Human sex differences

A gender difference is a disparity between male and female humans. This article focuses on quantitative differences which are based on a gradient and involve different averages. For example, men are taller than women on average, but an individual woman may be taller than an individual man.

Other articles describe differences which clearly represent a binary male/female spilt, such as human reproduction. Women give birth to babies; men never do.

Though some gender differences are controversial, they are not to be confused with sexist stereotypes.

Possible causes: some theories
The existence of a gender difference does not necessarily identify whether the trait is due to nature or environment. Some traits are obviously innate (for example, reproductive organs), others obviously environmental (for example, given names), while for others the relationship is either multi-cause or unknown.

From the viewpoint of evolutionary psychology, modern humans have inherited natural traits that were adaptive in a prehistoric environment, including traits that had different advantages for males versus females (see Sexual selection). Gender role theory claims that boys and girls learn the appropriate behaviour and attitudes from the family and overall culture they grow up with, and so non-physical gender differences are a product of socialization. These are not all mutually exclusive theories: it is possible that gender differences are partially innate but are then reinforced and exaggerated by the environment.

Some feminists see gender differences as caused by patriarchy or discrimination, although difference feminism argues for an acceptance of natural differences between men and women. Traditional masculists tend to see gender differences as inherent in human nature, while liberal masculists may challenge traditional roles.

Traditional Abrahamic religion sees gender differences as created by God: "He made them in his image: man and woman He made them." (Genesis 1:27) (see Role of women in Judaism, Christian views of women, Gender roles in Islam).

Physical differences


For information about how males and females develop throughout the lifespan, see sexual differentiation.

Appearances

 * On average, men are taller than women (See sexual dimorphism).
 * Men usually have more body hair than women.
 * Men’s skin is thicker (more collagen) and oilier (more sebum) than women’s skin.
 * Women generally have a smaller waist in comparison to their hips (see waist-hip ratio).
 * In men, the second digit (index finger) tends to be shorter than the fourth digit (ring finger), while in females the second tends to be longer than the fourth (see digit ratio).

Health

 * Women generally have a higher body fat percentage than men.
 * Women usually have lower blood pressure than men, and women's hearts beat faster, even when they are asleep.
 * On average, men are stronger than women, particularly in the upper body.
 * Female fertility declines after age 35 and ends with the menopause. Men are capable of fathering children into old age.
 * Men and women have different levels of certain hormones. Men have a higher concentration of androgens while women have a higher concentration of estrogens.
 * On average, girls begin puberty approximately two years before boys.

Neurological

 * On average, male brains have approximately 4% more cells and 100 grams more brain tissue than females do. However, both sexes have similar brain weight to body weight ratios. Men have larger left inferior parietal lobes, while women have proportionally larger Wernicke's and Broca's areas . Evidence of gender differences in the size of the corpus callosum is ambiguous.
 * Women generally have faster blood flow to their brains and lose less brain tissue as they age than men do.

Health
Women live longer than men in most countries (notable exceptions are Afghanistan and Pakistan). One possible explanation is that more men die young because of war, criminal activity, accidents, and heart disease. The gender gap is decreasing in many developed countries as more women take up unhealthy practices that were once considered masculine like smoking and drinking, and more men practice healthier living. In Russia, however, the gender gap has been increasing as male life expectancy declines.

The World Health Organization (WHO) has produced a number of reports on gender and health. The following trends are shown:
 * Overall rates of mental illness are similar for men and women. There is no significant gender difference in rates of schizophrenia and bipolar depression. Women are more likely to suffer from unipolar depression, anxiety, eating disorders, and post-traumatic stress disorder. Men are more likely to suffer from alcoholism and antisocial personality disorder.
 * Worldwide, more men than women are infected with HIV. The exception is sub-Saharan Africa, where more women than men are infected.
 * Adult males are more likely to be diagnosed with tuberculosis.
 * Before menopause, women are less likely to suffer from cardiovascular disease. However, after age 60, the risk for both men and women is the same.
 * Overall, men are more likely to suffer from cancer, with much of this driven by lung cancer. In most countries, more men than women smoke, although this gap is narrowing especially among young women.
 * Women are twice as likely to be blind than men. In developed countries, this may be linked to higher life expectancy and age-related conditions. In developing countries, women are less likely to get timely treatments for conditions that lead to blindness such as cataracts and trachoma.
 * Women are more likely to suffer from osteoarthritis and osteoporosis.
 * Worldwide, 2.7 times as many men as women die in traffic accidents.

