A karyotype, or chromosome "map," for a typical human male, showing X and Y chromosomes. A typical human female has two X chromosomes.

Image courtesy National Human Genome Resource Institute

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Introduction to How Women Work

If you believe what you see on TV, women are inscrutable, conniving, hysterical and apt to change their minds without reason or warning. Some women's magazines perpetuate these stereotypes by offering advice on how to entrap men or keep them guessing. And some of the basic differences between men and women can seem a little confusing, depending on your point of view. So it's not surprising that one of the most requested articles in the history of HowStuffWorks is "How Women Work."

The irony is that from conception until the eighth week of gestation, male and female bodies are almost exactly the same. The only difference is at the chromosomal level, deep inside the embryos' cells. Inside every cell of a person's body, DNA is tightly wound into pairs of structures called chromosomes. One pair of chromosomes determines whether the person is male or female. Except in the case of extremely rare abnormalities, a person with two X chromosomes is female, and a person with one X chromosome and one Y chromosome is male. For a few weeks, these chromosomes are all that differentiates male embryos from female embryos.

­Of course, by the time embryos grow into adults, there are big differences between male and female bodies. On average, females are shorter and smaller than males are, although females have a higher percentage of body fat. Typically, female bodies have reproductive organs that can support a developing baby and nourish it after its birth. Their blood pressure is lower, and their heart beats faster, even when they're asleep [Source: FDA]. Female bodies also have faster blood flow to their brains and lose less brain tissue as they age than male bodies do [Source: Psychology Today].

­And then, of course, there are hormones, which a lot of people view as a huge difference between men and women. But every person's body, whether it's male or female, uses hormones to regulate and control a wide range of processes. Hormones are the products of the endocrine system, which includes numerous glands located in various parts of the body. For example, two well-known hormones are adrenaline, which comes from the adrenal gland, and insulin, which comes from the pancreas. These and other hormones are vital to the lives and health of all people.

­­Sex hormones, on the other hand, work a little differently in male and female bodies. In male bodies, the testes produce the hormone testosterone, which regulates sperm production and causes masculine secondary sex characteristics. In female, the ovaries produce hormones like estrogen and progesterone, which regulate reproductive processes. Male bodies convert a little testosterone into estrogen, and females' bodies make small amounts of testosterone, so neither hormone is exclusive to one sex or the other.

A man's testosterone levels can fluctuate throughout the day as his body regulates its production of sperm. But a woman's sex hormone levels fluctuate as part of her reproductive cycle, which takes about a month to complete. During a woman's childbearing years, the recurring changes in her hormone levels can cause symptoms like irritability and moodiness, known as premenstrual syndrome (PMS). When a woman reaches perimenopause, her body slows down its production of sex hormones. During the process, her levels of estrogen and progesterone can vary significantly, causing symptoms like hot flashes and trouble sleeping.

Sex hormones can affect a woman's emotions and physiology throughout most of her life. But contrary to some people's perceptions, they're not responsible for every facet of her behavior. In this article, we'll look at some other common perceptions and stereotypes about women as we examine how they work.

Confusing on Purpose?

One common stereotype is that women give mixed signals, especially when it comes to romantic involvement. A study at the University of Texas at Austin suggests that the sexes misunderstand one another and that there are evolutionary forces involved. The confusion may come from early human men trying to have more descendants while early human women tried to protect themselves from deception [Source: Psychology Today].

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Women and Emotions

A 2001 Gallup poll asked American adults whether a series of qualities applied more to men or to women. Ninety percent of those surveyed said that the characteristic "emotional" applied more to women. The survey didn't ask about particular emotions or specify positive or negative connotations for the word "emotion." But it seems likely from the results that most Americans view women as either able to experience or prone to experiencing a wider, more intense range of emotions than men do.

Are women more emotional than men are? Do they cry more?

The perception that women cry more than men is pretty widespread. But as babies and children, boys and girls cry about the same amount on average. Only during puberty do girls begin to cry more than boys do. According to a 2005 New York Times article, by age 18, women cry four times as much as men.

A possible explanation for this is the hormone prolactin, which contributes to how much people cry. Prolactin is present in blood and tears, and it's more prevalent in women than in men. Women's tear ducts are also shaped a little differently from men's, which could be either a cause or an effect of increased crying [Source: New York Times]. In addition, people who are depressed may cry four times as much as people who are not, and two-thirds of people diagnosed with depression are women [Psychology Today].

Of course, another common explanation is that some societies encourage women to cry while discouraging men from crying. In the United States, an exception to this standard seems to be the business world. In some businesses, crying is discouraged -- a woman who cries in the office may be viewed as weak or ineffectual [Source: New York Times].

In the next section we'll look at how women handle stress.

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Women and Stress

Are women more stressed out than men are?

Women sometimes have a reputation for being worriers. According to a 2005 Gallup poll, women are more worried about a range of social issues than men are. Significantly more women than men answered that they worried "a great deal" about seven of the 12 issues in the survey.

Stud­ies show that, in addition to worrying more often, women may be physiologically prone to experiencing more stress. For example, the amygdala of the brain processes emotions like fear and anxiety. In men, the amygdala communicates with organs that take in and process visual information, like the visual cortex. In women, though, it communicates with parts of the brain that regulate hormones and digestion. This may mean that stress responses are more likely to cause physical symptoms in women than in men [Source: Live Science].

In addition, women's bodies produce more stress hormones than men's bodies do. Once a stressful event is over, women's bodies also take longer to stop producing the hormones. This may be a cause or an effect of women's tendency to replay stressful events in their minds and think about upsetting situations [Source: Psychology Today].

