We social animals must balance the need to avoid infections with the need to interact with conspecifics. To that end we have evolved, alongside our physiological immune system, a suite of behaviors devised to deal with potentially contagious individuals. Focusing mostly on humans, the current review describes the design and biological innards of this behavioral immune system, laying out how infection threat shapes sociality and sociality shapes infection threat. The paper shows how the danger of contagion is detected and posted to the brain; how it affects individuals’ mate choice and sex life; why it strengthens ties within groups but severs those between them, leading to hostility toward anyone who looks, smells, or behaves unusually; and how it permeates the foundation of our moral and political views. This system was already in place when agriculture and animal domestication set off a massive increase in our population density, personal connections, and interaction with other species, amplifying enormously the spread of disease. Alas, pandemics such as COVID-19 not only are a disaster for public health, but, by rousing millions of behavioral immune systems, could prove a threat to harmonious cohabitation too.

我们社会动物必须平衡避免感染的需要和与同种动物互动的需要。为此，除了生理免疫系统之外，我们还进化了一套旨在应对潜在传染性个体的行为。目前的评论主要关注人类，描述了这种行为免疫系统的设计和生物学内部结构，阐述了感染威胁如何塑造社交性和社交性如何塑造感染威胁。该论文展示了如何检测传染的危险并将其发布到大脑；它如何影响个人的择偶和性生活；为什么它加强了群体内部的联系，却切断了群体之间的联系，导致对任何外表、气味或行为异常的人产生敌意；以及它如何渗透到我们的道德和政治观点的基础。当农业和动物驯化导致我们的人口密度、个人联系以及与其他物种的互动大幅增加时，这个系统已经到位，极大地扩大了疾病的传播。唉，像 COVID-19 这样的流行病不仅是公共卫生的灾难，而且通过唤醒数百万的行为免疫系统，也可能对和谐共处构成威胁。