Fitness in the universe: Choices and necessities

We live in a universe of chance, but not of accident. Repeatedly in the course of its development choices have been made for which one can ask the reasons. One such choice is fundamental: if the proton had not so much greater mass than the electron, all matter would be fluid; and if the proton did not have exactly the same numerical charge as the electron — or some simple multiple of that charge — virtually all matter would be charged. If a universe were started with charged hydrogen, it could expand, but probably nothing more. Hydrogen, carbon, nitrogen and oxygen play as fundamental — and irreplaceable — roles in the metabolism of stars as of living organisms. Both metabolisms are coupled, through radiation from the stars providing the energy on which life must come ultimately to run on the planets. In the course of their evolution on the Earth, living organisms have found their way repeatedly and exclusively to certain types of organic molecule to perform specific functions; so, for example, the chlorophylls for photosynthesis, and carotenoids for plant phototropism and for vision. It is argued that some measure of necessity has governed these choices; and that an extended principle of natural selection has operated at all levels of material organization to produce such elements of order and compatibility in the universe.