), however, lists "sex" as both "Either of the two divisions, designated female and male, by which most organisms are classified on the basis of their reproductive organs and functions" and "One's identity as either female or male," among other definitions.Historian Thomas W. Laqueur suggests that from the Renaissance to the 18th century, there was a prevailing inclination among doctors towards the existence of only one biological sex (the one-sex theory, that women and men had the same fundamental reproductive structure).