A number of factors combine to 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. Differences in socialization of males and females may decrease or increase the size of sex differences.
Definition
Psychological sex differences refer to emotional, motivational or cognitive differences between the sexes. Examples include a greater male tendencies toward violence, or that the female brain appears to have a strong affinity for empathy.
The terms "sex differences" and "gender differences" are at times
used interchangeably, sometimes to refer to differences in male and
female behaviors as either biological ("sex differences") or environmental/cultural ("gender differences"). This distinction is difficult to make owing to failures of parsing one from the other.
History
Beliefs about sex differences have likely existed throughout history.
In his 1859 book On the Origin of Species Charles Darwin proposed that, like physical traits, psychological traits evolve through the process of sexual selection:
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.
Two of his later books, The Descent of Man, and Selection in Relation to Sex (1871) and The Expression of the Emotions in Man and Animals (1872) explore the subject of psychological differences between the sexes. The Descent of Man and Selection in Relation to Sex includes 70 pages on sexual selection in human evolution, some of which concerns psychological traits.
Psychological traits
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. An infamous sexual
reassignment case was that of David Reimer.
Reimer was born biologically as a male but was raised as a female
following medical advice after an operation that destroyed his
genitalia. The reassignment was considered to be an especially valid
test of the social learning concept of gender identity for several of
the unique circumstances of the case. Despite the hormone therapies and surgeries, Reimer failed to identify as a female.
According to his and his parents' accounts, the gender reassignment has
caused severe mental problems throughout his life. At the age of 38,
Reimer committed suicide.
Some individuals hold a different gender identity than that assigned at birth according to their sex, and are referred to as transgender.
These cases often involve significant gender dysphoria. How these
identities are formed is unknown, although some studies have suggested
that male-to-female transgenderism is related to androgen levels during
fetal development.
Childhood play
Many different studies have been conducted on sex differences in the
play behavior of young children, often yielding conflicting results. One
study conducted on nineteen-month-old children revealed a male
preference for stereotypically "masculine" toys, and a female preference
for stereotypically "feminine" toys, with males showing more variance
in play behavior.
A study of thirteen-month-old children supported the theory that males
and females typically prefer toys typed to their gender, but instead
found females showing more variance instead of males. An additional study found that a gendered divide in regards to toys may express itself as early as nine-months of age.
Despite these apparent differences, a study of toddlers showed that
both boys and girls were equally active when playing, and both sexes
preferred toys that allowed them to express this.
The specific cause of this sex difference has also been
investigated. A study with 112 boys and 100 girls found that the
difference in play behavior appeared to be semi-correlated with fetal
testosterone. Girls with congenital adrenal hyperplasia
and thus exposed to high androgen levels during pregnancy tend to play
more with male-typical toys and less with female-typical ones.
However, some have argued that the characteristics of the condition
itself could also result in those girls preferring different types of
toys.
One study also claimed that one-day-old 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.
Research has shown that when male-typical toys are labeled as
female-appropriate, young girls become significantly more likely to play
with them.
Certain studies have concluded that many end up treating infants and
toddlers differently based on their assumed gender, even if boys and
girls express the same behavior.
Children raised by lesbian mothers were reported by the parents to be
more androgynous in personality, suggesting that, if the reporting is
accurate, upbringing could influence certain gendered traits.
Human-like play preferences have also been observed in guenon and rhesus macaques, though the co-author of the latter study warned about over-interpreting the data.
Sexual behavior
Psychological theories exist regarding the development and expression of gender differences in human sexuality.
A number of these theories are consistent in predicting that men should
be more approving of casual sex (sex happening outside a stable,
committed relationship such as marriage) and should also be more promiscuous (have a higher number of sexual partners) than women.
A sociobiological approach applies evolutionary biology
to human sexuality, emphasizing reproductive success in shaping
patterns of sexual behavior. According to sociobiologists, since women's
parental investment
in reproduction is greater than men's, owing to human sperm being much
more plentiful than eggs, and the fact that women must devote
considerable energy to gestating
their offspring, women will tend to be much more selective in their
choice of mates than men. It may not be possible to accurately test
sociobiological theories in relation to promiscuity and casual sex in
contemporary (U.S.) society, which is quite different from the ancestral
human societies in which most natural selection for sexual traits has
occurred.
Neoanalytic
theories are based on the observation that mothers, as opposed to
fathers, bear the major responsibility for childcare in most families
and cultures; both male and female infants therefore form an intense
emotional attachment to their mother, a woman. According to feminist
psychoanalytic theorist Nancy Chodorow,
girls tend to preserve this attachment throughout life and define their
identities in relational terms, whereas boys must reject this maternal
attachment in order to develop a masculine
identity. In addition, this theory predicts that women's economic
dependence on men in a male-dominated society will tend to cause women
to approve of sex more in committed relationships providing economic
security, and less so in casual relationships.
