Which characteristic is NOT considered a primary sex characteristic?

Primary sex characteristics refer to the essential reproductive structures directly involved in the production of gametes and in sexual reproduction. This includes organs such as ovaries in females, which produce eggs, and testes in males, which produce sperm. External genitalia, which include structures like the penis and vulva, also fall under the category of primary sex characteristics as they are crucial for reproduction.

Body hair, however, is not a primary sex characteristic. Instead, it is classified as a secondary sex characteristic. Secondary sex characteristics develop during puberty and are influenced by hormonal changes, such as increased body hair in males and females. These features are not directly involved in reproduction but rather serve to distinguish male and female bodies post-puberty based on appearance rather than reproductive functionality.

Therefore, body hair is the correct choice as it does not play a direct role in the reproductive process, making it distinct from the true primary sex characteristics.