Those things are caused by adaptation. That's miroevolution, as opposed to macroevolution, where you have a new species. It's not a matter of adding anything new to the genetic material of the population, but simply weeding out what is not working as well as some other variations. Adaptation occurs when the structure or function of an organism changes in ways that improve the chances for survival and reproduction in its environment.
The face and body of the Mongols result from adaptations to the bitter cold of Siberia. The body, and particularly the head, tends to be round, increasing body volume. The evaporative surface area of the skin is thus reduced relative to body volume, and less heat is lost. The nose is small and less likely to freeze, and the nostrils are narrow, warming the air before it reaches the lungs. Eyes are protected from the cold Siberian air by fatty folds of skin. The eye shape of the Mongoloid is a naturally adapted glare filter. Also, the epicanthal folds protect the inner eyes, giving them a "slanted" appearance, while the fatty pad in the eye lid keeps the eyeball warm, and gives the eyelids a "smooth" appearance.
