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  • Hi, my name is Nicholas Christakis and I'm a physician and a social scientist and the

  • discipline I'm going to be speaking about to you today is sociology.  Sociology is

  • the field in which you study human behavior and human experience and how it relates to

  • the fact that individuals are embedded within larger groups and collections of individuals.

  •  When you see an individual as a member of a group or the collectivity you get a completely

  • different perspective on that person and on the groups of which they are a member and

  • in fact, in sociology we explore a fundamental tension and that tension arises because of

  • two facts.  On the one hand you yourself have your own identity and your own agency

  • and your own ability to make choices that affect your life, but on the other hand there

  • is a collective responsibility for your life as well and it turns out that collective supra-individual

  • factors can have as much to do with all kinds of aspects of your life, including whether

  • you live or die as your own genes or your own choices and it turns out that supra-individual

  • collective factors can have as much to do with what happens to you in your life and

  • even with whether you live or die as things within you, your own genes or your own choices.

Now

  • supra-individual factors such as where you live, what kind of networks you are a part

  • of, social interactions you are a part of, what kind of institutions are nearby, for

  • instance governments or hospitals, all of these are critical in shaping your life and

  • all of our lives and these supra-individual factors can include things like inequality,

  • culture and religion as well.

Supra-individual factors like where you live or where you are

  • located in these vast face-to-face networks that we human beings assemble or what kinds

  • of formal institutions are near you like governments or hospitals for example can have as much

  • to do with what happens to you in your life as your own decisions and your own actions.

  •  Other sorts of things are important too, like inequality or culture or religion and

  • those sorts of supra-individual factors have a similar importance.

This is the difference

  • between what we want to understand as structure and agency between social constraints and

  • opportunities on the one hand and individual choices and actions on the other hand and

  • a second key idea beyond that first one-
This the difference between structure and agency,

  • between collective constraints and opportunities that constrain and permit you to do certain

  • kinds of things in your life on the one hand and your own individual choices and actions

  • that permit you to do other sorts of things on the other hand.  That is the first big

  • idea that I’d like to communicate today.  

The second big idea that sociology

  • explores and that I would like to communicate today is that collective phenomena are not

  • mere aggregations of individual phenomena.  There is something different, something

  • special about groups of people, about collectivities that does not reside within the individuals

  • themselves, something that emerges, something that transcends, something that is above and

  • not a part of solely individual kinds of things that you might think of.  

A second

  • key idea in sociology is that collective phenomena are not mere aggregations of individual phenomena.

  •  There is something special, something weird almost about groups of individuals, about

  • collectivities, something weird that you cannot see if you just study individuals, but that

  • you must study whole groups of people in order to really understand.

So how did I become interested in these crazy ideas?  Actually

  • I started my career as a physician and I went to medical school and at the time I wanted

  • to be a reconstructive surgeon and I wanted to operate on people who had cranial facial

  • abnormalities or people whose extremities had been cut off and reattach these extremities

  • and I used to cut class my first year of medical school and go operate with some of the surgeons

  • at Children’s Hospital in Boston and I did this for quite awhile and eventually as we

  • would operate on these kids they were primarily kids, one after another, day after day, I

  • came to the realization that the kind of healthcare that I wanted to practice was not the kind

  • that took care of people one at a time, but rather, the kind that tried to take care of

  • whole populations of people.  I mean I wanted to understand why do groups of people become

  • sick, not just why do individuals become sick and how can we make groups become well, not

  • just individuals become well one at a time and part of this was prompted by my realization

  • that I was running around putting my fingers in the dike.  One hole after another was

  • springing water and we were running around, all of us, trying to plug these holes and

  • I was interested in how can we make a better dike, how can make a situation in which fewer

  • people become sick to begin with, in which we spring fewer holes to begin with, in the

  • dike as it were and in fact I began to ask what I came eventually to see as sociological

  • questions about the origins of illness and disease and suffering and death in our society

  • and I wanted to understand how we could have a sociological response, a collective response

  • to these sorts of problems and in fact this dovetails to some extent with an interest

  • in public health, which can be contrasted with a kind of interest in clinical medicine

  • which takes care of patients one at

  • a time.  

  • So let’s start by taking a look at a personal testament, a very seemingly individualistic

  • statement that a human being is making about their own life, about what would seem to be

  • a quintessentially private individualistic decision, namely whether to take your own

  • life and to commit suicide.  This is Charlotte Perkin Gilman’s suicide note.  She was

  • 75 years-old when she took her life and the note says:  “The time is approaching when

  • we shall consider it abhorrent to our civilization to allow a human being to die in prolonged

  • agony which we should mercifully end in any other creature.  Believing this choice to

  • be of social service in promoting wiser views on this question, I have preferred chloroform

  • to cancer.” 

And the note said:  The time is approaching when we shall consider

  • it abhorrent to our civilization to allow a human being to die in prolonged agony which

  • we should mercifully end in any other creature.  Believing this choice to be a social service

  • in promoting wiser views on this question, I have preferred chloroform to cancer.”

  •  

So despite the fact that this woman is taking her life and despite the fact that

  • she is writing a suicide note notice that the note contains or eludes to kind of connections

  • to others even as she was ending her own life.  She bemoans the fact that society is not

  • sensitive to her pain and even while dying she is trying to make a contribution to society.

  •  She is trying to be connected to other individuals.  

Here is another note:  “Dear God,

  • please have mercy on my soul.  Please forgive me.  I can’t stand the pain anymore.”

  •  And that note was written by a 76 year-old grandmother who isolated by depression and

  • disability crawled into her basement freezer to kill herself by the cold and you might

  • ask what kind of a social system permits this to happen, permits one of its members to be

  • so alone, to feel so isolated that this is the choice that they would make and in fact

  • you might ask was this suicide truly an individual act, was it really purely an individual choice. 

Another

  • one, Ron Berst jumped off the Golden Gate Bridge and in his will he donated $10,000

  • to AIDS research.  This is his note:  “To the San Francisco Police Department or equivalent

  • jurisdiction.  This is to state that I, Ron R. Burst did take my own life due to the fact

  • that I have the disease AIDS and it has progressed both rapidly and to the point where number,

  • I constantly feel ill and have almost no energy and number two, I very soon expect to become

  • a burden to my friends and family and I do not want to put any of them through such an

  • ordeal.  I sincerely regret any inconvenience that this may have caused anyone involved.

  •  I honestly believe that a fast end such as this while one is still able, yet ill enough

  • to justify it is easier on my close friends who have been so unbelievably supportive emotionally

  • for me and my family who have been no less so than to drag this out.  I did not give

  • up.”

So again in Mr. Berst’s note notice the social concern.  His death is

  • not an individual act at all.  First of all, it was public.  He jumped off the Golden

  • Gate Bridge.  People saw him.  Second, it was guided by a concern for others.  He is

  • worried about his friends and family and third, it is infused with the social ties that connect

  • him to his family and his friends.  

Now there is another way that suicide is social

  • as well.  It is not just the connection the individual has to others.  It is the responsibility

  • that others have to the individual.  It is about how social and structural factors constrain

  • or permit individual acts even like suicide.  For example, this is an image of the Golden

  • Gate Bridge from which Ron Berst jumped and this bridge is unusual in its design because

  • the sidewalk as you can see is directly next to the edge of the image.  He walked along

  • the sidewalk and then just jumped over that railing, stood there and jumped right over.

