Ovaries usually release only one egg at a time (fraternal twins, which occur when two eggs are fertilized at nearly the same time, are the exception to this rule), and usually only one ovary releases an egg per menstrual cycle. That’s why mittelschmerz occurs somewhat to the left or right of center—on the side that releases the egg. Some women experience it on both sides, though this is rare. It’s not entirely clear what causes the pain; possibly, the release of blood or other fluids when the follicle ruptures irritates the peritoneum, the tissue lining the inside of the abdomen. But clearly, mittelschmerz is no cause for alarm—and for women trying to get pregnant, it’s actually a little bit of painful good news.
By the way, even though ovulation in humans may cause some discomfort, it’s nothing compared to what some animals go through. Cats and rabbits, among others, belong to a class of animals called induced ovulators—they don’t ovulate on a regular cycle, but only when induced to ovulate by sexual intercourse. And how are they induced? In cats, barbs on the male’s penis cause pain on withdrawal; this stimulates the release of hormones, which then cause ovulation. So, if you’ve ever heard a female cat screaming at the end of intercourse, now you know why. There’s good reason to wonder whether it’s a scream of pleasure of one of agony.
One more thing about menstruation: you’ve probably heard the idea that women who spend a lot of time together end up having the same cycles—the apocryphal story is about women in a college dorm. Well, there’s a lot of conflicting evidence about this. The original study was by Dr. Martha McClintock in 1971 (which was, in fact, a study of women in a college dorm), and it showed that the participants’ cycles synchronized over time. Other studies have shown no evidence of menstrual synchrony. If it does exist, it’s likely that it occurs through some form of olfactory signal women pick up from one another about their cycles. In fact, there is a documented synchrony effect in rodents, called the Whitten effect, in which the females’ menstrual cycles become synchronized when exposed to the urine of males.
Then there’s the whole connection between menstruation, months, and moonlight. In our culture we follow the Roman calendar, which is a solar calendar based on the position of the earth in its annual orbit around the sun. Other cultures, such as Islamic ones, have used purely lunar calendars. In a lunar calendar, the length of months corresponds to the length of the moon’s cycle from full moon to full moon. And more than a few people have been struck by the similarity between the rhythms of the moon and the rhythms of fertility—the moon cycles every 29.5 days, and the average menstrual cycle is said to be 28 days, although there can be a lot of variation, even in the cycle of the same woman. Does the moon control the menstrual cycle? There is some theorizing that the two are somehow connected; it is thought that the pineal gland (located deep within the brain), receives information about environmental light levels through the eyes and optic nerve, which then affects or interacts with our biological clocks. But most scientists discount this idea. As the astronomer George O. Abell wrote in Science and the Paranormal:
The moon’s cycle of phases is 29.53 days, while the human female menstrual cycle averages 28 days (although it varies among women and from time to time with individual women); this is hardly even a good coincidence! The corresponding estrus cycles of some other mammals are 28 days for opossums, 11 days for guinea pigs, 16 to 17 days for sheep, 20 to 22 days for sows, 21 days for cows and mares, 24 to 26 days for macaque monkeys, 37 days for chimpanzees, and only 5 days for rats and mice. One could argue, I suppose, that the human female, being more intelligent and perhaps aware of her environment, adapted to a cycle close to that of the moon, while lower animals did not. But then the 28-day period for the opossum must be a coincidence, and if it is a coincidence for opossums, why not for humans?
WHEN IT COMES to anatomy, the clitoris is in a class by itself. Quite literally. It’s the only organ in the human body, in men or women, that has only one function—to make its owner feel good. The penis has reproductive responsibilities and elimination system duties. Breasts have parenting priorities. But the clitoris stands alone. And it stands a bit taller than you might think.
Most people think the clitoris is just a small nub. But that’s not the case at all. Like the penis, the clitoris has a shaft, called the clitoral body; from the head of the clitoris it extends back about an inch and a half and then divides into legs, called crura, that extend down around two to three inches, surrounding the vaginal canal—the whole thing looks like a large wishbone except the unifying shaft is perpendicular to the legs. The clitoris is made up of erectile tissue—and when a woman is sexually aroused, the clitoris (like its counterpart, the penis) fills with blood and becomes erect.
Of course, clitoral stimulation isn’t the only way that women can have an orgasm. Women can have orgasm through both vaginal and anal stimulation. Women can have orgasm when just their breasts or nipples are touched. Women, in fact, can have orgasm just by thinking about whatever turns them on.
We know that the pudendal nerve transmits orgasm-producing sensations received from clitoral stimulation to the brain; it serves the same function in the penis. So how do sensations from the vagina get transmitted to the brain? Through the pelvic nerve—and there are other nerves that convey information from the cervix and uterus. This possibly explains how all those body parts (including the clitoris), when stimulated together, can produce a “blended” orgasm in some women.
There are also well-sourced reports of breast orgasm going back a half-century or more, including the Kinsey report. More recently, in The Science of Orgasm, Komisaruk, Beyer-Flores, and Whipple write: “There are documented cases of women who claim they can experience orgasm just by thinking—without physical stimulation. Their bodily reactions of doubling heart rate, blood pressure, pupil diameter, and pain threshold bear out their claim.”
