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.

它们每周都会出现在我的电子邮箱里，一点一点地啃噬着我的灵魂。友善的语言，微笑的表情，以及迎合自尊心的社交邀请，所有这些都被我心怀愧疚地忽视了。原因在于，我认同邓巴数字(Dunbar’s number)的概念——即我们灵长类动物的大脑限制着我们有能力保持的有意义的社交对象人数，使其不超过约150人——而我在领英(LinkedIn)上的好友人数已经超过了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.

牛津大学(Oxford university)人类学家罗宾·邓巴(Robin Dunbar)教授提出了这个以他名字命名的数字。邓巴发现，从新石器时代的村落、罗马帝国的军团，到一份普通的圣诞节贺卡寄送名单，人类群体的规模具有惊人的相似性。他就此提出假说，即我们的社交注意力并不是在150个知心朋友之间平均分配的，而是像洋葱那样分层分布；5个最亲密的联系人位于我们社交圈的最里层，外一层是10个人，再向外的两层分别是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.

现在，一项针对手机通话的研究试图检验邓巴教授的假说——即我们的感情亲密度是像俄罗斯套娃那样分层分布的——进而帮助理解我们如何给自己的社交关系分层。在芬兰阿尔托大学理工学院(Aalto University School of Science)同事们的合作下，邓巴教授研究了2007年欧洲的手机通话数据集，这其中包含了3500万用户进行的总计60亿次通话。两个人之间通话的频率是反映他们感情亲密度的近似指标。数据中剔除了那些仅做紧急呼叫或仅拨打商务电话的人；只有那些和至少100个人多次往返呼叫的人被包括了进来。

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.

通过梳理通话的人际网络和应用聚类算法，研究人员发现，人们倾向于将他们的社交圈划分为四至五层。平均而言，社交圈分为四层的个体拥有4个最亲近的知己，往往是亲戚，他们与这些人的通话最为频繁，再向外一层有11人，最外面的两层分别是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).

对于那些社交圈分为五层的个体来说，每一层分布的朋友人数略有不同：3个最亲密的联系人在最里层，往外的各层依次是7人、18人、43人、和134人。上述分析结果上月出现在了arXiv网站上，科学家们向这个网站上传自己的研究成果用于学术讨论（有些时候——当然并不总是如此——这是在由同行评议的正式期刊发表的前奏）。

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.

尽管根据这项分析，社交“分层”的概念似乎是站得住脚的，但分析中指出的差异或许意味着，分层的层数对应于不同的社交倾向。从上述研究衍生出的一个观点是，社交圈分为四层的个体也许是内向型人，而社交圈分为五层的个体可能是外向型人。

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.

这篇论文有其局限性：它仅仅考察了一年时间内的数据。友谊可以是短暂的，因时因地而变，并反映我们在特定阶段的生活状态。联络的频率并不总是与友情的深浅成正比；长期关系常常不需要密集的看护也能茁壮发展。

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.

但同样可能的是，这项研究捕捉到了友谊的独特快照：2007年的数据集代表了智能手机普及之前的社交格局，早于人们开始习惯性地在移动设备上通过Facebook或其他网站维持友谊。研究人员指出，这些数据还表现出了颇有说服力的一致性。它直观地映照出了真实生活：即便搬家或者换工作会导致我们所处的环境随之改变，老相识也会被新朋友所取代。社交分层的具体人员构成或许会发生变化，但分层本身保持不变。

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，我们当中几乎没有人能拥有超过200个的有意义社交关系。这一上限应促使社交网站在一个数字意义上人际关系混杂的时代完善他们的服务。持久存在的与他人联系的人性需要——如今这种愿望按一下按钮就能得到表达——最好与大脑无力应对过度数字化交往的局限取得平衡。

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.”

在通常的接受或拒绝一项邀请的二元选择之外，还应有第三个更有礼貌、同时在科学上也更准确的选项以供勾选。该选项应表述如下：“并非我不愿你加入我的社交圈，但我目前还在等待我的第四个社交层出现空缺。”