And

  • this is a picture of Kevin Hines who almost met the same fate as Mr. Berst.  In September

  • of 2000 at the age of 19 suffering from depression he went to the Golden Gate Bridge and he stood

  • there for 40 minutes crying.  No one approached him to ask what was wrong and then eventually

  • a tourist came up and asked him if he could take her photograph.  Hines interpreted this

  • as a clear sign that no one cared.  He took the picture and then when she walked away

  • he turned around and he jumped right over the railing, but instantly he says he realized

  • that he had made a mistake.  He changed his mind.  “Oh shit,” he thought, “I don’t

  • want to die.”  “What am I going to do?” he later recalled.  In midair he came up

  • with a plan to save his life as he described as follows:  “It was simply this.  “A;

  • God save me, B; throw your head back and C; hit feet first.”  And it takes four seconds

  • to drop the 220 feet from the height of the Golden Gate Bridge to the water and you eventually

  • reach a speed of 75 miles per hour and among the over 1,200 people who have jumped off

  • the bridge since 1937 only 26 are believed to have survived and interestingly a large

  • percentage of those who attempt the jump when they are interviewed afterwards say that they

  • regretted the decision as soon as they jumped.  

For example, another jumper, Kevin

  • Baldwin was 28 and also severely depressed in August of 1985 when he jumped and he later

  • said the following thing:  “I still see my hands coming off the railing.  I instantly

  • realized that everything in my life that I thought was unfixable was totally fixable

  • except for having just jumped.”

It is 220 feet from the deck of the bridge to

  • the water and it takes just four seconds to reach the bottom and by which point you are

  • traveling at 75 miles per hour.

Even allowing for the fact that we cannot know

  • what all the successful suicides would have said had we been able to interview them these

  • kinds of reports by people who jumped and survived beg the question of how to prevent

  • these kinds of supposedly purely individual acts.  What would happen to these people

  • if somehow society could have prevented them from jumping, if there somehow had been a

  • structure in place which had constrained the agency of these individuals?  One landmark

  • study conducted in 1978 of 515 people who were removed from the Golden Gate Bridge before

  • they had jumped and followed them for an average of about 26 years afterwards found that 94%

  • were still alive or had died of natural causes many years later, so suicidal behavior is

  • acute and crisis driven and if the individual is prevented from acting on their suicidal

  • impulses by those around him it might not be repeated.

There are quite a number of remarkable things about

  • such stories.  No doubt these individuals and their illnesses are central actors in

  • the experience of the individual, but I want to highlight two other observations.  One

  • is the role of the perceived indifference expressed by the person that Kevin encountered.

  •  This point points to an important theme in sociology, the rule of social connection

  • in our personal experience and the role of our embededness in the lives of others.  So

  • one thing I would like to highlight is the perceived indifference on the part of the

  • person that approached Kevin.  One thing that I would like to highlight is the perceived

  • indifference on the part of the person, the tourist that approached Kevin because this

  • highlights an important theme or an important idea in sociology, namely the idea that we

  • are all connected to each other.  The role of connection in our experience of the world

  • and the role of our embededness in others is in fact a key consideration or a key point

  • that sociologists are interested in.  

The other important thing to realize from these

  • stories is the importance of extra individual factors that help determine individual outcomes

  • as I alluded to the role of structure versus the role of agency.  Now the Golden Gate

  • Bridge has a foot path adjacent to the railing unlike most bridges and people still regularly

  • kill themselves from it and if you look at the Golden Gate Bridge you can see some ideas

  • about how we might constrain individual agency, how we might as a society respond to prevent

  • people from jumping.  For example, suicide barriers such as this one at other sites have

  • drastically reduced and often even eliminated suicides such as at the Eifel Tower, the Empire

  • State Building or the Sydney Harbor Bridge, but a barrier has not been put at the Golden

  • Gate Bridge for reasons that many, myself included find a bit silly.  Namely, that

  • it would somehow ruin the aesthetics of the bridge, but here is an artist rendering of

  • one possible solutions and it doesn’t look so bad.  This argument it turns out has been

  • around for years, but finally in February of 2010 the Golden Gate Bridge Board after

  • many years of lobbying agreed to put some suicide nets under the bridge to catch jumpers,

  • but they did not agree to assign the use of any toll revenue for this purpose, so still

  • there is nothing there to prevent suicide.

So this is a particularly specific and dramatic

  • illustration of the interplay between structure and agency, between policy decisions made

  • at the collective level and the ability of an individual even to stay alive.  Moreover,

  • this is a particularly powerful illustration not only of the issue of structure versus

  • agency, but also of more complicated ideas, namely, the issue of group level phenomena

  • or of emergence which is the second big idea I would like to talk to you about today.

Now

  • suicide has been used as an example to illustrate this idea ever since 1897 by a very famous

  • sociologist by the name of Emile Durkheim who wrote about this topic and Durkheim had

  • a number of arguments including the following.  He said or he wroteso Durkheim had a

  • number of arguments about suicide including the following.  He wrote:  “The individual

  • is dominated by a moral reality greater than himself, namely, collective reality.  When

  • each people is seen to have its own suicide rate more constant than that of general mortality,

  • that its growth is in accordance with a coefficient of acceleration characteristic of each society,

  • when it appears that the variations through which it passes at different times reflect

  • the rhythm of social life and that marriage, divorce, the family, religious society, the

  • army, etcetera affect it in accordance with definite laws then these states and institutions

  • will no longer be regarded simply as characterless, ineffective ideological arrangements.  Rather

  • they will felt to be real, living, active forces which because of the way they determine

  • the individual prove their independence of him, which if the individual enters as an

  • element in the combination whence these forces ensue at least control him once they are formed.”

So

  • the individuals come and go in Durkheim’s analysis.  People come and go, but the rates

  • of suicide stay the same, so he was looking at suicide rates in different religious groups

  • in different periods in France and he found that these rates are constant across time

  • and vary across religious groups even though the individual members of those groups in

  • those particular times changed dramatically, so the Protestants in 1800 France are completely

  • different than the human beings who are the Protestants in 1850 France and yet the suicide

  • rate let’s say is the same.  Hence this constancy of rates and this variation across

  • societies is indicative of something else going on beyond individual choice or brain

  • biology.  It is as if the society determines thisit is as if the society determines

  • this seemingly purely individual act, suicide.  Hence this constancy of rates and this variation

  • across societies is indicative of something else going on beyond individual choice or

  • individual biology.  It is as if society determines this seemingly purely individual

  • act, this seemingly purely individual choice.  So you see groups can have properties of

  • their own and the individuals within them are affected by those properties.

  • Sociologist have been studying social networks beginning with the pioneering work of Georg

  • Simmel in the 1890s and they have been doing this, studying networks for well over 100

  • years and social networks are one particular kind of supra-individual factor that can affect

  • individual choices, that can shape your destiny and shape what happens to you in your life.

  •  Now by social networks I don’t mean Facebook or MySpace of the kinds of recent networks

  • that many of you might be thinking about.  I actually mean the kind of face-to-face

  • networks that human beings have been making for tens of thousands of years.  In fact,

  • ever since we lived on the African Savannah. 

Now each of us forms or inherits certain kinds

  • of connections to friends, to coworkers, to our relatives, to our neighbors and each of

  • those individuals in turn also has friends and coworkers and relatives and neighbors

  • and as a result of this we form this incredibly ornate, almost baroque structure known as

  • social networks and we precede to live out our lives embedded within these networks.

Now

  • what is the difference between a group and a network?  Here is a picture of a group

  • and a group maybe of 100 people.  Each dot represents a person, but a network in addition

  • to the 100 people also has ties, the ties that connect the people to each other and

  • it has specific ties at that and there are two kinds of networks, artificial networks

  • and natural networks.  So for example, here is an example of one of the simplest type

  • of artificial networks you can imagine, a bucket brigade.  It is

  • a simple linear network.  It has 100 people to which we have added 99 ties.  

