Connected Preface Nicholas Christakis James Fowler fundamental rules that govern both the formation and operation of social networks Chapter 1 In the Thick of It epidemics of violence a single murder can set off a cascade of killings 75 of all homicides involve people who knew each other often intimately prior to the murder social networks also include those who might save your life Bucket Brigades and Telephone Trees the whole is greater than the sum of its parts can increase the effectiveness of human beings simply by arranging them differently particular configurations group can be defined by an attribute ex women Republicans lawyers or as a specific collection of individuals to whom we can literally point ex those social network collection of people that includes a specific set of connections between those in the group people right over there Types of Networks Unconnected group no ties present Bucket Brigade every person except first and last is connected to two other people by a mutual tie Telephone Tree everyone except first and last is connected to three other people there are no mutual ties cid 127 Military Squads every member knows every other member very well connections are all two way network community a group of people who are much more connected to one another than they are to the other groups of connected people found in other contagion deals with what if anything flows across the ties ex germs money violence fashion happiness obesity parts of the network shape a network s structure or topology Rules of Life in the Network 2 fundamental aspects of social networks connection deals with who is connected to whom 5 rules 1 We shape our network how many people we re connected to how densely interconnected our friends and family are how central we are to the social network 2 Our networks shape us 3 Our friends affect us 4 Our friends friends friends affect us cid 127 Milgram s famous sidewalk experiment 5 The network has a life of its own La Ola the wave hyperdyadic spread the tendency of effects to spread from person to person to person beyond an individual s direct social ties decisions of a passerby to copy a behavior were influenced by the size of the crowd exhibiting it not orchestrated by someone with a megaphone has a life of its own flocks of birds and schools of fish emergent properties new attributes of a whole that arise from the interaction and interconnection of the parts Six Degrees of Separation and Three Degrees of Influence people are all connected to one another by an average of six degrees of separation your friend is one degree from you your friend s friend is two degrees and so on cid 127 Milgram experiment involved giving a few hundred people who lived in Nebraska a letter addressed to a businessman in Boston more than a thousand miles away they were asked to send the letter to someone they knew personally goal was to get it to someone they thought would be more likely than they to have a personal relationship with the Boston buisnessman number of hops from person to person that the letter took to reach the target was tracked on average 6 hops were required three degrees of influence rule everything we do or say tends to ripple through our network having an impact on our friends one degree our friends friends two degrees and even our friends friends friends three degrees three possible reasons our influence is limited intrinsic decay explanation by the time information reaches four degrees it may no longer be accurate or reliable network instability explanation evolutionary purpose explanation we may not have stable ties to people at four degrees of separation given the constant turnover in ties all along the way cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 we may not be able to influence people four degrees removed from us because in our hominid past there was no one who was four degrees removed from us Chapter 2 When You Smile the World Smiles with You Tanzania 1962 epidemic of laughter at a girl s boarding school cid 127 Our Ancestors Had Feelings emotions consist of several elements we have a conscious awareness of our emotions we know when we re happy they affect our physical state show how we feel on our faces they re associated with specific neurophysiological activity they re associated with visible behaviors laughing crying for our ancestors the spread of emotions probably served an adaptive purpose Emotional Contagion affective afference cid 127 mirror neuron system Emotional Stampedes An Unbearable Sweetness Tracking the Spread of Emotions The Spread of Happiness 10 more likely at two degrees 6 more likely at three degrees Life on the Hedonic Treadmill emotions spread from person to person because of two features of human interaction we are biologically hardwired to mimic others outwardly and in mimicking their outward displays we come to adopt their inward states ex if your friend feels happy she smiles you smile and in the act of smiling you also come to feel happy cid 127 mass psychogenic illness MPI when emotions spread from person to person and affect large numbers of people outbreaks of epidemic hysteria are not restricted to children and school they have been documented in adults too experience sampling method uses a series of alerts at unexpected times to prompt subjects to document their feelings thoughts and actions while they are experiencing them a person is 15 more likely to be happy if directly connected to a happy person one degree each happy friend a person has increases the person s probability of being happy by about 9 and each unhappy person decreases it by 7 we appear to have a set point for personal happiness that is not easy to change personal happiness appears to be strongly influenced by our genes estimated that long term happiness depends 50 on a person s genetic set point 10 on their circumstances and 40 on what they choose to think and our friends happiness has an affect on us but it only lasts for about a year we get used to our friends being happy do Alone in the Crowd loneliness is the feeling of being disconnected each extra friend reduces by about two days the number of