But why do you fall in love with one person rather than another?

This is what Match.com - the internet dating site - came and asked me almost five years ago. And since then - and at the time I said 'I don't know - psychologists know that we tend to fall in love with somebody from the same socio-economic background, same general level of intelligence, same general level of good looks, similar level of education and religious and social values. Your childhood plays a role, but nobody knows how. Timing plays a role. But you can walk into a room and everybody is from your background and same general level of intelligence and good looks, and you don't fall in love with all of them. So I began to think maybe basic body chemistry plays a role. Maybe we're naturally pulled toward some people rather than others. So I began to look through all the genetic data, the data on neuro-transmitters, the data on hormones, to see if there were some chemicals in the brain associated with personality traits that drove you toward some people rather than others.

Now there's a lot of chemicals in the brain, but most of them keep the eyes blinking or the heart beating etc. There are very few that are associated with personality traits. And those few are these four brain systems:

Norepinephrine Dopamine System

Serotonin System

Testosterone System

Estrogen and Oxytocin System

What I did was I created a questionnaire to see to what degree you expressed the traits associated with these four chemical systems. And then - 8 million people have taken the questionnaire. I watched in a group of 28,000 people who was naturally drawn to whom. So I'm going to go through the very broad personality styles - we're all a combination of all of them; these are brain systems, not cubby holes, but we do have personalities and we express some more than others. And then I want to talk about who's drawn to who and then how I feel this can be used in the business community.

The Dopamine, norepinephrine - I looked at 40,000 people. In this system - if you tend to be very expressive of these two chemical systems - I call them the Explorer - bad term, but it's the best I had at the time. They're novelty seeking, risk-taking, energetic, spontaneous, impulsive, optimistic, sexual, curious, they've got the most interest - highly creative - if you give someone el dopa for Parkinson's creativity tends to go up. Often very Liberal, open-minded. There's a downside to every personality type - they tend to be more manic, unpredictable, reckless and unreflective - these people look out, not in. I did a study of 178,000 people to see what words these people use - 'adventure' top word used by this high dopamine type. Spontaneity, energy, new, fun, traveling, passion, active, outgoing. I think Obama is a perfectly wonderful example of that - he even moves like a high dopamine person; a high dopamine person moves with a sense of style, which he does. And they also have quite a bit of facial expression, which he has. Highly optimistic man. There's a humor magazine in the United States called, The Onion. On the day he won the election it read 'Black Man Given Worst Job in the World.' And indeed he got it, and still has it.

Serotonin - I call them the builder; it's a bad term, had I read my Plato at the time I would have called them the 'Guardian'. These are the pillars of society. The genetics of the Serotonin system are associated with being conventional, traditional, cautious - they're not scared, but they're cautious, calm, social, very managerial - these are the middle-managers often of the world. Orderly, persistent, details - don't give them the big theory, they like the details. Loyal, conscientious, they respect authority, they like to follow the rules, they tend to be more religious, and they're very good with numbers. Bad side of them, they tend to be more stubborn, closed-minded, controlling etc. The top word these people use is family, morals, respect, loyal, trustworthy - used that one twice, and values. I think Gordon Brown - of course these people haven't taken my questionnaire, but by watching what they say and reading what the Economist and other magazines say about them. Ah, this is from the Economist, that he is a 'control freak', very detail-oriented, very much of a networking man, religious, frugal, PhD in History, I think that actually does say something about the details - these historians do like the details. I think Colin Powell is another very good example.

The third type is the high testosterone type - I called them the 'Director'. Plato called them The Rational. That's a better term for it. In a study of 40,000 people - analytical, logical, strategic - very strategic, direct, decisive, tough-minded, very good at what scientists call rule-based systems, everything from math, computers, engineering, music, skeptical, rank-oriented. You inject testosterone in a monkey and it will fight for rank. Emotionally contained. These are the people at Davos who don't move their face - they'll move their mouth, but none of the face. And their fingers of course with the Blackberry. Highly self-disciplined and emotionally contained. Poorer verbal skills and poorer people skills. Tend to be aloof and more aggressive. The words they use - intelligence, debate, geek, nerd, ambitious, driven, politics, challenge - they gotta have it be real. They're the lease religious of the group. Sarkozy - I'm sorry there are some people in the audience who know him much better than I do - direct, blunt, tough-minded, and I think - of course we're a combination of all of them, very much the explorer too. And it was very interesting after the G20 met in London, he called Obama weak. And um, the Director hits you in the face, the Explorer stabs you in the back and is much more nuanced. I think these two men come from very different biological styles and simply didn't understand each other. Hilary Clinton I think is a very good example of a woman who is high testosterone type. I don't know if you watched CNN recently, but when she was in Haiti, not only did she - she showed almost no facial expression while she was uh, with bodies all around her - very much the high testosterone type - the Chinese were astonished by how blunt she was.

Fourth type - Estrogen and Oxytocin. These people see the big picture. Imaginative, fine linguistic skills, very fine people skills, intuitive, it's called theory of mind, trusting, nurturing, emotionally-expressive, egalitarian, idealistic. Downside of it is indecisive - these people live in a world of 'it depends'. 'It depends, we could do this, we could do that, it depends.' They see all these possibilities. More unforgiving, gullible, effusive, etc. The top word they use is passion in this study of 178,000. Real, heart, kind, sensitive. These are the big readers of the world. Sweet, random, other three types are not big on random and it's one of their top 10 words. And empathy. And I think Bill Clinton is a very good example. Language skills - the whole world knows he can't stop talking. Real people skills. I'm glad our government sent him into North Korea to get those girls out and not his wife. Very emotionally expressive. Cried when Hilary gave her speech at the Democratic convention. And I don't know about the rest of the world, but in America he is well known for the statement 'I feel your pain'. Probably does have more mirror neurons in his mind and probably does feel some of your pain. And he's a high on testosterone. You can be high on testosterone and estrogen. High on one, high on the other. I think Charles Darwin was another supremely fine negotiator. Synthesized all of um science at the time. And I think that Klaus Schwab is the world's finest negotiator today - sees the enormous picture and all of the relationships and has tremendous compassion for humankind on Earth.

So you take my questionnaire and you're given a pie chart - we're all a combination of all of them of course. And then I was able to study a lot of other things about many of the habits of all of these people. But Match.com wanted to know - they didn't really care who you were - they were interested in why you fall in love with one person rather than another. So I watched and 28,000 people who's drawn to whom.

Female explorer goes for the Male Explorer.

Male explorer goes for the Female Explorer

Female Builder - traditional type - wants Traditional.

Male Builder - traditional - wants Traditional.

In these two cases, similarity attracts.

Female Director - Hilary Clinton - goes for the Male Negotiator, the opposite.

Male Director goes for the Female Negotiator, their opposite.

Female Negotiator goes for the Male Director.

And the Male Negotiator for the Female Director.

That's Bill Clinton and Hillary.

In this case, opposites attract.