The primary objective of this proposal is to investigate environmental influences on male reproductive functioning among the Turkana of Kenya. The investigators have conducted exemplary research on the reproductive ecology of Turkana women and the proposed research will extend their studies. The Turkana are divided into settled and nomadic groups which differ in diet and activity patterns. Additionally, strong seasonality in food supply leads to dietary variation as well. The investigators will utilize blood and urine samples to obtain profiles of testosterone and gonadotropins as well as other indicators of physiological functioning and body composition. From prior studies it is known that ecological factors strongly affect female reproductive biology. The current study will be one of the first to explore the role of ecology in male reproductive function.