Editor's note: The following is an excerpt from the new book, Subliminal: How Your Unconscious Mind Rules Your Behavior, by Leonard Mlodinow. Copyright © 2012 by Leonard Mlodinow. Published by arrangement with Pantheon Books, an imprint of The Knopf Doubleday Publishing Group, a division of Random House, Inc.

In a guest post for the SA network blog Streams of Consciousness, Mlodinow describes the importance of being social. He also wrote the article, "The Elusive Theory of Everything," with Stephen Hawking in the October 2011 Scientific American.

When I was in high school, the few times I gathered the courage to approach a girl, the experience felt like I was administering a ­multiple-choice test and she kept answering, “None of the above.” I had more or less resigned myself to the fact that a boy who spent his free time reading books on non-Euclidean geometry was not likely to be voted “big man on campus.” Then one day when I was in the library looking for a math book, I took a wrong turn and stumbled upon a work whose title went something like How to Get a Date. I hadn’t realized people wrote instructional books on subjects like that. Questions raced through my mind: Didn’t the mere fact that I was interested in such a book mean it would never fulfill the promise of its title? Could a boy who’d rather talk about curved space-time than touchdown passes ever score himself? Was there really a bag of tricks?

The book emphasized that if a girl doesn’t know you very well—and that applied to every girl in my high school—you should not expect her to agree to a date, and you shouldn’t take the rejection personally. Instead, you should ignore the possibly enormous number of girls who turn you down and keep asking, because, even if the odds are low, the laws of mathematics say eventually your number will come up. Since mathematical laws are my kinds of laws, and I’ve always believed that persistence is a good life philosophy, I took the advice. I can’t say the results were statistically significant, but decades later, I was shocked to find that a group of French researchers essentially repeated the exercise the book had suggested. And they did it in a controlled scientific manner, achieving results that were statistically significant. Furthermore, to my surprise, they revealed a way I could have improved my chance of success.

***

French culture is known for many great attributes, some of which probably have nothing to do with food, wine, and romance. But regarding the latter, the French are thought to especially excel, and in the experiment in question, they literally made a science of it. The scene was a particularly sunny June day in a pedestrian zone in the city of Vannes, a medium-sized town on the Atlantic coast of Brittany, in the west of France. Over the course of that day, three young and handsome French men randomly approached 240 young women they spotted walking alone and propositioned each and every one of them. To each, they would utter exactly the same words: “Hello. My name’s Antoine. I just want to say that I think you’re really pretty. I have to go to work this afternoon but I wonder if you would give me your phone number. I’ll phone you later and we can have a drink together someplace.” If the woman refused, they’d say, “Too bad. It’s not my day. Have a nice afternoon.” And then they’d look for another young woman to approach. If the woman handed over her number, they’d tell her the proposition was all in the name of science, at which time, according to the scientists, most of the women laughed. The key to the experiment was this: with half the women they propositioned, the young men added a light one-second touch to the woman’s forearm. The other half received no touch.

The researchers were interested in whether the men would be more successful when they touched the women than when they didn’t. How important is touch as a social cue? Over the course of the day, the young men collected three dozen phone numbers. When they didn’t touch the women, they had a success rate of 10 percent; when they touched them, their success rate was 20 percent. That light one-second touch doubled their popularity. Why were the touched women twice as likely to agree to a date? Were they thinking, This Antoine is a good toucher—it’d probably be fun to knock down a bottle of Bordeaux with him some night at Bar de l’Océan? Probably not. But on the unconscious level, touch seems to impart a subliminal sense of caring and connection.

Unlike non­Euclidean geometry, touch research has many obvious applications. For example, in an experiment involving eight servers and several hundred restaurant diners, the servers were trained to touch randomly selected customers briefly on the arm toward the end of the meal while asking if “everything was all right.” The servers received an average tip of about 14.5 percent from those they didn’t touch, but 17.5 percent from those they did. Another study found the same effect on tipping at a bar. And in another restaurant study, about 60 percent of diners took the server’s suggestion to order the special after being touched lightly on the forearm, compared with only about 40 percent of those who were not touched. Touching has been found to increase the fraction of single women in a nightclub who will accept an invitation to dance, the number of people agreeing to sign a petition, the chances that a college student will risk embarrassment by volunteering to go to the blackboard in a statistics class, the proportion of busy passersby in a mall willing to take ten minutes to fill out a survey form, the percentage of shoppers in a supermarket who purchase food they had sampled, and the odds that a bystander who had just provided someone with directions will help him pick up a bunch of computer disks he drops.

You might be skeptical of this. After all, some people recoil when a stranger touches them. And it is possible that some of the subjects in the studies I quoted did recoil but that their reactions were outweighed by the reactions of those who reacted positively. Remember, though, these were all very subtle touches, not gropes. In fact, in studies in which the touched person was later debriefed about the experience, typically less than ­one-third of the subjects were even aware that they had been touched.

So are touchy-feely people more successful at getting things done? There is no data on whether bosses who dole out the occasional pat on the head run a smoother operation, but a 2010 study by a group of researchers in Berkeley found a case in which a habit of congratulatory slaps-to-the-skull really is associated with successful group interactions. The Berkeley researchers studied the sport of basketball, which both requires extensive second-by­second teamwork and is known for its elaborate language of touching. They found that the number of “fist bumps, high fives, chest bumps, leaping shoulder bumps, chest punches, head slaps, head grabs, low fives, high tens, half hugs, and team huddles” correlated significantly with the degree of cooperation among teammates, such as passing to those who are less closely defended, helping others escape defensive pressure by setting what are called “screens,” and otherwise displaying a reliance on a teammate at the expense of one’s own individual performance. The teams that touched the most cooperated the most, and won the most.

Touch seems to be such an important tool for enhancing social cooperation and affiliation that we have evolved a special physical route along which those subliminal feelings of social connection travel from skin to brain. That is, scientists have discovered a particular kind of nerve fiber in people’s skin—especially in the face and arms—that appears to have developed specifically to transmit the pleasantness of social touch. Those nerve fibers transmit their signal too slowly to be of much use in helping you do the things you normally associate with the sense of ­touch: determining what is touching you and telling you, with some precision, where you were touched. “They won’t help you distinguish a pear from pumice or your cheek from your chin,” says the social neuroscientist pioneer Ralph Adolphs. “But they are connected directly to areas of the brain such as the insular cortex, which is associated with emotion.”

To primatologists, the importance of touch is no surprise. Nonhuman primates touch each other extensively during grooming. And while grooming is ostensibly about hygiene, it would take only about ten minutes of grooming a day for an animal to stay clean. Instead, some species spend hours on it. Why? Remember those grooming cliques? In nonhuman primates, social grooming is important for maintaining social relationships. Touch is our most highly developed sense when we are born, and it remains a fundamental mode of communication throughout a baby’s first year and an important influence throughout a person’s life.