Evolution

Evolution was the development and change of organisms over time. It was closely linked to mutation and natural selection, although specifically it was a long-term process of adaptation, concerning the development of species in relation to "survival of the fittest".

It meant that everything from bilateral symmetry to five fingers and five toes was the result of a random mutation that conferred a slight advantage over other random mutations. Possessors would therefore have a slightly greater chance of not dying and therefore a greater chance of passing their mutated genes on to their offspring. That advantage was entirely down to local conditions, including the chemistry of the planet, the weather, the geology and the predators. Therefore different mutations would occur on different planets and different species would evolve differently. (PROSE: Slow Decay)

On Earth, a human scientist, Charles Darwin, "discovered" and popularised the idea in the 19th century. (AUDIO: Bloodtide, TV: Ghost Light)

Characteristics
Evolution took place over aeons. The Eighth Doctor once stated that evolution didn't work backwards. (AUDIO: Scherzo) However, it was believed the Macra had "devolved," having once been empire-builders, but eventually becoming savage beasts in the far future. (TV: Gridlock)

Evolution usually began with creatures emerging from a "primordial soup." While the process took time, accelerated evolution could be achieved such as when Josiah Samuel Smith and Control evolved through different forms during their centuries on Earth, eventually evolving into a "Victorian gentleman" and "lady." (TV: Ghost Light)

On Earth
According to Doctor Kory, earliest life on Earth started in the sea, before developing for millions of years until man was created. (COMIC: The Sea Monsters)

Light and the Reverend Ernest Matthews separately found the concept abhorrent, though for different reasons, the former because of his love of stasis and hatred of change, the latter because he found it repugnant to have evolved from monkeys, contrary to the Garden of Eden myth. (TV: Ghost Light)

The Seventh Doctor told Ace that examples of actual evolution were quite rare in Earth science, and that the universe was big enough for all the conflicting theories of species development to have some validity. (PROSE: Cat's Cradle: Witch Mark) Through a Time Manipulator, the Rani meant to redirect evolution wherever, in her opinion, it had taken the wrong route, i.e. saving the dinosaurs from extinction. (TV: Time and the Rani)

Professor Richard Lazarus had created a machine that rejuvenated himself, or, in simpler terms, a machine that allowed him to make himself younger. This transformation also accidentally unlocked a rejected option for human evolution, making him a scorpion-like mutant. (TV: The Lazarus Experiment)

Elsewhere
The Time Lords evolved more quickly than other species due to prolonged exposure to the Time Vortex through such openings as the Untempered Schism. (COMIC: Old Girl) River Song was experimented on to have similar characteristics after having been conceived in the Vortex. (TV: A Good Man Goes to War)

Davros wished to determine the ultimate evolution of the Kaled race and to direct it. The result of this was the Daleks. (TV: Genesis of the Daleks) After escaping the Battle of Canary Wharf, Dalek Sec and the Cult of Skaro arrived in 1930s New York. Dalek Sec wished to determine the ultimate evolution of the Daleks, which resulted in the human-Dalek. (TV: Daleks in Manhattan / Evolution of the Daleks)