Are women more jealous than men are?

In some people's minds, women are more jealous and possessive than men are, especially in the context of romantic relationships. But research suggests that women aren't more jealous than men -- they're just jealous about different situations.

In one German study, researchers showed participants images of several scenarios. The participants used a computer to describe which of the scenarios would be more upsetting. The results suggest that, across cultures, women find emotional infidelity more upsetting than sexual infidelity. Men's responses varied across cultures, but in general they were jealous of sexual infidelity [Source: Human Nature].

On the other hand, a study at the University of California at San Diego measured participants' blood pressure and heart rate rather than asking them to describe their responses. Men had greater physical reactions to physical infidelity, while woman reacted with about the same intensity to both scenarios. Women who were in committed relationships were more upset by physical infidelity than those who were not. However, 80 percent of the women in the study thought emotional infidelity would be more upsetting to them than physical infidelity [Source: Psychology Today].

Next, we'll look at some common perceptions of how women learn and communicate.

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Women: Brains, Bodies and Barbies

In 1992, Mattel Toys released a talking Barbie doll that said the phrase, "Math class is tough!" The doll caused controversy, especially among parents and teachers who thought that it reinforced the stereotype that girls are not good at math. Standardized test scores seemed to support the stereotype -- in general, boys' scores in math were higher than girls' [Source: Psychology Today].

Research into the differences in men's and women's brains also seemed to support the idea that men should be better at math. Men have 6.5 times more gray matter in their brains than women do. Women have 10 times more white matter. Gray matter creates processing centers in the brain, and white matter creates the connections between them. In other words, men have lots of areas for processing concrete data -- like mathematical equations -- and women have lots of connections that allow them to see and process patterns [Source: Live Science]. Some researchers believe that this difference in brain structure supports the idea that men are better at math while women are better at language. ­

­ H­owever, other researchers argue that men aren't really better at math. Girls often make better grades in math than boys do. Researchers theorize that the stereotype that women are not good at math may be partly to blame for this discrepancy. According to Dr. Robert Josephs of the University of Texas-Austin, women fear that their performance on standardized tests will prove that they're bad at math. For this reason, they don't do as well on tests, regardless of whether they've made good grades in math classes. Men, on the other hand, see such tests as an opportunity to prove that they are good at math, so they perform better [Source: Psychology Today].

In addition, women tend to receive higher scores on math tests when they take them without men in the room. According to one study that evaluated men and women who had made similar SAT scores, women's scores increase by up to 12 percent when taking tests without men in the room. Researchers say this is due to a stereotype threat, or a fear that a person will conform to a common stereotype [Source: Cook].

Regardless of how well they score on standardized tests, women seem to be able to develop math skills that are equal to men's. A large-scale analysis of data also suggests that there's very little difference between men and women's abilities in math [Source: Economist].

The Barbie doll: favorite childhood toy or self-esteem destroyer?

Image courtesy Stock.xchng

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Women and Pain

Do women have a higher pain tolerance than men?

Some people suppose that, because they are able to bear children, women have a higher pain tolerance than men do. However, several studies do not support this theory. A study at the Pain Management Unit of the University of Bath reported that women feel more pain in their lifetimes and that they feel pain for longer durations than men do. One experiment involved men and women submerging their arms in ice water. In that experiment, women had a lower pain threshold and lower tolerance for pain than men did [Source: Live Science].

Women's brains also respond a little differently to pain than men's brains do. There is considerable overlap in the areas of the brain that respond to pain and stress, but women's limbic centers become active in addition to these areas. The limbic center is responsible for a person's emotions, so this suggests that women are likely to have emotional responses to pain and stress. Researchers theorize that this is because of the traditional gender role of women as caregivers [Source: Science Daily].

Does Barbie really make women hate their bodies?

In 1995, researchers at the University of Arizona studied how African-American and Caucasian girls viewed their bodies [Source: University of Arizona]. They asked teenaged girls to describe their own bodies as well as what a perfect girl would look like. African-American girls were reluctant to assign physical traits to an ideal girl, but Caucasian girls gave roughly the same description. Their idea of an ideal girl was 5 feet 7 inches tall, weighed about 100 pounds and had long hair. Researchers called this description "a living manifestation of a Barbie doll" [Source: Quindlen].

Some researchers have used this as evidence that Barbie dolls encourage women to strive to have bodies that are unattainable. Some say Barbie is responsible for breast implants and eating disorders. However, there hasn't been a large-scale study directly linking playing with Barbie dolls to low self-esteem or increased eating disorders. There haven't been any studies proving that girls want to look like Barbie dolls, either. In fact, a 2005 British study revealed that girls often deface or mutilate their Barbie dolls while leaving their other toys unharmed [Source: Live Science].

However, one study has suggested that toys with unattainable proportions might affect a person's self-image. But the study didn't involve Barbie -- it involved male subjects and Ken dolls as well as action figures like the Hulk and G.I. Joe. The men in the study reported a more negative self image after playing with hyper-muscular action figures than after playing with Ken [Source: Sex Roles: A Journal of Research]. If playing with a toy can affect men in this way, it may affect women similarly.

Doctors and scientists are still discovering other similarities and differences in men and women, and they've made some surprising discoveries. For example, after World War II, pharmaceutical companies feared that drug tests could harm pregnant women and that women's hormones could affect test results. So, they tested drugs primarily on men. But in the last several years, the medical community has discovered that women and men often have different responses to drugs. For this reason, human trials of new drugs include both men and women [Source: The Science of Sex and Gender in Human Health]. You can learn more about how gender affects physiology, psychology and other human traits by following the links on the next page.

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Lots More Information

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