The Sexual Strategies Theory by David Buss and David P. Schmitt is an evolutionary psychology theory regarding female and male short-term and long-term mating strategies which they argued are dependent on several different goals and vary depending on the environment.
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.
According to social learning theory,
sexuality is influenced by people's social environment. This theory
suggests that sexual attitudes and behaviors are learned through
observation of role models such as parents and media figures, as well as
through positive or negative reinforcements for behaviors that match or
defy established gender roles.
It predicts that gender differences in sexuality can change over time
as a function of changing social norms, and also that a societal double standard
in punishing women more severely than men (who may in fact be rewarded)
for engaging in promiscuous or casual sex will lead to significant
gender differences in attitudes and behaviors regarding sexuality.
Such a societal double standard also figures in social role theory,
which suggests that sexual attitudes and behaviors are shaped by the
roles that men and women are expected to fill in society, and script theory,
which focuses on the symbolic meaning of behaviors; this theory
suggests that social conventions influence the meaning of specific acts,
such as male sexuality being tied more to individual pleasure and macho
stereotypes (therefore predicting a high number of casual sexual
encounters) and female sexuality being tied more to the quality of a
committed relationship.
Intelligence
With the advent of the concept of g, or general intelligence,
some form of empirically measuring differences in intelligence, was
possible, but results have been inconsistent. Studies have shown either
no differences, or advantages for either sex. 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 women and men 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." Arthur Jensen in 1998 conducted studies on sex differences in intelligence through tests that were "loaded heavily on g"
but were not normed to eliminate sex differences. His conclusions he
quoted were "No evidence was found for sex differences in the mean level
of g. Males, on average, excel on some factors; females on others".
Jensen's results that no overall sex differences existed for g has been
strengthened by researchers who assessed this issue with a battery of
42 mental ability tests and found no overall sex difference.
Although most of the tests showed no difference, there were some
that did. For example, they found females performed better on verbal
abilities while males performed better on visuospatial abilities.
One female advantage is in verbal fluency where they have been found to
perform better in vocabulary, reading comprehension, speech production
and essay writing. Males have been specifically found to perform better on spatial visualization, spatial perception, and mental rotation. Researchers had then recommended that general models such as fluid and crystallized intelligence be divided into verbal,
perceptual and visuospatial domains of g, because when this model is
applied then females excel at verbal and perceptual tasks while males on
visuospatial tasks.
There are however also differences in the capacity of males and
females in performing certain tasks, such as rotation of objects in
space, often categorized as spatial ability. Other traditionally male advantages, such as in the field of mathematics are less clear.
Although females have lesser performance in spatial abilities, they
have better performance in processing speed involving letters, digits
and rapid naming tasks, object location memory, verbal memory, and also verbal learning.
Memory
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. Females have also demonstrated to have better verbal memory.
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.
Aggression
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, although less physical; 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.
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".
According to the 2015 International encyclopedia of the social and behavioral sciences, sex differences in aggression is one of the most robust and oldest findings in psychology.
Past meta-analyses in the encyclopedia found males regardless of age
engaged in more physical and verbal aggression while small effect for
females engaging in more indirect aggression such as rumor spreading or
gossiping. It also found males tend to engage in more unprovoked aggression at higher frequency than females. This replicated another 2007 meta-analysis of 148 studies in the journal of Child Development which found greater male aggression in childhood and adolescence. This analysis also conforms with the Oxford Handbook of Evolutionary Psychology
which reviewed past analysis and found greater male use in verbal and
physical aggression with the difference being greater in the physical
type. A meta-analysis of 122 studies published in the journal of Aggressive Behavior found males are more likely to cyber-bully than females.
Difference also showed that females reported more cyber bullying
behaviour during mid-adolescence while males showed more cyber bullying
behaviour at late adolescence.
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 be 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). Another evolutionary theory explaining gender differences in aggression is the male warrior hypothesis,
which explains that males have psychologically evolved for intergroup
aggression in order to gain access to mates, resources, territory and
status.
Personality traits
Cross-cultural
research has shown gender differences on the tests measuring
sociability and emotionality. For example, on the scales measured by the
Big Five personality traits 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,
extroverted, 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
egoistically 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 2014 meta-analysis by researchers Rebecca Friesdorf and Paul Conway found that men score significantly higher on narcissism than women and this finding is robust across past literature.
The meta-analysis included 355 studies measuring narcissism across
participants from the US, Germany, China, Netherlands, Italy, UK, Hong
Kong, Singapore, Switzerland, Norway, Sweden, Australia and Belgium as
well as measuring latent factors from 124 additional studies.
The researchers noted that gender differences in narcissism is not just
a measurement artifact but also represents true differences in the
latent personality traits such as men's heightened sense of entitlement
and authority.