So if women can have orgasms without genital stimulation, it seems clear that orgasm is something that happens in our minds. Which means, just like when it comes to our sense of smell or taste, it’s something we perceive with an astonishing level of variability between people—not just an automatic bodily response to sexual stimulation. And, of course, anyone who has ever been “not in the mood” has experienced the mental blanket your mind can throw over what would otherwise be a most stimulating situation. All of which goes to show that orgasm isn’t just a simple reflex.
It’s a state of mind.
And there’s new evidence that a woman’s state of mind about her relationship is directly related to the quality of her orgasms.
Researchers in Switzerland and California used functional magnetic resonance imaging (fMRI) to map the brains of women involved in sexual relationships—and they discovered that the more in love a woman was with her partner, the easier, better, and more intense her orgasms were. That’s good news for romantics everywhere. And it gets even better. Because new studies of a powerful hormone called oxytocin seem to show that, just as stronger love produces better orgasms, more orgasms may contribute to stronger love.
Oxytocin, called the “love hormone” by some, is involved in all kinds of intimacy. Physiologically, it can trigger lactation, labor contractions, and the jolts of a woman’s pelvis when she’s having an orgasm. It’s found in semen, too. It’s also a natural painkiller (but not to be confused with the often abused drug oxycodone). And oxytocin goes through the roof during orgasm—up to five times its normal level. The synthetic version of oxytocin, called pitocin, or “pit” for short, has been given to millions of women to induce and speed up labor. Pitocin can actually increase pain because of the sustained uterine contractions, rather than the usual phased contractions that occur naturally.
But oxytocin doesn’t just have physiological effects; it can behave as a neurotransmitter too, regulating emotions. It’s deeply connected to the mother-child bond, and probably the father-child bond (new studies show that oxytocin levels shoot up when a father holds his baby), as well as bonding between sex partners. Dr. Kathleen
C. Light from the University of North Carolina at Chapel Hill has found that oxytocin levels climb not only when couples have sex but even when they hold each other, hug, and hold hands. Although it’s still experimental, oxytocin is even thought to help with the symptoms usually associated with autism. Initial studies found that the administration of oxytocin improved the ability of adults diagnosed with autism to comprehend speech colored by emotions such as anger and sadness. It’s also thought that the “love drug” Ecstasy raises levels of oxytocin through its main ingredient, the synthetic chemical methylenedioxymethamphetamine, or MDMA, which is thought to explain some of the increased feelings of sociability that the drug produces.
If oxytocin improves bonding between couples, and orgasms increase oxytocin levels in people, well, science has caught up to what millions of couples have known for thousands of years—keeping things good in the bedroom can keep things good outside of it as well.
CHAPTER 2
boys to men
As boys begin to make the journey to becoming men, there’s one piece of anatomy that gets the lion’s share of human attention—and most of the myth. And the biggest myth of all is that women always want them bigger. But before you pull out the tape measure, let’s add some perspective. One thing’s for sure—you’re not hung like a gorilla. The truth is, when it comes to penis size, humans dwarf gorillas: an adult gorilla’s erect penis is only about 1.5 inches long. In fact, humans have the largest penis of any primate—not just relative to body size but in actual size.
On top of that, men may be surprised to know that their partners are likely to think they look just great down there, even if they don’t. A 2006 study found that, while only 55 percent of men were satisfied with the size of their penis, 85 percent of women were quite satisfied with the size of their partner’s penis. So, if size doesn’t seem to matter to most women, does size matter at all? Well, not in the way you might think. Remember, for most women the most sensitive parts of a woman’s genitals are on the outside and just inside her body—the clitoris, the vulva (which includes the labia minora), and the first three to four inches of the vagina (which is also surrounded by the clitoral crura). The average erect penis is over five inches long, and additional length may not improve sexual sensation for all women. When researchers have asked women whether they care about penis size in relation to pleasurable intercourse, the results square with what we know about the physical location of the pleasure centers in the female genitals. Women tend to care a lot less about length than men think—and a little bit more about width. Which makes sense, because additional width may mean more stimulation of the clitoris by causing more pull on the nerve-rich labia minora or stimulation of the introitus and anterior part of the vagina (more on this later).
Of course, there’s one way in which size definitely matters—condom fit. About ten years ago, I encountered a rather peculiar local phenomenon while working at a Thai nongovernmental agency (NGO) that was involved in HIV prevention. Western men who frequented the red-light district kept reporting problems with Thai condoms that we were providing—they were breaking. Well, guess what? The locally produced Thai condoms were smaller than those in Western countries.
Although the field of cross-cultural sizing has yet to be fully explored, there are some indications that Europeans are generally larger than Asians, and that’s true for their erect and flaccid penises too. And, while the difference may not matter from a sexual perspective, it can make all the difference in the world when it comes to safer sex. For AIDS prevention, the difference in condom and penis size may not be just a cultural curiosity—it can be deadly.
