The Origins of Humanity and the Protective Role of Dark Skin: The Evolution of Vitamin D
Since the dawn of civilization, humans have inhabited the Eastern African continent approximately 300,000 years ago as their birthplace. In this tropical region, the prevalence of dark skin played a crucial role in protecting individuals from the intense sunlight. (1)
As our ancestors ventured beyond Eastern Africa, the expansion of human habitat began, gradually spreading across the Northern and Southern Hemispheres 75,000 years ago.(1) However, as they encountered colder climates and reduced sunlight exposure, significant changes or evolutionary pressure occurred in the human population, including the gradual lightening of skin color.
The Expansion of Human Habitation and the Lightening of Skin Color
The migration of humans to different regions exposed them to varying climates and levels of ultraviolet (UV) radiation. In response to these environmental factors, human skin adapted through natural selection. Over time, individuals living in regions with lower sunlight intensity developed lighter skin tones to facilitate the synthesis of vitamin D.
As humans moved away from the equator and inhabited higher latitudes, the penetration of Ultraviolet B Radiation (UVB) decreased in the tropic north of the Tropic of Cancer and south of Tropic of Capricon. (2) Consequently, our bodies had to possess the ability to synthesize Vitamin D3 more efficiently, leading to the gradual lightening of skin color. The production of Vitamin D3 declines with the increased concentration of eumelanin pigmentation. (2) However, it is important to note that skin color alone could not entirely compensate for the reduced UVB exposure, necessitating alternative means to meet the body's vitamin D requirements. Pleistocene Homo erectus, for example, living outside of tropics would derive the Vitamin D3 from the Vitamin D3-rich foods such as oily fish and marine mammals. (2)
The Importance of Vitamin D and Changes in Supplementation Methods
Vitamin D plays a crucial role in maintaining healthy bones, regulating immune function, and supporting overall well-being. As the human habitat expanded to regions with limited sunlight, the need for vitamin D supplementation became apparent. Early humans turned to fish, shellfish and a carnivorous diet as sources of vitamin D, replenishing their levels through dietary means. By doing so, people begun to show the dependency from the sunlight and the regions of dwelling.
The human body primarily synthesizes vitamin D3 when exposed to ultraviolet B (UVB) radiation, particularly in the range of 280-315 nm (especially 295-297 nm). (2) Equatorial regions benefit from better UVB penetration, allowing for more efficient synthesis. However, as humans ventured to higher latitudes, the diminished UVB penetration necessitated physical adaptations to enable increased vitamin D3 synthesis.
High Latitude and the Synthesis Capability of Vitamin D
As humans migrated to higher latitudes with lower UVB penetration, the ability to synthesize vitamin D3 became a physiological requirement. The gradual lightening of skin color, through genetic changes, allowed for improved synthesis of vitamin D3 in response to limited UVB exposure. More specifically, the variation on the activation of the MC1R protein, which is the main factor for swtiching of color from yellow-red pheomelanin to brown-black eumelanin, changed the color pattern of the human race in the specific region. (2) However, even with these adaptations, skin color alone could not fully address the challenge. Consequently, humans began to rely on dietary sources to supplement their vitamin D requirements.
In conclusion, the human journey from Africa to various regions worldwide brought about significant changes in both our habitat and our physiology. The evolution of skin color, from darker to lighter tones, reflects our species' ability to adapt to different environmental conditions. However, the complex interplay between genetics, sunlight exposure, and dietary practices ultimately shaped our ability to maintain adequate vitamin D levels for optimal health and survival.
Reference
Carlberg C. Vitamin D in the Context of Evolution. Nutrients. 2022 Jul 22;14(15):3018. doi: 10.3390/nu14153018. PMID: 35893872; PMCID: PMC9332464.
Jablonski NG, Chaplin G. The roles of vitamin D and cutaneous vitamin D production in human evolution and health. Int J Paleopathol. 2018 Dec;23:54-59. doi: 10.1016/j.ijpp.2018.01.005. Epub 2018 Mar 29. PMID: 29606375.
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