You hear social networks these days and what do you think of? You think of Facebook, you think of MySpace, you think of Twitter. But we are interested in the social networks that actually came before this internet revolution made us so aware of them. If you think about it, we've always had friends, we've always had family members. In fact, part of what makes us human is the fact that we live in these webs of humanity. Now, the remarkable thing is that when each of us makes all of these different choices about who we're going to connect to, what we get is we get an agglomeration that makes this beautiful structure that's complex and ubiquitous and has a form that is the same from one network to another network to another network. And this leads us to ask the question, how do these networks form? What is their purpose and how do they affect us? Well, we've come up with a number of different research findings that we've tried to simplify in our book. We shape our networks. And that's what this diagram displays. Each one of these lines, each one of these is a choice about who we bring into our network. But we're also interested not just in the way these networks are shaped but also in the way they affect us, in what flows through these networks. For the first time, now that we have data like this, we are able to get a bird's eye view of networks, like the networks that you live in, and we're able to see what happens to you and how that affects what happens to other people. And it's this kind of view of the human super organism that has really started to change the way we think about ourselves as human beings. We are connected. We are connected in ways that these other social species are, like schools of fish and flocks of birds. Every friend makes you healthier. Every friend makes you happier. And that's a point that we have said over and over again, but it gets lost sometimes whenever it's transmitted to other people. This cartoon actually gets it right. So this is Kathy, which is shocking that these individuals got it right, but they sat down and they feel a little anxious because they hear that weight gain is spreading from person to person. But their reaction is, when the waiter comes up, oh, she'll have a dry salad and a glass of water. And this conveys this idea that if you want to achieve healthier lifestyles, that you can't just do it alone, you have to get your friends and family involved. You have to acknowledge the fact that you're connected, and that this rule of the social network, this third rule of social networks, that friends affect us is critically important if we want to make a positive change in our life. Now, we've also shown that this is true for affective states, like happiness. And so you notice here what we have is we have a cluster of happy people, these yellow nodes in this network. And we also have a cluster of unhappy people, which appropriately are colored blue. And we've done this for now for loneliness and also for depression. And what this finding is showing us is that it's not just behaviors that are spreading through networks, it's also these emotional states that are spreading through networks. And what's really important is that what we found in the behavior studies is that your friend who lives hundreds of miles away has just as big an impact on you as your friend who lives next door. Now, that sounds a little puzzling, but if you think about the people who really consider your close friends, you might not only see them, but once a year, like maybe a Thanksgiving or Christmas. But if you find out that they've just started exercising, or if you look at them and they look really great because they've lost a few pounds, that can have a really big effect on how you see yourself. And so we think that what's spreading is not this tendency to eat dinner together. It's not this tendency to go down to the bar together or to go smoking together. It's this tendency to transmit ideas, these norms of behavior, so that when you make your life better, you're actually making the lives better of your friends and family as well. We also talk about things besides health in the book. We talk about financial contagions. It turns out when people were making this run on the bank in England, first time they'd seen a bank run in over 100 years, a lot of the people that were interviewed, they didn't get out of the bank because they thought the bank would fail. They got out of the bank because they thought everyone else thought the bank would fail. And this has important implications not just for Northern Rock, but for the meltdown that we've experienced over the last year or two in our own economy. The people who do trading and mall street are not immune to this. They're human beings as well, and they have to make money as well and preserve money as well, and you can get these kinds of contagions. Well, one thing we're finding in study after study after study is that your friends, friends, friends have an impact on you. They're going to impact whether you're not your obese, whether or not you smoke, whether or not you drink, whether or not you're happy, whether or not you're lonely, whether or not you're depressed. This is all information that we've gotten from the Framingham Heart Study. They're also going to impact whether or not you exhibit altruism. Cooperation can spread in these networks. If you do a KINDAC to one person, they'll do a KINDAC to another person, and it will also spread up to three degrees of separation and no further. But the real thing that we're interested in is this evolutionary purpose idea, this idea that human social networks are in our nature, that really we have evolved in groups of about 150 people over the last hundreds of thousands of years or so. And if that's the case, then we wouldn't have lived in groups where we were separated by anybody at more than three degrees of separation. So we've actually started to take this evolutionary argument seriously by doing twin studies to see whether or not heritability, whether or not genes can explain some of the variation in people's social network structure. And we find that it does. So, genes help to explain about half of the variation in the number of people who name you as a friend, about half of the variation in where you sit in the network in terms of whether or not you're central, like the life of the party, or whether or not you're peripheral, like a wallflower. But even more remarkably, it influences whether or not your friends are friends with each other, because some people have the tendency that they want to introduce their friends each other, and some people like George Costanza say no way I want to keep these people separate. And this suggests to us that there are some important lessons that we need to take online as a result of the fact that we have grown up over hundreds of thousands of years in these social networks. So just to give you an idea, this is a picture of a real network in a dorm room of 105 close friendships, and we can add some other natural relationships. We can add the ethnic clubs, memberships, we can add roommates, but now let's add Facebook. That's a very, very different reality. But what we're finding in our studies of Facebook is that actually all those Facebook friends don't make a difference. It's only your close social relationships that matter. So when we limit our studies to just people who upload pictures of one another, we get a map that looks like this. And what do we find? We find clusters of Smilers, people smile on the profile pictures, and we get clusters of non-smilers. People who don't smile are supposed to. And this is exactly what we find in framing him. We're also now looking at obesity online and trying to see whether or not it's possible, not just to see these influence effects online, but whether or not it's possible to intervene and to help us spread these interventions from one person to another. And so let me just wrap up by saying that social networks really influence lots of things. The influence, Broadway musicals have had more time, I would tell you about it. But they also really influence our ideas about ourselves. So here's someone who hears us say that you're affected by your friends friend, and how does he react to it? He's not going to try hard at all. And a lot of people when they hear us tell this story, these huge effect sizes for how your social network affects you, their reaction is, well, that's the end of free will. I might as well give up. But that's not the way I think about this. I personally have reacted to this new evidence by losing five pounds and keeping it off. And it's because I know that I'm not just changing my own outcome. I'm potentially changing my son's life and my son's friend's life and my son's friend's mother's life. When I come home at the end of the day, I put on my favorite song and I try to make myself a little bit happier for exactly the same reason. Because I'm not just taking care of myself. I'm taking care of all my friends and family and their friends and family. If you tell someone they don't influence anybody, they're not going to do anything. But if you tell them the influence of thousand people, they'll change their lives. And that's why I think it's so critical for us to understand first and foremost how and why we are connected. Thank you very much.