A species was a single, distinct kind of lifeform possessing common attributes.

Species arose by the evolutionary process of speciation. (AUDIO: The Case of the Missing Gasogene)

The Third Doctor claimed that every species had its own weakness. (TV: The Time Warrior)

Shockeye believed that species which were at the top of the food chain, such as humans, had the finest flavour of all. (TV: The Two Doctors)

The First Rani conducted experiments on what she called "inferior species". (TV: Time and the Rani)

The Seventh Doctor claimed that he hadn't seen many examples of species crossing. (TV: Delta and the Bannermen)

The Eighth Doctor implied to Grace Holloway that he had the ability to change into another species when he regenerated. (TV: Doctor Who)

The Ninth Doctor claimed that the Fourth Great and Bountiful Human Empire encompassed a million species. (TV: The Long Game)

Rose Tyler said that the Ninth Doctor liked to insult species when he was stressed. (TV: The Doctor Dances)

The Tenth Doctor claimed that almost every species in the universe had an irrational fear of the dark. (TV: Silence in the Library)

The Twelfth Doctor asked himself why he couldn't meet a decent species. (TV: Deep Breath)

The Twelfth Doctor told Osgood that she was a credit to her species. (TV: The Zygon Inversion)

The Twelfth Doctor identified at least twenty-seven different species on a London trap street, fifteen of whom were known for aggression. (TV: Face the Raven)