Everyone

  • is connected to the guy on the right and to the guy on the left and assembling the people

  • in this fashion gives this group of people properties it didn’t have before like the

  • ability to efficiently transport debris or the ability to put out a fire.  If these

  • people weren’t assembled in the network in this fashion, this linear network they

  • couldn’t do it as well as they otherwise might or you could take the same 100 people

  • and the same number of ties and organize them in the form of a telephone tree.  This was

  • an old fashioned technology to efficiently transmit information before we had the internet,

  • so the person in the middle indicated by the arrow he would have a list of two people that

  • he was supposed to call let’s say to notify everyone about the closure of a school because

  • of a snow day or something.  He would call two people.  Each of those people would call

  • two people and the information about the school closure would rapidly and efficiently and

  • accurately be transmitted throughout this group.

So you take the same number of

  • people, the same number of ties.  You have a different kind of organization like in this

  • form and now this group of people has totally different properties than the bucket brigade.

  •  

A bucket brigade is an arrangement in which you line people up and you have a

  • bucket that moves from one end to the other.  People pass the bucket along and this can

  • be done either to transport water for example to put out a fire.  This was an old fashioned

  • technology that people used or it can also be used to transport debris.  If you want

  • to transport debris a great distance instead of having people running haphazardly transporting

  • buckets one at a time you can have a series of buckets that are run to the front and the

  • full buckets are moved to the rear of the line.

Or we could take the same number

  • of people, 100 people, but now a different number of ties and assemble them into a completely

  • different organization, for example, into military companies.  Here we have 100 men

  • and women composed into 10 squads of 10 people and within each squad everyone knows each

  • other very well.  There is a dense interconnection of ties and this kind of organization, this

  • kind of structural organization is able to elicit from these individuals something that

  • wasn’t present there before, namely, a willingness to die for each other, so this structural

  • form of organizing people is able to call forth from the individual people or foster

  • the emergence of new properties that weren’t necessarily there before.

But real social

  • networks differ and don’t look anything like or naturalbut natural social networks

  • look nothing like the artificial networks we just saw.  They look more like this network.

  •  Here is a slide in fact of such a natural network illustrating one of our own studies

  • and this image was one that we made in order to help understand the role of social networks

  • in the obesity epidemic.  

This image helped us to understand the role of social

  • networks in obesity.  Beginning a few years ago, maybe 10 or 20 years ago it had become

  • fashionable to speak about the obesity epidemic and it was clear that obesity was epidemic

  • in one meaning of the word, meaning that there is more of it than there was before.  For

  • example, just in the last 10 years the prevalence of obesity has gone from about 20% to about

  • 30% and fully two-thirds of Americans are now overweight or obese, so something is going

  • on that has given rise to an increasing amount of obesity and there are a number of structural

  • factors that have been suggested as causing the obesity epidemic because we don’t really

  • believe that there is something biological going on here even though the individual’s

  • biology can explain variation between people and how big they are our biology hasn’t

  • changed that much over the last 30 years.  So something social, something else must

  • be going on to help explain why obesity has been rising so much and people have offered

  • a number of structural explanations.  Maybe there is a declining real price of food.  Food

  • is cheaper than it used to be, so by basic economics youre going to buy more of it.

  •  Maybe it is the marketing of food, the way food is marketed to us or the fat composition

  • of food or there have been other sorts of changes that affect how many calories we use

  • up every day in the course of our lives.  We have more sedentary lifestyles.  There has

  • been a change in occupations.  We have a more service oriented economy than a labor

  • oriented economy.  There is a changing pace of life in our society.  The design of our

  • cities, urban design and suburban design, people don’t move around as much anymore

  • and people had offered all of these kinds of explanations for the obesity epidemic,

  • but we wondered whether we could add an explanation, whether we could understand obesity as being

  • truly epidemic, as if something were spreading from person to person.  It wasn’t just

  • a metaphoric epidemic.  It was a literal epidemic.  

Could we find evidence for

  • a kind of social contagion whereby weight gain in one person could affect weight gain

  • in other people to whom they were connected and in fact like the collective rates of suicide

  • we can understand obesity as being a collective phenomenon as well and we live environmentand

  • in fact we began to think about obesity in a sociological way.  Could we think about

  • obesity and the epidemic of obesity as being somehow related to the suicide example I was

  • discussing earlier where something collective seems to be determining individual’s likelihood

  • of killing themselves?  Could something collective be contributing to individuals changing their

  • body size?  

So we needed a special kind of data to do this and this image shows

  • 2,200 people drawn from the very famous Framingham Heart Study in the year 2000.  Once again

  • every dot is a person and every line between them represents a relationship between the

  • two people and here we make bigger dots are bigger people and in addition we color the

  • dots yellow if people are properly obese.  There are 2,200 people shown on this image

  • and these people were taken from the very famous Framingham Heart Study and this image

  • shows them in the year 2000 and if you look at this image you can see clustering of obese

  • and non obese individuals within the image.  It is still a very complicated image, but

  • if you study it mathematically you can find evidence of these clusters, clusters of yellow

  • and red dots, so that people’s body size seems to be related to the body size of other

  • people to whom they are connected and we were able to analyze these data and discern evidence

  • for the clustering and interpersonal influence such that if people around you gained or lost

  • weight it affected you as well and it seemed to spread from person to person and from person

  • to person to person and even from person to person to person to person, so that weight

  • gain seemed toand weight loss seemed to spread within the network and one uses various

  • kinds of statistical methods to analyze such data ranging from all kinds of statistical

  • models to social network analysis to actual experiments that one can do.

All right,

  • now in the process of studying the obesity epidemic we did something else as well because

  • we also made movies about how social networks change across time and our initial motivation

  • was to see if we could literally visualize the spread of obesity from person to person

  • to person to person within the network.  Now getting the data and getting the data into

  • shape and analyzing it statistically and making this movie took five years of my colleague

  • James Fowler and my life and cost about a million dollars, so this little video I'm

  • about to show you is a 30 second animation of a real social network, real data that took

  • that long and that much money to make and my children joke that actually on a per-second

  • basis it was more expensive than Avatar, but much less interesting, but the reason we made

  • this image was that we had in our minds the following kind of metaphor.  

Many of

  • you may have done an experiment in high school in which you took a water table and your dropped

  • a pebble on the water and then you had these waves that emerged from where the pebble hit

  • the water and these waves would hit the perimeter of the table and bounce back and if you did

  • it just right you would get a standing wave on the surface of the water and if you didn’t

  • do that experiment you probably had another experience as a kid which was sloshing around

  • in your bathtub and probably remember that if you sloshed just right in your bathtub

  • you can get your body into sync with a wave and get a big wave that will come out of the

  • bathtub and splash onto the floor and make a big mess and that is a kind of a standing

  • wave as well and what we thought we might be able to do was to see waves of obesity

  • within the social networkand what we thought we would be able to do would be to see waves

  • of obesity within the social network because you can imagine networks as a kind of socio-topological

  • surface, a kind of hyper dimensional surface and that it might be possible to see waves

  • within this network so that as I gain weight it makes my friends gain weight and as my

  • friends gain weight it makes their friends gain weight and you literally could get a

  • wave within the surface.

