Biological sex

Biological sex [is] constituted by sex characteristics (chromosomes, gonads, internal genitalia, external genitalia, hormones and secondary sexual manifestations).

Sex-appropriate masculine or feminine traits are not an innate psychological need but are derived from social expectations to act in ways which supposedly affirm or validate biological sex. Individuals are taught that it is not enough to know they are biologically male or female, but they must also act in ways which supposedly affirm their biological sex.