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More than seventy years ago, George Wald noted the vital importance of the additional energy that respiration provides for complex life using oxygen as a terminal electron acceptor. “It is difficult to overestimate the degree to which the invention of cellular respiration released the forces of living organisms,” he wrote in a well-known Scientific American article. “No organism that relies wholly on fermentation [glycolysis] has ever amounted to much.… Respiration used the material of organisms with such enormously greater efficiency as for the first time to leave something over.… To use an economic analogy, photosynthesis brought organisms to subsistence level; respiration provided them with capital. It is mainly this capital that they invested in the great enterprise of organic evolution.”24 Thus, bees buzz and hummingbirds hum, squids and chameleons change color, amoebas engulf prey, crows solve problems, and humans build rockets to the stars, only because oxidation releases metabolic energy in quantities much greater than are needed for merely sustaining the basic metabolism of the cell.
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