Chapter 1- A group can be defined by an attribute (for example: women, democrats, lawyers) or as a specific collection of individuals to whom we can literally point (“those people, right over there) - A social network, like a group, is a collection of people, it includes something more: a specific set of connections between people in the group. These ties, and the particular pattern of these ties, are often more important than the individual people themselves.- A social network is an organized set of people that consists of two kinds of elements: human beings and the connections between them. - Real, everyday social networks evolve organically from the natural tendency of each person to seek out and make many or few friends, to have large or small families, to work in personable or anonymous workplaces. - A network’s shape, also known as its structure or topology, is a basic property of the network.- When a group is constituted as a network, there is a particular pattern of ties that connects thepeople involved, the topology.- There are two fundamental aspects of social networks, whether they’re simple or complex: 1)connection – which has to do with who is connected to whom 2) contagion – which pertains to what, if anything, flows across the ties- Understanding why social networks exist and how they work requires that we understand certain rules regarding connection and contagion – the structure and function – of social networks.Rule 1: We shape our network- Humans deliberately make and remake their social networks all the time (ex: homophily – the conscious or unconscious tendency to associate with people who resemble us)- We choose he structure of our networks in three important ways: 1) we decide how many people we are connected to 2) we influence how densely interconnected our friends and family are 3) we control how central we are to the social network - If you know Alexi, and Alexi knows Lucas, and Lucas knows you, this relationship is transitive – the three people involved form a triangle  Those with high transitivity are usually deeply embedded within a single group, while those with low transitivity tend to make contact with people from several different groupswho do not know one another, making them more likely to act as a bridge between different groups.Rule 2: Our Network Shapes Us- Our place in the network affects us in turn- Whether your friends and other social contacts are friends with one another is crucial to your experience of life Transitivity can affect everything from whether you find a sexual partner to whether you commit suicide - How many contacts your friends and family have is also relevant  When the people you are connected to become better connected, it reduces the number of hops you have to take from person to person to reach everyone else in the network (You become more central)- Being more central makes you more susceptible to whatever is flowing within the network Rule 3: Our friends Affect Us- What actually flows across the connections is crucial, in addition the shape.- One fundamental determinant of flow is the tendency of human beings to influence and copy one another.- The simple tendency for one person to influence another has tremendous consequences whenwe look beyond our immediate connectionsRule 4: Our Friends’ Friends’ Friends Affect Us- People copy their friends’ friends, and their friends’ friends’ friends.- Hyperdyadic spread, or the tendency of effects to spread from person to person to person, beyond an individual’s direct social ties. - To observe hyperdyadic spread: 1) observe entire network 2) Get information about the ties and the people they connect at more than one time, otherwise we have no hope of understanding the dynamic properties of the network Rule 5: The Network Has a Life of Its Own- Social networks can have properties and functions that are neither controlled nor even perceived by the people within them - These properties can be understood only by studying the whole group and its structure, not by studying isolated individuals (culture, traffic jams).- An excitable medium is one that flips from one state to another depending on what others around it are doing.- Social networks have emergent properties: new attributes of a whole that arise from interaction and interconnection of the partsSix degrees of Separation and Three Degrees of influence- People are all connected to one another by an average of “six degrees of separation” – Milgram- Intrinsic-decay explanation – our affect dies off after three degrees of influence- Network-instability explanation – links beyond three degrees are unstable (people die, divorce happens)- Evolutionary-purpose explanation – (evolutionary biology) – humans appear to have to have evolved in small groups in which everyone would have been connected to everyone else by three degrees or less In our hominid past, there was no one who was four degrees removed from us- No matter the reasons, the Three Degrees Rule appears to be an important part of the way human social networks function, and it may continue to constrain our ability to connect, eventhough technology give us access to many more people - Connection and contagion are the structure and function of social networksConnected- Social networks have value precisely because they can help us to achieve what we could not achieve on our own- Social networks can dramatically reinforce two different kinds of inequality in our society: 1)situational inequality – some are better off socioeconomically 2) positional inequality – someare better off in terms of where they are located in the network - Social networks provides a distinct way of seeing the world b/c it is about individuals and groups, and about how the former actually become the latterChapter 2Our Ancestors Had Feelings- The development of emotions in humans, the display of emotions, and the ability to read the emotions of others helped coordinate group activity by three means: facilitating interpersonalbonds, synchronizing behavior, and communicating information. - Emotional contagion fosters interaction synchronyEmotional Contagion- Emotions spread form person to person b/c 2 features of human interaction: we are biologically hardwired to mimic others outwardly, and in mimicking their outwardly displays, we come to adopt their inward states- Prosopagnosia – losing the ability to read facial expressions - People imitate