Cordoni Giada, Brescini Martina, Pirarba Luca, Giaretto Florinda, Norscia Ivan
Department of Life Sciences and System Biology, University of Torino, Turin, Italy.
Am J Biol Anthropol. 2025 May;187(1):e70061. doi: 10.1002/ajpa.70061.
Play Face (PF) and Full Play Face (FPF) in the great apes-homologous to human smile and laugh-face-have been considered a single phenomenon. However, if natural selection has preserved two expressions, probably their adaptive value differs.
We collected video data on play interactions in two lowland gorilla groups (N = 21; Gorilla gorilla gorilla) housed at La Vallée des Singes and the ZooParc de Beauval (France). Lacking a tool tailored for gorillas during this study, we analyzed facial action-unit activation via chimpFACS and OpenFace.
We found that PF and FPF activated partly different action units as it occurs for chimpanzees and humans' PF/FPF. We detected the rapid replication (Rapid Facial Mimicry [RFM]) of either PF or FPF that was associated with longer play sessions. Not-mimicked PF was linked to increased play session variability (different types of play patterns) measured via the Shannon Index, whereas not-mimicked FPF was associated with increased play asymmetry (imbalance between offensive/defensive patterns) measured via the Play Asymmetry Index.
Lowland gorillas may use PF to manage sessions that are more complex in terms of pattern types and FPF-a more salient signal-to prevent misunderstandings when the session is imbalanced. RFM of both expressions may favor the prolongation of play sessions by increasing player synchronization and possibly emotional sharing. Our study opens the door to further comparative studies on playful expressions in humans and other primates as a way to fine-tune possible emotional communication and delineate potential evolutionary roots of Hominidae facial communication.
在大猩猩中，游戏脸（PF）和全游戏脸（FPF）——与人类的微笑和大笑脸同源——一直被视为一种单一现象。然而，如果自然选择保留了这两种表情，那么它们的适应性价值可能有所不同。
我们收集了两组圈养在法国拉瓦勒德辛格斯和博瓦尔动物园（ZooParc de Beauval）的低地大猩猩（N = 21；山地大猩猩指名亚种）游戏互动的视频数据。在本研究中，由于缺乏专门针对大猩猩的工具，我们通过黑猩猩面部动作编码系统（chimpFACS）和OpenFace软件分析面部动作单元的激活情况。
我们发现，PF和FPF激活的动作单元部分不同，这与黑猩猩和人类的PF/FPF情况相同。我们检测到PF或FPF的快速复制（快速面部模仿[RFM]），这与更长的游戏时间相关。未被模仿的PF与通过香农指数测量的游戏会话变异性增加（不同类型的游戏模式）有关，而未被模仿的FPF与通过游戏不对称指数测量的游戏不对称性增加（进攻/防御模式之间的不平衡）有关。
低地大猩猩可能使用PF来管理模式类型更复杂的游戏会话，而FPF——一种更显著的信号——用于在游戏会话不平衡时防止误解。两种表情的RFM可能通过提高玩家同步性以及可能的情感共享来促进游戏会话的延长。我们的研究为进一步比较人类和其他灵长类动物的嬉戏表情打开了大门，以此来微调可能的情感交流，并描绘人科动物面部交流的潜在进化根源。