So this little video animation I'm about to show you was

  • both the most exciting and the most depressing moment of my scientific career.  Okay, again,

  • so every dot is a person.  Every line between them is a relationship.  Again we make the

  • dot size proportional to people’s body mass index, so bigger dots are bigger people and

  • we color the dots yellow if they are properly obese, if their BMI is above 30.  The red

  • perimeter dots are woman and the blue perimeter dots are men, but you can ignore that for

  • now and on this image we only show two kinds of relationships.  The gray lines indicate

  • spousal connections and the purple lines indicate friendship connections, so two people connected

  • by a line who have the same body size it’s not because are brother and sister or father

  • and child and they share genes in common.  These are purely volitional social relationships

  • and so in a minute were going to takeput this network into motion.  Were going

  • to take daily cuts through the network for 32 years, every single day, evaluating the

  • structure and status of the network and what youre going to see across time is youre

  • going to see people be born and die.  Image nodes are going to appear and disappear.  Youre

  • going to see relationships form and break.  Youre going to see marriages and divorces,

  • friendings and de-friendings, the real old fashioned kind of de-friending, not the Facebook

  • kind of de-friending and youre going to see people, dots get bigger and smaller as

  • people gain and lose weight.  Mostly youre going to see the dots getting bigger and youre

  • going to see a sea of yellow because this period of time from 1971 to 2003 includes

  • the period of the obesity epidemic and when you look at this image I want you to tell

  • me or I want you toand when you look at this image I want you to think about, as we

  • were thinking about, could we see a wave, evidence of spread in the image.

So here

  • you go.  

Okay, so as you see this image we begin in 1971.  Youre going to see

  • the network evolve across time.  Youre going to see lots of relationships form.  The

  • epidemic is going to begin to peak in the sort of late 1980s, 1990s.  Youre going

  • to see more and more people become yellow.  Youre going to see people move around.

  •  At some point youll see some particular individuals get bigger and sort of move to

  • the center of the network and by the end youre going to see mostly yellow, but youre going

  • to see clusters of yellow and green nodes within the network indicating clusters of

  • obese and non obese individuals.

Okay, so if you look at this little movie what you

  • can see is, is that every dot is a person.  Every line between them is a relationship

  • between the two people and here we only show two kinds of relationships, not genetic relationships.

  •  The gray lines show spousal connections and the purple lines show friendship connections

  • and we make the dot size-

So here we begin in 1971.  You can see a lot of people.

  •  The relationships are changing.  People are marrying and divorcing each other, friending

  • and de-friending each other, real de-friendings, the old fashioned kind again and you can see

  • people are gaining and losing weight.  Youre going to see a sea of yellow.  Were approaching

  • now the growth of the epidemic.  You saw that one person gained a lot of weight and

  • moved to the middle of the network there.  Now were in 1991, 1993.  Were looking

  • at the network as it changes.  Most of the people are gaining weight.

Okay, so now

  • youre seeing the network evolve.  People are marrying and divorcing each other, friending

  • and de-friending each other.  Youre going to see people gain weight and lose weight.

  •  Mostly they are going to gain weight.  Youre going to see a sea of yellow.  That woman

  • up at the top there at 12:00 she is gaining a lot of weight now.  She is moving right

  • to the middle of the network.  Now youre going to see the growth of the epidemic.  Youre

  • going to see mostly a sea of yellow at this point in time as the epidemic is really kicking

  • off and were approaching the end of the animation now in just a moment and by the

  • end you can see that there are clusters of obese and non obese yellow and green sectors

  • within the network.

But when you look at this the question is did you see this wave

  • or not and we didn’t’ see it.  Like I said this was both the most exciting and the

  • most depressing moments of our scientific careers because we were convinced that if

  • we went to the trouble to collect these data and make this type of image after five and

  • a half years of effort we would be able to see this wave, but when we looked at this

  • we didn’t’ see it and it took us a whole day to figure out why and the reason is that

  • obesity is not a uni-centric epidemic.  It doesn’t have a point source.  It is a multi-centric

  • epidemic.  It has many sources and the proper analogy is not a single pebble being dropped

  • on the surface of a pond, but a whole handful of rocks being thrown on the surface.  Every

  • rock falling plunk, plunk, plunk makes these little concentric waves, but the waves interfere

  • with each other and you get this choppy surface, this chop on this socio-topological surface,

  • this hyper dimensional object that is a social network.

So there are kinds of statistical

  • and mathematical tools are required to discover or uncover the extent to which there is a

  • wave and using these tools we were eventually able to show just theand using these tools

  • we were eventually able to show this type of influence from person to person within

  • the network.

But the interesting thing as we made this image was that it totally

  • shifted my perspective on what was happening here because I came to see the world differently.

  •  This network when you look at it, it moves.  Things flow within it.  It changes and

  • evolves.  It is resilient to injury.  It has a memory.  It has a kind of a coherence

  • and an endurance across time.  I came to see social networks as living things, as a

  • kind of human super organism.  They have a life of their own of which we are all a

  • part and you and you can think of human beings in this way as having these kinds of properties,

  • these emergent properties because we partake of this bigger whole.  Because we are a part

  • of this other living thing you can think of us as being constituent parts of it and our

  • membership in this bigger thing affects us just like the point Durkheim was making earlier

  • about the suicide rates in France in the 19th century.

Now what might be a possible

  • mechanism of the spread?  How might we be affected or how might obesity be spreading

  • from person to person?  One possibility is that the alter, the other person, the alter’s

  • appearance or behavior could change the ego, that would be me, the ego’s behavior.  So

  • the alter is over there and I'm the ego.  They change their appearance or behavior and that

  • spreads and affects my appearance or behavior and an alternative idea is that the alter’s

  • appearance or behavior changes my expectations or perceptions of norms, so here what spreads

  • from person to person is not a behavior, but rather an idea.  

So now what might

  • be some possible mechanisms that might explain the spread of obesity?  One possibility is

  • that the alter’s appearance or behavior could change the ego’s behavior.  So here

  • the idea is that your friend, the alter says let’s go have muffins and beer, which is

  • a terrible combination, but your friend suggested it, so you agree and you adopt your friend’s

  • muffin and beer eating behavior and this contributes to your obesity.  

A second possibility

  • is that the alter’s appearance or behavior changes the ego, that’s you—a second possibility

  • is that the alter’s appearance or behavior changes the ego’s expectations or norms.

  •  Here what spreads from person to person is not an actual behavior, but rather an idea.

  •  So as your friends gain weight it changes your idea about what an acceptable body size

  • is and so willy-nilly you follow suit and you gain weight as well.

So now what

  • might be some possible mechanisms or explanations of the spread of obesity?  So here we might

  • think of the alter, that is the other person and the ego, that is you.  So one possibility

  • is that the alter’s appearance or behavior could change the ego’s appearance or behavior,

  • so for example, your friends say let’s go have muffins and beer.  That is a terrible

  • combination, but your friend suggested it, so you copy your friend’s behavior and you

  • gain weight as a result of the muffin and beer diet that you have assumed.

A second

  • possibility is that the alter’s appearance or behavior changes your expectations or perceptions

  • of norms.  Here what spreads from person to person is not a behavior, but rather an

  • idea and when we analyzed our data we found evidence for both sorts of phenomena.  We

  • found some suggestive evidence that as the people around you change their body size it

  • resets your expectations about what an acceptable body size is and so you go on to gain weight

  • or lose weight accordingly as well.

Now many social sciences take people’s tastes

  • and desires as a given and they try to figure out why people do what they do given that

  • they have particular tastes or desires.  How do they maximize their utility?  But one

  • of the distinctive ideas of sociology is that it seeks to understand where do these tastes

  • and desires come from in the first place.  Why do you want what you want?  Why do

  • you desire what you desire?  And in part it turns out that our desires and our wants

  • are determined by the collective, are determined by the groups of which we are members and

  • longshoreman and social critic Eric Hoffer once opined, “When people are free to do

  • as they please they usually imitate each other.”  Our choices and experiences depend on what

  • other around us are doing and feeling from obesity to smoking to voting or even to our

  • emotions and in a sense this means that we have less free will than we think we might

  • have.

