References Cited

Tyrannosaurus no longer stalks its prey across North America. There are no pterosaurs sailing majestically overhead. Trilobites no longer crawl on the sea floors of Earth. Today, other predators roam in search of a meal. Birds soar the skies, and crabs scuttle across the ocean bed. 
Life on Earth has changed through time. It has evolved. Change through time is a widely accepted meaning of the word evolution. We speak of the evolution of the English language, the evolution of the automobile, or the evolution of politics in the United States. In natural history, biological or organic evolution means change in populations of living organisms on planet Earth through time.

Charles Darwin defined biological evolution as “descent with modification,” that is, change in organisms in succeeding generations. Another way of saying this is, “species of organisms originate as modified descendants of other species” (Hurry, 1993). Biological evolution is the derivation of new species from previously existing ones over time.

Evolution is the central unifying concept of natural history; it is the foundation of all of modern paleontology and biology. This booklet presents a non-technical introduction to the subject of evolution. Here you will find straightforward definitions of important terms as well as discussions of complex ideas. 

This brief introduction to the rich and fascinating history of the theory of evolution cannot present in detail the vast body of evidence that has led to the current understanding of evolutionary processes. Our aim is to provide a sense of the history, strength, and power of this important scientific theory. We hope that this booklet will help you sense the wonder and excitement that paleontologists and other students of evolutionary science feel when they contemplate the long and intricate history of life on 
Earth.

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