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 [ph] 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 wrote—so 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 this—it 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 natural—but 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 you’re 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 environment—and 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 to—and 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 network—and 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 we’re going to take—put this network into motion. We’re going to take daily cuts through the network for 32 years, every single day, evaluating the structure and status of the network and what you’re going to see across time is you’re going to see people be born and die. Image nodes are going to appear and disappear. You’re going to see relationships form and break. You’re 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 you’re going to see people, dots get bigger and smaller as people gain and lose weight. Mostly you’re going to see the dots getting bigger and you’re 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 to—and 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.