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Everything indicates that this is the result of an evolutionary adaptation of the Mongoloids, the biological group of the human species to which almost all Orientals belong. At least that’s what the most accepted scientific theories preach today. According to these hypotheses, the so-called palpebral fissure (the space between the upper and lower eyelids) is smaller in Japanese, Chinese, Koreans and other peoples as a practical matter. “Probably, this trait must have been an advantage for inhabitants of cold regions, since its function is similar to that of the glasses used by skiers, which have a slit-shaped display to reduce the light reflected by the snow. This explanation seems to be quite logical, because the Mongoloids appeared in an icy area in North Asia at the end of the last ice age, around 10,000 years ago”, says anthropologist Walter Neves, from USP.
In fact, as the white sea of cold regions reflects up to 85% of the sunlight that reaches the surface, those who live in these places may have long-term vision problems. “Ultraviolet radiation reflected by snow can cause momentary blindness, in addition to cataracts and retinal damage. This would explain the predominance of those with slanted eyes in natural selection”, says ophthalmologist Élcio Sato, from the Federal University of São Paulo (Unifesp). It doesn’t hurt to remember that, even with the palpebral fissure closed, Orientals see perfectly.