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cell: The basic structural and functional unit of most living organisms. Cell size varies, but most cells are microscopic. Cells may exist as independent units of life, as in bacteria and protozoans, or they may form colonies or tissues, as in all plants and animals. Each cell consists of a mass of protein material that is differentiated into cytoplasm and nucleoplasm, which contains DNA. The cell is enclosed by a cell membrane, which in the cells of plants, fungi, algae, and bacteria, is surrounded by a cell wall. There are two main types of cell, prokaryotic and eukaryotic.
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Cenozoic: The era of geologic time from 65 mya to the present, a time when the modern continents attained their present-day configuration and modern animals and plants evolved.
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character: Any recognizable trait, feature, or property of an organism.
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chromosome: A structure in the cell nucleus that carries DNA. At certain times in the cell cycle, chromosomes are visible as string-like entities. Chromosomes consist of the DNA with various proteins, particularly histones, bound to it.
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chronology: The order of events according to time.
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clade: A set of species descended from a common ancestral species. A clade is also a synonym for a monophyletic group.
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cladogram: A branching diagram that illustrates hypotheses about the evolutionary relationships among groups of organisms. Cladograms can be considered as a special type of phylogenetic tree that concentrates on the order in which different groups branched off from their common ancestors. A cladogram branches like a family tree, with the most closely related species on adjacent branches.
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classification: The arrangement of organisms into hierarchical groups. Traditional biological classifications use the Linnaean system to classify organisms into species, genus, family, order, class, phylum, kingdom, and certain intermediate categorical levels. A number of non-Linnaean hierarchical classification systems have been proposed and are being actively discussed.
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coevolution: Evolution in two or more species, such as a predator and its prey or a parasite and its host, in which evolutionary changes in one species influence the evolution of the other species.
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common ancestor: The most recent ancestral form or species from which two different species evolved.
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continental drift: The process by which the continents move as part of large plates floating on Earth's mantle. See plate tectonics.
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convergence: The process by which a similar character evolves independently in two species. Also, a synonym for analogy; that is, an instance of a convergently evolved character, or a similar character in two species that was not present in their common ancestor. Examples include wings (convergent in birds, bats, and insects) and camera-type eyes (convergent in vertebrates and cephalopod mollusks).
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convergent evolution: The evolution of species from different taxonomic groups toward a similar form; the development of similar characteristics by taxonomically different organisms.
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creationism: The religious doctrine that all living things on Earth were created separately, in more or less their present form, by a supernatural creator, as stated in the Bible; the precise beliefs of different creationist groups vary widely. See separate creation.
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creation science: An assortment of many different, non-scientific attempts to disprove evolutionary theory, and efforts to prove that the complexity of living things can be explained only by the action of an "intelligent designer."
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Darwinian evolution: Evolution by the process of natural selection acting on random variation.
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Darwinism: Darwin's theory that species originated by evolution from other species and that evolution is mainly driven by natural selection. Differs from neo-Darwinism mainly in that Darwin did not know about Gregor Mendel’s discoveries about inheritance.
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Darwin, Charles: The 19th-century naturalist considered the father of evolution. His landmark work, On the Origin of Species, published in 1859, presented a wealth of facts supporting the idea of evolution and proposed a viable theory for how evolution occurs—via the mechanism Darwin called "natural selection." In addition to his prolific work in biology, Darwin also published important works on coral reefs and on the geology of the Andes, and a popular travelogue of his five-year voyage aboard HMS Beagle.
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DNA: Deoxyribonucleic acid, the molecule that controls inheritance in most organisms.
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