Excerpt: 'You: Being Beautiful' on the Biology of Sex

Read an excerpt of Dr. Oz's book that delves into the biology of sex.

ByABC News via via logo
March 08, 2009, 5:28 PM

March 9, 2009 — -- In the book he co-wrote with Michael Roizen, Dr. Mehmet Oz takes a look at beauty in all its aspects.

"You: Being Beautiful" is an "owners manual" to discovering inner and outer beauty and lends advice for work, love and life.

In the excerpt below, Oz takes a look at the biology of sex and the scientific side of what gets men and women all hot and bothered.

Read an excerpt of the book below and then click here to read more from the "GMA" Library.

The Biology of Sex

Humans are the most sexual species around. How do we know? (The answer isnot from National Geographic specials.) One example: Women are sexually activefor almost their entire lives and throughout all times of their menstrual cycle—meaning that they can choose to have sex even during times when they are physiologicallyunable to produce offspring. That means that sex must have somehigher purpose and function than simply reproduction. Another: Sex drive doesnot need to decrease with age, meaning that we strongly desire the physical connectioneven after we'reunable to bear children.

What's that higher purpose? For one, sex can serve as that nirvana momentbetween couples—a time when you feel complete happiness and intimacy, a timewhen you express your love to your mate. In other words, sex is designed to makeyou feel good. Real, real good. How good? For starters, consider that:

It's also interesting to look at the gender-basedevolutionary functions of sex.

Thousands of years ago, the woman felt that it was her job to grow the speciesand raise the children, so she needed someone who could protect the family. Herbody responded better to intimacy (she provided that intimacy so that men could help her reach orgasm). A man had different intentions.

When he saw a bunch ofmarauders marching through camp, he would get aroused by the threat to hisfamily and mate—a signal that his sperm needed to beat out other men'ssperm.

So a man responds sexually to anxiety, risk, and excitement, in contrast to awoman's desire for intimacy.

That hard-wireddifference is one way to explain the different ways that menand women feel aroused—and it'sthe basis for helping you figure out how tobetter mesh the sexual preferencesand differences in your own relationshipsso that you don'tonly gothrough the motions when it comesto sex but also experience the emotions.

While you may think that thebiggest sex organ of all is one that'scovered up by the latest style fromJockey or Victoria's Secret, yourbrain is actually your biggest sexorgan. Some researchers have saidthat sexual thoughts, for example,go through a man'sbrain once every52 seconds and through a woman'sonly once a day. And even conservative researcherssay that men have many more sexual thoughts than women do.

Perhapsthat'sbecause men have 2.5 times the amount of brain space devoted to sexualdrive that women do (or because women have more important things to thinkabout).

Sex, of course, is more than just thinking about it; it'salso about craving it.That craving originates in a part of the brain called the insula. Blocking messagesto the insula is one of the ways that cigarette cessation techniques work—goodnews for many, they don'tblock sexual craving messages; in fact, bupropion, thedrug we most often use in our breathe-free program with nicotine, actually increases libido in most people. The insula (rememberit from chapter 8?), a primitive area ofthe brain, is especially active in women who havemore frequent orgasms.

Let's now look at the way men and womenbiologically work when it come to sex:

WOMEN: During sex, your pupils dilate, nostrilsflare, heart rate increases, oxytocin level increases,sweat glands open for cooling, breastsenlarge by 25 percent, and nipples increase inheight by half an inch. Infrared cameras alsoshow increased blood flow to the lips, nose, andlabia. All of these things happen as the sexualstimuli build up to the almighty orgasm (see Figure10.3).

A good question to ask right about now: Whydo women have orgasms?

Evolutionarily, it was one of the ways that women couldtell whether a man would be a good lifelong partner, because it could help womendistinguish between a caring, patient male and a selfish or impatient one. Nevertheless,female orgasm can be so subtle that some women don'teven know whenthey'vehad one.

Here'swhat happens:

During intercourse, your vaginal walls make fluids that let your partner'spenis slide with just the right amount of friction. Together with the sights,sounds, and smells of sex, the stimulation to the clitoris, labia, and breasts allbuilds up a crescendo of intense physical sensation.

This is about the time whenyour brain tells your vagina and nearby muscles to contract. Why? To bring hispenis in deeper and increase the chance of his sperm hitting its target—the egg.

In the process, some women even ejaculate. During orgasm, the uterus dips inlike an anteater and sucks up the semen into the uterus to further increase thechance of fertilization.

The female orgasm also causes hormones to increase contractionsin the vagina and uterus and help move semen into the uterus (women who orgasm between 1 minute before and 45 minutes after their partner'sejaculationhave a higher tendency to retain sperm compared to those who don'thavean orgasm).

The female orgasm, of course, isn'tan easy thing to describe.

The brain serves as the main conductor in this symphony,but it might involve many different instruments,sometimes including the area known as the G-spot,which is parallel to a gathering of nerves on the maleprostate.

