Evolutionary Adaptation of Human Lens to Ultraviolet Radiation and Hypoxia

Abstract

Sarah I Y Ahmed, Rayan S Ali and Eltahir AG Khali

Genetic evolution of human lens and vision in extreme environments of high ultraviolet radiation (UVR) and low oxygen at high altitudes is an evidence of intense past of Natural Selection. This review is an attempt to explain how the adaptive genes associated with high altitudes adaptation to extreme environments can improve human vision and protect from many ocular disorders. We hypothesized that both EPAS1 and MTHFR genes that are known to be strongly associated with high altitudes adaptation are, in turn, also associated with adaptation of human lens epithelium to the conditions of high UVR and hypoxia, which are believed to be the main causes of lens opacities and cataracts. We suggested that the oxidative stress that may result from UVR and hypoxia are responsible for the down-regulation of high-fidelity DNA repair mechanisms in ocular tissues, skin, and other tissues. This probably leads to high genetic flexibility and variations that influence the process of Natural Selection on the basis of competition between the cells that bear different genetic signatures. This would result in more adaptive populations of cells that are better capable of surviving such extreme conditions, resulting in a better adaptive vision. Therefore, we adopt the concept of “Therapy by adaptation”, to benefit from the human genetic heritage of ancient indigenous populations like Tibetans and their adaptive physiological response to extreme environments and how to explore these adaptive mechanisms for the prevention and cure of hypoxia-related and UVR-related disorders like cataracts.

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