Now this sort of interpersonal influence and these sorts of network affects

  • can be shown experimentally too, not just using the kinds of observational data I have

  • shown you so far.  To give another illustration of how we are affected by those around us

  • and to get around some of the potential problems of using observational data to study social

  • processes and try to make causal claims to try to really nail down what is happening

  • here it’s very helpful to also do experiments where you randomly assign people to interact

  • with each other in controlled environments to see can you find evidence that we are actually

  • affected by other people even in potentially important and counterintuitive ways.

So

  • one experiment that I'm going to who you involved taking 240 college students and having them

  • play a game in which they were each given a little bit of money and if they contributed

  • the money to the group, they were randomly assigned to interact with three strangers

  • in groups of four, if they gave a little money to the group the experimenter would multiply

  • the money so the group would be better off even though the individual paid a price and

  • the question was could we find evidence that people were affected by the behavior by the

  • altruism of other people to whom they were connected.

So here is an illustration

  • of how the experiment is set up.  So at period one, which is shown in the far left column

  • there are six groups of people shown here and person A plays with persons B, C and D

  • and person E plays with persons F, G and H and so forth on down the column.  Then a

  • bell willthey play this contribution game.  Then a bell rings and they are randomly

  • assigned to play with new people and then a bell rings and they are randomly assigned

  • to play with new people and so it keeps going for a number of rounds and what can happen

  • is if you can take these data and you can reconfigure them to be a kind of social network.

  •  

So for example, you can see that the ego, person A on the far right there previously

  • had played with individuals E, I and M, the alters and those individuals had previously

  • played with the alter’s alters F, G and H, J, K and L and N, O and P, so you can ask

  • yourself the question how does F’s treatment of E affect E’s treatment of A.  Do people

  • learn if I'm kind to you, I'm not asking do you reciprocate the kindness and are kind

  • back to me.  I'm asking if I'm kind to you do you then go onto be kind to others?  Can

  • there be a kind of pay it forward phenomena within social networks?  Do people’s altruistic

  • impulses, do they depend in part on the behavior of other people around them with whom they

  • are interacting and in fact they do.  

It turns out that if you take this kind of network

  • data you can map it and get this kind of an image here, so for example, what you can see

  • is that Eleni [ph] in period one, if she is kind to Lucas, Lucas learns to be kind and

  • then goes onto be kind to Erica and Erica is kind to Jay and Jay is kind to Breckon

  • [ph].  You have a spread to three degrees of separation in this experimental network

  • of altruistic behavior.  You can see the signature of Eleni’s kindness to Lucas,

  • in Jay’s interactions with Breckon even though neither Jay nor Breckon ever saw or

  • interacted with Eleni or Lucas.  Things have literallyyou can literally show the spread

  • of this kind of altruistic behavior through the network and that is different than the

  • persistence across time.  There is the spread across people shown in the red outline and

  • there is then a persistence across time shown in the yellow outline, which is that if Eleni

  • is kind to Lucas, Lucas learns to be kind and he goes onto be kind to Erica in period

  • two and to Lisander [ph] in period three and to Bemi [ph] in period four and to Sebastian

  • in period five and to Nicholas in period six.  So Lucas learns to be kind and continues

  • to be kind with other people because Eleni treated him kindly initially and it turns

  • out if you compute all the downstream kindness that arose because of Eleni’s kindness to

  • Lucas the network functions like a kind of matching grant doubling the net benefits for

  • Eleni’s initial altruistic behavior with respect to Lucas.

So this affect thus

  • spreads across people and also as a separate matter persists across time and when all the

  • ripples through this network are added together you get much more benefit to the collective

  • than the sum of theof then the consequence of the individual benefits from the first

  • person’s behavior.

And when all these ripples are added together it is clear that

  • the network—I already said that.  This affect thus spreads across people and also

  • as a separate matter persists across time and you can see that the group as a whole

  • benefits out of proportion to the individual behaviors or individual contributions of the

  • constituent people. Okay, now one can also ask other deeper questions

  • like why do social networks look the way that they do.  They always kind of look like the

  • image I showed you earlier of the obesity network, but they never look like this picture.

  •  They never look like a regular lattice.  Why don’t we live our lives in this kind

  • of a structure?  Why don’t we make networks that look like this?  Well the striking patterns

  • of human social networks their ubiquity and their apparent purpose beg the question of

  • whether we have evolved to have them and to have particular kinds of networks in the first

  • place.  So now the question has become why do we form networks in the first placeand

  • so now the question has become why do we form social networks in the first place and why

  • do they have the structure that they do and to understand this we need to dissect network

  • structure a little bit first.

So first of all, notice that in this network every

  • position is the same as every other position.  Everyone has eight friends.  Every one

  • of their friends in turn has eight friends and if you took this surface and you wrapped

  • it around the surface of a donut, or a **** there would be nobody that was anymore towards the

  • edge or towards the middle of the network.  Everyone would be equally distant from the

  • edge, but real social networks look entirely different.  They look kind of like this image

  • of 105 college students at a diverse American university and so in fact if you look at this

  • image you can see the two nodes B in the upper left and D in the far right you can see that

  • they are different because they have a different number of connections.  B has four friends

  • and D has six friends and if you talked to them they would be aware of this difference.

  •  You could see the difference between the two people and they themselves would be aware

  • of this difference, but there are other aspects of the network and the location within the

  • network that are less obvious.  

Okay, but that is not the case with natural social

  • networks.  Natural social networks are very different, so for example, if you look at

  • this network you can see that different individuals have different kinds of locations within the

  • network.  Consider for example individuals B and D, B in the upper left and D on the

  • far right.  So B has four connections and D has six connections and if you talked to

  • those individuals they would know this about themselves.  I have four friends.  I have

  • six friends.  I have no friends.  I have 10 friends.  People know this about themselves

  • and that is obvious, but there are other aspects of our network that are less obvious.  For

  • example, compare, contrast nodes A and B.  They are different.  They both have four

  • friends, but A’s friends are by and large friends with each other and B’s friends

  • are not friends with each other.  This is known as transitivity.  The friend of a friend

  • of A’s is back again a friend of A’s, but the friend of a friend of B’s is not

  • a friend of B’s.  It reaches further within the network.  And finally look at C and D.

  •  C is in the middle and D is on the far right.  They both have six friends, but you can

  • see that there is something different between the two of them.  C is in the center of the

  • network and D is to the edge of the network and the bird’s eye view of this sort makes

  • these differences apparent and it turns out that where you are located within a social

  • network dependsScratch that.  I'm going to go back to C and D.

And if you look

  • at C and D you can see that they are different.  They both have six friends, but there is

  • something different about C compared to D and I can cultivate this intuition in you

  • by asking you who would you rather be if a deadly germ was spreading through the network.

  •  You would rather be D.  You should have the intuition that it is better to be on the

  • edge of the network because that person would be less likely to get what is spreading and

  • if they get it are more likely to get it later in the course of the epidemic.

Now let

  • me ask you who would rather be if a juicy piece of gossip were spreading through the

  • network?  Now you would rather be C, be in the middle of the network and get it and this

  • can be formulized mathematically the difference between these individuals and it is known

  • as I said as their centrality and this bird’s eye view of the network makes these sorts

  • of differences apparent and it turns out that where youre located within the network

  • whether you are A, B, C or D or types of individuals like that depends in part on your genes.  Again

  • depending on the circumstances faced different positions are different, so people often say,

  • Well what is the best location in the network?”  The answer is it depends.  If a germ is

  • spreading through the network it is better to be in one place, if information about where

  • to find a job is spreading through the network it is better to be in another place.  

