Practice English Speaking&Listening with: Nicholas Christakis: The Sociological Science Behind Social Networks and Social Influence

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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 Id 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 Childrens 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 lets 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 Gilmans 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 cant 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. Bersts 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 dont

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 doesnt 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 Durkheims 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 lets 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 dont 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 didnt have before like the

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

people werent assembled in the network in this fashion, this linear network they

couldnt 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 lets 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

wasnt 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 werent necessarily there before.

But real social

networks differ and dont 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 dont really

believe that there is something biological going on here even though the individuals

biology can explain variation between people and how big they are our biology hasnt

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 dont 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 wasnt 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 individuals 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 peoples 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 didnt

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 peoples 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 its 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 didntsee 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 didntsee 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 doesnt 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 alters

appearance or behavior could change the ego, that would be me, the egos 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 alters

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 alters appearance or behavior could change the egos behavior.  So here

the idea is that your friend, the alter says lets go have muffins and beer, which is

a terrible combination, but your friend suggested it, so you agree and you adopt your friends

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

A second possibility

is that the alters appearance or behavior changes the ego, thats youa second possibility

is that the alters appearance or behavior changes the egos 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 alters appearance or behavior could change the egos appearance or behavior,

so for example, your friends say lets go have muffins and beer.  That is a terrible

combination, but your friend suggested it, so you copy your friends behavior and you

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

A second

possibility is that the alters 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 peoples 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 its 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 alters alters F, G and H, J, K and L and N, O and P, so you can ask

yourself the question how does Fs treatment of E affect Es 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 peoples 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 Elenis kindness to Lucas,

in Jays 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 Elenis kindness to

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

Elenis 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

persons behavior.

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

the networkI 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 dont we live our lives in this kind

of a structure?  Why dont 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 As friends are by and large friends with each other and Bs friends

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

of As is back again a friend of As, but the friend of a friend of Bs is not

a friend of Bs.  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 birds 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 birds 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 didnt 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 lets 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 Toshis 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 wasntyou have created a reservoir of wealth, something that is capable

of being used in a fashion that wasnt 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 couldnt 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 couldnt 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 wasnt 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 wasnt 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 wasnt 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 wasnt 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 Colemans perception differs from

Borduexs and Putnams 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 Putnams perspective stresses the important role of official or formal institutions,

whereas, Colemans 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 doesnt 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 peoples interactions with each other.  It is not

a deliberate thing that we do.  We dont 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 individuals 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 Smiths 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 arent 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 arent just a product of your own

agency.  Dont 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.  

The Description of Nicholas Christakis: The Sociological Science Behind Social Networks and Social Influence