Hermaphrodite

Hermaphrodites were organisms which could perform the biological role of both males and females. (PROSE: The Ruins of Time)

On Earth
In 1963, Ian Chesterton taught his biology class, including Susan Foreman, about hermaphrodites, including snails and flowers. (PROSE: The Ruins of Time)

Circa 2360, it became popular among humans to become hermaphrodites. In 2363, the fad ended. Wanting to find a way to quickly populate colony planets, the Earth government conducted experiments in super-fertility with some of the hermaphrodites. (PROSE: Dead Romance)

Elsewhere
The Yaqex of Yaqexis and the Torcaldians of Torcaldi were hermaphroditic species encountered by the First Doctor. (PROSE: The Ruins of Time)

Alpha Centaurans were hermaphrodites, sometimes pejoratively referred to as "it". Nevertheless, the Third Doctor generally used masculine pronouns to refer to the Federation ambassador to Peladon. (TV: The Curse of Peladon)

Chelonians were hermaphrodites and all members could lay eggs. Despite this, Chelonians were referred to as males. (PROSE: The Highest Science)

The Sloathes, (PROSE: Sky Pirates!) the Brascans, (PROSE: Kursaal) and the Torcaldians (PROSE: The Ruins of Time) were also hermaphrodites.

Behind the scenes
In the real world, "hermaphrodite" is considered an antiquated, even offensive term, when applied to humans. The correct modern-day term is.