evolution

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A gradual process in which something changes into a different and usually more complex or better form.
• noun A result of this process; a development.
• noun Change in the genetic composition of a population during successive generations, often resulting in the development of new species. The mechanisms of evolution include natural selection acting on the genetic variation among individuals, mutation, migration, and genetic drift.
• noun The historical development of a related group of organisms; phylogeny.
• noun Astronomy Change in the structure, chemical composition, or dynamical properties of a celestial object or system such as a planetary system, star, or galaxy. Evolution often changes the observable or measurable characteristics of the object or system.
• noun A movement that is part of a set of ordered movements.
• noun Mathematics The extraction of a root of a quantity.

from The Century Dictionary.

• noun In ancestral development or phylogeny, the doctrine or opinion that the specific constitution or architecture which a germ-cell is held to possess at the beginning of its development, and to which the organization of the being that is generated from it is attributed, preexisted in the germ-cells of preceding generations. In the extreme form in which it was held by the embryologists of the seventeenth and eighteenth centuries it is the doctrine that since individual development is and always has been the unfolding of preexisting structure, each successive organism has existed, as such, from the beginning, in the germ-cells of its first ancestor, and in those of all successive ancestors, so that it is not the actual modem organism, but only its visibility or perceptibility by sense that is new. The modifications of this doctrine by more modern embryologists, who have sought to make it consistent with the progress of biological science, are too subtile and refined for concise statement.
• noun In biology, the doctrine or opinion, accepted as an established truth by all recent biologists, that all living beings have come into existence, in course of nature, by uninterrupted descent, without break of continuity, from a few ancient and simple forms of life, or from one.
• noun The act or process of unfolding, or the state of being unfolded; an opening out or unrolling.
• noun Hence The process of evolving or becoming developed; an unfolding or growth from, or as if from, a germ or latent state, or from a plan; development: as, the evolution of history or of a dramatic plot.
• noun Specifically— In biology: The actual formation of a part or of the whole of an organism which previously existed only as a germ or rudiment; ordinary natural growth, as of living creatures, from the germinal or embryonic to the adult or perfect state: as, the evolution of an animal from the ovum, or of a plant from the seed; the evolution of the blossom from the bud, or of the fruit from the flower; the evolution of the butterfly from the caterpillar; the evolution of the brain from primitive cerebral vesicles, or of the lungs from an offshoot of the intestine.
• noun The release, emergence, or exclusion of an animal or a plant, or of some stage or part thereof, from any covering which contained it: as, the evolution of spores from an encysted animalcule; the evolution of a moth from the cocoon, of an insect from the wood or mud in which it lived as a larva, of a chick from the egg-shell which contained it as an embryo.
• noun Descent or derivation, as of offspring from parents; the actual result of generation or procreation. As a fact, this evolution is not open to question. As a doctrine or theory of generation, it is susceptible of different interpretations. In one view, the germ actually preëxists in one or the other parent, and is simply unfolded or expanded, but not actually formed, in the act of procreation. (See ovulist, spermatist.) This view is now generally abandoned, the current opinion being that each parent furnishes materials for or the substance of the germ, whose evolution results from the union of such elements. See epigenesis.
• noun The fact or the doctrine of the derivation or descent, with modification, of all existing species, genera, orders, classes, etc., of animals and plants, from a few simple forms of life, if not from one; the doctrine of derivation; evolutionism. (See Darwinism.) In this sense, evolution is opposed to creationism, or the view that all living things have been created at some time substantially as they now exist. Modern evolutionary theories, however, are less concerned with the problem of the origination of life than with questions of the ways and means by which living organisms have assumed their actual characters or forms. Phylogenetic evolution insists upon the direct derivation of all forms of life from other antecedent forms, in no other way than as, in ontogeny, offspring are derived from parents, and consequently grades all actual affinities according to propinquity or remoteness of genetic succession. It presumes that, as a rule, such derivation or descent, with modification, is from the more simple to the more complex forms, from low to high in organization, and from the more generalized to the more specialized in structure and function; but it also recognizes retrograde development, degeneration or degradation. The doctrine is now accepted by most biologists as a conception which most nearly coincides with the ascertained facts in the case, and which best explains observed facts, though it is held with many shades of individual opinion in this or that particular. See natural selection, under selection.
• noun In general, the passage from unorganized simplicity to organized complexity (that is, to a nicer and more elaborate arrangement for reaching definite ends), this process being regarded as of the nature of a growth. Thus, the development of planetary bodies from nebular or gaseous matter, and the history of the development of an individual plant or animal, or of society, are examples of evolution.
• noun Continuous succession; serial development.
• noun In mathematics: In geometry, the unfolding or opening of a curve, and making it describe an evolvent.
• noun The extraction of roots from powers: the reverse of involution (which see).
• noun A turning or shifting movement; a passing back and forth; change and interchange of position, especially for the working out of a purpose or a plan; specifically, the movement of troops or ships of war in wheeling, countermarching, manœuvering, etc., for disposition in order of battle or in line on parade: generally in the plural, to express the whole series of movements.
• noun That which is evolved; a product; an outgrowth.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of unfolding or unrolling; hence, any process of growth or development.
• noun A series of things unrolled or unfolded.
• noun (Geom.) The formation of an involute by unwrapping a thread from a curve as an evolute.
• noun (Arith. & Alg.) The extraction of roots; -- the reverse of involution.
• noun (Mil. & Naval) A prescribed movement of a body of troops, or a vessel or fleet; any movement designed to effect a new arrangement or disposition; a maneuver.
• noun (Biol.) A general name for the history of the steps by which any living organism has acquired the morphological and physiological characters which distinguish it; a gradual unfolding of successive phases of growth or development.
• noun (Biol.) That theory of generation which supposes the germ to preëxist in the parent, and its parts to be developed, but not actually formed, by the procreative act; -- opposed to epigenesis.
• noun (Metaph.) That series of changes under natural law which involves continuous progress from the homogeneous to the heterogeneous in structure, and from the single and simple to the diverse and manifold in quality or function. The process is by some limited to organic beings; by others it is applied to the inorganic and the psychical. It is also applied to explain the existence and growth of institutions, manners, language, civilization, and every product of human activity. The agencies and laws of the process are variously explained by different philosophrs.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun general gradual directional change especially one leading to a more advanced or complex form; growth; development
• noun biology The change in the genetic composition of a population over successive generations.
• noun mathematics The extraction of a root from a quantity.
• noun military One of a series of ordered movements.
• noun dance, sports A turning movement of the body.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a process in which something passes by degrees to a different stage (especially a more advanced or mature stage)
• noun (biology) the sequence of events involved in the evolutionary development of a species or taxonomic group of organisms