Women usually do not have a single spot likesome magic sex-me-herebutton but rather a region of nerves likethose spread over the surface of the male prostate. That'sbecauseas a woman'sreproductive organs develop inutero, her rudimentary prostate moves away so thesenerves end up on the vaginal wall. So if you insertyour index finger upward into the vagina and makethe "come here" movement, you will touch theG-spot region that exists in some women.

The regionis often not that sensitive either, but you never know until you try. The fact that women can be stimulated to orgasmthrough not only the genitals but also the mouth, nipples, and other parts of thebody points to the complexity of the system—and reinforces the fact that the truebiology of sex really evolves within the brain. (One theory is that sexual stimuli arecarried from the cervix and uterus to the brain through the vagus nerve—one ofthe nerves stimulated during deep breathing and meditation.)

MEN: If you allow us a few moments to talk about the male anatomy, we think you'llbe pretty amazed.

Biologically, men's sexual organs are much different than those ofother species. For one, a man's penis doesn't have a bone, unlike those of other species.Why? The bone makes for easy and fast access for males in the animal kingdom(to inseminate their partners quickly); men give up the bone but gain a disproportionatelylarge penis for their body size in return.

The evolutionary implications: One,men use the penis as a tool of attraction, implying that women do place some value inusing it as a diagnostic for evaluating potential mates (not so overtly these days). Andtwo, the lack of bone implies that men do equate emotions with sex, since they mustbe aroused for an erection; instead of easy and fast access, which can be painful tothe females, it takes more care to have a sexual relationship between two people.

Another interesting observation: Humanshave proportionally smaller testicles than malesin other species; that's because other speciesneed to ejaculate more semen to fertilize partnerswho are in heat prior to other males of the tribeand ensure propagation of their genes.

Humanmales don't need the size because of the biologicaldrive to be monogamous (at least serially).

Now, it doesn'ttake a sexologist to know thepurpose of the male orgasm: Find the egg, fertilizethe egg, begin shopping for Barbies. Butwhat'sinteresting is that this mad dash to the eggisn'tsome New York City marathon where all thestarter sperm strap on their Nikes with the goal of making it to the finish line. Some of the sperm do that, but others are more likedefensive linemen. Their job: to stop other men'ssperm from scoring.

Somesperm even have a dual role—blocking other sperm but allowing their own spermwith their genes to penetrate more effectively.

Now, during a man'sorgasm, the brain is firing like a lit-uppinball machine,causing contractions in most muscles of the body. The purpose: Like a woman's,these contractions help increase the chance of pregnancy by enabling the penis topenetrate as deeply as possible. The glands that make semen, mostly the prostate,squeeze repeatedly, propelling sperm as deep and as far as possible. The prostate,by the way, is often referred to as the male G-spot, because it'smade up of someof the same types of tissues as some of the spots identified around the nerveplexus that is the G-spot in women and can be stimulated in a similar fashion bysome adventuresome couples.

Normally, ejaculation cannons semen forward through a man'surethra andout the tip of his penis. Semen, by the way, contains hormones like oxytocin thatalso have a feel-goodeffect on women. The reason ejaculation never gets mixedup with urine is that there'sa tiny muscle at the entrance of the bladder that preventssemen from slipping backward or urine from propelling forward during orgasm(it's a roadblock of sorts, so the only way for the semen to go is out). Now,some men suffer from what'scalled retrograde ejaculation, in which that tinymuscle doesn'twork right, causing semen to backtrack into the bladder ratherthan to the promised land (causes for this include some side effects of surgery ormedication).

Retrograde ejaculation doesn'taffect a man'sability to achieve anerection or ejaculate, but it may affect his fertility.

The opposite of retrograde ejaculation, of course, is when semen shoots outfaster than a round from an Uzi—something that can cause angst in men and stop a satisfying sex session in its tracks. Premature ejaculation can be caused by anumber of things, including medication, hormonal changes, high blood pressure,and stress.*

One of the other causes—an enlarged prostate. Since the prostategenerates 95 percent of the substance that comes out during ejaculation, it'snowonder that it has a lot to say about what comes out and when. Since an enlargedprostate gets more stimulation during sex, the friction can stimulate orgasm—leading a man to ejaculate whether he wants to or not.

* Premature ejaculation affects one-thirdof men. Some treatment options include antidepressantmedications (SSRIs) and behavioral techniques. Some docs suggest the man masturbate an hour or twobefore sex to help delay ejaculation during sex. Another technique is called the squeeze technique, inwhich the woman squeezes the penis at the point where the head meets the shaft for several seconds,right before a man feels like he'sgoing to ejaculate. That should help delay orgasm; wait 30 seconds,then continue.

YOU Tips!

Try Tantric. When you hear the term tantric sex, youmay assume that we'retalking about the ability tohave a sexual interlude that lasts longer than atranscontinental flight. But that'snot really the goalof tantric sex.

