Anthropology Question:

Eyes, like any other physical feature such as height, skin color, and shape of teeth for example, are influenced by the interaction of genes with the environment. We evolve features that best suit the environment and in the case of East Asians, the shape of their eyes has to do with limiting the amount of sand entering them. When the first North Asians entered that part of the world some 25, 000 years ago, they were exposed to extreme sand storms from the Gobi desert, thus evolving the more oval eye shape through time.

What is important to understand is that:

Genotype (genes) + Environment = Phenotype (physical features)