evolution

Scientific writing used it this way by Charles Lyell's Principles of Geology (1832), describing Lamarck's idea that sea creatures came first and others followed "by gradual evolution". In biology it is usually a mass noun, as in the theory of evolution or rapid evolution. Debates turn on its unit: Richard Dawkins's The Selfish Gene (1976) puts the individual or gene before the species.

The general sense, and the one that borrows freely from biology. The evolution of transportation can be described in terms of divergence, hybridization and selection, and Richard Dawkins's The Selfish Gene (1976) speaks of "cultural evolution" in birds, monkeys and ourselves. It need not mean improvement: the "paradoxical evolution" in Ben Travers's A Cuckoo in the Nest (1922) ends in rancor and intolerance.

Here the image of unrolling is still close. What develops was there from the start, folded up in the idea or argument the way a text lies inside a rolled scroll. That separates it from gradual change in a system, where new elements may enter along the way. Eckhart Tolle's "evolution of consciousness" in A New Earth (2005) sits near the border between the two.

Movement with nothing developing in it: this meaning keeps close to the rolling motion of the Latin root, volvō, "roll". It is the general case of the drill-ground maneuver, freed from troops and ships, so a marching band or a stunt team can perform evolutions. Read that way, the word counts moves made, not change over time, and has nothing to do with the biological meaning.

Nineteenth-century writers reached for it when watching a pirouette. Miss Langley's Will (1869) has "the whole evolution executed to perfection". Verbs of skill go with it, such as perform and execute, and it often sums up a whirl the writer has just described. Smollett also uses it for a wand waved mysteriously about the head, so it covers any showy turning motion, not only the dancer's.

A drill-ground word with eighteenth-century company. In Smollett's The Adventures of Peregrine Pickle (1751), regiments are "exercised and reviewed" in all their evolutions, and Frances Burney's Journals & Letters (1779) has an acting general coming over "between every evolution" to explain the maneuvers. The pairing is useful: an evolution is one set movement, counted one by one, while maneuvers names the tactical business as a whole.

Laboratory English, and almost always followed by the gas it names: the evolution of hydrogen, of carbon dioxide, of oxygen. When a metal meets an acid, the hydrogen rising at its surface is an evolution in this sense. Chemists also speak of gas evolution as something to watch and measure, a sign of how fast a reaction is going.