Sex differences in humans have been studied in a variety of fields. In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome, the type of gonads, the sex hormones, the internal reproductive anatomy (such as the uterus), and the external genitalia. Genetic sex is determined solely by the presence or absence of a Y chromosome. Phenotypic sex refers to an individual's sex as determined by their internal and external genitalia, expression of secondary sex characteristics, and behavior.
The sex of the individual can be defined in different ways, giving rise to different conceptual frameworks about what determines sex. Sex differences generally refer to traits that are sexually dimorphic. A subset of such differences is hypothesized to be the product of the evolutionary process of sexual selection.
Medicine
Sex differences in medicine include sex-specific diseases, which are diseases that occur only in people of one sex;
and sex-related diseases, which are diseases that are more usual to one
sex, or which manifest differently in each sex. For example, certain autoimmune diseases may occur predominantly in one sex, for unknown reasons. 90% of primary biliary cirrhosis cases are women, whereas primary sclerosing cholangitis
is more common in men. Gender-based medicine, also called "gender
medicine", is the field of medicine that studies the biological and
physiological differences between the human sexes and how that affects
differences in disease. Traditionally, medical research has mostly been
conducted using the male body as the basis for clinical studies. Similar
findings are also reported in the sport medicine literature where males
typically account for >60% of the individuals studied.
The findings of these studies have often been applied across the sexes
and healthcare providers have assumed a uniform approach in treating
both male and female patients. More recently, medical research has
started to understand the importance of taking the sex into account as
the symptoms and responses to medical treatment may be very different
between sexes.
Neither concept should be confused with sexually transmitted diseases, which are diseases that have a significant probability of transmission through sexual contact.
Sex-related illnesses have various causes:
- Sex-linked genetic illnesses
- Parts of the reproductive system that are specific to one sex
- Social causes that relate to the gender role expected of that sex in a particular society.
- Different levels of prevention, reporting, diagnosis or treatment in each gender.
Research has found that female doctors may be providing better care than male doctors in the U.S. and also in Canada.
Physiology
Sex differences in human physiology are distinctions of physiological
characteristics associated with either male or female humans. These can
be of several types, including direct and indirect, direct being the
direct result of differences prescribed by the Y-chromosome, and
indirect being characteristics influenced indirectly (e.g., hormonally)
by the Y-chromosome. Sexual dimorphism is a term for the phenotypic difference between males and females of the same species.
Direct sex differences follow a bimodal distribution. Through the process of meiosis and fertilization
(with rare exceptions), each individual is created with zero or one
Y-chromosome. The complementary result for the X-chromosome follows,
either a double or a single X. Therefore, direct sex differences are
usually binary in expression (although the deviations in complex
biological processes produce a menagerie of exceptions). These include,
most conspicuously, male (vs female) gonads.
Indirect sex differences are general differences as quantified by empirical data and statistical analysis. Most differing characteristics will conform to a bell-curve
(i.e., normal) distribution which can be broadly described by the mean
(peak distribution) and standard deviation (indicator of size of range).
Often only the mean or mean difference between sexes is given. This may
or may not preclude overlap in distributions. For example, most males are taller and stronger than females,
but an individual female could be taller and stronger than an
individual male. The extents of these differences vary across societies.
The most obvious differences between males and females include
all the features related to reproductive role, notably the endocrine
(hormonal) systems and their physiological and behavioral effects,
including gonadal differentiation, internal and external genital and
breast differentiation, and differentiation of muscle mass, height, and
hair distribution. There are also differences in the structure of
specific areas of the brain. For example, on average, the SDN (INAH3 in humans) has been repeatedly found to be considerably larger in males than in females.
Psychology
Research on biological sex differences in human psychology 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.
Chromosomal make up is important in human psychology. Women have
two X chromosomes while males have an X and Y chromosomal structure. The
X chromosome is much more active than Y and it affects behavior. Genetic researchers theorize that the X chromosome may contain a gene responsible for sociability.