So

  • you can think of networks as a kind of vast fabric of humanity and we all occupy particular

  • spots within the network.

There is another way that social networks affect us.  It is

  • not just what is happening to the people around us that might ripple through the network and

  • affect us.  It is the actual structure of the network itself.  Now think about these

  • two objects.  They are both made of carbon, but if you look at the structure of the objects

  • the graphite on the left is made of carbon atoms assembled and connected one way and

  • the diamond on the right is made of carbon atoms assembled and connected another way.

  •  So you connect the carbon atoms one way and you get graphite, which is soft and dark

  • and you connect the carbon atoms another way you get diamond, which is hard and clear and

  • there are two key intellectual ideas from this observation.  First, these properties

  • of softness and darkness and hardness and clearness do not adhere in the carbon atoms.

  •  They are not properties of the carbon atoms.  They are properties of the collection of

  • carbon atoms.  Second, which properties you get depends on how you connect the carbon

  • atoms to each other.

 Connect them one way you get one set of properties.  Connect

  • them another way you get a different set of properties and similarly the pattern of our

  • connections with each other affects the properties of groups.  It is the ties between people

  • that make the whole greater than the sum of its parts.  New properties emerge because

  • of the connections between people, because of the ties between people and not necessarily

  • because of the people themselves and in fact our experience of the world depends in part

  • on the actual structure of the social network ties around us and this is like the artificial

  • networks we saw at the beginning of the bucket brigade and the telephone tree.  You take

  • human beings and you assemble them one way.  You get one set of properties.  You assemble

  • them another way.  You get a different set of properties just like the carbon example.

Now

  • there is another example, a real life example now of how network structure might matter

  • distinct from what is flowing through the network and this is some work that was done

  • by Brian Uzzi and Northso here is a more specific human example of how social network

  • can affect the constituent individuals.  This is some work done by Brian Uzzi, a sociologist

  • at Northwestern University.  He became very interested in Broadway musicals and why some

  • Broadway musicals are a big success and other Broadway musicals are a total disaster and

  • what did is he put together a sample of over 300 Broadway musical production companies

  • and he looked at the structure of the production company, the network structure and assessed

  • how it was associated with the financial success and the critical acclaim of the Broadway shows

  • that those companies put on and if you look at this on the far left, imagine we have a

  • production company of one person in the middle and five people surrounding that individual

  • and we look at the social network ties and this individual in the middle is connected

  • to five other people. 

So here you see three cartoon images of how the networks might

  • be assembled.  On the far left you see that there is a central individual connected to

  • five other people and amongst those people there can be five times four divided by two,

  • ten possible connections and in there cartoon on the left you see there are none of those

  • connections.  Zero of ten of the ties are present and we would say that there is zero

  • percent density in this network.  On the cartoon on the far right you might see that

  • all 10 of the ties are present, so you have 10 out of 10, 100% density and density is

  • sort of like transitivity that we were talking about earlier and in the middle you see that

  • 4 of the 10 ties are present, so you have 40% density and what Uzzi did was he plotted

  • on the graph shown with a parabola he plotted on the X axis the density of the Broadway

  • musical production company and on the Y axis how successful the Broadway musical was, how

  • much money did it make and how many favorable reviews did it get and as you see by the parabolic

  • shape on the left if you have a network in which nobody knew each other from before the

  • show was a flop and at the other extreme if you see that everybody knew each other from

  • before the show was a flop, but in the middle if some of the people knew each other from

  • before and some of the people didn’t know each other from before, if there was intermediate

  • density the show was a big success, so what seems to matter here is it is not just the

  • individuals putting on the show.  It is the structure of the network that affects the

  • likely success of the show and Uzzi has gone on to show that there are similar work or

  • similar findings with respect to scientific collaborations in other sorts of groups that

  • people can assemble.

Okay, now it turns out were not the only species that assembles

  • ourselves into networks and gives rise to others sorts of special properties and so

  • to push this point home, this point about emergence, this idea that collectivities can

  • have properties that are not present in the individuals themselves let’s consider a

  • further example.  This is a slime mold.  It is a primitive amoeboid fungus and all this

  • fungus does I digest wood, so this thing lives on the forest floor and if you have ever lifted

  • up like a pile of leaves in the fall and they are wet and soggy and you see those little

  • white tubes under that is what this thing is doing.  The little fungus forms connections

  • to other nearby fungi.  They fuse and they make these long tubes and they digest wood

  • and they distribute the waste from their digestion through these tubes.  But it turns out individuals

  • of this species in connecting to each other form a kind of super organism with unexpected

  • properties.  

For example, they can solve mazes.

So if you take a maze and

  • you put it on a kind of **** plate and you put food at two different spots, the entrance

  • and the exit to the maze and by food here I mean something like wood or like an oat

  • flake.  If you put oat flakes at the entrance or the exit of the maze this simple organism

  • will change its shape and connect to the two sources of food by finding the minimum path

  • length solution between the two points.  If parts of the organism are spread out on the

  • gel they will reassemble to form a kind of single super organism and so it **** a kind

  • of maze solving property, a kind of primitive intelligence that is not present in the individual

  • organisms themselves and this work was done by a Japanese mycologist by the name of Toshi

  • Nagagaki [ph].

So here you are.  Here is the maze.  The amoeboid fungus is bubbling

  • up and connecting to each other.  There is the oat flakes at the entrance and the exit.

  •  It is surrounding the whole plate and youre going to see that all the paths are going

  • to die back except for the one shortest path through the maze.  In fact, this amoeboid

  • fungus is better able to solve mazes then Toshi’s graduate students, not better than

  • my graduate students thank goodness.  It is able to find the shortest, most efficient

  • path through the maze.  It is able to find the shortest, most efficient path through

  • the maze.  This maze solving ability is an emergent property of the amoeboid fungus.

So

  • it is obviously not a single amoeboid fungus that is solving this maze.  It is the fungi

  • working collectively that give rise to this property, this maze solving ability that emerges

  • from their interactions.  Obviously if you ask can this amoeboid fungus solve a maze

  • the answer is no, but the maze solving ability emerges as a result of the interactions.  In

  • fact, you can use this kind of maze solving ability or this ability to find the optimal

  • paths to do other sorts of things like here we show an image on the left is the rail network

  • designed by human beings in England and on the right is some work done by my colleague

  • Mark Fricker [ph] at Oxford University.  He took the map of England and he put little

  • oat flakes at every city and he plated the amoeboid fungus and the amoeboid fungus gave

  • rise to a path connecting or a set of paths connecting the oat flakes that actually imitated

  • and in many ways was better than the rail network the human beings had designed over

  • 200 years, so if you look at these two things side by side you see that the fungus is able

  • to design a railway system for England, in fact, a better system than the one that they

  • have.

Still what is the point of a connected life?  How does it help us as an individual

  • or as a species?  It turns out that social networks are a resource that we can all use.

  •  They are a kind of social capital.  Now most people when they think about capital

  • think about money, but really capital is any stock of resources that can be put to productive

  • use.  Two further key ideas, one of which is quite subtletwo further key ideas about

  • capital are that in order to create capital you have to invest skill and effort.  You

  • have to know something and do something in order to acquire capital and second and more

  • subtle you have to work upon the world and transmute it.  You have the change the world.

  •  You have to introduce changes in a substance that makes it more productive than it was

  • before, that makes it capable of yielding a higher rate of return than it was able to

  • do before.