The goal stems from the desire andability to have more of a physical and spiritualconnection during sex. Physically, for men, thatmeans developing the ability to, as tantrics say,"retain the seed"—that is, having the ability tocontrol ejaculation to allow sexual energy toflow. But the essence of that practice—and ofthe tactics below—is really about mindfulness,or being deeply aware of yourself, your partner,your life, and what'scalled the sacred lifeforce.

These tips can help you maximize yoursexual experience—and bring deeper emotionallevels to your relationship.

Play to Your Partner's Strengths

We all know the whole Mars and Venus debate. Men aredifferent sexual creatures than women. Men respond to new visual cues; women respond to friendlyemotional ones. Go a little deeper, and you understand that it'smore that men respond to fear andexcitement, and women respond to intimacy.

Instead of agreeing to disagree, couples shouldcapitalize on their differences to help make their partners more comfortable in bed. So what does thatmean? A man should make it a habit to look into his partner'seyes during sex: That eye lock is a wayto increase intimacy (and oxytocin). And a woman should acknowledge that her partner'sarousal maybe based more on urgency, meaning that it'snot so bad to have the lights on during sex, crave aquickie, or meet up for a lunch hour that involves absolutely no lunch at all.

Go Crazy

There'sa reason why bungee jumping, river rafting, and sneaking into the supply closetcan make the perfect first date. Doing novel things with another person stimulates dopamine—thefeel-goodchemical that'selevated when you'rein love.

Also, since men are aroused by fear andanxiety and heart rates are elevated during both attraction and danger, it increases the likelihood thata man will find his partner more attractive during a daredevil date. The dopamine is actually firinghigh when you first get together but not necessarily on the 80th date, so it'seven better to makespecial new adventures or variations more common the longer you'retogether.

Novel choices areespecially great for couples whose libido has diminished or whose sex life has gone stale.

Mix it Up

Guys, listen up. While men have orgasms in 95 percent of sexual encounters, somereports have women having orgasms in 69 percent of encounters.* Interestingly, the more varied thesexual activity, the more likely a woman is to have an orgasm.

* We couldn'thave made up a better number for this statistic if we tried, eh? Of course, getting these numbers is hard todo, and some reports have much lower numbers.

That means mixing it up amongmanual, oral, and genital stimulation. Oral sex, by the way, increases a woman'schance of havingan orgasm.

Open the Fridge

While you'reprobably thinking that we'regoing to tell you to get some chocolatesauce and whipped cream, the truth is that food plays a vital role in our sexual desire—somebecause of the smell, some because of the shape, and some because they alter your body chemistryto make you a more desirable mate.

Our choices:

Don'teatthe doughnuts (that slows blood flow dilation down);just smell. For women, it'slicorice and cucumbers.

Why? For women, the phallic shape subconsciouslyplays a large part in that. Another good one to smell forits pheromone effect: baby powder. It makes the femalepartner think of the evolutionary goal of sex, at leastsubconsciously.

One study also shows that caffeine may have a positiveeffect on female libido.

Get Your Drive Back

If you feel as if you'velost some of your sex drive, try these tactics forrestoring some of your long-lostlibido:

Change things up to charge things up.

Check Your Waist

Fat doesn'tjust make it hard for you to see your organs. It also makes it hardfor them to function, which is why increasing waist size means decreasing libido. One of the reasonswhy men lose libido: omental fat (fat around the belly). That omental fat converts testosterone toestrogen and thus diminishes sex drive.

So if you'reexperiencing a loss of sex drive, a doc may firstcheck the size of your testes (they should be roughly a ratio of 11/2 inches height to 1 inch width, orthree finger widths by two finger widths). If they'renormal size, it could mean that omental fat iscausing the testosterone drop. While you'relosing the belly fat, a medication called clomiphene,which blocks the conversion from testosterone to estrogen, may help.

If you want to keep your libido(or get it back), get your waist size to less than half your height.

Go All Lombardi on Him

When it comes to sex, some women are as silent as a 1920s movie.They fear that they can'ttell their men what they want in bed—maybe because they'reshy, maybebecause they'reembarrassed, or maybe because their partner'sego is as delicate as a silk blouse.

But the best thing you can do with your mouth to improve your sex life has nothing to do with theX-rated thoughts crossing your mind right about now; it'stalking.

Women need to teach, coach, andencourage their men to give them what they want—and how they want it. Believe us, it'smuch moreof an ego boost for men to know they'repleasing their women than not to know something waswrong in the first place.

Keep It Pumping

Good sex isn'tjust about blindfolds and finger paints. It'sreally about good bloodflow.

That ensures you'regetting the right nutrients to your brain, as well as the right stimuli to yoursex organs. So improving your sex life means avoiding the things that decrease blood flow (nicotine,drugs, saturated fat, trans fats, sugar, syrups, diabetes, high BP) and embracing the things thatincrease blood flow (exercise, avocados, fruits, vegetables, 100 percent whole grains, ginseng,ginkgo biloba, l-arginine, lemon, citriulline).

ABC News Live

ABC News Live

24/7 coverage of breaking news and live events