A survey conducted in India found that more than half of Indian men had penises that were about an inch shorter than the international standard that is used to manufacture condoms. If you’re an average-sized American who’s ever tried to buy clothes in Asia, or if you have a small build and try to find American clothes that fit, imagine what it must be like for some men and ill-fitting condoms.
Condoms, of course, are critical weapons in the fight against disease transmission, especially HIV. And if a condom doesn’t fit right, there’s a higher chance it will come off or break. This has led some experts to call for the production and advertisement of condoms in a much wider variety of sizes so that size differential doesn’t keep men from purchasing them.
So it looks as though one penis myth may have some basis in reality—there may be some variation in penis size across ethnic groups—and the few studies that have been done over the last few years suggest that may be true. But, for the most part, even that difference in penis size may be most pronounced and significant in the flaccid state, rather than the fully erect one. This may be the root of some men’s anxiety about penis size; most heterosexual men see many more flaccid penises than erect ones, so they don’t realize that there’s much less difference once erect. Average penises generally range from three to four inches in length when flaccid and from 4.5 to 5.5 inches when erect. Circumferences can range from three to four inches.
Height seems to vary among ethnic groups, but is the same thing true for penis sizes? A recent 2007 study of three hundred Indian men from Kerala revealed that their average flaccid penis length was significantly shorter than what was previously reported from studies measuring American and Jordanian men, but similar to the lengths reported from Nigeria and Israel. And, in the handful of studies measuring “stretched length,” South Indians from Kerala come out behind Americans, Israelis, and Jordanians but significantly ahead of Koreans. But, when actual erect (and not stretched) penis length was studied, the Kerala group was not that much different from the Americans, although still significantly behind the Israelis.
And why the difference among ethnic groups? Nobody is really certain, but I think it may have something to do with ancestral climate. According to this idea, which doesn’t perfectly explain all the ethnic differences, the colder the climate of your genetic origin, the smaller your flaccid penis. Why? The better to protect it from cold exposure and frostbite, of course. And sure enough, there’s a correlation to shorter fingers and toes in people from colder climes as well.
As to what all this really proves, the jury is still out. First of all, there’s a lack of uniform methodology to penis size studies, and this makes comparisons difficult at best. But one of the biggest limitations to all this research is that many of these studies, including the one from southern India, recruit their participants from clinics for sexual dysfunction.
A recent study that tried to sample a group of men who were not seeking medical treatment looked at over three thousand young Italian military recruits between the ages of seventeen and nineteen. The researchers must have been surprised to find that 2.5 percent of them had penises that were under 1.5 inches in length when flaccid and less than 2.75 inches when stretched. The study’s researchers reported these lengths to be borderline for the clinical classification micropenis, a term usually applied to a stretched penis length below about 0.75 inches in a newborn. Finally, when it comes to penis variation, there’s the issue of angle. Men with certain vertical angles (specifically penises that bend toward the abdomen) may provide more pleasure for their partners because they can better stimulate the nerve-rich anterior wall of the vagina, the area where the so-called G spot is said to be found.
In fact, many sexual aids or toys are especially designed for increased stimulation of the anterior vaginal wall. These devices have a similar curve or shape to those horizontally angled penises; they also make it easier for a woman to reach the area, especially when she masturbates. Of course, not all women respond the same way to this or any other type of stimulation, so men can relax: there is no perfect angle, just as there is no perfect size.
There is one angle that can cause some problems, though—for the man, not the woman. A penis with a horizontal angle, one that bends sharply to the left or right, can actually make sexual intercourse rather painful for the man.
UNDERSTANDING STANDARD PENIS si
ze is not a vanity exercise; it’s a public-health concern, as the example of the poorly fitting Thai condoms demonstrates. This is especially true when men use nonlatex condoms, which are less forgiving of differences in size than latex. Unfortunately, it’s not as easy as it seems to get a clear read on penis size across different populations. Scientists have been measuring penises for more than sixty years, but there’s still no consensus on what to measure, where to measure, or who should measure. Should you measure penises that are flaccid or erect? From tip of the glans to the base of the shaft—or all the way to the pubic bone? Should the measuring be done by a doctor in his or her clinic or by the subject in the comfort of his home? Must there be a standard temperature?
They say that you can tell how large a man’s penis is from his shoe size—which goes to show how little you can rely on what they say when it comes to penis myths. A 2002 study by two British urologists put that one to bed, showing absolutely no correlation between the size of one’s sneakers and the length of one’s penis. We still need a standard of measurement for a solid scientific understanding of standard penis length and deviation from it, among different ethnic groups. In the kind of consensus that only an informal international committee of unaffiliated parties could devise, most studies now measure something that only exists when it’s being measured—a stretched, flaccid penis. From the pelvic bone to the tip of the glans. At room temperature.
Even better, a pharmacologically induced erection by a professional. That’s one everybody can agree on—self-reported results tend to be mysteriously longer.
The normal male penis, whatever its size, is composed of two main parts: the glans, or head, and the shaft. The glans is homologous to the head of the clitoris, and like the clitoris, it is jam-packed (although on a per square foot basis not as generously) with highly sensitive nerve endings and quickly responds to stimulation.
How Sex Works Page 4