to the Americas via the Siberian Arctic 15,000 years ago. DNA analyses conducted since 2007 revealed the acceleration of evolution with regards to defenses against disease, skin color, nose shapes, hair color and type, and body shape since about 40,000 years ago, continuing a trend of active selection since humans emigrated from Africa 100,000 years ago. Humans living in colder climates tend to be more heavily built compared to those in warmer climates because having a smaller surface area compared to volume makes it easier to retain heat. People from warmer climates tend to have thicker lips, which have large surface areas, enabling them to keep cool. With regards to nose shapes, humans residing in hot and dry places tend to have narrow and protruding noses in order to reduce loss of moisture. Humans living in hot and humid places tend to have flat and broad noses that moisturize inhaled air and retain moisture from exhaled air. Humans dwelling in cold and dry places tend to have small, narrow, and long noses in order to warm and moisturize inhaled air. As for hair types, humans from regions with colder climates tend to have straight hair so that the head and neck are kept warm. Straight hair also allows cool moisture to quickly fall off the head. On the other hand, tight and curly hair increases the exposed areas of the scalp, easing the evaporation of sweat and allowing heat to be radiated away while keeping itself off the neck and shoulders. Epicanthic eye folds are believed to be an adaptation protecting the eye from overexposure to ultraviolet radiation, and is presumed to be a particular trait in archaic humans from eastern and southeast Asia. A cold-adaptive explanation for the epicanthic fold is today seen as outdated by some, as epicanthic folds appear in some African populations. Dr. Frank Poirier, a physical anthropologist at Ohio State University, concluded that the epicanthic fold in fact may be an adaptation for tropical regions, and was already part of the natural diversity found among early modern humans. Physiological or phenotypical changes have been traced to Upper Paleolithic mutations, such as the East Asian variant of the EDAR gene, dated to about 35,000 years ago in Southern or Central China. Traits affected by the mutation are sweat glands, teeth, hair thickness and breast tissue. While Africans and Europeans carry the ancestral version of the gene,