Data from: Variant at serotonin transporter gene predicts increased imitation in toddlers: relevance to the human capacity for cumulative culture

Cumulative culture ostensibly arises from a set of sociocognitive processes which includes high-fidelity production imitation, prosociality and group identification. The latter processes are facilitated by unconscious imitation or social mimicry. The proximate mechanisms of individual variation in imitation may thus shed light on the evolutionary history of the human capacity for cumulative culture. In humans, a genetic component to variation in the propensity for imitation is likely. A functional length polymorphism in the serotonin transporter gene, the short allele at 5HTTLPR, is associated with heightened responsiveness to the social environment as well as anatomical and activational differences in the brain's imitation circuity. Here, we evaluate whether this polymorphism contributes to variation in production imitation and social mimicry. Toddlers with the short allele at 5HTTLPR exhibit increased social mimicry and increased fidelity of demonstrated novel object manipulations. Thus, the short allele is associated with two forms of imitation that may underlie the human capacity for cumulative culture. The short allele spread relatively recently, possibly due to selection, and its frequency varies dramatically on a global scale. Diverse observations can be unified via conceptualization of 5HTTLPR as influencing the propensity to experience others' emotions, actions and sensations, potentially through the mirror mechanism.

累积文化（cumulative culture）表面上源自一套社会认知过程，其中涵盖高保真生产模仿、亲社会性与群体认同。上述过程中的后者，可通过无意识模仿或社会模仿得到促成。因此，模仿行为个体差异的近缘机制，或可为人类累积文化能力的演化历程提供关键阐释视角。就人类而言，模仿倾向的个体差异很可能存在遗传基础。血清素转运蛋白基因（serotonin transporter gene）存在一处功能性长度多态性，即5-HTTLPR的短等位基因，该多态性与个体对社会环境的增强反应性，以及大脑模仿神经环路的解剖结构与激活模式差异显著相关。本研究旨在探究该多态性是否会影响生产模仿与社会模仿的个体差异。携带5-HTTLPR短等位基因的幼儿，其社会模仿行为更为显著，且对演示的新颖物体操作动作的模仿保真度更高。由此可见，该短等位基因与两种模仿形式相关联，而这两种模仿形式或为人类累积文化能力的核心基础。该短等位基因的传播时间相对较近，其扩散可能受到选择压力的推动，且在全球范围内的等位基因频率分布差异悬殊。若将5-HTTLPR概念化为通过镜像机制（mirror mechanism）影响个体体察他人情绪、复刻他人行为并感知他人感官体验的倾向，则可将诸多不同的研究发现统一起来。