Most IQ tests are constructed so that there are no overall score
differences between females and males. Areas where differences have been
found include verbal and mathematical ability. IQ tests that measure fluid g
and have not been constructed to eliminate sex differences also tend to
show that sex differences are either non-existent or negligible.
2008 research found that, for grades 2 to 11, there were no significant
gender differences in math skills among the general population. Differences in variability of IQ scores have been observed in studies, with more men falling at the extremes of the spectrum.
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 (this is called stereotype threat).
In his book titled Gender, Nature, and Nurture,
psychologist Richard Lippa found that there were large differences in
women's and men's preferences for realistic occupations (for example,
mechanic or carpenters) and moderate differences in their preferences
for social and artistic occupations. His results also found that women
tend to be more people-oriented and men more thing-oriented.
Hartung & Widiger (1998) found that many kinds of mental
illnesses and behavioral problems show gender differences in prevalence
and incidence. "Of the 80 disorders diagnosed in adulthood for which sex
ratios are provided, 35 are said to be more common in men than in women
(17 of which are substance related or a paraphilia), 31 are said to be more common in women than men, and 14 are said to be equally common in both sexes."
Differences in male and female jealousy can also be observed.
While female jealousy is more likely to be inspired by emotional
infidelity, male jealousy is most likely to be brought on by sexual
infidelity. A clear majority of approximately 62% to 86% of women
reported that they would be more bothered by emotional infidelity and
47% to 60% of men reported that they would be more bothered by sexual
infidelity.
In 2005, Janet Shibley Hyde from the University of Wisconsin-Madison
introduced the gender similarities hypothesis, which suggests that
males and females are similar on most, but not all, psychological
variables. The research focused on cognitive variables (for example,
reading comprehension, mathematics), communication (for example,
talkativeness, facial expressions), social and personality (for example,
aggression, sexuality), psychological well-being, and motor behaviors.
Using results from a review of 46 meta-analyses, she found that 78% of
gender differences were small or close to zero. A few exceptions were
some motor behaviors (such as throwing distance) and some aspects of
sexuality (such as attitudes about casual sex), which show the largest
gender differences. She concludes her article by stating: "It is time to
consider the costs of overinflated claims of gender differences.
Arguably, they cause harm in numerous realms, including women’s
opportunities in the workplace, couple conflict and communication, and
analyses of self-esteem problems among adolescents." Hyde also stated elsewhere that "variations within genders are greater than variations between genders."
In 2011 Irina Trofimova found a significant female advantage in
time on the lexical task and on the temperament scale of social-verbal
tempo, and a male advantage on the temperament scale of physical
endurance which were more pronounced in young age groups and faded in
older groups. She suggested that there is a "middle age - middle sex"
effect: sex differences in these two types of abilities observed in
younger groups might be entangled with age and hormonal changes. The
study concluded that a one-dimensional approach to sex differences
(common in meta-analytic studies) therefore overlooks a possible
interaction of sex differences with age.
This hormones-based "middle age-middle sex effect", and also specifics
of the few psychological sex differences (verbal and physical) were
analysed in terms of the systemic evolutional tendencies driving sex
dimorphism.
Sociology
Crime
Statistics have been consistent in reporting that men commit more criminal acts than women. Self-reported delinquent acts are also higher for men than women across many different actions. Many professionals have offered explanations for this sex difference. Some differing explanations include men's evolutionary tendency toward risk and violent behavior, sex differences in activity, social support, and gender inequality.
Despite the difficulty of interpreting them, crime statistics
may provide a way to investigate such a relationship from a gender
differences perspective. An observable difference in crime rates between
men and women might be due to social and cultural factors, crimes going
unreported, or to biological factors (for example, testosterone
or sociobiological theories). Taking the nature of the crime itself
into consideration may also be a factor. Crime can be measured by such
data as arrest records, imprisonment rates, and surveys. However, not
all crimes are reported or investigated. Moreover, some studies show
that men can have an overwhelming bias against reporting themselves to
be the victims of a crime (particularly when victimized by a woman), and
some studies have argued that men reporting intimate partner violence find disadvantageous biases in law enforcement. Burton et al. (1998) found that low levels of self control are associated with criminal activity.
