when I was a hospice doctor at the University of Chicago.

大約15年前

And I was taking care of people who were dying and their families

我在芝加哥大學擔任安寧病房醫生

in the South Side of Chicago.

我負責照顧那些瀕臨死亡的人，與他們的家人

And I was observing what happened to people and their families

就在芝加哥南端

over the course of their terminal illness.

我觀察這些疾病末期的人，與他們家人，

And in my lab, I was studying the widower effect,

疾病帶給他們的影響

which is a very old idea in the social sciences,

我在實驗室研究守寡效應

going back 150 years,

這個想法不新穎

known as "dying of a broken heart."

150年前就有了

So, when I die, my wife's risk of death can double,

就是大家所知的「心碎而死」

for instance, in the first year.

就是，我死了，我妻子的死亡率在第一年

And I had gone to take care of one particular patient,

會增加一倍。

a woman who was dying of dementia.

當時我照顧一個

And in this case, unlike this couple,

失智症的婦人

she was being cared for

不像其他病人

by her daughter.

她是由她女兒

And the daughter was exhausted from caring for her mother.

負責照顧。

And the daughter's husband,

為照顧母親，她女兒已心力憔悴

he also was sick

而她女婿

from his wife's exhaustion.

也因為妻子的憔悴

And I was driving home one day,

而生病了。

and I get a phone call from the husband's friend,

我有天開車回家

calling me because he was depressed

接到一通女婿的朋友打來的電話

about what was happening to his friend.

他說，因為他朋友（女婿）生病

So here I get this call from this random guy

他也心情低落。

that's having an experience

這通陌生人的電話

that's being influenced by people

讓我有了這個體驗

at some social distance.

原來人與人的影響

And so I suddenly realized two very simple things:

不止於親近的人。

First, the widowhood effect

我因此意識到兩件很簡單的事情

was not restricted to husbands and wives.

第一，守寡效應

And second, it was not restricted to pairs of people.

並不侷限於夫妻

And I started to see the world

第二，並不侷限於兩個人而已

in a whole new way,

我開始以全新的視角

like pairs of people connected to each other.

來看這世界

And then I realized that these individuals

人們一對對連結著

would be connected into foursomes with other pairs of people nearby.

然後又有其他個體

And then, in fact, these people

與鄰近的這對連結，變成兩對

were embedded in other sorts of relationships:

然後這些人

marriage and spousal

又被其他關係包圍著

and friendship and other sorts of ties.

婚姻、夫妻、

And that, in fact, these connections were vast

友情等等連結

and that we were all embedded in this

事實上，這些連結很廣

broad set of connections with each other.

我們每個人之間

So I started to see the world in a completely new way

都是被這許多的連結連起來的。

and I became obsessed with this.

我開始用全新的角度看這世界

I became obsessed with how it might be

並為此著迷

that we're embedded in these social networks,

我著迷於圍繞著

and how they affect our lives.

每個人的人際網路

So, social networks are these intricate things of beauty,

與它的影響。

and they're so elaborate and so complex

人際關係是種美麗亦複雜的東西

and so ubiquitous, in fact,

它既精密、複雜

that one has to ask what purpose they serve.

卻又普及，事實上，

Why are we embedded in social networks?

我們會問，它的功能是什麼？

I mean, how do they form? How do they operate?

我們為什麼會處於人際網路中？

And how do they effect us?

它們如何形成？怎麼運作？

So my first topic with respect to this,

是怎麼影響我們的？

was not death, but obesity.

我的第一個要探討的主題，

It had become trendy

不是關於死亡，而是肥胖

to speak about the "obesity epidemic."

突然間，大家都討論著

And, along with my collaborator, James Fowler,

「肥胖流行症」

we began to wonder whether obesity really was epidemic

我和James Fowler合作

and could it spread from person to person

共同研究為什麼肥胖會流行

like the four people I discussed earlier.

還有它的傳染是否像我剛所提的

So this is a slide of some of our initial results.

那四個人那樣

It's 2,200 people in the year 2000.

這是我們最初的結果

Every dot is a person. We make the dot size

2000年研究的2200人

proportional to people's body size;

每個點是一個人，我們依據

so bigger dots are bigger people.

體型來做點的大小

In addition, if your body size,

大點點的人體型較大

if your BMI, your body mass index, is above 30 --

還有，體型、

if you're clinically obese --

BMI值超過30以上的

we also colored the dots yellow.

在醫學上被診斷為肥胖的

So, if you look at this image, right away you might be able to see

我們標為黃點

that there are clusters of obese and

各位可以看到這張圖

non-obese people in the image.

肥胖的人聚成一團

But the visual complexity is still very high.

不胖的人聚成一團

It's not obvious exactly what's going on.

不過視覺上看起來還是很複雜

In addition, some questions are immediately raised:

真正的情況看得不明顯。

How much clustering is there?

另一個馬上想到的問題是

Is there more clustering than would be due to chance alone?

圖中有多少聚集？

How big are the clusters? How far do they reach?

聚集的產生是否不單因為巧合？

And, most importantly,

這些聚集有多大？各自距離有多遠？

what causes the clusters?

