EXTERNAL PHENOTYPIC VARIATIONS IN MODERN HUMAN 3
Since modern humans ventured out of Africa, they spread across continents into a variety of habitats, from tropical zones to the arctic, and from lowlands to highlands. During migration, selective pressures in local environments (e.g., the cold climate, hypoxia, and endemic pathogens), together with random drift, have resulted in population-specific genetic variants, which further influenced variable phenotypes.
Skin pigmentation is one of the major phenotypic diversities in modern human. It’s usually dominated by melanin, a pigmentation located at base of epidermis. Globally skin color is highly correlated with latitude and the distribution of ultraviolet radiation (Barsh 2003). Population closer to equator tends to have dark skin for protection against UV, since overexposure may cause skin cancer. The Lighter skin in populations at higher latitude is underlying selection to maintain vitamin D synthesis, which is UV dependent process (Jablonski and Chaplin 2010).
Humans throughout the world differ in facial form, variations among continental regions accounted for 10% of facial difference, the studies on facial difference mainly focuses on skull remains and above all its been found that human skull variation has been shaped by neutral evolutionary process which is supported by the fact that phenotypic and geographic distance is also consistent with the idea (Jing G 2014)
Guo jing (2014).Journal of Human Evolution: Variations and signatures of selection on the human face.
[BLOG] Retrieved from www.sciencedirect.com/science/article/pii/S0047248414
Gregory S Barsh (2003). Plos BIOLOGY: What controls variation in human skin color? [BLOG] Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC212702/
Nina G. Jablonski George Chaplin (2010).PNAS article: Human skin pigmentation as an adaptation to UV radiation. [BLOG] .Retrieved from https://www.ncbi.nlm.nih.gov/pmc/article/PMC3024016/