Anterior cruciate ligament injuries, especially in basketball, occur more often in women than in men.

Certain conditions are X-linked recessive, in that the gene is carried on the X chromosome. Genetic females (XX) will have the disease only if both their X chromosomes are defective with a similar deficiency, whereas genetic males (XY) will have the disease if their only X chromosome is defective. For this reason, such conditions are far more common in males than in females. Examples of X-linked recessive conditions are hemophilia and Duchenne muscular dystrophy.

Psychology
In one large scale study, most cognitive abilities and psychological traits showed little or no average difference between the sexes. Where sex differences exist, there is often considerable overlap between the sexes; in addition, it is unclear how many of these differences hold true across different cultures. Nevertheless, certain trends can be found:
 * Men are more physically aggressive. Although women were once held to be less aggressive and competitive overall, modern experts such as Rachel Simmons have suggested that women simply tend to express aggression and competition in less physical ways.
 * In many situations, men are more prone to taking risks.
 * Women express their emotions more readily and report feeling a greater intensity of emotion.
 * In the big five personality traits, women score higher in Agreeableness (tendency to be compassionate and cooperative) and Neuroticism (tendency to feel anxiety, anger, and depression).
 * Demographics of MBTI surveys indicate that 60-75% of women prefer feeling and 55-80% of men prefer thinking.

Systemizing and empathizing
Simon Baron-Cohen claims that, in general, men are better at systemizing (the desire to analyze and explore systems and rules) and that women are better at empathizing (the ability to identify with other people’s feelings). More males than females are diagnosed with autism and Asperger syndrome. According to Cohen, since autistic and Asperger individuals are very high in systemizing and very low in empathizing, they are examples of an "extreme male brain".

Intelligence
Most studies show no significant difference in the average IQ for men and women. However, on average men perform better on tests of spatial and mathematical ability, while women perform better on tests of verbal ability and memory. Also, men's IQ has greater variance, that is, there are more men than women in the very high and very low IQ groups, with women's scores more concentrated around the average.

Communication
Deborah Tannen’s studies found these gender differences in communication styles :
 * Men tend to talk more than women in public situations, but women tend to talk more than men at home.
 * Females are more inclined to face each other and make eye contact when talking, while males are more likely to look away from each other.
 * Girls and women tend to talk at length about one topic, but boys and men tend to jump from topic to topic.
 * When listening, women make more noises such as “mhm” and “uhuh”, while men are more likely to listen silently.
 * Women are inclined to express agreement and support, while men are more inclined to debate.

However, not all research supports these claims. One study by Erina MacGeorge found only a 2% difference in the conversational styles of men and women, and reported that in general both sexes communicated in similar ways. Critics, including Suzette Haden Elgin, have suggested that Tannen's findings may apply more to women of certain specific cultural and economic groups than to women in general. There is no evidence to support the belief that women speak far more words than men.

Happiness
A commentary released by Pew Research Center addressed some questions about the way men and women view their lives :
 * Overall, women are happier than men with their lives, and reported more often that they had made personal progress in the last five years.
 * Women show greater concern about family and home life issues, while men express more concern about political issues. Men are happier with their family life and more optimistic about their personal future and that of their children.

Problems with research
Studies of psychological gender differences are controversial and subject to error. Many small-scale studies report differences that are not repeated in larger studies. Self-report questionnaires are subject to bias, particularly if the subjects are told that the questionnaire is testing for gender roles. It is also possible that commentators may exaggerate or downplay differences for ideological reasons.

Income
In many countries, there is a gender income gap which favors males in the labor market. For example, the median salary for U.S. women is 76% of that of U.S. men; however, studies find that U.S. women earn 98% of what men do when controlled for experience, education, and number of years on the job. The income gap in other countries ranges from 53% in Botswana to 92% in Malta. There is a debate to what extent this is the result of gender differences, lifestyle choices, or because of discrimination.

