What is a primary sex characteristic of males?

The primary sex characteristic of males is the ability to produce sperm. This characteristic is directly related to the biological functions associated with male reproductive anatomy and physiology. In terms of reproductive capability, males have specialized organs, such as the testes, which produce sperm and are critical in sexual reproduction. This capability sets males apart in terms of their role in fertilization and is a defining feature of male sexual development.

While the development of bodily hair, increase in muscle mass, and bone growth are secondary sex characteristics influenced by testosterone during puberty, they do not directly relate to the reproductive functions. These traits are associated with the physical changes that occur during puberty but are not essential to the reproductive biological aspect of being male. Therefore, the ability to produce sperm stands out as a primary characteristic essential for male reproductive role.