Mayhew Jessica A, Gómez Juan-Carlos
Centre for Social Learning and Cognitive Evolution and the Scottish Primate Research Group, School of Psychology and Neuroscience, University of St. Andrews, St. Andrews, Fife, Scotland, United Kingdom.
Anthropology and Museum Studies, Central Washington University, Ellensburg, Washington.
Am J Primatol. 2015 Aug;77(8):869-77. doi: 10.1002/ajp.22411. Epub 2015 Apr 6.
Human eye morphology is considered unique among the primates in that humans possess larger width/height ratios (WHR), expose a greater amount of visible sclera (SSI; width of exposed eyeball/width of visible iris), and critically, have a white sclera due to a lack of pigmentation. White sclera in humans amplifies gaze direction, whereas the all-dark eyes of apes are hypothesized to conceal gaze from others. This study examines WHR and SSI in humans (N = 13) and gorillas (N = 85) engaged in direct and averted gazes and introduces a qualitative assessment of sclera color to evaluate variations in sclera pigmentation. The results confirm previous findings that humans possess a larger WHR than gorillas but indicate that humans and gorillas display similar amounts of visible sclera. Additionally, 72% (N = 124) of gorilla eyes in this sample deviated from the assumed all-dark eye condition. This questions whether gaze camouflage is the primary function of darkened sclera in non-human primates or whether other functional roles can be ascribed to the sclera, light or dark. We argue that white sclera evolved to amplify direct gazes in humans, which would have played a significant role in the development of ostensive communication, which is communication that both shows something and shows the intention to show something. We conclude that the horizontal elongation of the human eye, rather than sclera color, more reliably distinguishes human from great ape eyes, represented here by gorillas.
人类眼睛形态在灵长类动物中被认为是独特的，因为人类拥有更大的宽高比（WHR），露出更多的可见巩膜（SSI；暴露眼球宽度/可见虹膜宽度），关键的是，由于缺乏色素沉着，人类有白色巩膜。人类的白色巩膜放大了注视方向，而猿类全黑的眼睛据推测是为了向他人隐藏注视。本研究考察了直接注视和回避注视状态下人类（N = 13）和大猩猩（N = 85）的WHR和SSI，并引入了对巩膜颜色的定性评估，以评估巩膜色素沉着的变化。结果证实了之前的发现，即人类的WHR比大猩猩大，但表明人类和大猩猩露出的可见巩膜量相似。此外，该样本中72%（N = 124）的大猩猩眼睛偏离了假定的全黑眼睛状态。这就引发了一个问题，即注视伪装是否是非人类灵长类动物深色巩膜的主要功能，或者巩膜无论是浅色还是深色，是否可以归因于其他功能角色。我们认为，白色巩膜的进化是为了放大人类的直接注视，这在明示性交流的发展中发挥了重要作用，明示性交流是既展示某事物又展示展示该事物意图的交流。我们得出结论，人类眼睛的水平伸长，而非巩膜颜色，更可靠地将人类与以大猩猩为代表在这里的类人猿眼睛区分开来。
