7 Truths About Hooking Up You Should Know (Says Science)

From "don't sleep together too soon" to "sow your wild oats before settling down," society is full of mixed messages about sex, love, dating and the intersection of the three. To get help deciding which advice to heed and which to skip, I asked scientists to explain some of their discoveries about human sexual behavior (yes, scientists do study such things). It turns out that their findings are often the exact opposite of what we tend to believe.

Here are 7 potentially surprising sex facts everyone should know:

1. Get frisky with 12 people before settling down.

Mathematicians have actually crunched the numbers on this, and while it's too complex to explain in full, here's the gist: When it comes to picking a great mate, your chances of picking right improve the more people you meet—up to a point. Settle down with your first or second sweetheart, and the fact that you have so few points of comparison means the odds are high that you may be selling yourself short.

Mow through thirty potential soul mates, though, and you likely have passed over someone who could actually make you happy were you to drop your pickiness. The right balance, it seems, is to carry on a romance with twelve people, then settle down with the very next person who floats your boat.

2. Men ogle women's faces more than their bodies.

When women strip down, they're often worried that men are eyeing their thunder thighs. Scientists tracked men's eyes to see where they land on naked photos. The result? Men spend the majority of their time looking at women's faces—not their bare bodies.

Guys may not even realize they're doing this, but they are! Scientists theorize that the reason for this is that women's faces contain clearer cues to their arousal levels than their bodies. Men, in other words, want to know that a woman is enjoying herself in bed—that's far more important to them than whether she looks porn-star perfect. So relax!

3. Size really doesn't matter.

Men will be relieved to know that the size of their penis doesn't impact women's ratings of their performance in bed. Scientists know this because they've actually measured hundreds of male volunteers' packages, then compared their dimensions to the total number of orgasms each delivered in the sack. They found that big and small models alike give the same number of orgasms.

4. The way your date smells matters more than looks.

No matter how attractive people appear, the way they smell is a far better predictor of chemistry. That's because your nose is a keen instrument for smelling a genetic blueprint called the major histocompatability complex, or MHC.

When certain people smell good, that means their MHC is complementary to your own, which means you'd produce strong offspring if you tried. When someone's MHC is not a good match to your own, you won't like the way they smell, and will probably move on.

5. Women on the Pill will pick the wrong mate.

The hormonal mix in birth control pills confounds a woman's sense of smell, steering her toward men with a genetic blueprint that's not very compatible to their own. So ideally, if you're looking for the perfect guy, you should use other forms of birth control until you've honed in on Mr. Right.

6. Men don't sleep around more than women. 

They just lie about the number of notches in their belt. Women, as we've long heard, indeed downplay the number of their sexual conquests, according to one study that ferreted out the truth by hooking female study subjects up to lie detectors.

Meanwhile, men tend to inflate their totals—if they've slept with two, they say ten. Not because they want to look like a stud, but because they honestly can't remember every encounter and decide to round up, a phenomenon scientists call the Men Are Pigs Hypothesis (no joke).

7. People have sex for many, many reasons.

Scientists have tabulated a total of 237 distinct reasons why people have sex. Some reasons are obvious (they were in love) but that barely scratches the surface. Some reasons are pragmatic (they want to burn calories), others are preventative (they want to keep someone from losing interest and having sex with someone else).

Still others have sex for religious reasons (they want to be closer to God), bragging rights, because they're bored, to relieve stress, to get to sleep, the list goes on and on.

Judy Dutton is the author of Secrets from the Sex Lab. To buy the book or read more about her, go to judy-dutton.com.