The central thesis of The Natural Selection of the Chemical Elements is that the inanimate environment and living organisms are intimately connected, and that the evolution of both has been interactive and interdependent: the environment and life developed together. The authors show that this can be explained in terms of the properties of the chemical elements and their compounds, especially as compounds have developed with time.

The first part of the book discusses the physical and chemical balance between ordered and disordered systems and then analyses organisation in both the animate and inanimate worlds. Appropriate thermodynamic and kinetic principles are given to support this analysis. The application of these principles to the development of both inorganic (geographical) and organic chemical systems is then described, providing a basis for understanding the evolution of life in terms of the interaction of both types of chemistry within ever more complex organisations.

The book concludes by examining the long-term consequences of man's selection and manipulation of chemicals for his own purposes which may have consequences for the long-term future of life from changes in the environment - not only due to bulk but also to trace element alterations.