A mongolid népeknek miétt vágott a szemük?

Wikipédia: Possible evolutionary function

The epicanthic fold is often associated with greater levels of fat deposition around the eyeball, a feature most accentuated in native North Siberian, Aleut and Inuit populations. The adipose tissue is thought to provide greater insulation for the eye and sinuses from the effects of cold, especially from freezing winds, and to represent an adaptation to cold climates. It has also been postulated that the fold itself may provide a level of protection from snow blindness. Though its appearance in peoples of Southeast Asia can be linked to possible descent from cold-adapted ancestors, its occurrence in various African peoples precludes a cold-adaptive explanation for it appearing in the latter groups. The epicanthic fold found in some African people has been tentatively linked to protection for the eye from the high levels of ultraviolet light found in desert and semi-desert areas.

Ha fordítást szeretnél röviden: A szemgolyó körüli zsírlerakódás nagyobb mértékű, így az észak-szibériai, aleut és inuit népeknél a hideg, és fagyás elleni védelemre alakulhatott ki, a jelenleg délebbre élő leszármazottaknál pedig megmaradt.