人们在难以数计的谎言诱惑下会怎样进行合作，是心理学和经济学研究中的重要课题。有关这个课题的研究通常集中于对“投桃报李”理论的研究，这个理论认为：人们总是倾向于向别人表现慷慨，除非对方表现出不慷慨的态度。在这个时候合作往往会终止。换句话说，人如果受到一次愚弄，或许是因为错在对方。如果再次受到对方愚弄，就只能怪自己不吸取教训了。

　　When he encounters such a withdrawal of collaboration, the theory goes, the malefactor will learn the error of his ways and become a more co-operative individual. And there is experimental evidence, based on specially designed games, that tit-for-tat does work for pairs of people. Human societies, though, are more complex than mere dyads. And until recently, it has been difficult to model that complexity in the laboratory. But a paper published this week in the Proceedings of the National Academy of Sciences by Nicholas Christakis and his colleagues at Harvard has changed that. Dr Christakis arranged for a collaboration-testing game to be played over the web, with many participants. As a result, he and his team have gained a more sophisticated insight into the way co-operation develops.

　　根据这个理论，一旦作恶的一方得不到对方的合作，他将会从自己的错误中吸取教训，并变成一个更具有合作精神的人。根据从特别设计的游戏中取得的实验证据，投桃报李的原则确实适用于成对的研究对象。不过人类社会要比成对的研究对象复杂得多。直到最近为止，研究人员都很难在实验室中模拟出社会生活中的复杂情景。不过哈佛大学的尼古拉斯?克里斯塔（Nicholas Christakis）和他的同事们本周在《美国国家科学院院刊》上发表的论文改变了这个现实。克里斯塔博士设计了一个能够在互联网上供多人参与的合作测试游戏。根据这个游戏，克里斯塔博士和他的团队获得更多的资料，得以了解合作关系的演变规律。

　　Dr Christakis used what is known as a public-goods game for his experiment. At the beginning of such a game, points are doled out to each participant. During every round, players are given the opportunity to donate points to their neighbours. Points so donated are augmented by an equal number from the masters of the game. If everyone co-operates, then, everyone ends up richer. A “defector” who refuses to donate to his co-operating neighbours will, however, benefit at the expense of those neighbours. At the game’s end, the points are converted into real money, to ensure that proper incentives are in place.

　　克里斯塔博士在实验中使用了一种称为公开物品的游戏。在比赛开始时，每个参与者都获得一定的分数。在每轮游戏中，游戏者都有机会给周围的人一些分数。游戏的主持人会将参与者给予别人的分数翻倍。如果每个人都采取合作的态度，那么每个人都会得到更多的分数。游戏中的“叛逃者”，即拒绝将分数赠送给邻人的参与者，能够从别人的损失中获益。在游戏结束时，所有的分数都会转换成实际的金钱，以保障游戏具有适当的激励机制。

　　To play his large-scale public-goods game, Dr Christakis recruited 785 volunteers via Mechanical Turk—a service provided by Amazon, an online retailer, that works by farming out small tasks to an army of individual workers. Each volunteer was randomly assigned links to, on average, eight other players. Together, they played repeated rounds of one of three variations of the game.

　　为了将这个公开物品游戏推而广之，克里斯塔博士通过土耳其机器人（Mechanical Turk）召集了785个志愿者（土耳其机器人是亚马逊推出的一种服务，它的作用相当于网络零售商，能够将小型的任务分配给数量庞大的人群完成）。每个参与者都能够随机分配到几个邻人，平均来说，每个人一般能分到八个邻人。他们一起参与三种不同游戏形式，在每种形式中都会反复玩上几轮。

　　In the first, participants always interacted with the same group of people. In the second, the connections were randomly reshuffled after each round. In the final version, one-third of the possible pairings between participants were chosen at random after each round (such pairs may or may not, therefore, have been dealing with each other in the previous round). One player from each pair was first told or reminded of how the other had behaved in the previous round, and was then asked whether he wanted to break his connection with that player, if he already had one, or form a new connection, if he had not.

　　起初，参与者总是与同组人玩。接下来，每结束一轮，参与者之间的联系都会随机打乱，并重新分组。在最后的阶段，每一轮结束时都会随机挑选出三分之一的参与者让他们有机会重新配对（这些将要配对的参与者之前是否曾经合作过并不重要）。每对组合中都会有一个人能够首先得知合作对方或将要合作的参与者在过去的游戏中表现如何，然后会问他是否还愿意和对方合作（如果他已经和对方结伴），或者是否愿意和对方结伴（如果他尚未和对方结伴）。

　　In all versions of the game, roughly 60% of players started out co-operating. However, in the first two, this decreased over time as the pernicious influence of the freeloaders spread. The larger the fraction of a subject’s partners who defected in a given round, the less likely that person was to co-operate in the next—classical tit-for-tat. However, this tit-for-tat retaliation was not enough to save co-operation, and after a dozen rounds only 10-20% of the players were still willing to co-operate.

　　在游戏的三种模式中，大约有60%的参与者起初都愿意表现合作精神。不过在前两种形式中，合作者的数目随着不劳而获者不断散播的消极影响，而逐渐减少。在特定的游戏中，调查对象的合作者中如果存在越多的人扮演叛逃者，该对象在下一轮游戏中就越不愿意表现合作精神——这正是典型的投桃报李精神。不过这种投桃报李的回馈态度无法维持合作关系，在大约12轮游戏后，只有大约10-20%的参与者仍然愿意表现合作精神。

　　In the variant where participants had some choice over whom they interacted with, though, the amount of co-operation stayed stable as the rounds progressed. When Dr Christakis and his team looked at how the relationships between players were evolving in this third version, they found that connections between two co-operators were much more likely to be maintained than links that involved a defector. Over time, the co-operators accumulated more social connections than the defectors did.

　　不过在游戏的第三种形式中，即参与者有权选择合作对象时，愿意表现合作精神的人数并没有随着游戏次数的增加而减少。比较过三种游戏形式中参与者相互关系的演变规律后，克里斯塔博士和他的团队发现二个同是合作者之间的关系要比其中一个是叛逃者之间的关系更容易维持。随着时间的推移，合作者比叛逃者积累了更多的社会关系。

　　Furthermore, as they were shunned, the defectors began to change their behaviour. A defector’s likelihood of switching to co-operation increased with the number of players who had broken links with him in the previous round. Unlike straightforward tit-for-tat, social retaliation was having a marked effect.

　　不仅如此，由于受到大家的回避，叛逃者也开改变自己的行为。如果在上一次游戏中有越多的参与者拒绝与某个叛逃者合作，那么这个人在下一次的游戏中就越可能变成合作者。与单纯的投桃报李相比，社会回馈更有助于维系人与人之间的关系。

　　The next question, then, is whether such a mechanism holds outside the laboratory. To find out, Dr Christakis has forged links with some anthropologists. They hope to report the answer soon.

　　接下来的问题是这一机制是否能推广到实验室之外呢？为了找到这个问题的答案，克里斯塔博士已经与一些人类学家取得合作。他们希望能够尽快回答这个问题。

　　numerous adj.很多的 withdrawal n.退回 convert v.(使)转变(化) retailer n. 零售商; 零售店 pernicious adj. 有害的, 致命的