing either no differences or advantages for both sexes, with most showing a slight advantage for males. One study did find some advantage for women in later life, while another found that male advantages on some cognitive tests are minimized when controlling for socioeconomic factors. The differences in average IQ between men and women are small in magnitude and inconsistent in direction, although the variability of male scores has been found to be greater than that of females, resulting in more males than females in the top and bottom of the IQ distribution.
According to the 1995 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." Lewis Terman's analysis of scores on the first version of the Stanford-Binet IQ test concluded "Accordingly, our data, which for the most part agree with the results of others, justify the conclusion that the intelligence of girls, at least up to 14 years, does not differ materially from that of boys either as regards the average level or the range of distribution." There are however differences in the capacity of males and females in performing certain tasks, such as rotation of objects in space, often categorized as spacial ability. Other traditionally male advantages, such as in the field of mathematics is not so clear-cut.
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.
A meta-analysis of scientific studies concluded that men prefer working with things and women prefer working with people. When interests were classified by RIASEC type http://en.wikipedia.org/wiki/Holland_Codes (Realistic, Investigative, Artistic, Social, Enterprising, Conventional), Men showed stronger Realistic and Investigative interests, and women showed stronger Artistic, Social, and Conventional interests. Sex differences favoring men were also found for more specific measures of engineering, science, and mathematics interests.
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.
A 2003 worldwide survey by the Pew Research Center found that overall women stated that they were somewhat happier than men with their lives. Compared to the previous report five years earlier women more often reported progress with their lives while men were more optimistic about the future. Women were more concerned about home and family issues than men who were more concerned about issues outside the home. Men were happier than women regarding the family life and more optimistic regarding the children's future.
Childhood conduct disorder and adult antisocial personality disorder as well as substance use disorders are more common in men. Many mood disorders, anxiety disorders, and eating disorders are more common in women. One explanation is that men externalize stress while women internalize it. Gender differences vary to some degree for different cultures. Women are more likely than men to show unipolar depression. One 1987 study found little empirical support for several proposed explanations, including biological ones, and argued that when depressed women tend to ruminate which may lower the mood further while men tend to distract themselves with activities. This may develop from men and women being raised differently.
Men and women do not differ on their overall rates of psychopathology, however, certain disorders are more prevalent in women, and vice versa. Women have higher rates of anxiety and depression (internalizing disorders) and men have higher rates of substance abuse and antisocial disorders (externalizing disorders). It is believed that divisions of power and the responsibilities set upon each sex are critical to this predisposition. Namely, women earn less money than men do, they tend to have jobs with less power and autonomy, and women are more responsive to problems of people in their social networks. These three differences can contribute to women's predisposition to anxiety and depression. It is believed that socializing practices that encourage high self-regard and mastery would benefit the mental health of both men and women.
One study interviewed 18,572 respondents, aged 18 and over, about 15 phobic symptoms. These symptoms would yield diagnoses based on criteria for agoraphobia, social phobia, and simple phobia. Women had significantly higher prevalence rates of agoraphobia and simple phobia, however there were no differences found between men and women in social phobia. The most common phobias for both men and women involved spiders, bugs, mice, snakes, and heights. The biggest differences between men and women in these disorders were found on the agoraphobic symptoms of “going out of the house alone” and “being alone”, and on two simple phobic symptoms, involving the fear of “any harmless or dangerous animal” and “storms,” with relatively more women having both phobias. There were no differences in the age of onset, reporting a fear on the phobic level, telling a doctor about symptoms, or the recall of past symptoms.
One study interviewed 2,181 people in Detroit, aged 18–45, seeking to explain gender differences in exposure to traumatic events and in the development or emergence of post traumatic stress disorder following this exposure. It was found that lifetime prevalence of traumatic events was a little higher in men than in women. However, following exposure to a traumatic event, the risk for PTSD was two times higher in women. It is believed this difference is due to the greater risk women have of developing PTSD after a traumatic event that involved assaultive violence. In fact, the probability of a woman developing PTSD following assaultive violence was 36% compared to 6% of men. The duration of PTSD is longer in women, as well.
