Evolutionary models and empirical evidence suggest that outgroup threat is one of the strongest factors inducing group cohesion; however, little is known about the process of forming such cohesive groups. We investigated how outgroup threat galvanizes individuals to affiliate with others to form engaged units that are willing to act on behalf of their in-group. A total of 864 participants from six countries were randomly assigned to an outgroup threat, environmental threat, or no-threat condition. We measured the process of group formation through physical proximity and movement mirroring along with activity toward threat resolution, and found that outgroup threat induced activity and heightened mirroring in males. We also observed higher mirroring and proximity in participants who perceived the outgroup threat as a real danger, albeit the latter results were imprecisely estimated. Together, these findings help understand how sharing subtle behavioral cues influences collaborative aggregation of people under threat.

进化模型和经验证据表明，外群体威胁是诱导群体凝聚力的最强因素之一；然而，人们对形成这种有凝聚力的团体的过程知之甚少。我们调查了外群体威胁如何激励个人与他人建立联系，以形成愿意代表其内群体采取行动的参与单位。来自六个国家的总共 864 名参与者被随机分配到外群体威胁、环境威胁或无威胁条件。我们通过身体接近度和运动镜像以及解决威胁的活动来测量群体形成的过程，发现外群体威胁引起了男性的活动和增强的镜像。我们还观察到，将外群体威胁视为真正危险的参与者的镜像和接近度更高，尽管后者的结果估计不准确。总之，这些发现有助于了解分享微妙的行为线索如何影响受到威胁的人的协作聚集。