Life does not emerge across arbitrary temperature ranges. Instead, biological systems operate within relatively narrow thermal windows in which DNA, enzymes, proteins, membranes, and cellular structures remain simultaneously functional. Traditional explanations typically treat these limits separately through enzyme kinetics, protein stability, membrane fluidity, and DNA integrity. In the present work, we explore an alternative unifying perspective. We propose that biological temperature windows may reflect a deeper compatibility regime mediated by the structural-dynamic state of water. Water is considered not merely as a passive solvent, but as an active medium influencing biological readability, catalytic compatibility, folding stability, membrane behavior, and cellular organization. Building upon previous analyses of water-state-dependent functional behavior, we examine DNA hydration, enzyme activity, protein folding, membrane dynamics, and cytoskeletal organization as coupled manifestations of water-mediated biological compatibility. We introduce the concept of a water window: a range of conditions in which water remains sufficiently structured to support recognition and organization while remaining sufficiently dynamic to allow transition and adaptation. Within this framework, biological temperature optima are interpreted not as isolated maxima of individual processes, but as local expressions of a broader compatibility landscape. The resulting model generates experimentally testable predictions and provides a conceptual framework connecting molecular, cellular, and environmental aspects of biological function.
Balevsky et al. (Sun,) studied this question.