Which of the following is NOT one of the three theories of skin pigmentation distribution patterns?

The theory of water retention is not one of the primary explanations for skin pigmentation distribution patterns. The other options focus on how skin color has evolved as an adaptation to various environmental pressures, particularly related to ultraviolet radiation (UVR) exposure and the body's needs for nutrients and vitamins.

For instance, UVR protection is a critical factor; populations from areas with high UVR levels tend to develop darker skin to protect against the harmful effects of UV radiation, such as skin cancer and vitamin D degradation. On the other hand, lighter skin has evolved in populations in regions with lower UVR, allowing for more efficient synthesis of vitamin D, which is vital in regions with less sunlight.

Nutrient protection, particularly concerning folate, is also a significant factor; darker skin can help preserve folate levels, which are essential for various biological processes and are vulnerable to UVR exposure.

Water retention, while important for many physiological processes, does not directly relate to the primary evolutionary pressures influencing skin pigmentation. Thus, the correct identification of water retention as not being one of the three main theories underlines the focus on adaptations related to UV radiation and nutrient synthesis, which are crucial for survival and reproductive success in different environments.