So for example, think about this.  You can have a forest.  You can invest

  • skill and effort.  You can clear the forest and you can make a farm and this farm is a

  • stock of capital.  It is more productive at least in terms of fruits and vegetables

  • and grains than the forest was and by investing skill and effort and working upon the land

  • and changing the land you have created a reservoir of wealth, something that is capable of doing

  • something that wasn’t—you have created a reservoir of wealth, something that is capable

  • of being used in a fashion that wasn’t possible before, so land and especially improved land

  • is a form of capital.

Or think about this idea.  You can take this tree.  You

  • can invest skill and effort and you can transmute the substance of the tree and mill it into

  • lumber and the lumber is more valuable than the tree.  It is a reservoir of wealth.  It

  • is a stock of capital and you can do things with the lumber that you couldn’t do with

  • the tree like make a violin.  You can invest still more skill and effort and convert the

  • lumber into a violin, which is more valuable than the tree because it reflects this additional

  • investment of skill and effort and because in having changed the wood even more youre

  • now capable of doing things with the violin you couldn’t do with the lumber like make

  • music.  So capital is a change that allows a substance to act in new ways and this is

  • part of what makes it a store of wealth and a source of productive power.  

Now

  • in the 1960s a key innovation in thinking took place spearheaded primarily by economist

  • Garyso a keynow a key innovation in thinkingnow a key innovation in thinking

  • among social scientists took place in the 1960s spearheaded primarily by economist Gary

  • Becker to begin to think about human beings as a form of capital, as a form of human capital

  • and the chief example of this is education.  If we endow someone with skills and knowledge

  • we have changed them and they have become more productive.  So if you look at this

  • sort of dissolute graduate student of mine on the far left you can invest skill and effort.

  •  You can clean him up so that he is no longer a drunkard and now he is capable of doing

  • things he wasn’t capable of doing before or you can invest still more skill and effort

  • and give him an education and now he is even more able to do things he wasn’t able to

  • do before.  So you have changed the substance of his mind.  You have reworked the real

  • world.  You have taught him things.  You have changed his brain and made him more productive

  • and more capable of doing things that he wasn’t previously able to do.

Now just like

  • physical capital is created by a change in the material world and human capital is created

  • by a change in persons social capital is a change in the relations among persons, a change

  • the renders the group more productive and capable of doing things it wasn’t previously

  • able to do, so social capital can arise in at least two senses when we think about social

  • organization.  First we can think in terms of what is flowing through the group and across

  • these connections.  Is information flowing?  Is germs flowing?  Is information flowing?

  •  Are germs flowing?  Are emotions flowing?  Is altruism flowing?  Is this the kind

  • of network in which desirable things are flowing through the system?  Is this the kind of

  • group in which positive things are primarily moving first?

Second, social capital

  • can arise in a second sense, which is how the groups of individuals are organized or

  • connected in the first place.  This idea or the idea is that social capital is a property

  • of a collection of individualsthe idea is that social capitalthe idea is that

  • social capital is a property of collections of individuals, a property that did not exist

  • before the individuals were assembled into the kind of network group.  Moreover, the

  • idea is that social capital is a property of collections of individuals, a property

  • that did not exist before the people were assembled into this network and moreover,

  • a property that does not adhere within the individuals themselves.  It is a property

  • of the collection of individuals again illustrating the idea of emergence that we have been discussing.

Now

  • this idea was best advanced by sociologist James Coleman, but related ideas are found

  • in the work of Robert Putnam and Pier Borduex [ph] and Coleman’s perception differs from

  • Borduex’s and Putnam’s conception in a number of ways.  Borduex tends to see social

  • capital as residing within individuals and is more like what I would consider to be cultural

  • capital and Putnam’s perspective stresses the important role of official or formal institutions,

  • whereas, Coleman’s perspective on social capital is a bit more organic like what we

  • have been seeing, that social capital arises because of the interactions between people

  • that almost naturally take place, that are a part of our very fabric as social animals.

Now

  • one of the important aspects of social capital is that it is a public good.  Now a public

  • good is one in which there is no exclusivity in consumption.  So everyone can benefit

  • from it.  Think about the difference between this cake and this lighthouse.  If you have

  • a cake there are two things you can do with it that are relevant to what were discussing

  • right now.  First of all, you can prevent anyone else from eating the cake.  It is

  • your cake.  No one else can touch it.  And second, if you eat the cake there is none

  • of it left for either you or anyone else to use, but think instead about the good that

  • is the light that comes from the lighthouse.  Your using that light to avoid crashing

  • on the shore doesn’t prevent anyone else from using the light, not only that, but there

  • is no way to consume the light.  There is no way to use it all up.  More light is there,

  • so this good is totally different than the cake and that is the kind of aspects or those

  • are the kinds of properties that a public good like a lighthouse has.  It is a good

  • in which there is no exclusivity of consumption and in which the good is sort of inexhaustible.

  •  This is not right.

So a public good is one in which there is no exclusivity in

  • consumption and everyone can benefit from it and public goods typically arise by accident

  • and social capital may beand public goods typically arise by accident.  Maybe one group

  • of people puts up the lighthouse because they are really concerned about it, maybe a port

  • authority or a private entity that is concerned about their ships not crashing, but now that

  • they have put it up everyone can benefit and their benefits do not reduce the ability of

  • the intended individuals to benefit.

Social capital is sort of like that.  It is a public

  • good.  It arises by accident from people’s interactions with each other.  It is not

  • a deliberate thing that we do.  We don’t set out to make it and once we create it though

  • everyone can benefit from it

  • Social scientists have developed a number of overarching approaches to understanding

  • human behaviors in human society.  One classic way of understanding collective behaviors

  • is to look at individuals themselves.  For example, we can see markets or elections or

  • riots as the mere byproduct of individual’s decisions to by and sell goods, to vote or

  • to express anger and the classic example of this approach, which is known as methodological

  • individualism is provided by Adam Smith’s conceptions of markets where each individual

  • transacting their business as if guided by an invisible hand gives rise to a kind of

  • an efficient market where each individual acting in the furtherance of their own interest

  • as if guided by an invisible hand gives rise to markets.

Now another classic way of

  • understanding collective human behavior dispenses with individuals and focuses on groups, groups

  • with collective identities that cause people within the groups to act in concert.  Some

  • scholars in this tradition like Karl Marx even believe that groups can have their own

  • consciousness imbuing them with a kind of indivisible personality that cannot be deduced

  • or understood from the actions of its members. 

Others have also focused on the primacy of group

  • culture.  For example, as we saw sociologist Emile Durkheim argued that the relatively

  • constant rate of suicide within particular religious groups and in particular places

  • at particular times could not be explained by the actions of individuals and must be

  • properly understood as a property of the collective, as a property of the groups.  How was it

  • he wondered that people came and went, but the suicide rate in French Protestants stayed

  • the same.  This is known as methodological holism and this approach sees collections,

  • sees groups, sees society as being distinct from the individuals, distinct from the constituent

  • individuals and sees society and groups as having properties that cannot be deduced merely

  • from studying the constituent individuals.

Now in the 20th century social scientists often

  • focused on how membership in particular kinds of groups having particular kinds of attributes

  • such as race or class for example could explain the behavior of the individuals within them.

  •  Now in the 20th century many social scientists focused on how membership of individuals within

  • groups denoted by particular attributes or characteristics, for instance, race or class

  • affected or helped determine the behavior of those individuals and maybe gave rise to

  • collective phenomena, but the social network approaches, some of which we have been discussing

  • today offer a further way of understanding human society and in fact a way perhaps best

  • suited for the 21st century.

Social networks are about both individuals and groups and

  • in fact they are about how individuals become groups by connecting to each other.  Interconnections

  • between people can give rise to phenomena that are not present with individuals themselves

  • and that are not reducible to the solitary desires and actions of the individuals.  

