5.0: Introduction

In which we change gears, from evolutionary biology to the physical and chemical properties of organisms. These properties shape and constrain biological behaviors. We consider how molecules interact and react with one another and how these interactions and reactions determine the properties of substances and systems, particularly the continuous, bounded, non-equilibrium system that is life.

All biological systems and processes, from those involved in cellular integrity, growth, replication, movement, and differentiation to thoughts and feelings, obey the rules of chemistry and physics. What makes biological systems unique is that, unlike simpler systems that move toward thermodynamic equilibrium, living organisms maintain a non-equilibrium state. Chemical reaction systems can be assembled de novo. So far, this is not true for organisms and the cells they are composed of; every biological system has an uninterrupted history going back billions of years. So, we start by clarifying what it means when we say that a system is at equilibrium versus when it is in a obligate non-equilibrium (living) state. A biological system at equilibrium is dead, and not ever, ever coming back to life.

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