The power of fitness in mammals: perceptions from the African slipstream

Evolutionary physiology is the emerging physiological discipline. Unlike environmental physiology or ecophysiology, whose definitions have long been made quite clear, evolutionary physiology has a broader scope of objectives, and its definition lacks a concise treatise. This paper presents the argument that the lack of a common definition of evolutionary physiology is retarding the unification of the mechanistic and amechanistic physiological sciences, a multidisciplinary obligation crucial for a holistic understanding of a physiological basis of fitness. The divide between mechanistic "how" questions, devoted primarily to homeostasis, and evolutionary "why" questions, concerned with understanding phenotypic and genotypic physiological variation, remains broad and is currently not conducive to synergy in the physiological disciplines. Unification may be facilitated, however, by embracing a common currency of measurement and analysis. A likely candidate is the cascade of energy from the environment to offspring and the evolution of physiological form and function, including homeostasis, associated with power management. This currency approach seeks to identify an energetic basis of fitness, namely, whether or how the evolution of life-history traits is influenced by energetic constraints and/or trade-offs.