Final answer:
The belief that 'sex' determines 'gender' is known as Essentialism, suggesting inherent traits prescribe societal gender roles.
Step-by-step explanation:
The concept in question pertains to the belief that a single metaphysical nature causally determines the identity and characteristics of a group of entities. With specific reference to gender, this belief aligns with the definition of Essentialism. Essentialism posits that 'sex' or anatomical makeup, inevitably determines 'gender', encapsulating societal roles, behaviors, and interpretations of bodies. This view implies that there are inherent traits or qualities that define the categories of male and female, which in turn prescribe certain expectations and roles within society. Biological determinism, related to this notion, argues that behavioral differences between men and women are inherent due to biological sex distinctions.