Sex (trait)

Biological sex was a physical trait of many races, including humans (TV: Doomsday) and Time Lords. Sex was flexible for Time Lords:

"Biological sex is flexible among my people, and gender is merely a social construct."

- Thirteenth Doctor

The Cybus Industries Cybermen of Pete's World sought to remove human sex to become identical. (TV: Doomsday)

Human women were sometimes regarded as the "fairer sex" (TV: Carnival of Monsters, The Time Warrior, The Ark in Space, The Talons of Weng-Chiang, Twice Upon a Time) while human men were regarded as the "dominant sex". (TV: The Time Monster)