The

  • issues of social capital and emergence and the phenomena of social networks illustrate

  • the issue of how we explain social phenomena, so methodological individualism seeks explanations

  • for social phenomena such as social class, markets, power, institutions and so forth

  • by saying that they must be formulated as or reducible to the characteristics or actions

  • of individuals.

Methodological holism on the other hand sees each social entity,

  • a group or institution or a network as having a totality that is distinct from and that

  • cannot be understood by merely studying the individual component elements.  So for example,

  • you can understand markets perhaps by using a methodological individualistic approach,

  • but if youre interested in understanding market bubble or panics you might need a more

  • methodological holism approach and the methodological holism also refers back to the example, the

  • carbon example-

The issues of social capital and emergence and the phenomena of

  • social networks that we have been discussing illustrate the issue of how we can come to

  • explain social phenomena using alternative approaches.  On the one hand we have methodological

  • individualism.  Here in this perspective, explanations for social phenomena such as

  • social class, markets, power, institutions and so forth must be formulated as or reducible

  • to the characteristics or actions of individuals.

On the other hand we could have methodological

  • holism.  Here this perspective sees each social entity, group, institution or network

  • as having a totality that is distinct from and that cannot be understood by merely studying

  • its individual component elements.  So for example, we may be able to understand markets

  • by using an approach of methodological individualism, but if we want to understand market panics

  • or bubbles we probably need an approach that uses methodological holism and holism in fact,

  • as you probably have gathered is related to emergence.  Various social phenomena, for

  • example, culture can have an enduring reality that transcends individuals and Durkheim for

  • example argued that social facts can and must be studied by looking at groups of individuals,

  • not individuals themselves.

Social capital is complicated because certain aspects of

  • it arise as byproducts of individual actions, so it is true that individuals choose their

  • friends, but in choosing their friends they give rise to a collection, a network that

  • has its own properties, so while the individuals contribute in some sense to the emergence

  • of this phenomenon they are not a part of the phenomenon.  The phenomenon is distinct

  • from the individuals and in fact, in some ways you can think about the study of social

  • networks as illustrating something else, another big idea because it is part of a much broaderand

  • in fact the study of social network illustrates something elseand in fact the studyand

  • in fact the study of social networks illustrates something else.  It is part of what I call

  • a much broader assembly project of modern science. 

For the last 400 years swept

  • by a reductionist fervor and by considerable success scientists have progressively dissected

  • matter into ever smaller bits, so we disassembled life into organs and then cells and then molecules

  • and then genes and we disassembled atomsand we disassembled matter into atoms, then nuclei,

  • then subatomic particles and we have invented everything from microscopes to super colliders

  • to study ever smaller bits of matter, but across many disciplines right now scientists

  • are now trying to  put all the parts back together again whether theyre trying to

  • putbut across many disciplines right now scientists are trying to put the bits back

  • together again whether it is macro molecules into cells, neurons into brains, species into

  • ecosystems, nutrients into foods or people into networks,  Scientists are changing-

Scientists

  • are turning their attention into how and why the parts fit together to make the whole and

  • how interconnection can give rise to properties that aren’t present within the component

  • parts.  Understanding the structure and function of social networks and the phenomenon of emergence

  • within social networks is thus part of this larger scientific movement.

But sociology

  • has always been doing this.  It has always sought to put the parts back together and

  • to make a bigger whole.  It has always realized that the whole is greater than the sum of

  • its parts.  Moreover, sociology has always emphasizedmoreover, sociology has always

  • emphasized the ways in which actually the parts have properties that are not present

  • withinmoreover, sociology has always emphasized the extent to which we are not in fact masters

  • of our own destiny and in this regard sociology touches on ancient philosophical concerns

  • such as free will.

Because whatand in this regard sociology has concerned itself

  • with another ancient philosophical concern, namely, the issue of free will because sociology

  • is interested in the ways in which what happens to you aren’t just a product of your own

  • agency.  Don’t just depend on your own choices and actions, but depend on broader

  • structural factors outside of your control like the race of your parents or your birth

  • order or your birth weight or the talents you happen to be born with or super structural

  • factors such as the networks you belong to or which country you were born in or the relative

  • wealth of these countries or the culture of these countries or the other attributes that

  • surround you that you as a part of now come to partake of and as a result determine your

  • destiny just as much as your own individual choices and actions.  

It is the tension

  • between structure and agency that we opened with.  To what extent do our destinies depend

  • on our own behavior and to what extent do they depend on these larger factors that we

  • have been discussing today?

In other words, how does what happened toin other

  • words how does what happens to you depend not just on what you choose to do, but what

  • others choose to do and what the whole society around you and the whole culture around you

  • dictate as your destiny above and beyond what you dictate as your own destiny.

And

  • the field is only going to get better.  Look, if you had asked social scientists even 20

  • years ago what was their fantasy of the ideal kind of data that they could have they would

  • say oh my goodness we would love it if we could have these little tiny helicopters that

  • were microscopic and invisible and they flew on top of every person and they monitored

  • this person 24 hours a day looking at what this person was buying, what this personwho

  • this person was interacting with, where this person was, what this person was thinking

  • and if they could do this for millions of people in real time that would be amazing.

  •  We would have a kind of data that would allow us to understand society and individual

  • behavior in a way we never could before, but of course that is what we have now.  In our

  • everyday use of cell phones and credit cards and online networks and blogs and all these

  • administrative records that we leave behind us we leave these little digital breadcrumbs

  • as we move about our lives that can be pulled together and studied using new analytical

  • and computational tools that give us whole new insights into how and why society operates.

So

  • for example there all kinds of such pervasive data that are available nowadays, telephony

  • data, internet data, video cameras in cities, RFID devices in all kinds of products and

  • other places, administrative records regarding emergency room visits or crimes, transactions

  • records, geographic information, voluntary losses of anonymity, people participating

  • in citizen science and contributing their information for others to use or even personal

  • genetic information.

And the availability of all these new kinds of data heralds the

  • onset of a new kind of computational social science.  The availability of data of this

  • kind is only increasing and will continue to increase and these data properly analyzed

  • and with the proper concern for researchand these data properly analyzed and subject to

  • theand these data properly analyzed and subject to ethical rules can allow us to understand

  • and address all kinds of important social problems from violence to poverty to epidemics

  • to political extremism.

In 1969 sociologist Morris Zelditch asked rhetorically can you

  • really study an army in the laboratory and nearly half a century later the answer appears

  • to be yes and this will offer us all sorts of new opportunities and raise new questions

  • both intellectual and philosophical about how and why humans and the groups they form

  • do what they do.  

Nearly half a century later the answer appears to be yes and this

  • will raise all sorts of questions both intellectual and philosophical.  Nearly half a century

  • later the answer appears to be yes and this will offer all sorts of new opportunities

  • both intellectualand this will offer all sorts of new opportunities and raise all sorts

  • of new question both intellectual and philosophical about how and why humans and the groups that

  • they form do what they do.  If you want to understand all this and be a part of all this

  • then you need to understand sociology.  If you want to understand all of this and be

  • a part of this then you need to understand sociology. 
 
This will offer all sorts

  • of new opportunities and raise all sorts of new questions both intellectual and philosophical

  • about how and why humanthis will offer all sorts of new opportunities and raise all

  • sorts of new questions both intellectual and philosophical about how and why humans and

  • the groups that they belong to do what they do.

If you want to understand all of

  • this then you need to understand sociology.  Thank you.  

  •  

Hi, my name is Nicholas Christakis and I'm a physician and a social scientist and the

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