Preface

In his preface to the original 1984 version of this document, Frank Press, my predecessor as president of the National Academy of Sciences, called attention to a pair of illustrations similar to the ones on the front and back of this booklet. The first is a photograph of Earth from space—the one on this booklet was taken by the GOES 7 satellite in 1992 as it passed over Earth and captured in graphic detail Hurricane Andrew. The second shows a map of the world prepared during the 7th century by the scholar Isidore of Seville. As Press pointed out, both illustrations reflect the efforts of humans to understand the natural world. "How then," he wrote, "can the two views be so different? The answer lies at the very heart of the nature of this system of study we call science."

Since those words were written, the mapping of Earth has provided further powerful examples of how science and science-based technologies progress. Beginning in the early 1990s, a network of satellites has allowed anyone with a hand-held receiver to know his or her position on Earth to within a few feet. This Global Positioning System* (GPS) now is being used to locate vessels lost at sea, study plate tectonics, trace open routes through crowded city streets, and survey Earth's surface. Yet the technology originated with a purely scientific objective—the desire to build extremely accurate clocks to test Einstein's theory of relativity.

The tremendous success of science in explaining natural phenomena and fostering technological innovation arises from its focus on explanations that can be inferred from confirmable data. Scientists seek to relate one natural phenomenon to another and to recognize the causes and effects of phenomena. In this way, they have developed explanations for the changing of the seasons, the movements of the sun and stars, the structure of matter, the shaping of mountains and valleys, the changes in the positions of continents over time, the history of life on Earth, and many other natural occurrences. By the same means, scientists have also deciphered which substances in our environment are harmful to humans and which are not, developed cures for diseases, and generated the knowledge needed to produce innumerable labor-saving devices.

The concept of biological evolution is one of the most important ideas ever generated by the application of scientific methods to the natural world. The evolution of all the organisms that live on Earth today from ancestors that lived in the past is at the core of genetics, biochemistry, neurobiology, physiology, ecology, and other biological disciplines. It helps to explain the emergence of new infectious diseases, the development of antibiotic resistance in bacteria, the agricultural relationships among wild and domestic plants and animals, the composition of Earth's atmosphere, the molecular machinery of the cell, the similarities between human beings and other