Employment
According to a 2004 report by the US department of labor :
 * 52.9% of American women are in the labor force versus 73.3% of men.
 * 70.7% of women with children under 18 are in the workforce (up from 47% in 1975), compared with 94% of men with children under 18.
 * Approximately 26 percent of employed women usually work part time, compared with about 11 percent of employed men.
 * 5.6% of employed women and 8% of men are self-employed.
 * Women in nonagricultural industries work 35.9 hours per week versus 41.6 hours for men.
 * Women account for more than half of all workers in the following industries: financial activities, education services, healthcare, leisure and hospitality, and office and administrative support. Women are far more likely than men to be social workers, paralegals and legal assistants, teachers, nurses, speech pathologists, dental hygienists, maids and housekeeping cleaners, and childcare workers.
 * More men than women work in the following industries: mining, construction, transportation and utilities, farming, computer and mathematical occupations, engineering, and architecture. Men are far more likely than women to be chief executives, firefighters, police and patrol officers, electricians, dentists, and surgeons.

The Urban Institute reported in 2000 that male teens in the U.S. are more likely than female teens to work 20 or more hours per week.

These figures will be different for other parts of the world.

Occupational death
The majority of occupational deaths occur among men. In one U.S. study, 93% of deaths on the job involved men, with a death rate approximately 11 times higher than women. The industries with the highest death rates are mining, agriculture/forestry/fishing, and construction, all of which tend to employ more men than women.

Parental leave
Many countries, including Mexico, India, Germany, Brazil, and Australia require companies to grant 12-week maternity leave for working women at full pay. Paternity leave is not available to the same extent, although some countries such as Sweden are trying to close this disparity.

Insurance
Insurance companies often charge different rates for men and women:
 * Health insurance is less expensive for young and middle aged men.
 * Automobile insurance companies charge more for teenage boys than their female counterparts.
 * Life insurance is higher for males than for females.

Consumer behaviour
Price discrimination can favor either men or women. For example, some night clubs offer discounts or free entry for women, while some hairdressers offer cheaper haircuts for men.

According to a 2000 report, women purchase or influence the purchase of 80% of all consumer goods and influence 80% of health-care decisions.

Education
Worldwide, men are more likely to be literate, with 100 men considered literate for every 88 women. In some countries the difference is even greater; for example, in Bangladesh only 62 women are literate for every 100 men.

In an OECD study of 43 developed countries, 15-year-old girls were ahead of boys in literacy skills and were more confident than boys about getting high-income jobs.

As of October 2005, women made up 57% of all college students in the United States. This is repeated in other countries; for example, women make up 58% of admissions in the UK and 60% in Iran. 

Suicide
In western countries, males are much more likely to die by suicide than females (usually by a factor of 3–4:1); while 69 out of 74 non-western countries found an excess male mortality from suicide.

While there are more completed male suicides than female, females are more likely to attempt suicide. One possible explanation is that males tend to use more violent, immediately lethal methods than females. Another theory is that females are more likely to use self-harm as a cry for help or attention while males are more likely to genuinely want to end their lives.

Crime
Men are more likely to commit violent crime and to be incarcerated. However, this gender gap is decreasing.

With the exception of rape, men are more likely to be victims of violent crime.

Honesty
In a honesty study conducted in the American city of Belleville Illinois - 100 identical wallets containing money and valuables were intentionally 'lost' in front of hidden cameras. In that particular study, the dishonesty rate for men was higher then that of women: Of the 51 females tested - 7 (14%) were dishonest and kept the wallets. Of the 49 males tested - 19 (39%) were dishonest and kept the wallets.

Internet use


In an American study, the percentage of men using the Internet was ahead of the percentage of women, although this difference disappeared in the under 30s. Men log on more often, spend more time online, and are more likely to be broadband users. Women are more likely to e-mail friends and family about a variety of topics. Men are more likely to use the Internet to pay bills, participate in auctions, and for recreation such as downloading music and videos. Men and women are equally likely to use the Internet for shopping and banking. 

