Introduction

Beginning perhaps with Anaximenes of Miletus (fl. c. 2550 years before present), various ancient Greeks portrayed man as a microcosm of the universe. Each human being was made up of the same elements as the rest of the cosmos – earth, air, fire and water. Twenty-six centuries later, and several hundred years after the dawn of modern science, it is somewhat humbling to realize that our view of ourselves is fundamentally unchanged.

Our knowledge of the matter of which we are made, however, has become much more sophisticated. We now know that all living organisms are composed of hydrogen, the lightest element, and of heavier elements like carbon, nitrogen, oxygen, and phosphorus. Hydrogen was the first element to be formed after the Big Bang. Once the universe had cooled enough, hydrogen condensed to form stars. Then, still billions of years ago, the heavier atoms were synthesized in the interiors of stars by nuclear fusion reactions. We are ‘made of stardust,’ to quote Allan Sandage (b. 1926), an American astronomer.

Our starry origin does not end there. For the Sun is the primary source of the energy used by organisms to satisfy the requirements of life (Fig. 1.1). (Recent discoveries have revealed exceptions to this generalization: see Chapter 9). Some organisms acquire this energy (Greek, en, in + ergon, work) directly; most others, including humans, obtain it indirectly.