Education
A world map showing countries by gender education disparity, 2010.
Sometimes and in some places, there are sex differences in educational achievement. This may be caused by sex discrimination in law or culture, or may reflect natural differences in the interests of the sexes.
Leadership
Research has been undertaken to examine whether or not there are sex
differences in leadership. Until recently, leadership positions have
predominantly been held by men. Women were rarely seen in senior leadership positions leading to a lack of data on how they behave in such positions.
The two main lines of research contradict one another, the first being
that there are significant sex differences in leadership and the second
being that gender does not have an effect on leadership.
Women and men have been surveyed by Gallup each year concerning
workplace topics, and when questioned about preferences of a female boss
or a male boss, women chose a preference for a male boss 39% of the
time, compared to 26% of men displaying preference for a male boss.
Only 27% of females would prefer a boss of the same gender.
This preference, among both sexes, for male leadership in the
workplace has continued unabated for sixty years, according to the
survey results.
Religion
Sex differences in religion can be classified as either "internal" or
"external." Internal religious issues are studied from the perspective
of a given religion, and might include religious beliefs and practices
about the roles and rights of men and women in government, education and
worship; beliefs about the sex or gender of deities and religious
figures; and beliefs about the origin and meaning of human gender.
External religious issues can be broadly defined as an examination of a
given religion from an outsider's perspective, including possible
clashes between religious leaders and laity;
and the influence of, and differences between, religious perspectives
on social issues. For example, various religious perspectives have
either endorsed or condemned alternative family structures, homosexual
relationships, and abortion. External religious issues can also be examined from the "lens of gender" perspective embraced by some in feminism or critical theory and its offshoots.
Social capital
Sex differences in social capital are differences between men and
women in their ability to coordinate actions and achieve their aims
through trust, norms and networks. Social capital
is often seen as the missing link in development; as social networks
facilitate access to resources and protect the commons, while
cooperation makes markets work more efficiently.
Social capital has been thought of as women's capital as whereas there
are gendered barriers to accessing economic capital, women's role in
family, and community ensures that they have strong networks. There is
potential that the concept can help to bring women's unpaid 'community
and household labor',
vital to survival and development, to the attention of economists.
However, research analyzing social capital from a gendered perspective
is rare, and the notable exceptions are very critical.
Suicide
Sex differences in suicide have been shown to be significant; there
are highly asymmetric rates of attempted and completed suicide between
males and females. The gap, also called the gender paradox of suicidal behavior, can vary significantly between different countries. Statistics indicate that males die much more often by means of suicide than do females, however reported suicide attempts are 3 times more common among females than males.
This paradox is partially explained by the methodology, with females
more often choosing medication-induced overdosage, and males more often
turning to weapons such as firearms or knives.
Financial risk-taking
Sex
differences in financial decision making are relevant and significant.
Numerous studies have found that women tend to be financially more
risk-averse than men and hold safer portfolios.
A May 3, 2015 article in the Wall Street Journal by Georgette Jasen
reported that "when it comes to investing, men sometimes have their way
of doing things, and women have different ways."
Scholarly research has documented systematic differences in financial
decisions such as buying investments versus insurance, donating to
ingroups versus outgroups (such as terrorism victims in Iraq versus
USA), spending in stores, and the endowment effect-or asking price for goods people have. The majority of these studies are based on the theory of agency-communion developed by David Bakan in 1966;
according to this theory, due to factors such as socialization, males
are typically more agentic (focus on self, upside potential,
aggressiveness) and females typically more communal (focus on others,
downside potential, and nurturing). This framework robustly explains
many financial decision making outcomes.