最重要的還有

So we did some mathematics to study the size of these clusters.

形成聚集原因是什麼？

This here shows, on the Y-axis,

所以我們將這些聚集的大小數據化

the increase in the probability that a person is obese

可以看到，縱軸是

given that a social contact of theirs is obese

一個人因為週遭朋友

and, on the X-axis, the degrees of separation between the two people.

而變胖的可能性

On the far left, you see the purple line.

橫軸是兩個人之間，分離的程度

It says that, if your friends are obese,

最左邊，紫色長條顯示

your risk of obesity is 45 percent higher.

如果你的朋友都過胖

And the next bar over, the [red] line,

你過胖的機率比別人高45%

says if your friend's friends are obese,

旁邊的紅色長條

your risk of obesity is 25 percent higher.

代表如果你朋友的朋友都過胖

And then the next line over says

你過胖的機率比平均高出25%

if your friend's friend's friend, someone you probably don't even know, is obese,

下一個長條表示

your risk of obesity is 10 percent higher.

如果你朋友的朋友的朋友－即使你都不認識－過胖

And it's only when you get to your friend's friend's friend's friends

你過胖的機率比平均高出10%

that there's no longer a relationship

只有到了你朋友的朋友的朋友的朋友

between that person's body size and your own body size.

幾乎沒有關係可言

Well, what might be causing this clustering?

你們的體型才不會互相影響。

There are at least three possibilities:

那形成這種聚集的原因是什麼？

One possibility is that, as I gain weight,

至少三種可能

it causes you to gain weight.

第一，當我體重增加

A kind of induction, a kind of spread from person to person.

你體重也增加

Another possibility, very obvious, is homophily,

這是誘導性，在人與人之間的傳染

or, birds of a feather flock together;

第二，很明顯的，同質性

here, I form my tie to you

也就是「物以類聚，人以群分」

because you and I share a similar body size.

我和你的聯繫

And the last possibility is what is known as confounding,

是因為我們體型相同

because it confounds our ability to figure out what's going on.

最後一個可能性是混雜法

And here, the idea is not that my weight gain

我們搞不清楚狀況是什麼

is causing your weight gain,

意思是，你體重增加的原因

nor that I preferentially form a tie with you

不是因為我體重增加

because you and I share the same body size,

也不是我選擇與你有關聯

but rather that we share a common exposure

而是因為我們有一樣的體型

to something, like a health club

所以我們會去類似的地方

that makes us both lose weight at the same time.

例如健身房等等

When we studied these data, we found evidence for all of these things,

我們一起瘦身的地方

including for induction.

我們研究這些數據，發現以下一些證據

And we found that if your friend becomes obese,

包含誘導性

it increases your risk of obesity by about 57 percent

我們發現，如果你的朋友變胖

in the same given time period.

同一時期裡，你變胖的機會

There can be many mechanisms for this effect:

立刻增加57%

One possibility is that your friends say to you something like --

造成這種效果有很多機制

you know, they adopt a behavior that spreads to you --

一種情況是，你朋友的行為傳染給你

like, they say, "Let's go have muffins and beer,"

他們可能會對你說：

which is a terrible combination. (Laughter)

「我們吃馬芬鬆糕配啤酒吧」

But you adopt that combination,

這搭配好糟糕

and then you start gaining weight like them.

但你習慣這樣吃以後

Another more subtle possibility

你就會開始和他們一樣變胖

is that they start gaining weight, and it changes your ideas

另一種可能

of what an acceptable body size is.

是他們開始增胖，你開始改變了

Here, what's spreading from person to person

對於正常體型的看法

is not a behavior, but rather a norm:

這種人與人傳染情況

An idea is spreading.

不是行為改變，而是標準改變。

Now, headline writers

有越來越多人接受這種想法。

had a field day with our studies.

有些記者

I think the headline in The New York Times was,

將我們的研究寫成報導

"Are you packing it on?

我想紐約時報的頭條是：

Blame your fat friends." (Laughter)

「變胖了嗎？」

What was interesting to us is that the European headline writers

「怪你朋友吧！」

had a different take: They said,

我們覺得有趣的是，歐洲的記者

"Are your friends gaining weight? Perhaps you are to blame."

寫了不同的頭條：

(Laughter)

「你朋友變胖了嗎？是你害的！」

And we thought this was a very interesting comment on America,

(笑聲)

and a kind of self-serving,

我們覺得很有趣，這反應出美國人那種

"not my responsibility" kind of phenomenon.

有點自私、

Now, I want to be very clear: We do not think our work

「不干我的事」的態度

should or could justify prejudice

到此，我要澄清，我們並不認為

against people of one or another body size at all.

這研究能被拿來

Our next questions was:

當作身材歧視的正當理由

Could we actually visualize this spread?

我們下一個問題是：

Was weight gain in one person actually spreading

這種擴散要如何視覺化？

to weight gain in another person?

一個人變胖是否會連帶影響

And this was complicated because

另一個人的體重？

we needed to take into account the fact that the network structure,

這很複雜

the architecture of the ties, was changing across time.

