要想逃脱饿狼的追捕，一只羊并不需要跑得比狼快，只需要比其他羊快就行了。这是一种自私的行为，而不是以整体利益为目的的团队合作行为。研究人员认为，正是这种自私性决定了群居动物的行为。但长期以来，关于羊群自私性的理论一直没有得到研究数据的支持。
现在，科学家们通过对羊群在躲避牧羊犬时的运动方式的分析，证明上述理论是正确的。这一成果刊发在《当代生物学》（Current Biology）杂志网络版。为了寻求安全，每只羊都拼命朝着羊群的中心奔跑，而不是直接从狗的身边跑开。
马萨诸塞大学阿默斯特分校的生物学家Theodore Stankowich说：“对大型动物在野外的二维空间信息进行测量是一件很难的事情。他们得益于一次独特的机会，在一种受控的环境中对羊群进行研究，试图对上述问题作出解答。”
此前，对于海豹、螃蟹和鸽子的研究表明，这些动物之所以群居也是出于自私的目的，但研究者们缺乏精确的数据来证明这一点。
伦敦大学皇家兽医学院的生物学家Andrew King和他的同事们在46只羊和一只训练有素的澳大利亚牧羊犬身上安放了GPS系统，然后让狗去看管这群羊，同时以秒为单位记录下每只动物的位置。接下来，他们对数据进行分析，以确定是什么因素影响了羊的路径。
结果表明，根据羊群的中心位置就可以很好地预测出羊的运动路线。每只羊既不是以直线方式从狗身边跑开，也不是向各个方向散射，更不是跟随身边的羊，而是全都拼命向着羊群中心跑。当狗位于70米之外时，羊群开始聚拢；在它们作为一个整体向前移动时，每只羊不断地、尽量地靠近中心位置。（生物谷Bioon.com）
doi:10.1016/j.cub.2012.05.008
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Selfish-herd behaviour of sheep under threat
Andrew J. King1, , Alan M. Wilson1, Simon D. Wilshin1, John Lowe1, Hamed Haddadi1, Stephen Hailes2 and A. Jennifer Morton3
Flocking is a striking example of collective behaviour that is found in insect swarms, fish schools and mammal herds [1]. A major factor in the evolution of flocking behaviour is thought to be predation, whereby larger and/or more cohesive groups are better at detecting predators (as, for example, in the many eyes theory), and diluting the effects of predators (as in the selfish-herd theory) than are individuals in smaller and/or dispersed groups [2]. The former theory assumes that information (passively or actively transferred) can be disseminated more effectively in larger/cohesive groups, while the latter assumes that there are spatial benefits to individuals in a large group, since individuals can alter their spatial position relative to their group-mates and any potential predator, thus reducing their predation risk [3]. We used global positioning system (GPS) data to characterise the response of a group of prey animals (a flock of sheep) to an approaching predator (a herding dog). Analyses of relative sheep movement trajectories showed that sheep exhibit a strong attraction towards the centre of the flock under threat, a pattern that we could re-create using a simple model. These results support the long-standing assertion that individuals can respond to potential danger by moving towards the centre of a fleeing group [2].
