靈長類動物的大腦限制 朋友圈真能無限大?

They turn up weekly in my inbox, gnawing away at my soul. The kind words, the smiling faces, the ego-stroking invitations to connect, all of which I guiltily ignore. The thing is, I buy into the idea of Dunbar’s number — that our primate brains limit us to meaningful social contact with no more than about 150 people — and I am already exceeding 200 on LinkedIn.

它們每週都會出現在我的電子郵箱裏，一點一點地啃噬着我的靈魂。友善的語言，微笑的表情，以及迎合自尊心的社交邀請，所有這些都被我心懷愧疚地忽視了。原因在於，我認同鄧巴數字(Dunbar’s number)的概念——即我們靈長類動物的大腦限制着我們有能力保持的有意義的社交對象人數，使其不超過約150人——而我在領英(LinkedIn)上的好友人數已經超過了200人。

Professor Robin Dunbar, the Oxford university anthropologist who came up with the eponymous figure after noting the strikingly similar sizes of human groupings ranging from Neolithic villages to Roman legions to an average Christmas card list, has posited that our social attention is not distributed evenly among those 150 confidantes but instead layered like an onion; five closest contacts in the innermost layer, then 10 in the next, followed by 35 and 100.

牛津大學(Oxford university)人類學家羅賓·鄧巴(Robin Dunbar)教授提出了這個以他名字命名的數字。鄧巴發現，從新石器時代的村落、羅馬帝國的軍團，到一份普通的聖誕節賀卡寄送名單，人類羣體的規模具有驚人的相似性。他就此提出假說，即我們的社交注意力並不是在150個知心朋友之間平均分配的，而是像洋蔥那樣分層分佈；5個最親密的聯繫人位於我們社交圈的最裏層，外一層是10個人，再向外的兩層分別是35人和100人。

Now a study of mobile phone calls has attempted to test Prof Dunbar’s hypothesis about our Russian doll-like shells of emotional intimacy, providing insight into how we stratify our social connections. Along with colleagues at Finland’s Aalto University School of Science, Prof Dunbar looked at a 2007 data set of European mobile phone calls, comprising 35m users making a total of 6bn calls. The frequency of calls between two people was a proxy for emotional closeness. Those who made just emergency or business calls were excluded; only those making reciprocal calls to at least 100 people were included.

現在，一項針對手機通話的研究試圖檢驗鄧巴教授的假說——即我們的感情親密度是像俄羅斯套娃那樣分層分佈的——進而幫助理解我們如何給自己的社交關係分層。在芬蘭阿爾託大學理工學院(Aalto University School of Science)同事們的合作下，鄧巴教授研究了2007年歐洲的手機通話數據集，這其中包含了3500萬用戶進行的總計60億次通話。兩個人之間通話的頻率是反映他們感情親密度的近似指標。數據中剔除了那些僅做緊急呼叫或僅撥打商務電話的人；只有那些和至少100個人多次往返呼叫的人被包括了進來。

By scanning networks of calls and ap-plying clustering algorithms, researchers found people tended to have either four or five layers in their social onion. On average, those with four layers had: four closest confidantes, often relatives, whom they dialled most frequently; 11 in the next layer; then 30 and 129.

通過梳理通話的人際網絡和應用聚類算法，研究人員發現，人們傾向於將他們的社交圈劃分爲四至五層。平均而言，社交圈分爲四層的個體擁有4個最親近的知己，往往是親戚，他們與這些人的通話最爲頻繁，再向外一層有11人，最外面的兩層分別是30人和129人。

For those with five layers, the number of friends was split slightly differently: three closest contacts; then 7, 18, 43 and 134. The analysis appeared on the arXiv server last month, where scientists can upload results for academic discussion (sometimes, but not always, as a precursor to peer-reviewed publication).

對於那些社交圈分爲五層的個體來說，每一層分佈的朋友人數略有不同：3個最親密的聯繫人在最裏層，往外的各層依次是7人、18人、43人、和134人。上述分析結果上月出現在了arXiv網站上，科學家們向這個網站上傳自己的研究成果用於學術討論（有些時候——當然並不總是如此——這是在由同行評議的正式期刊發表的前奏）。

While the idea of social “layering” seems robust according to this analysis, the variations noted suggest that the number of layers corresponds with a social spectrum. One idea to emerge from the study is that individuals with four layers might be introverts while those with five are extroverts.

儘管根據這項分析，社交“分層”的概念似乎是站得住腳的，但分析中指出的差異或許意味着，分層的層數對應於不同的社交傾向。從上述研究衍生出的一個觀點是，社交圈分爲四層的個體也許是內向型人，而社交圈分爲五層的個體可能是外向型人。

The paper has limitations: it looked at just one year of data. Friendships can be impermanent, varying across time and place, and reflecting our lives at particular stages. Frequency of contact does not always correlate with depth of relationship; longstanding bonds often do not need intensive tending to bloom.

這篇論文有其侷限性：它僅僅考察了一年時間內的數據。友誼可以是短暫的，因時因地而變，並反映我們在特定階段的生活狀態。聯絡的頻率並不總是與友情的深淺成正比；長期關係常常不需要密集的看護也能茁壯發展。

But it is also possible that this study captures a unique picture of friendship: a 2007 data set represents the social world before smartphone ubiquity, and before people routinely began maintaining friendships on Facebook and other online sites on their mobile devices. There is also a persuasive consistency in the numbers, the researchers note. This intuitively mirrors real life: even if a house move or a job change forces a change of circumstances, old acquaintances are superseded by new ones. The exact components of the layers may change but the layers themselves remain intact.

但同樣可能的是，這項研究捕捉到了友誼的獨特快照：2007年的數據集代表了智能手機普及之前的社交格局，早於人們開始習慣性地在移動設備上通過Facebook或其他網站維持友誼。研究人員指出，這些數據還表現出了頗有說服力的一致性。它直觀地映照出了真實生活：即便搬家或者換工作會導致我們所處的環境隨之改變，老相識也會被新朋友所取代。社交分層的具體人員構成或許會發生變化，但分層本身保持不變。

Few of us, it should be noted, exceed 200 meaningful social relationships. This limit should prompt networking sites to refine their services in a digitally promiscuous age. The enduring human need to connect — a desire that can now be expressed at the touch of a button — should ideally be balanced against the inability of our brains to cope with an excessive degree of digital schmoozing.

值得指出的是，我們當中幾乎沒有人能擁有超過200個的有意義社交關係。這一上限應促使社交網站在一個數字意義上人際關係混雜的時代完善他們的服務。持久存在的與他人聯繫的人性需要——如今這種願望按一下按鈕就能得到表達——最好與大腦無力應對過度數字化交往的侷限取得平衡。

Instead of the usual binary options to either accept or decline an invitation, there could be a third box to click that is both more gracious and scientifically accurate. It would read: “It’s not that I don’t want you to join my network, but I’m just waiting for some space to come up on my fourth layer.”

在通常的接受或拒絕一項邀請的二元選擇之外，還應有第三個更有禮貌、同時在科學上也更準確的選項以供勾選。該選項應表述如下：“並非我不願你加入我的社交圈，但我目前還在等待我的第四個社交層出現空缺。”