Meta-analytic studies have also found males on average to be more
assertive and having higher self-esteem. Females were on average higher
than males in extraversion, anxiety, trust, and, especially,
tender-mindedness (e.g., nurturance).
Women have also been found to be more punishment sensitive and men
higher in sensation seeking and behavioural risk-taking. Deficits in
effortful control also showed a very modest effect size in the male
direction.
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 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.
Empathy
Current literature find that women demonstrate more empathy across studies. Women perform better than men in tests involving emotional interpretation, such as understanding facial expressions, and empathy.
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 women and men 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 women and
men, 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.
A review published in the journal Neuropsychologia found that women are better at recognizing facial effects, expression processing and emotions in general. Men were only better at recognizing specific behaviour which includes anger, aggression and threatening cues. A 2006 meta-analysis by researcher Rena A Kirkland from the North American Journal of Psychology
found significant sex differences favouring females in "Reading of the
mind" test. "Reading of the mind" test is an ability measure of theory
of mind or cognitive empathy in which Kirkland's analysis involved 259
studies across 10 countries. Another 2014 meta-analysis in the journal of Cognition and Emotion, found overall female advantage in non-verbal emotional recognition across 215 samples.
An analysis from the journal of Neuroscience & Biobehavioral Reviews found that there are sex differences in empathy from birth which remains consistent and stable across lifespan.
Females were found to have higher empathy than males while children
with higher empathy regardless of gender continue to be higher in
empathy throughout development. Further analysis of brain tools such as event related potentials found that females who saw human suffering had higher ERP waveforms than males. Another investigation with similar brain tools such as N400
amplitudes found higher N400 in females in response to social
situations which positively correlated with self-reported empathy. Structural fMRI studies found females have larger grey matter volumes in posterior inferior frontal and anterior inferior parietal cortex areas which are correlated with mirror neurons in fMRI literature. Females were also found to have stronger link between emotional and cognitive empathy.
The researchers found that the stability of these sex differences in
development are unlikely to be explained by any environment influences
but rather might have some roots in human evolution and inheritance.
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.
Throughout prehistory, females nurtured and were the primary caretakers
of children so this might have led to an evolved neurological
adaptation for women to be more aware and responsive to non-verbal
expressions. According to the Primary Caretaker Hypothesis,
prehistoric males did not have same selective pressure as primary
caretakers so therefore this might explain modern day sex differences in
emotion recognition and empathy.
Emotion
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 women and men 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.
Women show significantly greater activity in the left amygdala when encoding and remembering emotionally disturbing 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.
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 family life and more
optimistic regarding the children's future.
Research has shown that women are more likely than men to use emoticons in text messaging.
Ethics and moral orientation
Meta-analysis on sex differences of moral orientation have found that women tend towards a more care based morality while men tend towards a more justice based morality. This is usually based on the fact that men have a more slight utilitarian reasoning while women have more deontological reasoning which is largely because of greater female affective response and rejection of harm-based behaviours. A meta-analysis published in the 2013 journal of Ethics and Behaviour after reviewing 19 primary studies also found women have greater moral sensitivity than men.
Mental health
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 tend to
externalize stress while women tend to 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 women and men 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 suggested that socializing practices that
encourage high self-regard and mastery would benefit the mental health
of both women and men.
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 women and men 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.
Women and men 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).
Cognitive control of behavior
Females tend to have a greater basal capacity to exert inhibitory control over undesired or habitual behaviors than males and respond differently to modulatory environmental contextual factors.
For example, listening to music tends to significantly improve the rate
of response inhibition in females, but reduce the rate of response
inhibition in males.
A 2010 meta-analyses found that women have small, but persistent,
advantages in punishment sensitivity and effortful control across
cultures.
A 2014 review found that In humans, women discount more steeply than
men, but sex differences on measures of impulsive action depend on tasks
and subject samples.
Possible causes
Biology
Genetics
Psychological traits
can vary between the sexes through sex-linkage. That is to say, what
causes a trait may be related to the chromosomal sex of the individual. In contrast, there are also
"sex-influenced" (or sex-conditioned) traits, in which the phenotypic
manifestation of a gene depends on the sex of the individual. Even in a homozygous dominant or recessive female the condition may not be expressed fully.
"Sex-limited" traits are characteristics only expressed in one sex.
They may be caused by genes on either autosomal or sex chromosomes.
Evidence exists that there are sex-linked differences between the male and female brain.
Epigenetics
Epigenetic changes have also been found to cause sex-based differentiation in the brain. The extent and nature of these differences are not fully characterised.
It has been shown that sex differences in some abilities (such as
verbal processing, sensation seeking, speed in physical activities) are
more apparent mostly in younger ages and subside after the age 30. Differences in socialization of males and females may decrease or increase the size of sex differences.