Men and women are both equally likely at developing symptoms of schizophrenia, but the onset occurs earlier for men. It has been suggested that sexually dimorphic brain anatomy, the differential effects of estrogens and androgens, and the heavy exposure of male adolescents to alcohol and other toxic substances can lead to this earlier onset in men. It is believed that estrogens have a protective effect against the symptoms of schizophrenia. Although, it has been shown that other factors can contribute to the delayed onset and symptoms in women, estrogens have a large effect, as can be seen during a pregnancy. In pregnancy, estrogen levels are rising in women, so women who have had recurrent acute episodes of schizophrenia did not usually break down. However, after pregnancy, when estrogen levels have dropped, women tend to suffer from postpartum psychoses. Also, psychotic symptoms are exacerbated when during the menstrual cycle, estrogen levels are at their lowest. In addition, estrogen treatment has yielded beneficial effects in patients with schizophrenia.
Pathological gambling has been known to have a higher prevalence rate, 2:1, in men to women. One study chose to identify gender-related differences by examining male and female gamblers, who were using a gambling helpline. There was 562 calls placed, and of this amount, 62.1% were men, and 37.9% were women. Male gamblers were more likely to report problems with strategic forms of gambling (blackjack or poker), and female gamblers were more likely to report problems with nonstrategic forms, such as slots or bingo. Male gamblers were also more likely to report a longer duration of gambling than women. Female gamblers were more likely to report receiving mental health treatment that was not related to gambling. Male gamblers were more likely to report a drug problem or being arrested on account of gambling. There were high rates of debt and psychiatric symptoms related to gambling observed in both groups of men and women.
There are also differences regarding gender and suicide. Males in Western societies are much more likely to die from suicide despite females having more suicide attempts.
The "extreme male brain theory" views autism as an extreme version of male-female differences regarding "systemizing" and empathizing abilities. The "imprinted brain theory" argues that autism and psychosis are contrasting disorders on a number of different variables and that this is caused by an unbalanced genomic imprinting favoring paternal genes (autism) or maternal genes (psychosis).
Fundamental sex differences in genetics, hormones and brain structure and function may manifest as distal cultural phenomena (e.g., males as primary combatants in warfare, the primarily female readership of romance novels, etc.). In addition, differential socialization of males and females may have the effect of decreasing or increasing the magnitude of sex differences.
Division of labor between the sexes
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.
In January 2005, Lawrence Summers, president of Harvard University, unintentionally provoked a public controversy when several attendees discussed with reporters some statements he made during his lunchtime presentation at an economics conference at the National Bureau of Economic Research. In analyzing the disproportionate numbers of men over women in high-end science and engineering jobs he suggested that part of discrepancy may be due in part to the conflict between employers' demands for high time commitments and women's disproportionate role in the raising of children. He also suggested that well documented greater variability among men (in comparison to women) on tests of cognitive abilities  may be due to intrinsic factors, adding that he "would like nothing better than to be proved wrong." The controversy generated a great deal of media attention; it contributed to the resignation of Summers the following year, and led Harvard to commit $50 million to the recruitment and hiring of women faculty. Stimulated by this controversy, in May 2005, Harvard University psychology professors Steven Pinker and Elizabeth Spelke debated "The Science of Gender and Science".
In 2006, Danish psychologist and intelligence researcher Helmuth Nyborg was temporarily suspended from his position at Aarhus University, after being accused of scientific misconduct in relation to the documentation of a peer-reviewed paper appearing in the journal Personality and Individual Differences, in which he showed a 3.15-point IQ advantage of men over women. This led to a review of his work by an investigative committee. Nyborg was defended — and the university criticized — by other researchers in the intelligence field.
In July 2012, IQ researcher Jim Flynn was widely misquoted in the media as claiming that women had surpassed men on IQ tests for the first time in a century. In a 2012 lecture, Flynn responded by denouncing the media reports as distortions, and made it clear that his data instead showed a rough parity between the sexes in a few countries on the Raven's Matrices for boys and girls between the ages of 14 and 18. Women, he argued, had previously scored lower than men on the Raven's tests, but reached equality with men in these nations as a result of exposure to modernity by entering the professions and being allowed greater educational access. Flynn stated that the minute variations that did appear were statistically negligible and were not attributable to differences in cognitive ability.
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- Heritability of IQ
- List of psychological tests by gender difference
- Sex differences in humans
- Sociology of gender
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