Valentine, J. W. Department of Geology, University of California, Santa Barbara, California.
Thomson, Keith S. Oxford University Museum of Natural History, Oxford, United Kingdom.
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- Interrelationships of animal groups
- History of major animal groups
- Chordate origins
- Links to Primary Literature
- Additional Readings
The processes of biological and organic change in animals by which descendants come to differ from their ancestors. Animal evolution encompasses the theory that modern animals are the modified descendants of animals that formerly existed and that these earlier forms descended from still earlier and different organisms. The concepts of evolutionary biology and their relationship to phylogeny (the genealogical history of organisms, both living and extinct), adaptation, and speciation were formulated by Charles Darwin. Much of Darwin's conclusions emanated from his investigative study of animals. Animals are multicellular organisms that feed by ingestion of other organisms or their products, being unable to derive energy through photosynthesis or chemosynthesis. Animals are currently classed into approximately 36 phyla, and each of these phyla has evolved a distinctive body plan or architecture. Representatives of the major animal groups are depicted in Fig. 1. See also: Adaptation (biology); Animal; Animal kingdom; Charles Darwin and his theory of evolution; Macroevolution; Organic evolution; Phylogeny; Speciation; Species concept
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