Variable: Physiological Cycles

Homo sapiens has evolved a series of physiological cycles that deeply influence human behavior. For example, diurnal cycles of night and day create peaks of labor and leisure activity; menstrual cycles control reproduction patterns. The life cycle is roughly similar across cultures: birth, childhood, labor, marriage, child rearing, retirement from labor, and death. Each stage of the life cycle creates expectations and norms for behavior (including the use of resources [see Burch and DeLuca 1984]). Measurement can include the proportion of the population at each stage of the life cycle. These cycles create predictable patterns of activity within the human ecosystem: park-going during daylight hours, increases in energy demands during early morning hours (for showering, cooking, heating, and so forth), rituals at each juncture of life cycle stages (such as weddings and funerals). While physiological cycles rarely may change, they may substantively impact human ecosystem functioning at several scales.

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