Sexual characteristics refer to the traits that distinguish males and females in a species. These traits can be divided into two categories: primary and secondary. Primary sexual characteristics are directly related to reproduction, such as the presence of ovaries in females and testes in males. Secondary sexual characteristics, on the other hand, develop during puberty and include features like breast development in females and facial hair in males. In humans, these characteristics are influenced by hormones like estrogen and testosterone. They play a significant role in physical appearance and can also affect behavior. Understanding sexual characteristics helps us appreciate the diversity of life and the biological differences between genders.