因為我們要考慮到網路的結構、

In addition, because obesity is not a unicentric epidemic,

連結的構造方式，是隨時在改變的

there's not a Patient Zero of the obesity epidemic --

還有，肥胖症不是種只有單一中心的流行病

if we find that guy, there was a spread of obesity out from him --

沒有肥胖流行病的「零號病人」－

it's a multicentric epidemic.

疾病的原始帶原者是不存在的

Lots of people are doing things at the same time.

它是有許多中心的

And I'm about to show you a 30 second video animation

很多人同時做著相同的事

that took me and James five years of our lives to do.

我給大家看個30秒動畫

So, again, every dot is a person.

我和James花五年研究出來的

Every tie between them is a relationship.

每個點都是一個人

We're going to put this into motion now,

每條線表示他們的關連

taking daily cuts through the network for about 30 years.

我們現在放給大家看

The dot sizes are going to grow,

一睹30年的人際網路變化

you're going to see a sea of yellow take over.

點的大小開始變化

You're going to see people be born and die --

會看到越來越多黃點

dots will appear and disappear --

也可以看到人們的出生、死亡

ties will form and break, marriages and divorces,

點的消失與形成

friendings and defriendings.

連結的形成與斷裂，結婚與離婚

A lot of complexity, a lot is happening

友情的產生與破裂

just in this 30-year period

非常複雜，這30年時間

that includes the obesity epidemic.

發生了許多事情

And, by the end, you're going to see clusters

包括肥胖的流行

of obese and non-obese individuals

最後，你可以看到

within the network.

肥胖、不肥胖的個體

Now, when looked at this,

在這網路裡

it changed the way I see things,

看著這張圖

because this thing, this network

改變了我看事情的角度

that's changing across time,

因為這個網路

it has a memory, it moves,

隨時間變換的網路

things flow within it,

它是有記憶的、會移動的

it has a kind of consistency --

裏面也有很多流動

people can die, but it doesn't die;

它擁有著一種持續性

it still persists --

人會死亡，但它不會

and it has a kind of resilience

永久存在

that allows it to persist across time.

它有種恢復力

And so, I came to see these kinds of social networks

能隨時間存在著

as living things,

我將這些人際網路視為

as living things that we could put under a kind of microscope

活的東西

to study and analyze and understand.

是我們可以放到顯微鏡下觀察、研究、

And we used a variety of techniques to do this.

並加以了解的東西

And we started exploring all kinds of other phenomena.

我們用了很多方式研究

We looked at smoking and drinking behavior,

並開始探索其他現象

and voting behavior,

我們觀察吸菸、酗酒的人、

and divorce -- which can spread --

有投票習慣的人、

and altruism.

離婚的人－這也會傳染

And, eventually, we became interested in emotions.

還有無私。

Now, when we have emotions,

最後，我們對情緒感興趣

we show them.

人的情緒一來

Why do we show our emotions?

馬上展現出來

I mean, there would be an advantage to experiencing

為什麼展現情緒？

our emotions inside, you know, anger or happiness.

我是說，如果能把生氣、開心等情緒

But we don't just experience them, we show them.

放在心裡應該是種優點吧

And not only do we show them, but others can read them.

我們不只有情緒，我們會展現出來

And, not only can they read them, but they copy them.

我們不只會展現出來，其他人還解讀的出來

There's emotional contagion

他們不只解讀的出來，還會複製那情緒

that takes place in human populations.

這就是人類社會的

And so this function of emotions

情緒傳染

suggests that, in addition to any other purpose they serve,

這些情緒的功能

they're a kind of primitive form of communication.

還顯示他們有其他用途

And that, in fact, if we really want to understand human emotions,

他們是一種最基本的溝通方式

we need to think about them in this way.

如果我們真想了解人類的情緒

Now, we're accustomed to thinking about emotions in this way,

我們就需要將之視為如此

in simple, sort of, brief periods of time.

我們短時間內，已經習慣

So, for example,

將情緒視為溝通方式

I was giving this talk recently in New York City,

舉個例子，

and I said, "You know when you're on the subway

我最近在紐約也做了演講

and the other person across the subway car

我說：「你搭地鐵時，」

smiles at you,

「坐你對面的人」

and you just instinctively smile back?"

「對你微笑」

And they looked at me and said, "We don't do that in New York City." (Laughter)

「你會直覺的也對他微笑。」

And I said, "Everywhere else in the world,

觀眾看著我，說：「在紐約沒人這樣做。」

that's normal human behavior."

我說：「紐約除外，世界其他地方」

And so there's a very instinctive way

「這是正常現象。」

in which we briefly transmit emotions to each other.

這是種直覺性的動作

And, in fact, emotional contagion can be broader still.

簡單的將情緒傳給他人

Like we could have punctuated expressions of anger,

事實上，這種情緒傳染是可以很廣的

as in riots.

就像暴動中，展現憤怒情緒

The question that we wanted to ask was:

的間接表達

Could emotion spread,

我們想問的問題是：

in a more sustained way than riots, across time

情緒傳染是否不止

and involve large numbers of people,

在地鐵中相互微笑的兩人而已