Brain structure and function
When it comes to the brain there are many similarities but also a
number of differences in structure, neurotransmitters, and function. However, some argue that innate differences in the neurobiology of women and men have not been conclusively identified.
Structurally adult male brains are on average 11–12% heavier and 10% bigger than female brains. Despite this, because of relative difference in body size the brain-to-body mass ratio does not differ between the sexes.Other studies have stated b igger male brain size can only be partly accounted by body size. Researchers also found greater cortical thickness and cortical complexity in females and greater female cortical surface area after adjusting for brain volumes.
Given that cortical complexity and cortical features are positively
correlated with intelligence, researchers postulated that these
differences might have evolved for females to compensate for smaller
brain size and equalize overall cognitive abilities with males. Women have a greater developed neuropil or the space between neurons, which contains synapses, dendrites and axons and the cortex has neurons packed more closely together in the temporal and prefrontal cortex.
Females also have greater cortical thickness in posterior temporal
and inferior parietal regions compared to males independent of
differences in brain or body 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 a 2013 meta-analysis, researchers found on average males had larger grey matter volume in bilateral amygdalae, hippocampi, anterior parahippocampal gyri, posterior cingulate gyri, precuneus, putamen and temporal poles, areas in the left posterior and anterior cingulate gyri, and areas in the cerebellum bilateral VIIb, VIIIa and Crus I lobes, left VI and right Crus II lobes. On the other hand, females on average had larger grey matter volume at the right frontal pole, inferior and middle frontal gyri, pars triangularis, planum temporale/parietal operculum, anterior cingulate gyrus, insular cortex, and Heschl's gyrus; bilateral thalami and precuneus; the left parahippocampal gyrus and lateral occipital cortex (superior division).
The meta-analysis found larger volumes in females were most pronounced
in areas in the right hemisphere related to language in addition to
several limbic structures such as the right insular cortex and anterior cingulate gyrus.
Amber Ruigrok's 2013 meta-analysis also found greater grey matter
density in the average male left amygdala, hippocampus, insula, pallidum, putamen, claustrum and right cerebellum. The meta-analysis also found greater grey matter density in the average female left frontal pole.
According to the neuroscience journal review series Progress in Brain Research, it has been found that males have larger and longer planum temporale and Sylvian fissure while females have significantly larger proportionate volumes to total brain volume in the superior temporal cortex, Broca's area, the hippocampus and the caudate. The midsagittal & fiber numbers in the anterior commissure that connect the temporal poles and mass intermedia that connects the thalami is also larger in women.
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. In the cerebellum, the region of the
brain that plays an important role in motor functions,
males showed higher connectivity between hemispheres, and females
showed higher connectivity within hemispheres. This potentially provides
a neural basis for previous studies that showed sex-specific difference
in certain psychological functions. Females on average outperform males
on emotional recognition and nonverbal reasoning tests, while males outperform females on motor and spatial cognitive tests.
In the work of Szalkai et al. have computed structural (i.e., anatomical) connectomes of 96 subjects of the Human Connectome Project,
and they have shown that in several deep graph-theoretical parameters,
the structural connectome of women is significantly better connected
than that of men. For example, women's connectome has more edges, higher
minimum bipartition width, larger eigengap, greater minimum vertex cover than that of men. The minimum bipartition width (or the minimum balanced cut) is a well-known measure of quality of computer multistage interconnection networks,
it describes the possible bottlenecks in network communication: the
higher this value is, the better is the network. The larger eigengap
shows that the female connectome is a better expander graph than the connectome of males. The better expanding property, the higher minimum bipartition width and the greater minimum vertex cover show deep advantages in network connectivity in the case of female braingraph. Szalkai et al.
have also shown that most of the deep graph theoretical differences
remain in effect if big-brained women and small-brained men are
compared: i.e., the graph theoretical differences are due to sex, and
not the brain volume-differences of the subjects.
Hormones
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.
Research on the ovulatory shift hypothesis
explores differences in female mate preferences across the ovulatory
cycle. Non-pill using heterosexual females who are ovulating (high
levels of estrogens) were shown to have a preference for the scent of
males with low levels of fluctuating asymmetry.
Certain research has also indicated that ovulating heterosexual females
display a preference toward masculine faces and report greater sexual
attraction to males other than their current partner,
though this has been called into question. A meta-analysis of 58
studies concluded that there was no evidence to support this theory. A different meta-analysis partially supported the hypothesis, but only in regards to "short-term" attractiveness.
A later study of Finnish twins found that the influence of
"context-dependent" factors (such as ovulation) on a female's attraction
to masculine faces was less than one-percent.
Additionally, a 2016 paper suggested that any possible changes in
preferences during ovulation would be moderated by the relationship
quality itself, even to the point of inversion in favor of the female's
current partner.
Culture
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, differences in socialization of males and females may
have the effect of decreasing or increasing the magnitude of sex
differences.
