Biology  5/e   Raven/Johnson
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Evolutionary theory: The tendency of animals to overproduce results in a struggle for survival in the face of limited resources. Organisms with traits better suiting them to compete will have greater success in the struggle and will survive to reproduce, passing on their unique traits. Differential survival among the diverse organisms eventually results in the formation of new species.

Evolutionary history: The earth is about 4.6 billion years old. The oldest fossils of living things are about 3.5 billion years old. All life evolved in the sea until about 410 million years ago, when invasion of the land began. Throughout the history of living things, continental drift has had a profound influence. Continental movements have caused extinction through loss of habitat and have accelerated evolution by increasing competition through formation of land bridges and isolation through loss of land bridges. Throughout all continental migrations, adaptation to climatic change by the living "passengers" was often the key to survival.

Symbiosis: The living together of two dissimilar organisms. Once, the term was used for a mutually beneficial relationship. This connotation is no longer used. "Living together" and interacting is symbiosis.

Classification: Three domains are recognized: Archebacteia, Eubacteria, and Eukarya. Six kingdoms are recognized: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia. Kingdoms are divided into phyla (divisions in plants, ) which are subdivided into classes. Classes are divided into orders, and in turn, families, genera, and species.

Choanoflagellates: The choanoflagellates are believed to be ancestral to sponges and possibly, to the rest of the animal kingdom. Choanoflagellates have a single flagellum surrounded by a "picket fence" collar of filaments used to strain food particles from the sea.

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