Marriage and sexuality


Dating and marriage customs are dependent on culture and differ greatly across countries and even in subcultures within the same country. For example, many marriages in India are arranged, whereas in the Western World most people choose their own partners. In most societies, men are generally expected to play the more active role in the early stages of courtship, for example in asking the woman for a date.

Age at first marriage
Men are older, on average, when they marry.

Homosexuality
The demographics of sexual orientation in any population is difficult to establish with reasonable accuracy. However, most surveys find that a greater proportion of men than women report that they are exclusively homosexual, whereas more women than men report being bisexual. In most societies, homosexual and bisexual women are more widely accepted than their male counterparts.

Numbers of unmarried people
In the USA, single men are greatly outnumbered by single women at a ratio of 100 single women to every 86 single men. This very much depends on age group, with 118 single men per 100 single women in their 20s, versus 33 single men to 100 single women over 65.

The numbers are different in other countries. For example, China has many more young men than young women, and this disparity is expected to increase. In regions with recent conflict such as Chechnya, women may greatly outnumber men.

Online dating
There are still more men than women in online dating websites. According to a November 2003 study by Jupiter Research, men are four times more likely than women to subscribe to an online dating site and twice as likely to browse, post, or respond to a profile.

Choosing a partner
In a cross-cultural study by David Buss, men and women were asked to rank certain traits in order of importance in a long-term partner. Both men and women ranked "kindness" and "intelligence" as the two most important factors. Men valued beauty and youth more highly than women, while women valued financial and social status more highly than men.

Orgasm

 * Men's orgasm is essential for reproduction whereas female orgasm is not. The female orgasm has thus no obvious function other than to be pleasurable.
 * Typical male orgasmic contractions lasts no more than a couple of seconds, while in women, such contractions lasting up to a minute are known.
 * According to Kinsey, for about 75% of all males, orgasm is possible to be attained within the first two minutes after initiation of sexual intercourse. For women the average time to reach orgasm is between 10 and 20 minutes. The swiftness of the male system virtually guarantees climactic orgasms for males but is usually too quick to give the female a penetration-induced orgasm. However, the average time to female orgasm via masturbation is significantly less at four minutes.
 * Male circumcision (removal of the foreskin) does not prevent the ability to orgasm, but female genital cutting usually does. However, the two procedures are not directly comparable; in particular, the phrase "female genital cutting" is used to refer to a wide variety of different practices, from minor ritual cuts to the labia (which are much less likely to impede orgasm) to complete excision of the clitoris.

Clothing


In most cultures, different sorts of clothing are considered appropriate for men and women.


 * In Western societies, skirts and dresses and high-heeled shoes are seen as women's clothing, while neckties are generally worn by men. Trousers were once seen as exclusively male clothing but nowadays are worn by both sexes. Male clothes are often more practical, but a wider range of clothing styles is available for females. Males are typically allowed to bare their chests in a greater variety of public places. It is generally acceptable, to some degree, for a woman to wear traditionally male clothing, but not the other way around.
 * In India, saris are commonly worn by women and dhotis (less commonly) by men.
 * Traditional Islam requires both sexes to wear hijab, or modest clothing. What qualifies as "modest" varies in different Muslim societies; however, women are usually required to cover more of their bodies than men are.  Articles of clothing worn by Muslim women for purposes of modesty range from the headscarf to the burka.
 * Scottish men may wear kilts on ceremonial occasions.

Miscellaneous



 * The sex ratio of males to females at birth is 105 boys to 100 girls. In some countries, such as China and India, this ratio is skewed, probably due to sex-selective abortion and infanticide.
 * Men have more responsibilities and presence in many religions or religious organizations. For example, the Roman Catholic church forbids women to become priests. Men have more rights under Sharia (Islamic law).
 * Some societies place restrictions on women during their menstrual cycle.
 * Men play in more sports.
 * In the United States, women are more likely to vote disproportionately for the Democratic Party. Women were more likely to oppose the 2003 invasion of Iraq. Men are disproportionately likely to vote Republican and support the invasion of Iraq.  Both sexes are equally likely to vote for independent candidates.
 * Women take longer to use the bathroom (see potty parity).
 * Typically, women spend more time than men doing childcare and household chores (see homemaker).